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^"m\ 


,.^: 


'■1^'^.:^\,  ^:, 


N  THE  CUSTODY  Or  THE 

BOSTON     PUBLIC   LIBRARY. 


CHEMICAL    ESSAYS. 


CHEMICAL    ESSAYS. 

B    Y 

R.     WATSON, 

D.  D.    F.  R.  S. 

AND  REGIUS  PROFESSOR    OF    DIVINITY    IK 
THE  UNIVERSITY  OF  CAMBRIDGE. 

VOL.  in. 

THIRD      EDITION. 


LONDON: 

PRINTED      BYJ.     DAVIS 

FOR   T.  EVANS,  PATERNOSTER-ROW. 


MDCCLXXXV, 


ADAMS 


CONTENTS, 

ESSAY 

I.  Of  Bitumens  and  Charcoal,  Page  i 

IL  Of  the  ^iantity  of  Water  ev apo-- 
rated  from,  the  Surf  ace  of  the  Earth 
In  hot  Weather,  5 1 

III.  Of  Water  dijfolved  in  Air,      75 

IV.  Of  Cold  produced  during  the  Eva- 
poration of  Water ^  and  the  Solu- 
tion of  Salts,  1 1 9 

V.  Of  the  Degrees  of  Heat  in  which 
Water  begins  to  part  with  its 
Air^   and  in  which  it  boils,        143 

VL  Of  Water  in  a  f olid  State :  of  the 
Heat  of  Spring  Water  -,  and  of  a 
probable  Caufe  of  the  Impregnation 
of  Julphureous  E'aiers,  171 

YIL  Of 


CONTENTS. 

ESSAY 

Wl,  Of  Derhyjhire  Lead  Ore,      207 

VI I L  Of  the  /melting  of  Lead  Ore,  as 
fra^iifed  in  Derhyfhire,  25 1 

IX.  Of  Silver  extraEiedfrom  Lead.i^o  i 

X.  Of  Red  and  White  Lead,        337 


A  D  V  E  R" 


ADVERTISEMENT. 


I  Have  every  reafon  to  be  fatisfied 
with  the  reception  which  has 
been  given  to  my  two  former  volumes 
of  Chemical  EfTays.  My  defign 
was  to  have  publijfhed  two  others  on 
the  fame  plan 3  but  this  is  the  laft 
for  which  I  fhall  ever  prefume  to 
intreat  the  indulgence  of  the  public. 
I  perceived,  as  I  proceeded  in  the 
work,  that  two  additional  volumes 
would  not  contain  half  the  materials 
which  I  had  colle6ted ;  and  defpair- 
ing  of  ever  finding  leifure  to  arrange 
the  whole,  I  have  contented  myfelf 
2  with 


(  "  ) 

With  putting  into  this  volurtie,  what 
gave  me  the  kail  trouble  in  revifmg. 
For  feveral  months  I  have  had  great 
reafon  to  believe,  that  an  attention 
to  health  ought  to  occupy  that  lei- 
fure,  which  I  have  hitherto  beftowed 
on  the  fiudy  of  chemiftry.  It  is  a 
fiiudy  of  fo  bewitching  a  kind,  that 
few  perfons  can  cultivate  it  with 
moderation,  or  fail  of  feeling  fymp- 
toivns  of  that  diforder  which  Beccher 
in  fpeaking  of  himfelf,  defcribes  in 
the  following  terms,* — cut  nee  Au- 
la Splendor  J  me  ceeonomi^e  ratio^  nee 
fama  integritaSj  nee  Janitatis  vigGVy 
quiequajn  p'ce  earhonibiiSy  venenis,  fti^ 
liginey  follibusy  et  furnis  valerepoteft^ 

*   Phy.  Subter.  Pra. 


ESSAY 


E    S    S    A    Y 


OF    BITUMENS    AND    CHARCOAL. 


'^I^HE  analyfes  of  pitcoal  and  of 
A  different  woods,  mentioned  in 
the  laft  ElTay,  may  ferve  as  inflances 
of  the  produdrs  obtainable  by  diftil- 
.lation  from  .Mruminous  and  vege- 
table fubilancestn  general.  They 
all  of  them  yield  water  impregnated 
with  an  acid,  and  often  alfo  with  a 
volatile  alkaline  fait,  air,  oils  of  dif- 
ferent colours,  weights,  and  confift- 
ence^,  and  a  black  coaly  refiduum. 
The  bitumens  generally  taken  notice 

VOL.  III.  A  of 


(       2      ) 

of  by  writers  on   Natural  Hiftory 
are,  with  refpedl  to  their  confiflence, 
either  as  fluid  as  oil^  or  as  thick  and 
tenacious  as  tar,  or  quite  folid.    The 
fluid  bitumens  are  two,  Naptha,  and 
PetrcleumyOr  rock-oil.  Thefe  are  oils 
which  differ  from  each  other  in  co- 
lour and  confifcence,  and  fome  other 
properties 3  the  naptha  is  pale,  light, 
and  very  inflammable;  the  petroleum 
is  yellow,  brown,  or  blackifn,  hea- 
vier and  lefs  inflammable  than  nap- 
tha :    its  difference  from  naptha  is 
attributed  to  its  containing  a  greater 
quantity  of  acid  in  its  compofltion. 
Both  thefe  oils  are  found  in  many 
parts  of  the  globe,  either  floating  on 
fpring  v/ater,  or  dripping  from  the 
crevices  of  rocks.     Mineral  fitch  \s 
a  bitumen  which  differs  from  petro- 
leum   in    being    thicker,    heavier, 

and 


(     3     ) 

and  more  glutinous ;  it  was  formerly 

-found  in  the  environs  of  Babylon,  and 
conftituted,  according  to  Vitruvius, 
when  mixed  with  lime,  the  cement 
which  was  ufed  in  building  the  walls 

^of  that  city.  At  prefent  it  is  met 
with  in  fcveral  parts  of  Europe,  and 
in  America,  where  it  drips  from 
rocks,  and  is  called  by  us  Barhadoes 
tar:    it  has  a  very  offenfive  fmell, 

.  and  great  tenacity,  and  is  called  by 
the  inhabitants    of    Auvergne,     in 

•  France,    where  it  exudes  from  the 

^  earth,  and  flicks  to  the  feet,  devils 
dung.  Tht  ^pballum,  or  jewj-pitcby 
is  a  bitumen  much  refembling  mine- 
ral pitchy  it  is  thrown  up  in  a?  liquid 
form  from  the  bottom  of  the  lake 
where  Sodom  and  Gomorrah  flood, 
otherwife  called  the  Deadfea^  or  the 

:lake  JJphaltes^  from  a  Greek  word 
A   1  denotin^y 


(     4     ) 

denoting  abitumen.  This  lake  in  the 
time  of  Efdras  yielded  Bitumen — re- 
memher  what  1  did  to  Sodom  and  Gomor- 
rah^ whoje  land  lieth  in  clods  offitch^. 
The  bitumen  floating  upon  the  fur- 
face  of  the  fait  water,  is  condenfed  by 
the  heat  of  the  fun  into  a  folid  form, 
and  is  gathered  by  the  Arabs  on  the 
Ihore  where  it  is  thrown.  It  is  faid 
to  be  the  fame  fubilance  which  the 
Egyptians  ufed  in  embalming  their 
mummies,  and  it  was  called  by  them 
mmnia  jyiineruUs,  f  This  bitumen  has 
been  found  in  many  places  of  Afia 
and  Europe,  as  v/ell  as  on  the  Ihores 
of  the  Dead  Sea^  ail  that  we  meet 
with  in  the  ihops,  is  either  an  arti- 
ficial compofition,  or  an  European 
afphaltum,  the  Eallern  ones  being 
fsldom  brought  into  Europe,    but 

ufed 

'^  Efd.  B.  2.  c.  2. 

•|  H^^il^lquiil's  Vov.  p.   285. 


(     5     ) 

iiled  by  the  natives  either  as  pitch 

for  their  fhios.   or   as  an  ing-redient 
in  varnilhing,  or  dying  wool. 

There  is  a  very  curious  experi- 
ment v/hich  illuftrates  the  relation 
which  thele  four  bitumens  bear  to 
each  other.  The  moil  tranfparent 
oil  of  turpentine,  refembling  nap- 
tha,  may  be  changed  into  an  oil  re- 
fembling petroleum,  by  mixing  it 
with  a  fmall  portion  of  the  acid  of 
vitriol  j  with  a  larger  proportion  of 
the  acid  the  mixture  becomes  black 
and  tenacious,  like  Barbadoes  tarj 
and  the  proportions  of  the  ingre- 
dients may  be  fo  adjufted,  that  the 
mixture  will  acquire  a  folid  confid- 
ence, like  afphaltum.  This  experi- 
ment teaches  us  to  conclude  that 
naptha,  petroleum,  Barbadoes  tar, 
and  afphaltum,  differ  chiefly  from 
A  3  each 


(    6     ) 

each  other,  with  refped  to  the  quan- 
tity of  acid  which  enters  into  their 
compofition  3  andthefiabftances  pro- 
cured by  diililling  pitcoaI>  or  refi- 
nous  vegetables  may  furnifli  no 
improbable  conjecture  concerning 
the  origin  of  thefe  bitumens. 

Let  us  fuppofe  then  a  fub terra- 
neous fire  to  be  fituated  in  or  near 
a  ftratum  of  pitcoal,  of  turf,  of 
foiTil  wood,  or  of  any  other  fuch 
bitumenous  matter^  it  is  manifeil 
that  the  inflammable  air,  and  the  dif- 
ferent kinds  of  oils,  which  were  col- 
3e6led  by  diililling  fmall  portions  of 
thefe  fubilances,  would  be  elevated 
by  the  heat  into  the  crevices  of  the 
fuperineumbent  ftrata j  the  light  and 
pale  oil  v/ould  be  a  fort  of  naptha,. 
or  petroleum,  the  black  and  tena- 
cious oil  v/ould  be  a  Barbadoes  tar, 

and 


(    7     ) 

and  this  might  be  fo  dried  by    the 

heat  as  to  become  an  afphakum. 
The  oils  not  being  mifcible  with 
water,  would  be  found  floating  upon 
its  lurfacej  as  it  ilTued  out  of  the 
bowels  of  the  earth,  and  being  very- 
inflammable,  might  conilitute  burn- 
ing wells,  fuch  as  have  been  met 
v/ith  near  Wigan,  atBrofely,  and  in 
many^-other  places :  or  v/here  the  oil 
did  not  m^eet  with  water,  or  was  too 
heavy  to  float  on  it,  we  may  conceive 
that  it  would  impregnate  the'porous 
ftrata  of  feveral  kinds  of  fliones  and 
earth.  Ithasbeenobferved  inanother 
place,*that  they  formerly  obtained  a 
fort  of  tar,  from  a  ftone  atBrofely, 
and  the  fcratum,  v/hich  is  called 
JJmle  in  Derbyfhire  is  fo  ftrongly  im- 
pregnated with  oil,  that  it  will  burn 
A  4  of 

*  Vol.  2.  p.  347 


(     8     ) 

of  itfdf,  when  fet  oa  fire -.the  work- 
men in  digging  through,  the  black 
ftone,  which  is  incumbent  on  the 
ihale,  fometimes  meet  with  eavitie& 
containing  a  thick  black  oil,-  which 
has  oozed  out  of  the  furrounding 
ftone.  One  of  the  greateft/c'^^i^j,  or 
Subterraneous  paiTages,  which  haS;,, 
perhaps  ever  been  formed  in  Great 
Britain,  is  that  which  is  called  Hell- 
car  fough,  in  Derbyfhires  this  foiigh- 
is  driven  through  a.ftratum  of  Ihale, 
and  the  workmen  are  much  troubled 
v/i th  inflammable  air,  which  general- 
ly breaks  into  the  fough,  through  the 
lame  crannies  which  give  paffage  to- 
little  flreams  of  water:  they  fecure 
themfelves  from  the  air,  by  keeping 
great  fans  conilantly  in  motion  5  for 
the  inflammable,  air,  being  lighter 
tlian  common  air^,  floats  near  the  roof 

of 


(    9    ) 

of  the  Tough,  and  being  drawn  down 
from  thence,,  and  mixed  with  the 
common  air  by  the  m^otion  of  the 
fans,  it  is  circulated  in  the  fough 
without  danger.  I  am  fenfible  that 
inflammable  air  may  be  produced  by 
various  other  ways,  as  well  as  by  the 
application  of  heat,  to  bitumenous 
flrata;  but  as  bitumens  do  yield  in- 
flammable air  by  diflillation,  it  is 
probable  enough,  that  fuch  as  is  met 
with  in  bitumenous  ftrata,  may 
fometimes  at  leafl,  be  referred  to 
the  adtion  of  a  lire,  fituated^.  per- 
haps, at  too  great  a  diftance  from 
the  furface  of  the  earth,  to  produce 
any  other  fenfible  effect. 

In  the  Duchy  of  Modena  in  Italy,, 
there  is  a  remarkable  rock,  which 
confirms  very  much  the  notion  of 
oils  and  pitchy  fubflancesj.  being  fe«^ 

parated 


(       lO       ) 

parated  from  bitumens  by  a  kind  of 
fubterraneous  difliUation.  The  in- 
habitants of  the  diftrict,  by  piercing 
the  fides  of  this  rock,  at  different 
diftances  from  its  fummit,  obtain 
oils  of  different  natures,  thickening 
and  growing  heavier  and  deeper 
coloured,  as  the  canals  through 
which  they  flow  approach  to  the  fur- 
face  of  the  earth  -,  at  the  diftance  of 
a  few  feet  below  the  furface,  they 
find  a  very  thick  oil,  which  in  dig- 
ging deeper  becomes  foft  as  butter, 
and  at  ftill  a  greater  depth,  it  is 
found  to  be  as  folid  as  pitch. 

Befides^//C(?^/and  afphaltum,  there 
are  three  other  folid  bitumens  which 
deferve  to  be  mentioned — Jet — 
Amber— Ambergris .  Jet  fo  much 
refembles  cannel  coal  in  its  colour, 
in  its  hardnefs,    in  its  receiving  a 

poliili. 


(  "  ) 

polifti,  in  its  not  foiling  the  fingers 
when  rubbed  upon  it,   and  in  other 
properties,  that  many  authors  con- 
found the  two  fubftances   together; 
and  indeed  they  agree  in   io  many 
qualities  that  it  is  fomewhat  difficult 
to  fay  in  what  they  difagree.     Jet, 
however,  when  warmed  by  fridtion, 
has  the  property  of  attrading  bits  of 
ftraw,     feathers,     and    other   light 
bodies;,   but  I  never  obferved   this 
property  in  any  of  the  cannel- coals 
which  I  have  tried.     This  property, 
if  it  may  generally  be  relied  on,   as 
appertaining  to  jet,  and  not  to  can- 
nel coal,  is  a  very  eafy  chara6leriilic, 
by  which  thefe  fubftances  may   be 
diftinguifned  from  each  other.     Jet 
is  faid  to  be  found  only  in  fimail  de- 
tached pieces,  and  that  it  is  thereby 
diflinguifhable   from  cannel    coal, 

which 


(       12       ) 

which  Is  found  in  large  beds.  Some 
think  that  the  woody  fibrous  tiflue 
of  jet,  may  ferve  to  diftinguiih  it 
from  cannel-coal,  but  whoever  ex- 
amines large  quanties  of  this  kind 
of  coal,  will  fee  many  pieces  which 
much  refemble  wood  in  texture. 
The  weight  of  a  cubic  foot  of  can- 
nel-coal  is  1 273  ounces;  a  cubic  foot 
of  jet  is  faid  by  one  author  to  weigh 
i238,*by  another  1 180  ounces,  j 

The  natural  hiflory  of  Amber  is 
very  obfcure.  This  bitumen  was 
for  a  long  time  thought  to  be  re- 
flrided  to  the  coafts  of  Pruflia,  on 
the  Baltic  Sea.  It  was  fuppofed  to 
owe  its  origin  to  the  ex,udations  of 
certain  trees  on  the  coaft  of  Sweden, 
v/hich  falling  into  the  fea,  were  there 
hardened  by  the  continual  adtion  of 

the 
*  Martin,,    f  Lewis,  Newm.  Chem. 


(  13  ) 
the  faltSj  and  thence  carried  by  par- 
ticular winds  to  the  open  coafls  of 
Pruffia.  This  opinion  was  fupported 
by,  and  fornned  to  account  for,  the 
ants,  flies,  fpiders,  leaves  of  trees, 
and  other  terrefbrial  matters,  which 
are  almofl  always  found  inclofed  in 
pieces  of  amber,  and  which  no  doubt 
muft  be  admitted,  as  proving  its  be- 
ing originally  in  a  -fluid  ftate.  In 
Pruffia  they  not  only  gather  amber 
on  the  fea  coaft,  but  they  frequently 
find  it  at  the  depth  of  eight  or  tea 
feet  beneath  the  furface  of  the  earth, 
but  at  no  great  diftance  from  the  fea. 
The  fuperincumbent  ftrata  are  fand, 
clay,  fofnl-wood,  pyrites,  fand  again, 
in  which  the  amber  is  found,  fome- 
^  times  in  detached  pieces,  fometimes 
in  little  heaps.  This  diftribution  of 
.the  ftrata,  where  amber  is  found,  to- 
gether 


(     14     ) 

gether  with  their  proximity  to  th€ 
fea,  has  madeitAvith  fome  degree  of 
probability  be  imagined,  that  this 
mineral  owed  its  fituation  to  the 
inundation  and  receffion  of  the  fe a, 
and  that  it  was  derived  partly  from 
an  oil  arifmg  from  the  decompofition 
of  vegetables  by  fubterraneous  fires, 
and  partly  -from  a  mineral  acid. 
Amber  is  frequently  found  in  Italy, 
where  they  have  no  fofTil-wood,  but 
great  ^ plenty  of  petroleum. 

The  natural  hiitory  of  ^w^^r^m  is 
asuncertainasthatofambei-junlefswe 
admit  the  defcription  which  has  been 
lately  given  of  its  origin,  as  the  true 
one.  We  are  told  that  ambergris  is 
a  part  of  the  Cachalot  or  Sper7naceti' 
whale,  "  It  is  found  in  this  animal, 
in  the  place  where  the  feminal  vefiels 
are  ufually  fituated  in  other  animals, 
I  It 


(     ^5     ) 
It  is. found  in  a  bag  of  three  or  four 

feetJong,  in  round  lumps,  from  one 
to  twenty  pounds  weight,  floating  in 
a  fluid  rather  thinner  than  oil,  and  of 
a  yellowifli  colour.   There  are  never 
feen  more  than  four  at  a  time  in  one 
of  thefe  bagSj  and  that  which  weigh- 
ed twenty  pounds^   and  v/hich  was 
the   largefl:  ever   feen,    was   found 
fingle.     Thefe  balls  of  ambergris  are 
not  found  in  ail  fiflies  of  this  kind^ 
but  chiefly  in  the  oldefl:  and  fl:rong- 
efl;.*"  This  account  feems  probable 
enough,  for  ambergris  is  a  fine  per- 
fume, and  we  know  that  other  per- 
fumes, fuch  as  civet,  muflc,  and  caf- 
tor,  are  fituated  in  the  inguinal  re- 
gions of  the  civet  cat,  the  muflc  ani- 
mal and  the  beaver. 

All  vegetable,    and  bitumenous, 

and 

*  Goldfmith's  Nat.  Hift.  Vol.-vi.  p.  220. 


(     i6     ) 

and  indeed  all  animal  fubflances. 
leave,  after  their  volatile  principles 
have  been  feparated  by  diftillation, 
a  black  coal.  Thefe  coals  differ  fome- 
vv'hat  from  each  other,  with  refpedt 
to  their  pronenefs  to  catch  fire,  and 
their  ability  to  fupport  it,  but  I  will 
content  myfelf  with  examining  the 
nature  of  the  refidue,  from  the  dif- 
tillation  of  wood. 

This  refidue  does  not  differ  from 
what  is  generally  called  charcoal  j  the 
flighteft  attention  to  the  manner  of 
obtaining  this  refidue,  and  of  making 
charcoal,  will  convince  us,  that  no 
difference  ought  to  be  expe6led. 
When  the  wood  is  diflilled,  its  com- 
munication with  the  external  air  is 
obllruded,  its  volatile  parts  are  ele- 
vated from  it,  by  the  heat  to  which 
itisexpofed^  and  the  relidue  is  that 

pari: 


(     17     ) 

part  of  the  wood  which  remains  af- 
ter all  the  volatile  parts  are  driven 
off.  In  making  charcoal  they  con- 
ilru6t  a  pile  of  wood  upon  the  fur- 
face  of  the  ground,  they  cover  the 
pile  with  a  coating  of  turf,  or  other 
fubflances,  and  make  the  coating  fa 
compadt,  that  it  will  not  admit  of 
air,  except  through  fome  little  round 
holes,  v/hich  are  purpofeiy  made  in 
it,  and  which  can  be  flopped  at  plea- 
fure.  When  the  pile,  thus  con- 
ftrudled,  is  ftt  on  fire,  part  of  the 
oil  of  the  wood  is  confumed  during 
the  burning  of  the  pile,  the  other 
part,  together  with  the  air  and  water 
contained  in  the  wood,  is  eraporatedj 
and  there  remains,  when  the  opera- 
tion is  iinifhed,  the  earthy  part  of 
the  wood,  called  in  that  Hate,  char- 
coal. Thus  the  making  of  charcoal 
VOL.  III.  B  is 


(     i8     ) 

is  a  kind  of  diftiUatior>,  for  the  coat« 
ing  which    furrounds    the    pile    of  ^ 
woo4s  may  be  compared  to  a  retort. 
Henckel  informs  us,  that  150 lbs, 
of  oal^j  will  produce  62  lbs.  of  char- 
coal * ;    but  he  does  not  inform  us 
whether  the  oak  was  dry  or  green, 
whether  it  had  its  bark  on  or  was  < 
peeled^  whether  it  was  all  heart  of 
oak,  or  partly  heart,  and  partly  fap, 
whether  the  operation  of  making  the 
charcoal  was  difcontinued  as  foon  as 
the  wood  ceafed  to  fmoke,  or  pro- 
trailed  feme  time  longer ;  and  yet  a 
difference  in  anyone  of  thefe  circum- 
llances,  will  fenfibly   influence  the 
weight   of  the  charcoal,  procurable 
from  a  definite  weight  of  wood. 

The  woods  which  I  converted  into 
charcoal,  were  dry,  and  had  been  fel- 
led 
•  *  Fo.rc  Satur,  c.  iv,  p*  5^0 


(     t9    ) 

led  many  years,  their  relative  weights 
were  taken  with  great  exa6tnefs. 
Weio-ht  of  a  cubic  foot  of 


■Water   --. 

iooo  avbir.  ounces*, 

Box        — 

9SO    ^ 

Oak        — 

892    .^— 

Alh        -- 

832    .— 

-  Mahogan)^  - 

^    816    ^^^-^ 

AValniit      - 

-     79^    "-— 

Deal 

^     615    — 

Authors  differ 

very  much  as  to  the 

weights  which 

they  have  afligned  to 

definite  bulks  of  the   fan  re  kind  oi 

wood.     Thus, 

one    efti mates    the 

weight  of  a  cubic  foot  of  dry  box  at 

1030*3  another  at  1201    ounces  f:. 

one  puts  the  v/eight  of  a  cubic  foot 

of  dry  oak  at  925  J  5  another  at  800 

ounces  II .     To    the    more   obvious 

B  2  fources 

*  Cotes  Hydros*  p.  73.  t  Fergufon*s 

Tab.  p.  237,    i  CoteSi    fj  Emerfon's  Mech^ 
p.  132. 


(      20      ) 

fources  of  this  diverfity,  in  the 
weights  of  equal  bulks  of  the  fame 
kind  of  wood, — fuch  as  the  wood 
being  green  or  dry,  being  cut  from 
the  boll  or  branch  of  a  tree, — one 
may  be  added,  which  has  not,  I  be- 
lieve, been  fufficiently  attended  to 
— I  mean  the  great  lofs  of  weight 
which  in  certain  circumfljances,  the 
fame  piece  of  wood  fuftajns,  by  a 
fimple  expofure  to  the  atmofphere, 
in  the  courfe  of  a  few  days. 

From  the  middle  of  a  branch  of 
an  oak  tree,  which  had  been  felled  in 
April,  and  expofed  without  its  bark, 
to  the' hot  fummer  of  1779,  I  cut, 
Sept.  4,  a  round  piece,  about  fix  in- 
ches in  diameter,  and  three  inthick- 
nefs :  Sept.  15;!  cut  from  the  heart 
of  this  piece  of  oak  a  fmall  flip,  3 
inches,  in  lengthy  .-J;  .of  an  inch  in 

thick- 


(  "  ) 

ihicknefs,  and  79  grains  in  weight  5 
at  tlie  fame  time,  I  cut  a  fimilar  flip 
from  the  fap  of  the  fame  piece,  the 
weight  of  which  alfo  was  79  grains, 
thefe  two  pieces  were  put  into  the 
drawer  of  my  ftudy  table,  and  being 
weighed  again.  Sept.  25,^  the  heart 
of  oak  had  loft  8  grains,  or  near  ^^V 
of  its  weight ;  the  fap  had  loft  1 2 
grains,  or  above  ~  of  its  weight.  Now 
if  the  weights  of  feveral  equal  bulks 
of  thefe  woods  had  been  taken  on 
the  15th,  and  on  the  25th  of  Sep- 
tember^  it  is  obvious,  (notwith- 
ftanding  the  contra6lion  they  might 
have  fuffered)  that  there  would  hava 
been  fome  difference  in  them  though 
the  woods  themfelves  appeared 
equally  dry  on  both  days. 

This  fpeedy  diminution  of  weight 

which  wood  undergoes  by  expofure 

33  to 


C      2i2      )• 

to  the  air,  being  a  matter  of  fome' 
importance  in  an  oeconomical  view, 
I  will  mention  another  experiment 
which  I  made  on   tlie  fiibje(it»     A. 
piece  of  afh  cut  March  ly,.  1780, 
from  the  middle   of  a  large   tree, 
which  had  been  felled  fix  weeks  be- 
fore,, was    accurately   weighed ;    its- 
weight  was  317  grains,  its  length  3 
inches,,  and  its   breadth  2.,    It  was^ 
weighed  again  March  24,  it  had  loft 
in  the  courfe  of  7  days  62  grains,  or 
near  ^  of  its  weight.     I  weighed  this 
fame  piece  of  wood  on  the  25th  of 
Auguft  in  the  fame  year,  but  it  had 
not  loft  any  thing  of  its  weight,  from 
the    24th    of  MarcL  to    the    25th 
of  Auguft.     The  two  pieces  of  oak,, 
mentioned  in   the  laft    experiment,, 
were  weighed  alfo,  on  the  25th  of 
Auguftj    1780,  they  had  neither  of 
3  them 


(    23    ) 

them   loft,  in  the  courfe  of  eleven 

months,  quite  i  grain;  hence  it  ap- 
pears ;  that  the  matter  which  is  dif- 
perfed  from  wood  after  it  is  cut,  is 
foon  evaporated  :  this  matte>  proba- 
bly confifts  chiefly  of  water.     The 
carriage  of  wood,  efpecially  by  land, 
is-  very  expenfive  :  if  an  oak  or  an 
alh  tree  was    cut   into    boards,  or 
fcantlings,  upon  the  fppt  where  it  is 
felled,  there  would  be  a  faving  of 
the   carriage   of  one  ton  in   fix  or 
feven,  from  the  evaporation  of  the 
fubftance  of  the  wood;   to  fay  no- 
thing of  chips  and  other  refufe  parts,  • 
It  is  well  known  that  all  wood 
becomes  heavier  than  water,  by  hav- 
ing the  air  extraded  from  the  pores, 
either  by  an  air-pump,  or  by  boiling 
it  in  water.     The  woods  of  which: 
J'  have  given   the  relative  weights, 
B  4  were 


(  24  ) 
were  all  of  them  rendered  heavier 
than  water,  by  a  long  continuance  in 
cold  water ;  for  the  heat  of  the  wa- 
ter in  w^hich  they  were  put^  never 
exceeded  60  degrees.  They  funk  in 
the  water  after  they  had  been  foaked 
in  it  for  different  lengths  of  time, 
but  it  required  above  ico  days 
foaking  before  the  deal  would  fink. 
After  they  had  all  lain  in  water  for 
1 10  days  J  I  took  them  out,  and  let 
them  dry  by  the  gradual  heat  of  the 
atmofphere  for  above  a  month;  I  then 
weighed  themj,  and  found  that  box, 
oak,  and  afli,  had  each  of  them  loft 
^V  o^  the  weight  they  had  before 
they  were  put  into  the  water;  but 
that  mahogany,  walnut,  and  deal, 
had  loft  only  ^L.  of  their  weight. 
This  lofs  of  weight  is  occafioned, 
partly  by  the  efcape  of  fome  portion 

of 


I    25    ; 

of  air,  and  partly  by  a  difTolution  of 
fome  of  the  other  principles  of  the 
woods  i  for  the  water,  in  which  they 
were  placed,  had  evidently  a6led 
upon  them,  its  colour  and  confid- 
ence being  both  changed,  Moft 
woods  contain  both  a  gummy  and  a 
reftnous  part ;  and  gums  being  folu- 
ble,  and  refins  not  foluble  in  water, 
we  can  have  no  difficulty  in  appre- 
hending the  reafon,  why  fome  forts 
of  wood  loofe  a  greater  proportion  of 
their  weight,  by  being  immerfed  in 
water,  and  afterwards  dried,  than 
others.  Since  the  fame  piece  of 
wood  has  very  different  weights, 
when  dry  and  when  foaked  with  wa- 
ter ;  the  covering  carts,  ploughs, 
and  other  hufbandry  gear,  ufually 
made  of  afli,  with  a  coarfe  kind  of 
paint  which  will  keep  out  the  rain. 


(     26    ) 

IS  a  pradice  full  as  iervlceable  in 
kfTening  the  weight  of  the  imple- 
ment which  is  to  be  moved  by  the 
llrength  of  a  man  or  horfe, .  as  in' 
preferving  the  wood  of  which  it  is 
made  from  decay, 

I  took  fquare  pieces  of  the  woods 
before  mentioned,  each  piece  being 
3  inches  in  length,  and  weighing 
exaftly  96  grains,  and  expofed  them^, 
when  covered  with  fand,  in  a  cru- 
cible, to  the  adtion  of  the  fame  fire, 
which  was  ilrong  enough  to  keep 
the  crucible  red  hot,  for  three 
hours ;  they  were,  at  the  end  of 
t:hat  time,  all  of  them  converted 
into  perfed  charcoals  ;  the  weights 
of  the  refpe6live  charcoals  were 
taken,  whilft  they  were  Hill  warm^. 
from  the  operation,, and  are  exprefled 
in  the  following  table  : 

Walnut 


(     27     ) 

Walnut      96  grns.  gave  25  grns. -of  charcoal 
Oak    —    96    —    —    22     — 

Box    —     96    —    —    20    ■ 

Mahogany  96     —    —    20     - 
i\fli     —    96    —    —     17     — 

Deal  —     9.6    —    —     15 

There  is  a  good  reafon  for  remark- 
ing, that  the  charcoals  were  weighed 
whim  they  were  warm,,  for  in  weigh- 
ing them  a  few  days  afterwards,  I 
found  that  they  had  all  increafed  in 
weight  in  eonfequence  of  Jomething 
which  they  had  attra6led  from  the 
atmofphere ;  their  weights  then  were 
■ — walnut  28  —  oak  24  —  box  23 
■ — mahogany  24  —  alh  18  —  deal 
16  — grains. 

The  quantities  of  refidue  remain- 
ing from  the  diftillation  of  96  ounces 
of  oak,  box,  and  mahogany,  were 
refpedively  30,  26!,  and  27!  oun- 
ces, 


(28  ) 
ces,  which  numbers  are  feverally 
larger  than  thofe,  exprefTing  the 
quantities  of  charcoal  obtainable 
from  96  parts  of  thofe  woods ;  this 
difference  may  proceed  from  the 
woods,  employed  in  the  two  procef- 
fes,  being  of  different  qualities,  or, 
more  probably,  from  the  heat  ia 
which  the  charcoal  was  made,  being 
greater  than  that  employed  in  the 
diilillation ;  for  the  ftronger  the  fire, 
the  lefs  is  the  quantity  of  charcoal, 
which  a  definite  weight  of  wood  will 
yield. 

In  making  charcoal  the  workmen 
obferve,  that  the  pile  of  wood  is 
fenfibly  .diminiHied  in  fize  by  the 
operation ;  this  proceeds  from  the 
fhrinking  of  the  wood.  All  the 
kinds  of  wood  which  I  charred  were 
diitiiniflied  in  all  their  dimenfions, 

the 


(       29      ) 

the  mahogany,  oak,  and  walnut, 
v/ere  the  lead  diminifhed,  and  the 
box  was  the  moft  dinr.inilhedj  I 
thought  it  had  lofl  an  eighth  part  of 
its  length.  This  diminution  not  on- 
ly  depends  upon  the  nature  of  the 
wood,  but  it  is  influenced  by  the 
flrength  and  continuance  of  the  heat, 
that  being  moil  diminifhed^  which 
has  fuftained  the  great^ft  heat. 

Though  charcoal,  from  every  fort 
of  wood,  is  incapable  of  being  de- 
compofed,  by  the  ilrongeft  fires  in 
clofe  velTels,  yet  it  is  a  compounded 
body,  and  may  be  decompofed  by 
being  burned  in  the  open  air. 

Van  Helmont  fays,  that  6  2  pounds 
of  oak  charcoal  will,  by  burning, 
yield  only  ilb.  of  white  afhes.  The 
other  6 1  pounds  which  are  difperfed 
into  the  air,  he  confiders  as  a  vapour 

of 


(      JO      ) 

of  an  elaftic  nature,  which  can  nei- 
ther be  colle6i:ed  in  vefTels,  nor  re- 
duced into  a  yifible  form.  This  va- 
pour he  called  by  a  new  nanfie,  gas^, 
Stahl  is  of  opinion,  that-iolbs.  of 
charcoal  made  from  porous  woods, 
fuch  as  fir  and  fallow^  will  not,  when 
burned  with  a  very  flow  fire,  yield 
^bove  lib.  of  allies f;  this  quan- 
tity however,  it  mud  be  remarked, 
is  above  fix  times  the -quantity  af- 
figned  by  Van  Helmont  to  oak, 
which  probably  contains  more  afhes 
in  a  definite  weight  of  charcoal,  than 
either  fir  or  fallow, 

GeofFroy, 

*  Hunc  fpiritum,  incognitura  ha^lenus, 
novo  nomine  gas,  voco,  qui  nee  vafis  cogi  nee 
incorpus  vilibile  reduci  poteft.  Van  Hel,  Op. 
om.  p.  103.  Some  derive  gas  from  the  Dutch 
ghoaft-fpirit ;  others  from  the  German  gafcht, 
a  frothy  ebullition. 

f  StahliiExper.  Numero  CCC.  p.  17*' 


(    3 1     ) 

GeofFroy,  from  ibmewhat  lefs  than 

34  ounces  of  the  charcoal,  remaining 

.  after  the  diftillation  of  the  heart  of 
guaiacum,  got  near  three  ounces  of 
white  afhe^,  by  calcining  the  coal  in 
an  open  fire  for    12  hours.     From 

.near  23 1  ounces  of  the  coal,  re- 
maining from  the  diftillation  of  the 

'fap  of  guaiacum^  he  got  near  if 
ounce  of  afhes.   And  %gl  ounces  of 

...the  coal,  from  the  bark  of  guaia- 

-  cum,  gave  him  13I  ounces  of  white 

:.  afhes*. 

Laftly,  M.  Sage  aflures  us  that 
100  pounds  of  charcoal   will  not, 

•■  when  burned,  furnifli  quite  2  ounces 
of  alhesf. 

Thefe  accounts,  it  muft   be  ac- 

know- 

*  Geof,  Mat.  Med.  or  treatife  on  foreign 
vVegeta.  by  Thicknefs.  p.  112. 

,f  Exper.  fur  F  Alk.  VoUfluor.  p.  2.70 


(     3^    ) 

Icnowledged,  differ  very  much,  as  to 

the  quantity  of  afhes  obtainable 
from  a  definite  weight  of  charcoal ; 
and  the  difference,  I  think,  is  much 
greater  than  what  can  wholly  be  at- 
tributed to  the  different  textures  of 
the  feverai  woods ;  a  part  of  this  di- 
verfity  may,  probably,  arife  from  a 
difference  in  the  manner  of  burning 
the  charcoal.  When  charcoal  is 
burned  in  fmall  quantities,  and  in  a 
flow  fire,  lefs  of  its  fubllance  will  be 
difperfed  into  the  air,  than  when  the 
quantity  is  larger,  and  the  ftream  of 
air  which  fupports  the  fire,  is  m.ore 
rapid.  This  feems  not  improbable  ; 
but  if  the  weight  of  the  afhes  re- 
maining from  the  burning  of  a  defi- 
nite weight  of  charcoal,  be  at  all  in- 
fi.uenced  by  the  degree  of  fire,  it 
feems    reafonable    to  fuppofe,   that 

what 


i    33     )       ^ 
wliat  is  driven  off  by  the  violence  of 

the  fire,  is  of  the  fame  earthy  nature, 
as  that  which  remains  when  the  fire 
is  more  moderate  ^  at  leaft  it  may  be 
argued,  that  when  charcoal  is  burn- 
ed with  a. flow  fire,  fome  of  its  prin- 
ciples, its  oily  principle  for  inflance, 
though  it,  probably,  alfo  contains  a 
faline  one,  are  more  completely  de- 
•compbfed,  than  when  it  is  confumed 
with  a  violent  fire,  and  that  the  d^e- 
'Compofition  of  thefe  principles,  gives 
an  additional  quantity  of  earth  or 
ialt  to  the  afhes. 

If  there  be  any  truth  in  this  notion, 
"we  muii;  not  fay,  th^  the  6i  pounds 
of  matter  which,  according  to  Van 
Helmont,  are  difperfed  into  the  air 
from  62  pounds  of  charcoal,  are 
wholly  of  an  elaftic  nature ;  fince 
they  may  confift  principally  of  an 
VOL.  Ill,  C  attenu- 


C     34     ) 

attenuated  earth,  which  being  driven 
off  by  the  current  of  air,  requifite 
for  the  maintenance  of  the  fire,  re- 
mains for  a  time  fufpended  in  the  at- 
mofpherical  air,  without  being  in  its 
own  nature  elaftic.  I  would  not  be 
underftood  to  fay,  that  the  whole  of 
what  is  dilTipated,  during  the  burn- 
ing of  the  charcoal,  is  an  attenuated 
earth,  Tince  it  is  certain,  that  the 
earth  of  theafhes  is  not  inflammable, 
and  that  charcoal  contains  fomething 
which  is  inflammable;  it  is  allowed 
alfo,  that  fimple  earth  is  inodorous, 
and  it  is  well  known,  that  charcoal, 
during  its  inflammation,  difperfes 
fomething  into  the  air,  which  has  a 
ftrong  fmell  -,  this  fomething  by  which 
charcoal  is  rendered  inflammable, 
and  by  w^hich  the  air  is  infeded  with 
a  particular  fmell,  during  the  burn- 
ing 


(     35     ) 

mg  of  the  charcoal.  Is  called  by  moft 

chemifls    the    phlogifton*.      This 
c  2  phlogiilon 

*  PhlogiftoH  is  a  conftituent  part  of  me- 
tallic fubftances,  and  it  feems,  when  fepa- 
rated  from  them,  to  he  of  an  elaflic  nature. 
I  diftilled  zinc  wiih  J^rong  acid  of  vitriol,  and 
obtained  a  portion  of  fulphur,  produced,  as 
it  fhould  feem,  by  the  acid's  uniting  itfelf 
with  the  phlogifton  of  the  zinc.  No  inflam- 
mable vapour  was  produced,  till  the  fulphur 
began  to  be  fublimed,  then  indeed,  there 
efcaped  a  vapour,  compofed,  I  think,  of  the 
attenuated  parts  of  fulphur,  which  upon  the 
approach  of  a  candle  took  fire.  Another 
portion  of  zinc  was  dillilled  with  iv^ak  acid 
of  vitriol  J  before  the  zinc  fdt  the  heat  of  the 
lire,  the  inflammable  air,  feparable  from  zinc 
by  a  weak  acid  of  vitriol,  pafled  into  the 
receiver,  and  being  fet  on  fire,  biirll  it  with 
a  great  explofion :  another  receiver  was  ap- 
plied, and  the  diflillation  continued  to  dry- 
nefs,  but  not  a  particle  of  fulphur  v/as  pro- 
duced, the  phlogifton  necefTary  for  its  for- 
mation having,  probably,  been  feparated 
from  the  zinc,  by  the  violent  action  of  the 

acid. 


(    36     ) 

phloglilon,  whether  it  be  an  elaftic 
inflammable  fluid,  or  an  unelaftic 
earth  of  a  particular  kind,  conflitutes^ 
probably,  but  a  very  fmall  portion 
of  the  weight  of  what  is  difperfcd. 
into  the  air,  from  burning  charcoal;: 
we  all  know  what  a  firong  fmell 
may  be  difFufed  through  a  large 
room,  from  the  ignited  fnuff  of  a 
candle,  or  from  a  very  fmall  piece 
of  charcoal,  which  has  not  been 
thoroughly  burned;  the  vapours 
ifluing  from  thefe  fubilances  are  of 
an  oily  faline  nature,  and  are  vifible^: 
the  vapour  of  charcoal,  though  it  is 
too  fubtleto  be  feen,  may  be  of  a 
nature  fomevv^hat  fnnilar,  and  capa- 
ble 

acid,  and  confumed  at  once  by  the  inflam- 
maticn.  May  it  not  from  the  comparifon 
of  thefe  experiments  be  conje6liired,  that  the 
phlogifton  of  metals  is  an  elaftic  inflamma- 
ble air  ? 


(     57     ) 

He   of  a  very   extenfive    diffufion 

through  the  air.  An  infant  has  been 
known  fuddenly  to  expire,  from  the 
fmoke  of  a  candle  blown  out  under 
its  nofe,  and  the  vapour  of  charcoal 
is  mod  dangerous,  when  the  char- 
coal has  not  b^en  thoroughly  burnt. 

It  has  been  found  by  experiment, 
that  the  comman  atmofpherical  air 
is  much  altered  in  its  properties,  by 
being  made  to  pafs  through  red  hot 
charcoal,  into  the  vacuum  of  an  air 
pumpi  it  then  extinguiihesthe  flam.e 
of  a  candle,  and  animals  die  in  it*. 
a  fimilar  change  takes  place,  when 
charcoal  is  confumed  in  an  apart- 
ment, which  has  not  a  fuflicient  fup- 
ply  of  frefh  air  ;  the  inflances  of  per- 
fons  who  have  unhappily  loft  their 
lives  in  fuch  air,  are  very  common  in 
c  3  all 

*  Plauklbee's  Exper.  p.  287, 


(  33  ) 
all  countries,  where  much  ufe  is: 
made  of  charcoal,  but  efpe daily  m 
Ruifia,  where  their  apartments  are 
heated  by  ovens,^  containing  red  hot 
charcoal*.  The  change  which  the 
atmofpherical  ^ir  undergoes,  from 
the  burning  of  charcoal,  may  pro- 
ceed either  from  the  air,  having  lolt 
fome  of  its  conflituent  parts  in  com..- 
ing  in  conta£l  with  the  burning  char- 
coal, or  from  its  having  gained 
fomething  from  the  charcoal,  or  from 
its  having  done  both  at  the  fame 
time;  jufl  as  water  which  palTes 
through  a  lump  of  fait  or  fu  gar,  lofes 

a  great 
*  Philof.  Tranf.  1779,  p.  325 — ^Where 
there  is  mention  made  of  the  Ruffian  method 
of  recovering  perfons  who  have  been  render- 
ed fenfelefs  by  the  vapour  of  the  charcoal ;  it 
conlifts  in  carrying  the  perfon  into  the  opea 
air,  rubbing  him  with  fnov/  or  cold  water,,  and 
pouring  water  or  milk  down  his  throat. 


(    39    ) 

a  great  part  of  the  air  it  contains  in 

its  natural  ftate,  and  gains  a  portion 
of  the  fait,  which  becomes  dilTolved 
in  it^  and  upoa  both  accounts  fufFers 
a  change  of  its  properties.  , 

It  is  generally  admitted,  that  char- 
coal and  all  other  bodies,  nitrous 
ones  excepted,  ceafe  to  burn,  as  foon 
as  they  ceafe  to  be  fupplied  with 
frefh  air,  and  the  air  has,  chiefly  on 
this  account,  been  thought  to  com- 
miinicate  ibmething  to  the  fire,  by 
which  the  fire  was  maintained,  and 
the  air  was  confuted.  And  this 
opinion  has.  been  confirmed  by  ob- 
ferving,  that  a  definite  quantity  of 
air  was  much  diminifned  in  bulk  by 
bodies  being  burned  in  it.  Thus, 
if  lo  cubic  inches  of  air  be  made  to 
pafs  through  red  hot  charcoal,  diey 
will  be  reduced  to  nine,  and  there 
c  4  are 


(     40    ) 

are  means  of  making  the  dimintrtios 
ftill  greater. 

Dr.  Hooke  advances  another  hy- 
pothefis  3  he  allows  air  to  be  necef- 
fary  to  the  fupport  of  fire,,  but  he 
thinks  that  it  contributes  to  this  fup- 
port,  not  by  imparting  any  thing  of 
its  own  fubfcance  to  the  fire,  but  by 
diJfGlving  the  inHammable  principle- 
of  bodies,  as  water  difTolves  falts  *: 
according  to  the  former  hypothefis 
air  is  ih^food  -,  according  to  this  it  is' 
the  receptacle  ovjolvent  of  fire. 

Dr.  Prieflly,  to  whofe  inventive 
genius  and  indefatigable  induftry  the 

philo- 
*  Hooke's  Micogr.  p.  103.  and  Pofthum„ 
Works  p.  169.  Jimcker  feems  to  have  en- 
tertained a  iimilar  notion — ingens  aeris 
quantitas  requiritur  ad  dljfoln^endas  et  recipi- 
€ndas  ignitas  illas  et  ultimo  motu  attenuatas 
particiilas,  unde  nili  fat  aeris  lit  extinguitui? 
ignis.    Junck.  Gonf»  Chem.  VoL  I.  p.  1 5.7. 


(41     ) 

philofophic  world  is  peculiarly  in- 
debted for  his  inquiries  into  the  na- 
ture of  fiditious  airs>  has  obferved^, 
that  common  air  is  diminifhed  one 
iifth  by  the  fumes  of  burning  char- 
coal y  and  this  dimunition,  he  thinks 
is  fome  how  or  other  effe6Ved  by  the 
air  being  highly  charged  with  the 
phlogiflon  of  the  charcoal  i  and  he 
obferves^which  agrees  very  well  with 
Dr.  Hookers  hypothefis,  that  when 
any  definite  quantity  of  air  is  fully 
faturated  with  phlogiflon  from  char- 
coal, no  heat  that  he  had  ever  ap- 
plied was  able  to  produce  any  more 
efFedt  upon  the  charcoal*. 

Though  common  air  is  diminifhed 
in  bulk  by  the  fumes  of  burning  char- 
coalj  and  of  other  bodies,  in  a  ftatc  of 
combuftion,  yet  a  bottle  or  a  bladder 

filled 

*  Philof.  Tranf.  i-^-^J,  p.  2 25 »— 230. 


I    42    ; 

filled  with  this  diminifhed  air,  weighs 
lefs  than  when  it  is  filled  with  com- 
mon air*,  in  the  proportion  of  1 83 
to  185,  That  5  cubic  inches  of 
common  air,  fnould  be  reduced  by 
the  fumes  of  burning  charcoal  to  4 
cubic  inches^  and  that  thefe  4  cubic 
inches  of  infeded  air,  ihould  Vvxigh 
lefs  than  4  cubic  inches  of  common 
air,  cannot  v/eli  be  accounted  for 
without  admitting,  that  a  part  of  the 
5  cubic  inches  of  atmofpherical  air, 
has  been,  by  fome  means  or  other, 
taken  away,  at  the  famiC  time  that  its 
bulk  was  reduced  to  4  cubic  inches. 
Being  defirous  of  feeing,,  whether 
the  property  1  had  obferved  in  char- 
coal, with  relpe6l  to  its  weighing  lefs 
when  it  v/as  quite  cold,  than  when 
it  was  Y/arm  from  the  fire  in  which 

k 
*  Prieft.  Exp.  and  Ob.  \ol.  11.  p.  94. 


(    43     ) 

it  had  been  made,  was  a  general  pro-, 
perty  appertaining  to  all  hot  and 
cold  charcoal,  I  weighed  feveral 
pieces  when  they  were  cold,  and 
again,  when  they  were  fo  hot  as  to  be 
handled  with  difficulty,  and  found 
that  they  all  loft  (they  were  of  the- 
fame  kind  of  wood)  about  i  part  in 
1 2  of  their  weight,  and  that  being 
left  to  cool  in  the  open  air,  they  re- 
gained what  they  had  loft  in  a  few 
days.  This  acquifition  of  weight 
was  made  moft  rapidly  at  firft,  a. 
piece  which  weighed  240  grains 
when  cold,  was  reduced  by  being 
heated,  to  220  grains,  and  being  left 
to  cool,  it  gained  9  grains  in  4  hours, 
and  1 5  grains  in  8  hours.  From  the 
manner  in  which  charcoal  is  made, 
it  is  probable  that  what  remains  ad- 
herent to  the  wood,  is  not  greatly 

differ- 


C     44     ) 

different  from  what  is  forced  from 
it  by  the  lad  degree  of  heat;  now" 
this  Gonfifts  of  an  acid,  and  an  oil 
rendered  thick  and  pitchy  by  its- 
union  with  an  acid;  may  we  not 
hence  fuppofe,  that  it  is  a  portion  of 
fixed  acid,  which  attracts  the  humi-- 
dity  of  the  air,  or  perhaps  the  air  it- 
felf,  when  the  charcoal  is  hot,  and 
becomes  faturated  therewith,  and 
that  what  was  attra6ted,  is  again  dri- 
ven off  when  the  charcoal  is  again- 
heated  5  and  thus  the  charcoal  be- 
comes again  capable  of  exerting  its 
attraction,  and  acquiring  an  encreafe 
of  weight^.  It  is  fome  confirmation 
of  this  hypothecs,  that  charcoal 
when  taken  out  of  hot  fand,.  takes 
fire  upon  expofure  to  the  air,  and 
for  much  the  fame  reafon,  probably, 
that  Homberg's    pyrophorus  takes 

fire 


(     45     ) 

fire  in  the  open    air*.     Guaiacum 

contains  a  flronger  acid  than  moft 
kinds  of  wood,  and  GeofFroy  has 
obferved  that  "the  coal  of  guaia- 
cum  being  taken  out  of  the  retort, 
and  expofed  to  the  air,  even  two  or 
three  days  after  the  procefs,  takes 
£re  imniediatqly  of  its  own  accord; 

provid- 
*  Homberg's  Tyrophorus  is  known  to 
<every  fchool-boy.  It  is  made  by  calcining 
together  for  a  proper  tinie,  and  in  proper 
<iuantities,  either  alum  or  any  fait  containing 
the  vitriolic  acid,  with  honey,  fugar,  flour,  or 
any  animal,  or  vegetable  fubftance,  capable 
of  being  reduced  to  a  eoal.  Part  of  the  vi- 
triolic acid  being  uncombined  with  the  phlo- 
gillon  of  the  coal,  and  being  in  a  dry  con- 
denfed  flate,  attrads  the  humidity  of  the  at- 
mofphere,  and  generates  fuch  a  degree  of  heat 
by  its  mixture  with  water,  as  is  fufl[icient  to 
'inflame  the  other  part  of  the  pyrophorus.  Py- 
Tophori  may  be  made  without  the  vitriolic  acidj 
butfome  acid  probably  enters  into  their  cona- 
cpoiition« 


(    46     ) 

provided,  that  when  the  diftillation 
is  over,  the  neck  of  the  retort  be 
carefully  flopped,  and  the  veflels  and 
furnace  be  left  to  cool  of  them- 
felves"*. 

This  property  of  increafing  in 
weight  by  expofure  to  the  air,  be- 
longs to  the  hot  coal  of  pitcoal,  as 
well  as  to  that  of  wood  -,  I  took 
fome  red  hod  cinders,  and  weighing 
them  in  that  ftate,  left  them  to  cool ; 
in  12  hours  they  had  gained  one 
75th  part  in  weight,  and  in  4  days 
they  had  gained  one  thirtieth  of 
their  weight.  Some  coak  whic:h  had 
been  burned  with  a  ftrong  fire, 
gained  much  lefs  than  the  cinders. 

It  has  been  obferved  in  another 
place,  that  charcoal  may  be  decom- 
pofed,  by  being   diftiiled  with  the 

acid 

*  Treatife  on  foreign  vege.  p,  1 1 1 . 


(  47  ) 
acid  of  vitriol* ;  this  acid  robs  the 
charcoal  of  its  inflammable  principle, 
and  reduces  it  to  an  earth  :  no  other 
menflruum  feems  to  have  any  a6cion 
upon  it.  What  alteration  might  be 
produced  in  charcoal,  by  quenching 
it  when  red  hot,  in  various  menftru- 
umSj  or  by  boiling  it  in  them,  or  by 
keeping  it  immerfed  in  them,  when 
cold,  for  a  long  time,  or  by  other 
lefs  obvieu5  procefTes,  it  does  not 
fall  ^within  my  defign  to  inquire. 

Animals  and  vegetables  are  foon 
reduced  by  putrefaction  to  an  earth.; 
many  forts  of  flones  and  metallic 
fubflances  are  crumbled  into  duft  by 
the  adlion  of  air  and  water ;  but  char- 
coal remains  unchanged  for  ages, 
whether  it  be  expofed  to  the  air,  or 
immerfed  in  water,  or  buried  in  the 
^arth.     The.  beams    of  the  theatre 

at 


(     48     ) 

at  Herculaneum  were  converted  into 
charcoal  by  the  Lava^  which  over- 
flowed that  city,  and  during  the 
lapfe  of  above  feventeen  centu- 
ries the  charcoal  has  remained 
as  entire  as  if  it  had  been  formed  but 
yefterday^  and  it  will  probably  con- 
tinue fo  to  the  end  of  the  world. 
This  incorruptibility,  as  it  may  be 
called,  of  charcoal  has  been  known 
in  the  moft  diftant  ages ;  for  it  has 
been  obferved  that  the  famous  temple 
of  Ephefus  was  built  upon  wooden 
piles  which  had  been  charred  on  the 
oiatfide.  The  cuftom  of  -charring 
the  ends  of  pofls  which  are  to  be 
fixed  in  the  earth  is  very  common, 
and  I  have  often  wondered  that  the 
fame  cuftom  has  not  prevailed  with 
.refpe(5t  to  the  wood  ufed  in  mines 
and  fubterraneaus  drains.  The  tim- 
I  bers 


C     49     ) 

hers  which  fupport^  in  many  places, 
the  roof  of  the  foughs  through 
which  there  is  a  current  of  water, 
are  wailed  away  in  a  fev/  years,  that 
part  of  them  efpecially  which  is  ex- 
pofed  to  the  alternatives  of  moifture 
and  drynefs  by  the  rifmg  and  falling 
of  the  water  is  foon  rotted,  and  this 
part  one  would  think  would  be  char- 
red with  ,ireat  advantao-e. 


I)  "ESSAY 


ESSAY      II 


©P  THE  QlTANTITr  OF  WATER  EVA- 
PORATED FROM  THE  SURFACE  OF 
THE  EARTH  IN   HOT  WEATHER. 

^I^HERE  are  many  operations- 
JL  conftantly  carrying  on  by  na- 
tural means,  v/hich,  though  they 
cfcape  the  ordinary  obfervation  of 
our  fenies^  fufficiently  excite  our  a- 
ftonilhment  when  once  difcovered. 
The  vafl:  quantity  of  a  particular 
kind  of  air,  with  which  the  atmof- 
phere  is  daily  impregnated,  from 
she  combuilion  of  all  forts  of  f  jel,  is- 
E>  2  one 


(  52  ) 
one  inftance  of  this  kind ;  and  the 
water  which  is  raifed  into  the  attnof- 
phere  fronn  the  furface  of  the  earth, 
is  another.  Who  would  have  con- 
jedured  that  an  acre  of  ground,, 
even  after  having  been  parched  by 
the  heat  of  the  fun  in  fun^imcr,  dif- 
perfed  into  the  air  above  1600  gal- 
lons of  water  in  the  fpace  of  tv/elve 
of  the  hotteil  hours  of  the  day  ?  No 
vapour  is  {een  to  afcend,  and  we 
little  fuppofe  that  m  the  hotteft  part 
of  the  day,  more  ufually  does  afcend 
than  in  any  other.  The  experiment 
from  which  I  draw  this  conclufion, 
is  fo  eafy  to  be  made,  that  every  one 
may  fatisfy  himfelf  of  the  truth  of  it. 
On  the  2d  of  June,  1779,  v/hen  the 
fun  ilione  bright  and  hot,  I  put  a 
large  drinking  glafs,  v/ith  its  miouth 
downw'iro''.   u-'/on  3  o-n^-rlr^t  wj^^rh 


C    53     ) 

was  mown  clofe ,  there  had  been  no 

rain  for  above  a  month,  and  the 
grafs  was  become  brown ;  in  lefs 
than  two  minutes  the  infide  of  the 
glafs  was   clouded  with   a  vapour, 

and  in  half  an  hour  droDS  of  v^ater 

i. 

began  to  trickle  down  its  infide,  in 
various  places.  This  experiment 
was  repeated  feveral  times  with  the 
fame  fuccefs. 

That  I  might  accurately  eftimate 
the  quantity,  thus  raifed,  in  any  cer- 
tain portion  of  time,  I  meafured  the 
area  of  the  mouth  of  the  glafs,  and 
found  it  to  be  20  fquare  inches  : 
there  are  1296  fquare  inches  in  a 
fquare  yard,  and  4840  fquare  yards 
in  a  ftatute  acre  -,  hence,  if  we  can 
find  the  means  of  meafuring  the 
quantity  of  vapour  raifed  from  20 
fquare  inches  of  earth,  fjppofe  in 
D  3  one 


(     54    ) 

one  quarter  of  an  hour,  it  will  be  an 
eafy  matter  to  calculate  the  quantity 
which  would  be  raifed  with  the  fame 
degree  of  heat,  from  an  acre  in  1 2 
hours.  The  method  I  took  to  mea- 
fure  the  quantity  of  vapour,  was  not 
perhaps  the  mod  accurate  which 
might  be  thought  of,  but  it  was  lim- 
pie  and  eafy  to  be  pradtifed  :  when 
the  glafs  had  flood  on  the  grafs-plat 
one  quarter  of  an  hour,  and  had 
collected  a  quantity  of  vapour,  I 
wiped  its  infide  with  a  piece  of  muf- 
-lin,,  the  weight  of  which  had  been 
previoufly  taken ;  as  foon  as  the" 
glafs  was  wiped  dry,  the  muHin  was 
weighed  again,  its  increafe  of  weight 
fhewed  the  quantity  of  vapour  which 
had  been  collefted.  The  medium 
increafe  of  weight,  from  feveral  ex- 
periments made  on  the  fame  day, 
J  between 


<     55    ) 

b-etween   12  and  3  o'clock,  was  6 

grains  colleded  in  one  quarter  of  an 
hoiir^  from  20  fquare  inches  of 
earth.  If  the  reader  takes  the  trou- 
ble to  make  the  calculation,  he  wilf 
find  that  above  1600  gallons,  reck- 
oning 8  pints  to  a  gallon,  and  efli- 
mating  the  weight  of  a  pint  of  wa- 
ter at  one  pound  avoirdupoife,  or 
7000  grains  troy  \7eight,  would  be 
raifed,  at  the  rate  here  mentioned^ 
from  an  acre  of  ground  in  24  hours. 
It  may  ealily  be  conceived  that 
the  quantity  thus  elevated,  will  be 
greater  v/hen  the  ground  has  been 
well  foaked  with  rain,  provided  the 
heat  be  the  fame ;  I  did  not  happen 
to  mark  the^hrat  of  the  ground  v^hen 
I  m.ade  the  forementioned  experi- 
ments i  the  t^o  following  are  more 
circumllantial :  the  ground  had  been 
D  4  wet^ 


(56     ) 

wetted  the  day  before  I  made  them 

by  a  thunder  fhower^  the  heat  of  the 
earth  at  the  time  of  making  them, 
eftimated  by  a  thermometer  laid  on 
the  grafs,  was  96  degrees ;  one  ex- 
periment gave  1973  gallons  from 
an  acre  in  1 2  hours,  the  other  gave 
1905.  Another  experiment  made 
when  there  had  been  no  rain  for  a 
week,  and  the  heat  of  the  earth  was 
no  degrees,  gave  after  the  rate  of 
aSoo  gallons  from  an  acre  in  12 
hours  ',  the  earth  was  hotter  than  the 
air,  as  it  was  expofed  to  the  reflec- 
tion of  the  fun's  rays  from  a  brick 
wall. 

The  heat  in  Bengal  in  the  fummer 
months  is  variable,  in  the  fhade  from 
98  to  120  degrees,*  and  in  the  fun 
it  probably  does  not  fail  Ihort  of 

140 
*  Phllof.  Tranf.   1767,  page  218,   and  for 
the  year  1775,  P«  *02, 


(57     ) 

140  degrees  j   hence,  after  the  earth 

has  been  well  drenched  by  the  over- 
flowing of  the  Ganges^  immenfe 
quantities  of  vapours  mufl  be  daily 
raifed,  to  the  amount,  perhaps,  of 
five  or  fix  thoufaitd  gallons  from  an 
acre,  in  twenty-four  hours.  The 
rainy  fcafon  in  Bengal  lafts  from  the 
beginning  of  June  to  the  middle  of 
October,  all  this  interval  isconfidered 
as  an  unhealthy  time,  but  efpecially 
the  latter  part  of  it ,  for  then  the 
earth  begins  to  grow  dry,  the  flime 
left  upon  its  furface,  confifting  of 
decayed  vegetables  and  other  putref- 
.cent  bodies,  begins  to  corrupt,  and 
the  fun  by  its  violent  and  continued 
action  raifes  up  into  the  air,  not  a 
pure  water,  but  water  impregnated 
-with  putrid  particles  of  all  kinds. 
Whether  a  merely  raoill  fituation 

be 


(     58    ) 

^e  unwholefome  may  be  mtvch 
queflioned,  but  that  moifture  arifing 
from  earth  or  water  in  a  ftate  of  pu- 
trefadion  is  fo,  cannot  well  be 
doubted.  The  overflowing  of  the 
Nile  puts  a  ftop  to  the  plague  in 
Egyp^  infomuch,  probably,  as  it  puts 
a  ftop  to  the  putrefadlion  of  the  ca- 
nals of  Grand  Cairo  and  other  places. 
Agues  and  putrid  fevers  are  much 
more  frequent  in  the  fens  of  Gam- 
hridgefnire  and  LincolnJInre  in  very- 
dry,  than  in  wet  years  ^  the  Irijh^  who 
annually  come  to  reap  the  harveft  in 
the  fens  of  Cambridgefhire,  have 
tieen  fo  fenfible  of  the  difference, 
that  for  the  three  or  four  years  laft 
^aft,  which  have  been  very  dry,  they 
Have  entered  upon  their  tafk  with 
great  reludance  and  apprehenfion  of 
what  they  call  the  Fen-Jhake,     The 

States 


(     S9     ) 

States  o(  Holland y  in  the  year  174.S, 

laid  the  country  around  Breda  under 
water,  and  ordered  the  water  to  be 
kept  up  till  the  wineer,  in  order  to 
flop  a  ficknefs  which  had  arifen  from 
the  moiil  and  putrid  exhalations  of 
half-drained  grounds.*  The  Arabs 
are  faid  to  take  a  horrid  kind  of 
vengeance  when  they  think  them- 
felves  injured  by  the  ^urks  at  Bajfora ; 
they  contrive  to  overflov\^  the  adjoin- 
ing country:  a  peftilential  fever  be- 
gins to  Ihew  itfelf  as  the  land  begins 
to  grow  dry  by  the  evaporation  of 
the  water,  and  it  rages  with  fuch 
violence  as  to  carry  off  many  thou- 
fands  of  the  inhabitants  of  that  city. f 
The  nature  of  the  foil  muft  have 
a  great  influence  on  the  health  of  the 

people 

*  Sir  J.  Pringle's  Dif.  of  the  Army,  p^  63* 
f  Ptiilol.  Tranf.  1778,  p.  215. 


(    6o    ) 

people  who  inhabit  it,  fo  far  as  that 
is  dependent  on  the  moifture  or  dry- 
nefs  of  the  air.  There  is,  probably, 
as  much  water  raifed  into  the   air, 
in  a  hot  day,  from  an  acre  of  ground 
in  the  fens  of  Camhridgejhire^   as  is 
raifed  in  two  or  three  days  from  an 
equal  furface  in  the  fandy  parts  of 
Norfolk  and  Suffolk^     Not  but  the 
moft  fandy  country  may  have  a  very 
moift  atmofphere,   when  water  hap- 
pens to  be  found  near  the   furface  j 
for  the  heat  of  the  fun  will  penetrate 
through  the  fand,  and  raife  the  water 
in  vapour,  which  will  find  an  eafier 
palTage   through   the  fand   than    it 
would  do  through  a  lefs  open  foil. 
Thus  the  foil  in  fome  parts  of  Dutch 
Brabant  is  a  barren  fand,  but  water 
is  every  where  to  be  met  with  at  the 
depth  of  two  or  three  feet,  and  in 

propor- 


(    6i     ) 

proportion  to  its  diflance  from  the 
furface  the  inhabitants  are  free  from 
difeafes.* 

Vegetation  muft  be  greatly  influ- 
enced by  the  quantity  of  water  which 
is  raifed  from  the  earth  ;  fome  foils 
retain  humidity  much  longer  than 
others,  and  one  great  ufe  of  marles 
and  other  manures,  is  to  render  the 
foil  on  which  they  are  put  lefs  liable 
to  be  deprived  of  its  moiflure  by 
the  heat  of  fummer.  The  water  in  af- 
cending  from  the  bofom  of  the  earth, 
moiftens  the  roots,  and  in  being  dif- 
folved  in  the  air,  it  affords  nutriment 
to  the  branches  of  vegetables ;  but 
as  vegetation  may  be  injured  either 
by  a  defe6t,  or  an  excefs  of  moiflure, 
and  as  different  plants  require  dif- 
ferent quantities  of  it,  for  attaining 

dieir 

*  D&f.  of  the  Ari-v,  d,  62. 


C     62     ) 

their  utmoil- perfe6tion^  it  merits  tne 
attentive  obfervation  of  the  farmer 
to  fuit  his  plants  and  his  manures  to- 
the  nature  of  the  foil.  There  aremany^ 
fandy  and  limeftone  foils,  which  are 
covered  almoft  with  flints  or  lime- 
ftone  pebbles;-  the  crop  of  corn 
would,  probably,  be  lefs,  if  thefc 
:0:ones  were  removed  ;  for  they  are 
ferviceable^  not  only  in  fheltering 
the  firft  germs  of  the  plant  from^ 
cutting  winds,  but  they  impede  the 
efcape  of  moiflure  from  the  earth ; 
the  afcending  vapour  ftrikes  upon^ 
that  furface  of  the  ftone  which  i^ 
eontiguous  to  the  earth,  and  is  there- 
by condenfed,  and  thus  its  further  af- 
cent  is  for  a  time,  at  leaft,. prevented,. 
Upon  the  fame  grafs-plat,  and 
contiguous  fto  the  glafs  ufed  in  the 
experiments^,  I  placed  a  filver  cup,. 

with. 


(    63     ) 

with  its  mouth   downwards,   of  a 

fhape  fimilar  to  that  of  the  glais,  and 
nearly  of  the  fame  dimenfions  3  but 
I  could  never  obferve  that  its  infide 
had  colleded  the  leaft  particle  of 
vapour,  though  I  frequently  let  it 
Hand  on  the  grafs  for  half  an  hour,. 
or  more.. 

By  means  of  a  little  bee's  wax,  I 
fattened  an  half  crown  very  near,  but 
not  quite  contiguous,  to  the  fide  of 
the  glafs,  and  fetting  the  glafs,  with^ 
its  mouth  downwards,  on  the  grafs,, 
it  prefently  became  covered  with  va- 
pour, except  that  part  of  it  which 
was  near  to  the  half  crown.  Not 
only  the  half  crown  itfelf  was  free 
from  vapour,  but  it  had  hindered 
any  from  fettling  on  the  glafs  which 
was  near  it,  for  there  was  a  little 
ring  of  glali  lurrounding  the  half 

crowa 


(     64     ) 

crown  to  the  diflance  of  I-  of  an  Inch 
which  was  quite  dry^  as  well  as  that 
-part  of  the  glafs  which  Vv^as  imme- 
diately under  the  half  crown;     it* 
feemed  as  if  the  filver  had  repelled 
the  water  to  that  diflance.     A  large 
red  wafer  had  the  fame  effe6t  as  the 
half  crown,   it  was  neither  wetted 
itfelf  nor    was    the   ring   of    glafs 
contiguous  to  it  wetted.    A  circle  of 
white  paper  produced  the  fame  efte6l, 
fo  did  feveral  other  fubilances,  which 
it  would  be  tedious  to  enumerate. 

Thefe  phenomena,  refpedlingthe 
different  difpofitions  of  different  bo- 
dies to  attradl  the  rijing  vapour,  are 
fimilar  to  what  others  have  taken 
notice  of  concerning  the  falling  of 
dew,  and  are,  probably,  to  be  ex- 
plained upon  the  fame  principles, 
whatever  they  may  be.     Mufchen- 

bro-k 


ibroek  placed  on  the  leaden  terras  of 
the  Obfervatory  at  Utrecht  velTels 
<of  glafs.,  china,  yarniflied  wood,  po- 
lifhed  brafs,  and  pewter 5  he  found  . 
.that  in  the  courfe  of  a  night  the  glafs, 
.china,  and  vflrniihed  wood,  had  col- 
Jedied  a  great  abundance  of  dew, 
•but  that  not  a  drop  had  fallen  on  any 
cof  the  poiifhed  metals*.  M.  du 
Fay  expofed  to  the  air,  when  the 
dew  was  falling,  two  large  funnels, 
one  made  of  glafs  the  other  of  po- 
iifhed pewter;  the  necks  of  the  fun- 
nels being  inferted  into  velTels  pro- 
per to  retain  any  moiilure  which 
might  be  colleded  by  them.;  he 
fometimes  found  in  the  morning  that  ■ 
the  veiTel  under  the  glafs  funnel  con- 
tained an  ounce  or  more  of  water^ 
VOL.  in.  E  but 

""  In  trod*  ad  Philof.  Nat,  Toixi.  2.  p.  990. 


t    66     ) 

fent  lie  never  obferved  fo  much  as  & 
drop  in  the  other*. 

A  great  part  of  the  water  which 
is  raifed  into  the  air  from  the  per- 
fpiration  of  the  earth  during  a  hot 
day,  defcends  down  again  upon  its 
furface  in  the  courfe  of  the  night; 
and  this  is  the  reafon  that  the  dews 
are  the  greateft  in  the  hotteft  wea- 
ther, and  In  the  hotteft  climates. 
The  earth  retains  the  heat  it  receives 
in  confequence  of  the  fun's  adtion 
longer  than  the  air  does;  water, 
moreover,  is  evaporabie  in  all  de- 
grees of  heat;  hence  water  may  con- 
tinue to  rife  from  the  earth,  when 
the  air,  being  cooled  by  the  abfence 
of  the  fun,  is  no  longer  able  to  fuftain 
what  is  thus  raifed,  or  to  retain  what 

.  *  Hift.  <Ie  I'Acad;  des  Scien.  i:749» 


(    67     ) 

it  had  taken  up  during  the  day  tinae, 
and  a  dew  from  thefe  different  caufes 
may,  under  <:ertain  circumfliances, 
be  found  both  to  rife  and  fall  during 
the  whole  night. 

Egypt,  at  one  feafon  of  the  year, 
is  fo  parched  up  by  the  hear,  thar 
the  furface  of  the  ground  becomes 
quite  rugged  with  fiffures;  at  this 
time  the  dew,  proceeding  from  the 
vapour  exhaled  from  the  earth,  is 
very  plentiful,  and  by  its  plenty  pre- 
vents the  total  deilruction  of  the 
country.  ^'  This  dew  is  particularly 
ferviceable  to  the  trees,  which  would 
otherwife  never  be  able  to  refift  the 
heat;  but  with  this  alTiftance  they 
thrive  very  well,  blolTom  and  ripen 
their  fruit.  Therefore,  the  upper 
parts  of  the  Egyptian  trees,  at  one 
time  of  the  year,  do  the  office  of 
E  2  roots, 


(     68     ) 

roots,  attradling  nourifliment  by 
their  abforbent  vcflels,  the  leaves, 
from  the  moift  air."* 

The  quantity  of  water  which  was 
condenfed  on  the  infide  of  the  glafs, 
I  found  to  be  accurately  proportion- 
able to  the  time .  during  which  it 
flood  on  the  grafs ;  for  in  one  ex- 
periment 6  grains  were  collected  in 
lo  minutes,  and  in  another  15  grains 
were  collected  in  25  minutes;  now 
the  proportion  of  6  to  10  is  the  fame 
as  that  of  15  to  25. 

•In  order  to  fee  whether  the  copious 
vapour  colledled  by  the  glafs  was 
owing  to  the  natural  perfpiration  of 
the  grafs,  or  to  a  kind  of  mechanical 
dillillation  from  the  body  of  the 
earth,  I  put  the  glafs  upon  a  foot- 
path which  was   dry,,  and  had   no 

grafs 
*  HafTelquiA^sVoy.  p.  455. 


(    69    ) 

grafs  growing  upon  it,,  the  vapour 
rofe  from  the  footpath  as  well  as 
from  the  grafs,  but  not  fo  abun- 
dantly.- 

From  what  has  been  advanced, 
it  may,  probably,  be  juftly  inferred, 
that  the  air  contiguous  toy  or  not 
far  removed  from,  the  furface  of  the 
earth,  whether  that  furface  be  plain 
or  mountainous,  barren,  or  covered 
with  vegetables,  will  be  much  more 
loaded  with  the  vapour  which  arifes 
conftantly  from  the  earth,  than  that 
which  is  at  the  diftance  of  even  a 
few  yards  from  the  furface.  This 
point  may  be  illuftrated  by  the  fol- 
lowing hypothecs Suppofe  the 

earth  to  be  a  globe  of  rock  fair,  and 
to  be  covered  with  water  to  the 
•height  of  a  mile;  imagine  the  wa^ 
ter*to-bc  divided  into  four:  fpherical 
E  3  Ihells, 


(    7°    ) 

fliells,  each  ^  of  a  mile  in  thicknefs. 

ISow  the  firft  fhell,  which  is  fup- 
pofed  to  be  contiguous  to  the  fur- 
face  of  the  fait,  v/ould  foon  faturate, 
Jtfelf  with  th^  fait,  and  becoming 
thereby  heavier  than,  the  water  at  a 
greater  dlftance,  it  would  not,  by 
the  ordinary  motion  of  the  winds 
and  tides,  foon  mix  itfelf  with  the 
whole  mafs  of  water  ; .  but  it  would 
contain  far  more  fait  in  folution  than 
the  fecond  fhell,  and  the  fecond 
would  contain  more  than  the  third, 
and  the  third  more  than  the  fourth. 
Let  us  further  fuppofe  the  fait  con- 
tained in  the  v/hole  of  the  water  to 
be  precipitated,  and  the  precipita- 
tion to  begin  from  the  flieli  fartheft 
removed  from  the  furface  of  the 
earth  ;  it  is  evident,  that  the  quan- 
tity of  the  precipitate  will  increafe, 
a  not 


C    7'     ) 

not  fimply  with  the  increafe  of  Ipace 
through  which  it  has  defcended,  but 
in  a  much  higher  proportion,  inaf- 
much  as  the  lad  (Bell,,  through  which 
it  defcends,  may  be  fuppofed  to  con- 
tain three  or  four  times  as  much  fait 
as  the  uppermoft.  In  like  manner,, 
it  feems  reafonable  to  fuppofe  that 
the  air  which  is  near  the  furface  of 
the  earth  will  be  greatly^  more  charg- 
ed with  water,,  which  it  diffolves  as 
water  diflblves  fait,  than  that  which 
is  fituated  at  the  diftance  of  even  a- 
few  yards  from  the  furface. 

Dr.  Heberden  was  the  firft  perfon^ 
who  took  notice^  that  a.  much  larger 
quantity  of  rain  falls  into  a  rain- 
gage  fituated  near  the  furface  of  the 
earth,  than  into  one  of  the  fame  di- 
menfions^  fituated  a  few  yards  above 
E  4  its 


(    7i     ) 
it*;  and  he  thinks   that  this  differ- 
ence is  to  be  explained  fronn  fome 
unknown    property    of    eledlricity. 
The  fad  is   placed  beyond  contro- 
verfy,  by  experiments  which  have 
been  made  at  various   places ;     at 
Liverpool  in  particular  it  has  been 
obferved,  that  ^^  a  veflel  (landing  on 
the  ground  in  a  fpacious  garden,  re- 
ceived douhle  the  quantity  of  rain 
which  fell   into    another   veffel    of 
equal   dimenlions  placed  near   the 
fame  fpot,  but  eighteen  yards  high- 
€r"f .     I  am  far  from  thinking  that 
the  foregoing  obfervations,   relative 
to  the  quantities  of  water  contained 

in  equal   bulks   of  air  at  different 

heights 

*  Phil.  TrarX  1769.  p;   361. 
^  See  an  ingenious  eflay  on  the  fubje6t,  by 
Dr,  Percival,  who  has  -explained  the  pheno- 
menon from  the  known  principles  of  eledtri- 
city.    Eflays  by  Dr.  Perci,  p.  112. 


(  n   ) 

lieights  from  the  furface  of  the  earth, 
contain  a  fatisfa6tory  explanation  of 
this  phenomenon ;  yet  it  may  be  re- 
marked:,  that  rain  gages  placed  at 
-equal  diftances  from  the  furface  of 
the  earth,     colle6ted    nearly  equal 
quantities  of  rain,    though   one   of 
them  was  fituated  on  a  plain,  and  the 
other  on  a  mountain  450  ; yards  in 
height  above  the  plain*  :  this  obfer- 
vation   is  fome  confirmation  of  the 
hypothefis  v/hich  has  been  mention- 
ed, as  on  that  fuppofition  it  follows, 
that  the  air  at  the  fame  diftance  from 
the  furface   of  the  earth,  is  equally 
impregnated  with  water,   other  cir- 
cumilances    being   the   fame,    and 
therefore   equal  quantities    of  rain 
ought  to  be  coUefted  by  vefTels  plac- 
ed at  equal  diftances  from  the  fur- 
face 

*  Philof,  Tranf.  1772,  p.  294, 


(    74    ) 

face  of  tbe  earth;  though  according 
to  the  fame  fuppofition,  a  much 
larger  quantity  ought  to  be  colie6ted 
by  a  vefiel  placed  on  the  furface,, 
than  by  one  placed  a  few  yards  above 
it.  Thus  this  hypothefiSj.  admitting 
its  truth,  (v/hich  future  experiments 
will  perhaps  eftablifh)  feems  as  if  it 
was  fufHcient  for  explaining  the  phe- 
nomenon i  I  would  be  underftood 
however  to  mention  it  witb  much 
diffidence,  and  was  I  as  nauch  fkilled 
in  ek6tricity,,as  the  very  worthy  and 
ingenious  perlbn,  who'  firft  noticed 
the  fa6l,  is  in  every  branch  of  natu- 
ral philofophy,,  I  might  probably 
have  feen  reafon  not  to  mention  it  at 
all. 


ESSAY 


ESSAY     m< 


OF    WATER    DISSOLVED    IK    AIR. 


W^E  have  fecn,  m  the  precedr- 
ing  ElTay,  that  large  quan- 
tities of  water  are  railed  from  the 
earth  in  the  hotteft  weather  ;  the  wa- 
ter, which  is  thus  elevated,  is  no 
more  vifible  in  the  air,  than  a  piece 
of  fu gar  is  vifible  in  the  water  where- 
in it  happens  to  be  diflblved,  nor  is 
the  tranfparency  of  the  air  injured 
by  the  water  it  has  received  from  the 

earthj, 


(    76     )• 

earth,  and  therefore  we  conclude,. 
that  the  water  is  not  merely  mixed 
with  the  air,  but  really  dijblved  m 
its  a  perfed  tranfparency  of  the 
fluid,  in  which  any  body  isdifTolved, 
being  efteemed  the  moft  unequivo- 
cal mark  of  its  folution. 

The  caufe  of  the  afcent,  fufpen- 
fion,  and  defcent  of  vapours,  is  not 
yet  fully  determined  -,  many  think 
that  eledricity  is  the  principal  agent - 
in  producing^  thefe  phenomena  *  i 
•whiift  others  are  of  opinion,  that  wa- 
ter is  raifed  and  fufpended  in  the  air, 
much  after  the  fame  manner  in  which 
falts  are  raifed  and  fufpended  in  wa- 
ter i  and  it  muft  be  owned  that  this 

opinion 

*  Philof.  Tranf.  1755.  p.  i24.-*'Elec^ 
tricitas,  vapores  ia  atirem  extoUit,.  in  aer« 
(fufpendit,  et  ex  acre  in  teilurem  depluit.  Prof. 
pavers  Exp,  de  Elec.  Theo»p.  106. 


'(    77    5 

opinion  (which  future  experience 
:may  fliew  not  to  be  wholly  incon- 
fiftent  with  the  other)  has  a  great 
appear-ance  of  probability. 

Salts,  in  general,  are  more  fpeedi - 
ly  dilTolved  in  warm  water  than  in 
cold  3  and  water,  in  like  manner,  is 
more  fpeedily  diflblved  in  warm  air 
than  in  cold.  We  have  a  fenfible 
proof  of  this,  in  the  exhalation  of 
dew,  it  being  much  fooner  dried  up 
in  places  expofed  to  the  diredl  rays 
of  the  fun,  than  in  the  fhade ;  be- 
caufe  the  air  in  the  ihade,  being  fome 
degrees  colder  than  that  in  the  fun, 
is  not  able  to  diflblve  the  fame 
quantity  of  water  in  the  fame  time. 

When  water  is  faturated  with  any 
kind  of  fait  in  a  definite  degree  of 
heat,  then  will  it  retain  the  fait  as 
long  as  it  retains  its  heat  s  but  if  the 

3  i^^^ 


C    78    ) 

heat  be  lefTened,  the  tranfparency  of 
the  folution  will  be  deftroyed,  a  part 
of  the  fait  will  become  viflble,  and 
fall  to  the  bottom,  in  confequence  of 
its  fuperior  weight ;  what  falls  to  the 
bottom  will  be  rediflblved,  as  Toon 
as  the  water  regains  its  heat.  It  is 
obvious  that  the  quantity  of  the 
fait,  which  is  precipitated  from  the 
cooling  of  th-e  water,  will  depend 
partly  on  the  degree  of  heat  in  which 
the  folution  is  fatu rated,-  and  partly 
on  the  degree  of  cold  to  which  the 
folution  is  reduced*  Thus'  water  of 
Bo  degrees  when  faturated  with  fait, 
contains  more  fait  than  it  would  do 
if  it  had  only  yodegrees  of  heat,  and 
in  being  cooled  to  50  degrees,  the 
precipitation  of  fait  will  be  greater 
in  the  firft  inftance,  than  in  the  fe- 
cond;  though  it  might,  probably,  be 

the 


(     79     ) 

the  fame,  if  the  folution  of  80  de- 
grees was  cooled  only  to  60,  and 
that  of  70  to  50.  Something  very- 
analogous  to  all  this  may  be  obfer- 
ved,  with  refpedl  to  the  folution  of 
-water  in  air.  In  mifty  weather,  we 
frequently  fee  the  milt  of  the  morn- 
ing intirely  vanishing  towards  the 
middle  of  the  day,  and  coming  on 
again  towards  the  evening ;  the  rea- 
fon  of  which  feems  to  be,  that  the 
air  being  warmed  by  the  approach 
of  the  fun  to  the  meridian,  is  able 
to  diffolve  the  morniiig  mifl,  but  ^ 
the  air  grows  colder  again  towards 
the  evening,  the  water  which  had 
been  perfedtly  dilTolved  by  the  mid- 
day heat  begins  to  be  precipitated, 
the  tranfparency  of  the  air  is  deftroy- 
ed,  and  an  evening  mift  is  formed. 
This  phenomenon  has  been  ob- 

ferved 


:(       8o      ) 

ferved  to  prevail,  in  the  coldell  ac- 
mofphere  that  has  ever  yet  been 
taken  notice  of,  on  the  furface  of 
the  globes  for  in  January  1735, 
when  the  cold  in  Sikeria  was  equal  to 
157  degrees  below  the  fre^zijig  point 
in  Farenheit's  thermometer,  the  low- 
er region  of  the  air  was  obfcured  by 
a  perpetual  cloud,  which  was  very- 
thick  in  the  morning,  thinner  to- 
wards noon,  and  thicker  again  at 
night*. 

Mifts  and  dew  will,  generally 
fpeaking,  be  the  greatefl  when  the 
•difference  between  the  heat  of  the 
airj  in  the  day  time,  and  at  nighty 
is  the  greateft,  becaufe  the  hotter  the 
day,  the  greater  is  the  quantity  of 
water  which  is  diffolved  -,  and  the 
colder  the  night,  the  greater  will  be 

the 

*  Novi  Commem  Petrap,  Tom.  vi.  p.  429* 


(     8i     ) 

the  quantity  which  is  precipitated. 
It  often  happens  that  there  is  no  mifc 
obfervable  towards  the  clofe  of  the 
day,  this  may  be  occafioned,  either 
by  there  being  little  difference  in 
the  heat  of  the  air  at  noon,  and  at 
night ;  or,  though  that  difference  be 
confiderable,.  yet  the  air  may  chance 
not  to  be  faturated  with  water,  and 
in  that  cafe  it  may,  even  in  the  night, 
be  warm  enough  to  retain  all  the 
water  it  had  difToIved  in  the  day 
time.  In  cold  weather  the  breath 
of  animals  becomes  vifibie,  becaule 
the  air  is  not  warm  enough  to. dif- 
folve  the  moiflure  which  is  exhaled 
from  the  lungs*. 

VOL.    III.  F  It 

^  The  breath  is  vifible  if  the  temperature 
of  the  air  be  colder  than  6i  degrees.  Caval, 
on  air  p.  400.  The  degree  of  cold  in  which 
it  is  vifible,  depends  partly  on  the  humidity, 
or'drynefs  of  the  air. 


(  ^\  }    - 

It  is  not  unufual  for  a  river  irr 
^vinter  tlme^  to  be  much  warmer  than 
the  aif;,  hence^  the  vapour  which  rifes 
from  the  river  is  condenfedy  the  air 
not  being  able  to  diiToIve  it,  and  a- 
cloud  or  mifl  of  fmall  elevation^  is 
fi^cn  to  accompany  the  fiver  in  its- 
courfe  t  this  appearance  ceafes,  as 
foon  as  the  river  is  frozen,  becaufe 
the  ice,  though  it  be  fubjeft  to  eva- 
poration, yet  it  does  not  yield  fo 
much  vapour  as  water  does^.- 

A  cubic  inch  of  rock  fait,  nitre,- 
or  any  other  kind  of  fait,  is  much 
longer  in  being  diffolved,  when  it  is 
in  a  compa6l  (late,  than  when  it  is 
r^;duc€d  into  a  fine  powder,  becaufe 
the  fair,  when  in  the  form  of  a  pov/- 

der^ 

■•*  Angara  fiuvius  node  glacle  confiilit,  quo 
Kido  nelula  ilia  perpetiia,  hue  ufque  ex  fluvio 
hoc  eveda  cclTavit.  Novi  Comp.  Fetrop, 
'Vo.  \1.   p.  436. 


(     83     ) 

licr,    has  a  much  Lirger  furface  ex- 
poicd,  to    the  adlion   of    the  water, 
than  h^it  was  In  one  folld  luiTip.    In 
like  manner^  the  air  will  diffolve  any 
definite    quantity   of    water  fooner, 
when  the  furface  of  the  water  is  in^ 
creaK^d  by  its  being  in  the  form  of  a 
vapour,  than  it  would  do  {(  the  wa- 
ter was  either  in  thtt  form  of  ice;>   or 
'u>  its  ordinary  fluid  fjate.  The  fmoke 
of  a  .chimney  confifcs  principally  of 
water,  in  the  ilate  of  vapouFj  and  it 
is    really    arconifning,     to   {ce    how 
quiclcly,   in  particular  flates  of  the 
atmofphcre;,  it  is  difk)]red  in  the  air. 
It  has   been    remarked,   that    the 
fmoke  of  miOunt  Vefiruius  is  miuch 
more    ftrong  and  viffble    in   rainy, 
tiian    in  fair  weathers*  if  this  phe- 
F  2  nomenon 

""  Lett,  fur.  La  Tviine-.-ak  par.  M.  Ferbcr> . 
p.  :S8. 


(    H    ) 

nomenon  does  not  proceed  from  the 
greater  quantity  of  water,  which  is 
raifed  from  the  mountain  in  wet, 
than  in  dry  weather  -,  it  may  be  ac~ 
counted  for,  from  the  greater  facility 
with  which  aqueous  vapours  are  dif- 
Iblved  in  a  dry  ferene  air,  than  in 
one  which  is  fo  faturated  with  water^ 
that  it  can  diflblve  no  more ;  which 
is  the  cafe,  in  general,  of  air,  which 
parts  with  its  water,  in  the  form  of 
rain  or  mifi. 

In  riding  upon  wet  fand  in  a  hot 
day,  a  kind  of  tremulous  motion  in 
the  air,  to  the  height  of  a  foot  or 
more  above  the  fand,.  may  be  obfer- 
ved  5  this  appearance  may  proceed 
from  hence,  that  the  water  in  riling 
from  the  fand,  is  not  immediately 
difTolved  in  the  air.  A  fimilar  appear- 
ance may  often  be  obferved  on  land> 

efpe- 


(     85     ) 

efpecially  in  corn  fields  towards  au* 
tumni  the  water  which  is  exhaled 
from  the  (landing  corn,  not  mixing 
itfelf  at  once,  fo  effedually  with  the 
air,  as  to  conftitute  with  it  an  appa- 
rently homogeneous  fluid.  Some- 
thing of  the  fame  kind  happens, 
when  either  faline  folutions,  wines, 
or  vinous  fpirits  of  any  kind,  are 
poured  into  a  glafs  of  water,  the 
compound  fluid  mufl  be  agitated, 
or  the  mixture  will  not  at  firil  be 
uniform. 

The  quantity  of  water  contained 
in  the  air,  even  in  the  driefl  weather, 
is  very  confiderable.  We  may  be 
faid  to  walk  in  an  ocean  ;  the  water 
indeed  of  this  ocean,  does  not  ordi- 
narily, become  the  objed  of  our 
fenfes,  we  cannot  fee  it,  nor,  whilft 
it  continues  diifolved  in  the  air,  do 
F  3  we 


(     86     ) 

we  feel  that  it  wets  us,  but  iris  frill 
v/ater,  thou2;h  it  be  neither  tan.Q-ible 
nor  vifible ;  jufc  as  fugar,  when  dif- 
folved  in  water;,  is  ftili  fugar,  though 
we  can  neither  fee  it  nor  i'ttl  it. 

Some  philofophers  have  doubted, 
whether  the  weight  of  the  air,  may 
not  chiefly  be  attributed  to  the  wa- 
ter which  is  conilantly  fufpended  in 
it  *.  But  whether  this  conjedture  be 
admitted  or  not,  the  power  which  the 
air  has  of  keeping  a  great  quantity  of 
water  difTolved  in  it,  may  very 
properly  be  applied  to  the  illuftra- 
tion  of  that  text,  in  which  it  is  faid, 
Gcd  divided  the  waters  which  were 
under  the  firmament^  from,  the  waters 
which  were  above  the  firmament  \^ 
without  having  recourfe  with  Efif- 

,  co^^iuSy 

*  Boerh.  Chem.  Vol.  I.  p.  461. 
f  Gen.  i.  7. 


C     ^7     ) 

'i'OpiuSy    to  the  very  unphilofophlcal 

fuppoficion  of  the  blue  ficy  being 
a  foliti  fubllance  compofed  of  con- 
gealed water*.  Some  are  puzzled 
to  find  water  enou2;h  to  form  an 
iiniverfal  deluge  -,  to  ajQiil  their  en- 
deavours it  may  be  remarked^  that 
was  it  all  precipitated  which  is  dif- 
folved  in  the  air,  it  might  probably 
be  fumcient  to  cover  the  furface  of 
'the  whole  earth,  to  the  depth  of 
above  thirty  feet. 

The  sir  not  only  diirolves  water, 

but  various  other  vapoursj  -wliich  con^ 

F  4  fiil 

^^  Extinia  iiv-e  fuprema  hajns  al'ris  regio 
attingit  fornicem  aihim  c^ruleiira,  in  quo 
poitca  die  quarta  il;ellse  fixss  collacatse  fifc- 
runt ;  qui  fornix  csraleus  mini  efie  videtiir 
aquarum  in  akum  elevataruiHj  et  cryftalli  im 
niorem  feu  condenfatarum,  feu  conglaciata- 
rum,  cccruleoque  colore  radiantium,  compa- 
,ge==.     Epia,  Ins.   Theoli  Lib.  iv.  d.   3. 


(     88     ) 

fill  partly  of  water,  and  partly  ofvola- 
tilefalts  and  oils.  All  vegetables,  whe- 
ther aromatic  or  not,  are  found  toper- 
fpire  verygreatly,and  thematterwhich 
they  perfpire,  could  it  be  condenfed, 
would,  probably,  be  fo  far  different 
from  pure  water,  as  to  have  both  a 
tafle  and  fmell.  The  nrratter  per- 
fpire d  by  animals,  without  f^veating, 
confifts  principally  of  water,  but  the 
water  is  ilrongly  impregnated  with 
odorous  particles.  It  has  been  faid 
of  Baron  Halkr,  that  he  could  fmell 
the  perfpiration  of  old  people,  at 
the  diflance  of  ten  y^rds  -,  this  is  by 
no  means  incredible,  for  the  human 
body  is  conftantiy  enveloped  in  an 
tnvifible  cloud,  arifmg  from  the 
great  quantity  of  matter  which  is 
infenfibly  perfpired.  Sa7i^orius  cM- 
iTiares  the  /e/iJU'Ie   excretions  of  a 

perfon 


(     89     ) 

perfon  who  eats  and  drinks   8  lbs  of 

food  in  14.  hours,  at  3  lbs,  and  the 
injenfihle  perfpiration  at  5  Ibsj  but  if 
we  fuppofe  the  infenfible  perfpira- 
tion in  this  clinfiate  (which  is  colder 
than  that  of  Venice^  where  he  made 
his  experiments)  to  amount  only  to 
one  half  of  our'food,  we  cannot  but 
csnclude,  that  it  muft  form  a  great 
icioud  around  us  ;  for  4  lbs  of  matter 
converted  into  a  vapour  as  heavy  as 
air,  would  occupy  a  great  fpace, 
amounting  to  above  50  cubic  it^u 
The  heat  of  the  human  body  is  ge- 
nerally between  90  and  100  degrees, 
this  degree  of  heat  is  fufficient  to 
raife  frorri  it,  by  a  kind  of  diililla- 
tion,  a  copious  vapour,  which  would 
become  vifible,  if  the  heat  was  in- 
creafedi  I  remember  having  been 
greatly  heated  and  fatigued  in   af- 


■cenaiiig 


(     go    ) 

cending  the  ladders  from  the  bottom 
of  the  copper  mine  at  E^cn  \  when 
;I  got  to  the  top  \  obfervedj  by  the 
light  of  a  candle,  a  thick  vapour 
reek-ing  from  the  body,  and  vifible 
around  it,  to  the  diflance  of  a  foot 
or  more. 

The  difpofition  of  the  air  for  dif- 
folving  either  pure  water,  or  the 
matter  perfpired  ^by  vegetables,  or 
.animals,  is  very  various,  depending 
chiefly  on  its  dcnfay-,  heat^  and  dry^ 
nejs.  The  power  which  dogs  have 
of  fcenting  the  animal  they  are  in 
purfuit  of,  m'Uil  be  much  anecfted 
by  this  difpofition  of  the  air ;  for 
the  air  through  which  the  animal 
has  pafied,  is  impregnated  with  the 
matter  perfpired  from  its  body  \  and 
this  matter  may  in  one  ftate  of  the 
air  be  fo  fpeedily  dilTolved,  and  fo 
"X  muck 


(     91     ) 

much  as.  it  were  diluted  with  airj  as 
to  make  either  no  impreflion,  or  a 
very  flight  one,  on  the  olfadory 
nerves  of  the  dog-,  v/hihl:  in  another, 
it  may  make  a  very  fenfible  one. 
And  if  we  fuppofe  the  perfpirable 
matter  not  to  coniiil  chiefly  of  wa- 
ter*, but  of  fuch  particles  as  are 
throv/n  off  by  perfumes,  without 
their  lofing  fenfibly  of  their  weight, 
frill  it  will  be  true,  that  the  ftate  of 
the  air  mufc  have  a  great  influence 

in 
*  If  the  whole  body  of  a  naked  .man,  ex- 
cept his  mouth  and  nofcriis,  was  flint  np  in  a 
glafs  cafe,  fo  thr^t  no  air  could  enter,  the 
matter  of  the  infenfible  perfpiration,  w^ould, 
probably,  be  condenfed,  and  ftand  as  dew  on 
the  inflde  of  the  glafs ;  and  I  apprehend  it 
%vould  not  differ  much  from  the  matter  of 
the  j\'?ij%le  perfpiration,  or  fvveat.  But  if  any 
•  one  be  difpofed  to  confider  the  infenfible 
jperfpirauon,   as  an  uncondenfable  fluid,  or  a 

•     -  kinjd 


(     92    ) 

in  rendering  them  fenfible ;  fince  it 

has  been  found,  that  on  the  tops  of 
very  high  mountains,  where  the  ftate 
of  the  air  is  very  different  from 
what  it  is  in  the  valleys  below,  the 
moft  odorous  bodies  lofe  either  in- 
tirely,  or  in  a  great  degree,  their 
powers  of  exciting  a  fmelL — The 
exiftenee  of  water  in  air  is  made  ap- 
parent various  ways. 

If  a  bottle  of  wine  be  fetched  out 
of  a  cool  cellar,  in  the  hotteil  and 
drieft  day  in  fummer,  its  furface 
will  prefently  be  covered. with  a  thick 
vapouc,  which,  when  tailed,  appears 

to 

kind  of  air  iimilar  to  that  which  arifes  from 
vegetable  fluids,  in  a  ilate  of  fermentation, 
(the  heat  of  fermenting  wort,  being  much 
the  fame  as  that  of  an  animal  body)  ftili  its 
mixture  with  the  atmofpherical  air,  muil.  de- 
pend very  much  on  the  weight,  humidity, 
and  other  properties  of  that  air« 


(     93     ) 

to  be  pure  water.  This  watery  va- 
pour cannot  proceed  from  any  exu- 
dation of  the  wine,  through  the 
pores  of  the  bottle,  for  glafs  is  im- 
pervious to  water,,  and  the  bottle 
remains  full,  and  when  wiped  dry,  it 
is  found  to  weigh  as  much  as  when 
taken  out  of  the  cellar.  The 
fame  appearance  is  obfervable  on 
the  outfide  of  a  filver,  or  other  vef- 
fel  in  which  iced  water  is  put  in 
fummer  timej  and  it  is  certain,  that 
the  water  which  is  condenfed  on  the 
furface  of  the  veiTel,  does  not  pro- 
ceed merely  from  the  moiflure  ex- 
haled by  the  breathing  of  the  people 
in  the  room,  where  this  appearance 
is  moft  generally  noticed,  becaufe 
the  fame  effed  will  take  place,  if 
the  velTel  be  put  in  the  open  air. 
Water  which  is  cooled  by  the  folu- 

tion 


(     94     ) 
tion  of  any  fair,   or  even  ipring  wa*^ 

ter,  which  happens  to  be  a  few  de- 
grees colder  than  the  air,  produces 
a  limilar  condenfafion  of  vapour  on 
the  outfide  of  the  veiTel  in  which  it 
is  contained.  Thefe  and  other. ap- 
pearances of  the  fame  kind,  are  to 
be  explained  on  the  fame  principle. 
Warm,  air  is  able  to  retain  more  wa- 
ter in  foiution  than  cold  air  can ; 
when  therefore  warm  air  becomes 
contiguous  to  the  outv/ard  furface 
of  a  veiTel,  containing  cold  liquor, 
it  is  prefently  cooled  to  a  certain  de- 
gree^ and  in  being  cooled,  it  is  forc- 
ed to  part  v/ith  fome  of  the  water 
which  it  had  diiTolved,  and  this  wa- 
ter, ceafing  to  be  fufpended  by  the 
air,  attaches  itfelf  to  the  furface  of 
the  cold  velTel. 

The  more   ancient  pliilcfophers, 

not 


(     95     ) 

not  fufpeftiilg  that  water  might  be 

diflblved  in  air^  were  of  opinion  that 
the  moidure  which  they  obferved 
adhering  to  the  outfides  of  velTels^. 
which  had'  been  cooled  by  having 
Ihowput  into  them,  proceeded  from 
a  tranfmutation  of  air  into  water*- 
But  there  fecms  to  be  no  more  rea- 
son for  this  fuppofition,  than  there 
would  be  for  laying,  that  water  waa 
changed  into  faltpetre,  from  obferv- 
ing  that  w^-ater  which  had  diiTolved 
as  much  faltpetre   as  it  could,  in  a 

certain 
*  Naturae  myftss  arcano  modo,  fed  faciii 
a'irem  in  aquam  medlis  caloribiis  cogere  doce- 
bit  abjeda  hsc  nix,  li  vitro  conicse  figure, 
intra  tripodem,  apice  deorfum  vergente,  Hif- 
penfo  indatur  nivis  vel  glaciei  fruilum. 
Quippe  fubjetSlo  vafciiio  excipiuntur,  exteri- 
ore  vitri  frigiditate  collects,  et  laterum  dc- 
clivifate  mahantes  aqiis  giittre.  Bartholinus 
tie  figiira  Nivis  p.  5.  See  alio  Boyle'^ 
Works,  Vol.  II.  p.  297. 


(96) 

certain  degree  of  heat,  depofited  a 

part  of  it,  when  that  degree  of  heat 
was  lefTened. 

Another  method  of  proving  the 
exiftence  of  water  in  the  cleareftair, 
is,  to  obferve  the  increafe  of  weighty 
which  certain  bodies  acquire  by  ex- 
pofure  to  the  open  air.  I  put  upon 
a  plate  8  ounces  of  fait  of  tartar, 
which  had  been  well  dried  on  a  hot 
iron  ;  the  day  was  without  a  cloud, 
and  the  barometer  flood  at  3oinGhes> 
in  the  fpace  of  three  hours,  from 
II  to  2  o'clock  in  the  afternoon,  the 
fait  had  increafed  in  weight  two 
ounces ;  in  the  courfe  of  a  few  days 
its  weight  was  increafed  to  twenty 
ounces,  it  was  then  quite  fluid,  and 
being  diftilled  it  yielded  a  pure  wa- 
ter equal  in  weight  nearly  to  the 
increafe  it  had  acquired  from  the  air,, 

and 


(97) 

and  therefore  it  is  rightly  inferred, 
that  water  was  the  fubflance  which 
it  had  attradted  from  the  air. 

Strong  acid  of  vitriol  is  another 
body  which  very  powerfully  attradls 
humidity  from  the  air.     An  ounce 
of  this  acid   has  been  obferved  to 
gain,  in  1 2  months,  above  fix  times 
its  own  weight.*     The  power  of  the 
acid  to  attrad  water  from  .the  air, 
depends   upon  its  flrength,    for   it 
may  be  fo  far  diluted,  that  inftead 
of  attrading  any  more  water  from 
the  air,  it  will,  by  evaporation  lafe  a 
part  of  that  which  it  had  acquired; 
when  sit  ,is  in  this  flate^   its  .weight 
varies  with  the  dry nefs  or  moiftnefs 
of  the  atmofphere,  and  it  becom.es, 
when  accurately  balanced  in  a  good 
f>air  of  fcales,  no  bad  kind  of  an  hy- 
voL.  HI.  G  grometer, 

*  Newm,  Chem,  by  Lewis,  p.  161. 


(    93     ) 

grometer.     The  time  in  which  any 
definite  quantity  of  acid  acquires  its 
greateft  weight  from  the  air,  depends 
partly  upon  the   quantity  of  water 
which  is  diffolved  in  the  air,   and 
partly  upon  the  furface  of  the  acid 
which  is  expofed  to  the  air,   it  hav- 
ing been  afcertained  by  experiment, 
that  the  quantity  attra(5led  from  the 
air,   in  a  definite  portion  of  time,  is 
greater   as   the   furface   is    greater. 
Hence,  inflead  of  a  twelve  months 
expofure  to  the  air  being  requifite 
to  make  one  ounce  of  acid  of  vitriol 
acquire  fix  ounces  of  water,  it  might 
pofTibly  acquire  that  weight  in  a  few 
minutes,   if  its  furface  was  enlarged 
in  a  due  proportion. 
^     Onions  and  other  bulbous  roots, 
"^hen  hung  up  in  a  room  Sheltered 
from  rain  and  dew,  are  obferved.  to 

germi« 


(     99    ) 

germinate-,    and  to   acquire  a  great 

mcreafe  of  bulk,  and  it  might  thence 
have  been  fufpeded,  that  they  at- 
tracted much  water  from  the  air, 
and  were  increafed  in  weight.  But 
though  they  may  increafe  in  bulk, 
they  are  found  to  decreafe  in  weight; 
the  root  itfelf  in  becoming  rotten, 
fupplies  nutriment  to  the  germinat- 
ing plant;  and  if  it  imbibes  any 
thing  from  die  air,  it  lofes  that  and 
more  by  perfpiratian.  An  onion 
on  the  26th  of  January,  when 
it  had  fcarce  begun  to  fliew  any 
figns  of  vegetation,  weighed  2^6 
grains;  on  the  i6thof  the  following 
May,  after  having  put  forth  feveral 
ftem.s  in  the  open  air,  it  weighed  only 
145  grains,* 

The  increafe  of  weight  which  the 
G  2  human 

*  Novi  Com.  Pctrop,  Toi-ti*  2.  p.  22^, 


(  lod  ) 

human  body,  in  nnany  cafes,  experi- 
ences from  the  water  which  the  pores 
of  the  body  fuck  in  from  the  air. 
is  another  very  fenfible  proof  of  the 
great  quantity  of  water  which  is 
conflantiy  diflblved  in  the  air. 
*'  Keil  has  proved,  that  a  young 
man  weakened  from  want  of  nou- 
rifhment,  but  in  other  refpedls 
healthy,  added  eighteen  ounces  to 
his  weight,  in  the  fpace  of  one  night, 
and  this  by  the  abforption  through 
his  pores.  Another  perfon  has  been 
feen  to  gain  4olbs.  weight,  in  the 
fame  manner,  in  the  fpace  of  a  day. 
M.  de  Haen,  is  of  opinion,  that 
dropfical  patients  abforb  more  than 
loolbs.  weight  every  day.  It  is 
fuppofed,  that  in  general,  the  body 
abforbs  more  than   ilb.   every  day 

by 


(     loi     ) 

by  the  pores.*"  The  (kin  of  a 
middle-fized  man,  is  equal  to  about 
1 5  fquare  feet,  and  if  we  fuppofe  the 
ikin  of  a  dropfical  perfon  to  be  20 
iqviare  feet,  then  will  each  fquare 
foot  imbibe  5lbs.  or  pints  of  water 
in  one  day. 

In  addition  to  thefe  inftances  I 
will  fubjoin  the  following  account, 
which  was  given  me  by  a  perfon  of 
credit  and  judgment.  A  lad  at  New- 
market, a  few  years,  ago,  having 
been  almoft  flarved,  in  order  that  he 
might  be  reduced  to  a  proper  weight 
for  riding  a. match,  was  weighed  at 
9  o'clock  in  the  morning,  and  again 
at  10,  and  he  was  found  to  have 
gained  near  30  ounces  in  weight  in 
the  courfe  of  an  hour,  though  he 
G  3  had 

*  Treatife    of    Phyfic    by    Zimmerman* 
Vol.  II.  p.  128. 


had  only  drank  half  a  glafs  of  wine 
in  the  mterval.  The  wine  probably 
ftimulated  the  action  of  the  nervous 
iyftenn,  and  incited  nature,  exhaufted 
by  abftinence,  to  open  the  abfor- 
bent  pores  of  the  v/hole  body,  in  or- 
der to  fuck  in  fome  nourifhment 
from  the  air.  Something  fimilar  to 
this  was  the  cafe  of  the  negro,  who,, 
being  gibbetted  alive,,  regularly^ 
voided  every  morning  a  large  quan- 
tity of  urine,,  but  difcharged  no 
more  till  about  the  fame  hour  the 
next  day,*  The  dews  of  the  even- 
ing at  Charles  Town  in  South  Ca- 
rolina, imbibed  by  his  body,  fupply- 
ing  a  fuperabundance  of  fiuids  in  the 
night,,  and  a  fufhcient  quantity  ta 
fupport  perfpiration  in  the  day.  It 
laasbeen  obferved  that  "neither hogs 

nor 

*  Me^kal  Tranf.  VoL  II.  p.  £05* 


(     I03     ) 

nor  beails  of  burden  ever  drink  ia 
Jamaica^  and  yet  they  are  continu- 
ally fweating.  The  air  is  fo  moift, 
that  the  abforbi ng  pores  of  thefe 
animals  imbibe  a  fufficiency  of  wa- 
ter.*" The  imbibition  of  water 
through  the  pores  of  the  flcin  is  an 

acknowledged    fa61: '-^  it  is  well 

known,  that  perfons  who  go  into  a 
warm  bath,  come  outfeveral  ounces 
heavier  than  they  went  in,  their 
bodies  having  imbibed  a  correfpon- 
dent  quantity  of  water. f  Part  of 
the  utility  of  medicated  .and  vapour 
baths,  depends  upon  this  prmciple 
of  imbibition  by  the  pores  :  and  it  is 
faid  that  thirft  may  be  allayed  by 
bathing  in  warm  fea  water^  th€  pores 
G  4  im- 

♦  Treatife  of  Phyf.  Vol.  II.  p.  loi. 
t  Goldlmith's  Hiil.  of  the  Earth.    Vol.  I. 
p,  238.-398. 


(     104     ) 
imbibing^  the  water  and  carrying  it 
to  the  inteftines,    but  not  fuffering 
the  diffolved  fait  to  accompany  the 
water. 

With  refped  to  the  quantity  of 
water  fufpended  in  the  whole  atmof- 
phere,  or  even  in  a  column  of  the 
atmofphere,  of  a  definite  bafis,  in- 
cumbent on  any  particular  Ipot,  it 
cannot  be  afertained  with  precifion, 
unlefswe  knew  fome  method  of  de- 
priving the  air  of  all  the  water  it 
contains,  and  could  at  the  fame  time 
make  the  experiment  at  different 
diftances  from  the  furface  of  the 
earth.  For  it  is  not  only  probable, 
that  a  cubic  yard  of  air,  contiguous 
to  the  furface  of  the  earth,  contains 
.at  different  times  very  different 
^quantities  of  water,  even  at  the  fame 
place,  according  as  the  ^rround  is 
3  moift 


(    I05     ) 

moid  or  dry,  or  the  temperature  of 
the  weather  warm  or  cold  ;  but  we 
have  great  reafon  to  believe,  that  at 
the  fame  inflant  of  time,  a  cubic 
yard  of  air  which  touches  the  furface 
of  the  earth,  contains  as  much  wa- 
ter as  three  or  four  cubic  yards, 
which  are  fituated  at  the  diilance  of 
thirty  or  forty  yards  above  it.  For 
the  water  which  rifes  from  the  fur- 
face  of  the  ocean,  from  the  perfpi- 
ration  of  organifed  bodies,,  whether 
vegetable  or  animal,  or  from  the 
mere  a61:ion  of  the  fun  on  a  moifl 
earth,  in  being  diiTolved  in  the  air  as 
foon  as  it  rifes,  makes  the  air  near 
the  furface,  heavier  than  that  which 
is  at  a  diftance  from  it,,  and  on  that 
account  the  motion  of  the  air,  unlefs 
it  be  violent,  will  not  readily  mix 
the  lower  and  heavier  air,  with  the 

higher 


(      io6      ) 

higher  and  lighter^  and  the  lower  air 
will  confequently  contain  nn ore  water 
in  a  definite  bulk,  than  the  higher. 
To  what  has  in  a  former  EfTay  been 
obferved  on  this  fubjedt,  the  follow- 
ing illuftration  may  be  added.  If 
into  a  deep  drinking  glafs  half  full 
of  water,  you  gently  pour  a  glafs  of 
port  or  claret,  you  v/ill  fee  the  wine 
mixing  indeed  itfelf  flowly  with 
the  water,  but  that  part  of  it  which 
is  near  the  water,  will  be  much  more 
impregnated,  in  any  definite  portion 
of  time,  with  water,  than  the  more- 
remote  parts ;  it  will  be  a  confider- 
able  time  before  the  water  will  be 
uniformly  difFu fed  through  the  wine,, 
if  they  are  left  undifturbed  ;  nor 
does  a  gentle  undulating  motion 
foon  mix  them,  and  this  difficulty  of 
mixing  them  vyoiild  be  Hill  much 

greater. 


(     I07     ) 

greater,  if  there  was  a  greater  dif- 
ference in  their  refpedlive  weights,,. 
or  if  the  upper  parts  of  the  wine  were 
kfs  denfe  than  the  lower.  Now  this 
is  the  cafe  in  the  air,  which  is  not 
only  above  800  tincies  lighter  than 
water,  but  its  parts,  which  are  far 
removed  from  the  furface,  are  much 
lefs  denfe  than  thofe  which  are  con- 
tiguous to  it.  That  denfe  air  holds 
more  water  in  fokition  than  rarefied 
air,  is  proved  from  hence  j  that  v/heo. 
common  air  is  rarefied  ^under  the 
receiver  of  an  air  pump,  a  part  of 
the  water  which  is  contained  is  pre- 
eipitated^  in  the  form  of  dew;  this 
anfwers  to  tlie  precipitation  of  fait 
from  a  faline  folution,  when  part  of 
the  water  is  taken  away,  which  held 
the  fait  in  folution.  Hence,  as  cold 
teudj^  to  render  the  air  mare  dtnfc^ 

it 


C     i<58     ) 
itcertainly  contributes  to  its  holding- 
more  water  in  folution  than  it  would' 
do,  if  it  was  more  rarefied  under  the 
fame  degree  of  heat :  but  as- hot  air 
diflblves  more  water  than  cold  air, 
and  as  air  is  rarefied  by  heat,  it  is 
evident,  that  the  denfity  and  heat  of 
the    atmofphere    in    fome    meafure 
counteract  each  other,  with  refpe6t 
to  the  power  the  air  has  in  diflblving 
water:  the  law   according  to  which 
this  power  varies,  in  different  de- 
grees of  heat  and  condenfation,  is- 
not  determinable  from   any  experi- 
ments which  have  yet  been  m.ade. 

It  may  not  be  improper  to  take 
notice  in  this  place,  of  an  obje<5lion 
v/hichisufuaily  made  to  the  dodrine 
here  advanced, — - — of  water  being 
fufpended  in  the  air  by  folution — It 
is  alTerted,  that  water  is  .  as  evapor- 

able 


(     109     ) 

able  in  an  exhaufted  receiver,  where 
there  is  no  air,  as  in  the  open  air  *. 
It  is  certain,  that  heat  will  evaporate 
water,  and  great  degrees  of  it  may, 
probably,  evaporate  it  fader  in  vacuOy 
than  in  the  open  air,  inafmuch,  as 
the  prefTure  of  the  air  may  tend  to 
:obflru(St  the  adion  of  the  heat,  in 
converting  the  water  into  vapour. 
Thus,  quickfilver  is  not,  I  appre- 
;hend,  evaporable  in  the  open  air,  yet 
it  has  long  been  remarked  to  be 
ccvaporable  ini;^f//^,  as  may  be  col- 
le6ted  from  th^  little  globules  of 
quickfilver,  generally  found  adher- 
ing to  the  upper  part  of  a  barome- 
ter, and  which  arife  from  the  vapour 
which  infenfibly  efcapes  from  the 
:furface  of  the    quickfilver   in    the 

tube. 

•  Berlin  Mem.  1746.    Waller   de  .afcem 
ivapo.  in  vacuo. 


(     no    ) 

tute.  But  though  heat  may  be  one 
caufe  of  the  evaporation  of  water, 
the  attradlion  between  air  and  water, 
upon  whatever  principle  it  depends, 
may  be  another.  The  fad  moreover, 
upon  which  the  objedion  is  found- 
ed,  is  very  quellionable,  and  not  ge- 
nerally to  be  admitted.  A  china 
faucer  which  contained  3  ounces  of 
water,  lofh  nothing  of  its  weight  un- 
der an  exhauiled  receiver  in  the 
fpace  of  4  hours  ;  whilft  a  fimilar 
faucer,  containing  an  equal  quantity 
of  water,  loft,  in  the  fame  time,  in 
the  open  air,  one  drachm  and  eight 
grains ;  the  heat  of  the  atmofphere 
being  between  48  and  50  degrees  *. 
Many  readers  are  gratified  with 
feeing  the  general  progrefs  of  any 

philo- 

*  See    Dr.   Dobfon's    ingenious  Obferv^- 
tions  in  Philof.  Tranf.  1777,  p.  256, 


(  "I  ) 

philofophical  opinion,  from  its  being 
firft  fuggefledj  till  its  being  general- 
ly admitted.  The  hiftory,  indeed, 
of  philofophy,  is  one  of  the  moil 
pleafing  purfuits  which  a  fpeculative 
mind  can  be  engaged  in,  but  it  re- 
quires great  leifiire  and  ability  to 
cultivate  it  with  fuccefs.  It  is  not 
every  diftant  hint  which  he  throws 
out,  that  can  entitle  a  philofopher  to 
the  credit  of  being  the  firfl:  framer 
of  an  hypothecs ;  nor  on  the  other 
hand  are  w^e  haftily  to  reje6t  the 
maxim,  that  ^^  all  novelty  is  but  ob- 
livion", inafmuch  as  we  frequently 
fee  old  opinions  putting  on  the  ap- 
pearance of  new  difcoveries,  from 
their  being  drefifed  out  in  a  new 
form. 

Natural     philofophy    principally 
confiils  in  exploring  by  experiment, 

the 


(  112  ) 

tlie  phenomena  refulting  from  the 
mutual  aflion  of  different   bodies 
upon  each  other.    Thefe  phenomena 
are  innumerable,    no  arithmetic  can 
reckon  up  the  various  ways  in  which 
terreftrial  bodies  may,  by  natural  or 
artificial  means,  be  brought  to  ope- 
rate on  one  another.   To  this  caufe 
may  we  attribute  the  immenfe  num- 
*ber  of  volumes  on  experimental  phi- 
■lofophy,  which  have  been  publifhed 
in  Europe   fince  Bacon  pointed  out 
the  proper  method  of  ftudying  na- 
ture.    This  circumflance,  joined  to 
the  uniformity  which  muft  ever  at- 
tend the  operations    of  nature    in 
fimilar  circumftances,  may  juflly  in- 
title  different  men  to  the  honour  of 
having  made  the  fame  difcoveries, 
it  being  much  eafier  to  make  an  ex- 
periment,   which    may   have  be^n 

made 


(     113    ) 

made  before,  than  to  read  all  that 
has  been  written  in  different  ages 
and  countries  on  natural  appear- 
ances. 

Bo^or  Halleyy  in  the  year  1691^ 
propofed  to  the  Royal  Society,  his 
opinion  concerning  the  origin  of 
-fprings :  in  this  trad  he  exprefTes 
•himfelf  in  the  following  manner, 
«  the  air  of  itfelf  would  imbibe  a 
certain  quantity  of  aqueous  vapours, 
and  retain  them  like  f alts  dijfolved  in 
water ^  the  fun  warming  the  air,  and 
raifing  a  more  plentiful  vapour  from 
the  water  in  the  day  time,  the  air 
would  fuftain  a  greater  portion  of 
vapour,  as  warm  water  would  hold 
more  diflblved  falts,  which  upon  the 
abfence  of  the  fun,  in  the  nights, 
would  be  all  again  difcharged  in 

VOL,  \iu  H  dews. 


(     "4    ) 

dews^  analagous  to  the  precipitation 
of  falts  on  the  cooling  of  liquors."* 

M.  Le  Roy  pubiifhed  an  ingeni- 
ous difiertation  on  the  foiubility  of 
water  in  air^  in  the  year  1 7  5  i ;  among 
other  experiments,  by  which  he  ii- 
lufcrated  his  hypothefis,  he  obferves 
that  if  a  large,  new,  hollow,  globular 
glafs  veflel,  with  a  narrow  neck,  be 
clofely  corked  up  in  a  clear  hot  day, 
the  water  contained,  in  the  apparent- 
ly dry  air,  will  be  precipitated,  and 
form  a  dew  in  the  infide  of  the  velTelj 
whenever  the  velTel  is  cooled,  and 
that  this  dew  will  vaniih,  being  re- 
difTolved  by  the  air  included  in  the 
veiTel,  as  foon  as  the  air  regains  its 
,heat. 

Do  of  or  Franklin  further  illuilrated 
ithis  principle,  of  water  being  foiuble 

in 
*  Philof.  Traaf.  No,  192. 


(  "5  ) 

in  air,  in  a  paper  which  was  read  be- 
fore the  Royal  Society  in  1756,  and 
afterwards  printed  in  his  works  *. 

In  the  French  Encyclopedicy  pub- 
liflied  in  1756,  we  meet  with  the 
following  pafiage — on  voit  par  la 
combien  fe  trompent  ceux  qui  s* 
imaginent  que  Fhumidite  qu'on  voit 
s'  attacher  autour  cFun  verre  plein 
d'une  liqueur  glacee  ell  une  vapeur 
condenfee  par  le  froid :  cet  tf^tty  de 
meme  que  celui'  de  la  formation  des 
nuages  de  la  pluie,  et  de  tous  les 
meteors  aqueux,  eft  une  vraie  preci- 
pitation chimique,  par  un  degre  de 
froid  qui  rend  V  air  incapable  de 
tenir  en  difiblution  toute  T  eau  dont 
il  s'  etoit  charge  par  V  evaporation 
dans  un  terns  plus  chaud ;  et  cette 
precipitation  eft  precifement  du  me- 
H   2  me 

*  Franklin  on  Elec.  p.  182. 


C      "6      ) 

me  genre  que  celle  de  la  creme  dc 
tartre,  lorfque  V  eau  qui  la  tenoit  en 
diflblution  s'  efl  refroidie.* 

Mufcbenl^roeky  ^mongHothcY  caufes 
which  he  affigns  for  the  fufpenfion 
of  vapour  evidently  alludes  to  the 
folution  of  water  in  air,  and  com- 
pares it  to  the  folution  of  falts  in 
v/ater.f 

But  though  a  great  many  philo- 
fophers  had  Ipoken  of  the  folubility 
of  water  in  air/  before  I>o5for  Hamil- 
ton^ yet  in  juilice  to  him  it  muft  be 
ov/ned,  that  no  one  has  treated  the 
fubject  more  diftindly,  or  applied  it 
more  fuccefsfully  to  the  explanation 
of  various  phenomena  than  he  has 
done,  in  an  elTay  which  was  read  to 

the 

*  Ency.  Fran.  T.  6.  p.  583.  Fol.  Ed. 
f  Introd.  ad  Phil,  Nat,  Vol.  II.  p.  965, 
pub.  1709. 


(     "7     ) 

the  Royal  Society  in  1765,  and 
afterwards  publifhed  with  other  ef- 
fays,  by  the  fame  author.*  The 
reader  will  be  very  well  pleafed 
with  feeing  this  principle  illuftrated 
in  an  effay  by  Mr.  White,  publiihed 
in  177 15  in  the  elegant  colledion  of 
Georgical  EiTays  by  BoEior  Htinter-\. 

*  Philo.  EfTays  by  Hugh  Hamilton,  D.  D. 
F,  R.  S. 

f  Georgical  ElTays  by  Do(5tor  Hunter. 
Vol.11,  p.  15. 


ESSAY 


E    S    S    A    Y       IV, 


OF  G0LD  PRODUCED  DURING  THE 
EVAPORATION  OF  WATER^  AND 
THE  SOLUTION  OF  SALTS. 

ON  the  27  th  of  March  1779,  when 
the  weather  had  been  for  fome 
time  very  dry,  I  put  a  thermometer 
into  a  glafs  of  water,  which  had 
been  heated  to  87  degrees,  by  Hand- 
ing expofed  to  the  dire6t  rays  of  the 
fun.  The  thermometer  was  then 
taken  out,  and  its  bulb  was  held  op- 
pofite  to  the  fun  which  ihone  very 
H  4  bright  3 


(       MO      ) 

bright  j  as  the  bulb  grew  dry  by  the 
evaporation  of  the  water,  the  mer- 
cury in  the  thermometer  funk  very 
fafii  it  continued  for  a  moment  fta- 
tionary  at  76  degrees,  and  then  it 
rofe  rapidly  to  90 ;  fo  that  1 1  de- 
grees of  cold  had  been  produced 
during  the  evaporation  of  the  water. 
On  another  day  in  the  fame  month, 
when  the  heat  in  the  Ihade  was  6S 
degrees,  I  put  a  thermometer  into  a 
glafs  of  water,  it  Hood  at  50  degrees  -, 
upon  taking  it  out,  the  mercury  ia- 
ftead  o^  finking  from  the  eifed  of 
evaporation,  began  immediately  to  rife 
from  the  efFea  of  the  heat  of  the 
atmofphere  upon  it.  I  put  the  ther- 
mometer into  the  fame  water,  heat- 
ed to  55  degrees,  and  taking  it  out, 
the  mercury  zoYiimwtd  ftationary  for 
fome  time,  and  afterwards  it  began. 

to 


(  1"-I  ) 

to  rife.     It  was  put  into  the  fame 
water  heated  to  58  degrees,  and  up- 
on being  taken  out,  the  mercury  did 
not  either  rife  or  continue  ftationary, 
but  it  funk  one  degree ;  when  the 
water  was  heated  to  60  degrees,  the 
thermometer  upon  being  talcen  out, 
funk  3   degrees  before  it  began  to 
rife.     Thefe   experiments    were   all 
made  in  the  fhade,  and  it  feems  as  if 
we  might  conclude  from  them,  that, 
57  was  the  degree  of  heat  in  the  wa- 
ter, in  which  the  cold  produced  by 
evaporation,   was  jufl  equal  to  the 
heat  produced  by   the    atmofphere 
which  then  furrounded   the  ball  of 
the  thermometer. 

The  degree  of  cold  produced  by 
evaporation,- depends,  probably,  up- 
on the  quicknefs  with  which  that  is 
accomplifhed :    now   the  quicknefs 

with 


(       122      ) 

with  which  water,  of  a  definite  tem- 
perature, is  evaporated,  is  influenced, 
partly  by  the  degree  of  heat  pre- 
vailing  in  the  atnaofphere  ;  partly  by 
the  wind  blowing  upon  the  thermo- 
meter ;^  partly  by  the  drynefs  or 
moiftnefs  of  the  air  ^  and  by  other 
caufes. 

September  30th  of  the  fame  year, 
when  the  heat  in  the  Ihade  was  64, 
degrees,  and  the  heat  of  the  water 
60,  the  thermometer  upon  being 
taken  out,  flood  ftationary  for  three 
minutes,  and  then  it  rofe  3  there  was 
a  gentle  fouth  wind.  On  the  next 
day  there  was  a  cold  dry  wind  from 
the  north,  the  water  and  air  were 
both  at  56  degrees,  and  the  thermo- 
meter on  being  taken  out  funk  to  52. 

Spirits  of  wine,  ether,  and  many 

other  fluids,  produce  cold  by  being 

3  cva- 


(       123       ) 

evaporated,  and  they  produce  a  much 
greater  degree  of  cold  than  water,  in 
confequence,  probably,  of  their  be-, 
ing  more  evaporable.  Thus,  vitrio- 
lic ether*,  which  is  one  of  the  moil 
volatile  fluids  in  nature,  has  been 
obferved  to  lower  Reaumur's  ther- 
mometer 40  degrees  below  the  freez- 
ing point  (which  anfwers  to  90  de- 
grees of  Fahrenheit's  fcale)-]-.  The 
experiment  is  mofl:  commodioufly 
made,  by  applying  a  piece  of  fine 
linen  wetted  with  ether  upon  the 
bulb  of  the  thermometer,  accelerat- 


ing 


*  Ether  is  made  by  difhlling  a  mixture  of 
fpirits  of  wine  and  oil  of  vitriol. — Ether  may 
be  made  alfo  by  diftilling  fpirits  of  wine  with 
the  feveral  acids  of  nitre,  fea  fak,  and  vine- 
gar, and  it  is  then  called  he  nitrous,  marine, 
acetous  ether. 

f  Chem.  Dia.  art.  Ether.  Or  Manuel 
de  Chymie.  par.  M,  Baume,  p,  375, 


(       124      ) 

ing  the  evaporation  by  blowing  on 
the  linen  with  a  bellows,  and  moift- 
ening  the  linen  as  it  becomes  dry, 
or  exchanging  it  for  a  frefh  piece 
which  is  wetted  with  ether.  Who- 
ever attenipts  to  afcertain  the  degrees 
of  cold  refpedively  produced  by  dif-  i 
ferent  fluids,  would  do  well  to  re- 
mark particularly  the  ftate  of  the 
atmofphere  with  refped  to  other  cir- 
cunnilances,  as  well  as  to  its  heat. 

Sailors  have  a  cuftom,  in  a  calm, 
to  hold  a  v/et  finger  up  into  the  air, 
and  if  one  fide  of  it,  in  drying,  be^ 
comes  colder  than  another,  they  ex- 
peft  wind  from  that  quarter.  This 
cuftom  is  not  without  its  foundation  ; 
for  an  almofl  infenfible  motion  of 
the  air,  will  evaporate  the  water 
from  one  fide  of  the  finger  fooner 

than 


(     125     ) 

than  from  another,  and  thus   pro* 
duce  a  degree  of  cold. 

There  is  a  fimilar  experiment,  by 
which  anyone  may  convince  himfelf 
that  cold  is  produced  by  evapora- 
tion ;  let  him  wet  a  finger  by  putting 
it  in  his  mouth,  and  then  hold  it  up 
in  the  air,  even  in  a  warm  room 
where  there  is  no  current  of  air,  he 
will  find  that  it  grows  cold  as  it  be- 
t:omes  dry  by  the  evaporation  of  the 
humidity. 

"  The  method  our  gentlemen 
make  ufe  of  to  cool  their  liquors,  is 
to  wrap  a  wet  cloth  round  the  bot- 
tle and  fet  it  in  the  land  wind  :  and^ 
what  is  very  remarkable,  it  will  cool 
much  foonerby  being  expofed  thus 
to  this  burning  wind,  than  if  you 
take  the  fame  method,  arid  fet  it  in 

the 


(    ii6    ) 

the  cold  fea- breeze."* — The  cold 
is  produced  by  the  evaporation  of 
the  water  from  the  wet  cloth,  and  as 
the  hot  land-wind  will  evaporate  the 
water  fooner  than  the  cold  fea-breeze^ 
it  is  not  to  be  wondered  at,  that  the 
liquor  is  fooner  cooled  when  placed 
in  the  former  wind  than  in  the  latter. 
"  Kempfer  relates,  that  the  wind? 
are  fo  fcorching  on  the  borders  of 
the  Perfian  gulph,  that  travellers  are 
fuddenly  fufFocated,  unlefs  they  co- 
ver their  heads  with  a  wet  cloth ; 
but  if  this  be  too  wet,  they  immedi- 
ately feel  an  intolerable  cold,  which 
would  become  fatal  to  them  if  the 
moiflure  were  not  fpeedily  diffipated 
by  the  heat. "J     The  cold,  which  i$ 

pror 

•^Ives's  Voy.  p.  77.  -     ■ 

I  Treatife  of  Phyfic  by  Zimmerman,  Vol. 
II,  p.  151. 


(     127     ) 
produced  by  the  ad  of  evaporation^ 
ceafes  as  Toon  as, that  is  finifhed,  by 
the  cloth  becoming  dry. 

The  manner  of  making  ice  in  the 
;Eafl  Indies,  has  an  evident  depend- 
ence on  the  principle  of  producing 
cold  by  evaporation  here  mentioned; 
On  large  open  plains  the  ice  makers 
dig  pits  about  30  feet  fquare  and  2 
deep;    they   ftrev/  the  bottoms    of 
thefe  pits,  about  eight  inches  or  a 
foot  thick,  with  fugar  canes,  or  with 
the  dried    ftems    of   Indian    corn. 
Upon  this  bed  they  place  a  number 
of  ungiazed  pans,  which  are  made  of 
fo  porous  an  earth,  that  the  water 
penetrates  through  their  v/hole  fub- 
flance.      Thefe    pans,     which    are 
about  a  quarter  of  an   inch  thick, 
and  an  inch  and  a  cpiarter  deep^  are 
filled,  towards  the  duik  of  the  even- 


ing 


(      I2S       ) 

ing  in  the  winter  feafon,  with  water 
which  has  been  boiled^  and  then  left 
in  that  fituation  till  the  morning, 
when  more  or  lefs  ice  is  found  in 
themj  according  to  the  temperature 
of  the  weather;  there  being  more 
formed  in  dry  and  warm  weather,  . 
than  in  that  which  is  cloudy,  though 
it  may  chance  to  be  colder  to 
the  feel  of  the  human  body.*  Eve- 
ry thing  in  this  procefs  is  calcu- 
lated to  produce  cold  by  evapora-  1 
tion,  the  bed  on  which  the  pans 
are  placed,  fufFers  the  air  to  have  a 
free  paflage  to  their  bottoms,  and 
the  pans,  in  conflantly  oozing  out 
water  to  their  external  furface,  will 
be  cooled  in  confequence  of  that 
watej  being  evaporated  by  a  gentle 
ftream  of  warm  dry  air,  the  power  of 

the 
'^  Philof,  Tranf,  for  1775,  p,  2^2, 


(       129       ) 

the  air  to  evaporate  water  depending 
much  upon  its  warmth  and  drynefs. 

They  have  a  kind  of  earthen  jar 
in  fome  parts  of  Spain,  called  Buxa- 
ros  which  are  only  half  baked,  and 
the  earth  of  which  is  io  porous,  that 
the  outfide  is  kept  moift  by  the  wa- 
ter filtering  through  ;  though  placed 
in  the  fun,,  the  water  in  the  pots  re- 
mains as  cold  as  ice  :*  and  it  probably 
is  colder  from  the  jar  being  placed 
in  the  fun,  becaufe  the  evaporation 
is  thereby  increafed. 

The  Blacks  at  Senegamhia  have  a 
fnnilar  method  of  cooling  water. 
«^  They  fill  tanned  leather  bags  with 
it,  and  hang  them  up  in  the  fun  5 
the  water  oozes  more  or  lefs  through 
the  leather,  fo  as  to  keep  the  out- 
ward, furface  of  it  wet,  which,  by  its 

quick 

*  Swinburne's  Trav.  p,  305. 
VOL.    III.  I 


(     130    ) 

quick  and  continued  evaporation^^ 
occafions  the  water  within  the  bag 
to  grow  confiderably  cool."-j- 

It  is  common  enough  for  labour- 
ing people,  in  the  height  of  fummer, 
to  drink  feveral  quarts  of  beer  or 
other  beverage  in  a  d-ay  ;  this  quan- 
tity is  principally  difcharged  from 
the  body  by  perfpiration ;  and  the 
cold  which  is  generated  during  the 
evaporation  of  the  fweat,  greatly 
contributes  to  keep  the  body  cool. 
Thus  has  Providence  contrived  to 
render  the  heat  of  the  torrid  zone 
Jefs  infupportable  to  the  inhabitants  j 
an  intenfe  heat  bathes  the  body  in 
iweat,  but  the  fweat  being  evaporated 
by  the  fame  heat  which  occafioned 
it,  a  degree  of  cold  is  generated  on 

the 

+  Philof.  Tranf.  1780.  p.  486. 


(  IJI  ) 

the  furface  of  the  body,  which  would 
not  otherwife  have  been  produced. 

It  feems  reafonable  to  attribute 
the  cold,  which  is  produced  in  thefe 
and  other  fimilar  circumftances,  to 
the  evaporation  of  the  water,  rather 
than  to  any  other  caufe  -,  becaufe 
when  the  bulb  of  a  thermometer  is 
wetted  with  different  fluids,  the  cold 
produced  has  a  manifeft  dependance 
on  the  evaporability  of  the  fluid 
with  which  it  is  wetted.  Thus, 
more  cold  is  produced  when  the 
thermometer  is  wetted  with  fpirits 
of  wine,  than  when  it  iz  wetted  with 
water,  becaufe  fpirits  of  wine  are 
more  evaporable  than  watery  and 
more  is  produced  when  it  is  wetted 
with  ether,  than  with  fpirits  of  wine, 
becaufe  ether  is  more  evaporable 
than  fpirits  of  wine.  No  cold  is  pro- 
I  2  duced 


(     13^     ) 

duced    when    the    thermometer    is 

fiiieared  with   Ihiieed  oil,  or  other 
oils  of  a  fimilar  nature,  becaufe  thefe 
oils  are   not  fenfibly  evaporable   in 
the  ordinary  heat  of  the  atmofphere. 
Strono;  acid  of  vitiiol  when  expofed 
to  the  air,  infread  of  lofing  any  thing 
of  its  weight,  acquires  an  increafc, 
by  attracting  the   humidity   of  the 
atmofphere  j  and  as  ilrong  acid   of 
vitriol  when  mixed  with  water,   ge- 
nerates a  degree  of  heat,  fo  the  bulb 
of  the  thermomieter,    v/hen  Vs^etted 
•with  flrong  acid  of  vitriol,  infiead 
of  being  cooled,  is  warmed,  and  the 
merciary  afcends,  in  confequence  of 
the  heat  produced  from  the  union 
of  the  acid  of  vitriol  with  the  water 
contained  in  the  air. 

When  water  is  refolved  into  va- 
pour, by  the  violence  of  a  fall  from 

a  con- 


(     U3     ) 

a  confiderable  height,  the  air  will 
difTolve  it  fooner  -,  and  in  diiTolving 
it  Iboner,  it  will,  probably,  produce 
more  cold  than  it  would  have  done, 
if  the  furface  of  the  water  had  not 
been  broken  :  hence  natural  and  arti- 
ficial cafcadeSj  may,  probably,  be  fer- 
viceable  in  cooling  the  air  furround- 
ing  them.  This  obfervation  is  pur- 
pofely  exprefied  in  different  terms, 
becaufe,  having  more  than  once  fprin- 
kled  the  floor  and  fides  of  a  room 
with  water  in  the  fummer  time, 
when  the  heat  of  the  air  in  the  room 
and  of  the  water  was  68  degrees,  I 
could  not  obferve  that  a  thermometer, 
hung  in  the  middle  of  the  room, 
changed  its  degree  of  heat  whilfl 
the  room  grew  dry.  In  very  hot 
climates  the  effe6b  may,  probably,  be 
different  -,  thus  we  are  told,  that  in 
I  3  the 


C    134    )  _ 

the  ifland  of  6'/.  Lewis.,  m  the  river 
Senegal,  '''  water  poured  on  the  floor 
of  a  room  for  the  purpofe  of  cool- 
ing the  air^  is  dried  up  in  an  inftant> 
and  there  \s/ome  efe5l  on  the  thermo- 
meter  placed  in  fuch  a  room/'* 

This  phenomenon  of  producing 
cold  by  evaporation,  had  been  men- 
tioned by  M.  Amontons  in  the  year 
1699.-1*  It  had  been  noticed  alfo  by 
M.  Mairan  in  i749^t  and  by  Miijf- 
chenhroeky  in  his  EiTai  de  Phyfique. 
Profefibr  Richmany  at  Peterfburgh, 
gave  an  account  of  feveral  experi- 
ments^  which  he  had  made  on  this 
fubjed  in   1747   and  i748j||  but  he 

did 

*  Philof.  Tranf.  1780.  p.  485. 

f  Mem.  de  V  Acad,  des  Scien.  a  Paris, 
1699. 

X  DiiTertation  fur  le  Glace. 

il  Novi  Comment.  Petrcp.  Tom.  I.  for 
1747  and  174S. 


(•   135     ) 
did  "not  explain  the  finking   of  the 

mercury  in  the  thermometer^  whilft 
its  bulb  grew  dry,  on  the  principle 
of  evaporation.  Dr.  Cuilen\\d,s  very 
particularly  iiluftrated  this  principle, 
in  a  paper  publifhed  in  1756;  and 
he  has  there  Hiewn  that  the  cold 
produced  was  greater,  when  the 
evaporation  was  made  in  vacuo, 
than  in  the  open  air.*  Laftly,  Pro- 
feiTor  Braun,  to  whom  the  world  is 
indebted  for  the  difcovery  of  freezing 
quickfilver,  has  made  a  further  in- 
veiligation  of  this  matter,  by  pub- 
lifhing  a  table  of  the  degrees  of  cold 
produced  during  the  evaporation  of 
different  fluids. f 

During  the  folution  of  falts  in  wa- 
ter 

-*  Effays,  Physical  and  Literary,  Vol.  II. 
Edinb.  1756.  p.  145. 

t  Novi  Commen.  Petrop.  Tom.  X.  1764,' 

I  4 


(     136     ) 

ter  either  cold  or  heat  is  generally 
produced,  but  more  commonly  cold. 
Fixed  alkaline  falts^  Glauber's  fait, 
and  white  vitriolj  produce  fmail  de- 
grees of  heat  during  their  folution, 
Sal  ammoniac  produces  the  greateil 
degree  of  cold,  of  any  fait  hitherto 
knov/n. 

When  Fahrenheit's  thermometer 
flood  at  68  degrees-^  both  in  the 
open  air,  and  in  the  water  which  v/as 
ufed  for  the  experiments-,  I  faturat- 
ed  equal  portions  of  water  with  fal 
ammoniac,  with  faltpetre,  and  with 
fea  fait.  The  fal  ammoniac  made 
the  m.ercury  fink  from  68  to  42  de- 
grees, hence,  26  degrees  of  cold 
were  produced ;  the  nitre  produced 
17  degrees,  and  the  fea  fait  produced 
only  2  degrees  of  cold.  I  repeated 
the  experiment  v^^ith  the  fea  fait  feve- 

ral 


(    /37     ) 

ral  times,  and  with  different  forts  of 

it,  but  I  could  never  obferve  that  it 
produced  above  2  or  at  mofl  2|-  de- 
grees of  cold.  The  experiments 
with  fal  ammoniac  and  faltpetre, 
agree  very  well  with  thofe  made  by 
M.  Eller^  and  mentioned  in  the  Ber- 
lin memoires  for  1 7  50  ;  fince  he  pro- 
duced almoil  27  degrees  with  fal 
ammoniac,  and  1 8  with  faltpetre. 
Boerbaave,  indeed,  made  the  ther- 
mometer defcend  through  £8  de- 
grees by  diffolving  fal  ammoniac  in 
water ;  but  he  had  reduced  his  fait 
to  a  very  fine  powder,  and  dried  it 
well  before  he  ufed  it;  and  a  differ- 
ence in  the  finenefs  of  the  powder  to 
which  the  falts  are  reduced  before 
they  are  diffoived,  may  make  a  dif- 
ference of  a  degree  or  tv/o  in  the 
cold  produced  ;  for  the  finer  the  fait, 

the 


(     '38     ) 

the  more  furface  has  the  water  to  a6t 
upon,  and  the  quicker  will  the  folu- 
tion  be  performed  -,  and  as  the  cold 
is  produced  only  by  the  ad  of  folu- 
tion,  the  fooner  that  is  accomplifh- 
ed,  the  lefs  effect  will  the  heat  of  the 
atmofphere  have,  in  reiloring  to  the 
water,  during  the  time  of  the  folu- 
tion,  any  part  of  the  heat  it  may 
have  been  deprived  of,  during  the 
immediate  a6lion  of  the  water  upon 
the  fait. 

Does  any  given  kind  of  fait,  dur- 
ing its  folution  in  water,  produce  the 
fame  number  of  degrees  of  cold, 
whatever  be  the  temperature  of  the 
water  before  folution  ?  I  have  only 
endeavoured  to  refolve  this  queflion 
with  refpe6l  to  fal  ammoniac,  and  it 
feems  to  me  that  the  quantity  of  cold 
produced,  is  not  influenced  by  the 

tempe- 


(     ^39     ) 

temperature  of  the  water.     In  the 

lummer  feafon  when  the  temperature 
of  the  air^  water^  and  fal  annmoniac 
were  each  of  them  70  degrees,  the 
water  fank  during  the  folution,  of  as 
much  fal  ammoniac  as  would  fatu- 
rate  it,  to  44  degrees,  or  through  26 
deirrees.  I  thawed  fome  fnow  in 
winter,  the  thermometer  ftood  in  the 
fnow  water  at  the  freezing  point,  or 
at  32  degrees  -,  by  putting  fai  am.mo- 
niac,  which  was  equally  cold,  into 
the  water,  the  thermometer  defcend- 
ed  during  folution  to  fix  degrees,  or 
through  16  degrees. 

The  pofTibility  of  freezing  water 
in  the  middle  of  fummer,  is  rightly 
enough  inferred  from  this  experi^ 
ment.  In  a  tub,  fuppofe  of  3  feet  in 
diameter,  place  a  bucket,  a  little 
taller  than  the  tub,  of  i  foot  in  dia- 
3  meters 


(     I40     ) 

meter ;  in  the  bucket  hang  a  Florence 
fiafk,  or  a  flat  lavender  water  bottle, 
fo  that  the  mouth  of  the  bottle  may 
be  above  the  rim  of  the  bucket :  fill 
thefe  veiTels  with  v/ater  heated,  fup- 
pofe,  to  70  degrees.  Saturate  the 
water  in  the  tub  VN^ith  fal  am.moniac, 
then  v/iil  the  70  degrees  of  heat  be 
reduced  to  44,  the  v/ater  lofing,  dur- 
ing the  folution  of  the  fait,  26  de- 
grees. The  water  in  the  bucket 
being furrounded  with  this  cold  fluid, 
will  itfelf  be  cooled ;  fuppofe  it  to 
be  cooled  only  to  50  degrees,  then 
by  faturating  it  with  fal  ammoniac, 
it  will  lofe  26  degrees  more  of  its 
heat,  and  be  cooled  to  24  degrees. 
The  water  in  the  bottle  being  im- 
merfed  in  a  fluid,  heated  only  to  24 
degrees,  will  foon  be  cooled  below 

the 


(     '41     ) 

the  freezing  pointer  32  degrees,  and 
confeqiiently  will  concrete  into  ice. 
The  cold,  in  all  thefe  cafes,  is  ge- 
nerated only  during  the  time  of  the 
folution.     The  water  recovers    the 
temperature  of  the  atmofphere  fooner 
or  later,  according  as  its  quantity  is 
lefs  or  greater,  and  as  the  furface  ex- 
pofed  to  the  air  is  greater  or  lefs ;  it 
is  here  fuppofed,  that  the  heat  of  the 
atmofphere  remains  the  fame.     The 
different  degrees  of  cold  produced 
by  different  falts,  do  not  depend  up- 
on any  general  caufe  which  has  yet 
been    difcovered,  nor  is    there  any 
very   fatisfaftory    reafon    given   for 
thefe,  and  other  fimilar  produdtions 
of  cold  or  heat.  The  time  may  come 
when  we  fliall  be   able  to  compre- 
hend the  reafon  wliy  the  acid  of  ni- 
tre has  fuch  different  efFeds  when 

mixed 


(      142       ) 

mixed  with  fnow  from  what  it  has 
when  mixed  with  fnow  water ;  when 
mixed  with  fnow  water  it  excites  a 
very  great  degree  of  heat ;  and  when 
mixed  with  fnow  it  produces  the 
greatefl  degree  of  cold  that  has  ever 
yet  been  obferved  *.  Rejourn  natura 
Jacrafua  nonfimul  tradit,  Initiatos  nos 
credimuSy  in  veftihulo  ejus  haremus. 
Ilia  Arcana  non  promifcue  nee  omnibus 
patent  s  reduEla  et  in  inferiore  Jacra- 
rio  claujajunt.  Ex  quihus  aliud  h^c 
^etas,  aliud  qu^ foft  nos  Juhibit,  ad/pi- 
ciet. 

f  Vol.  I.J).  267. 


ESSAY 


E    S    S    A    Y      V. 


OF  THE  DEGREES  OF  HEAT  IN  WHICH 
WATER  BEGINS  TO  PART  WITH  ITS 


THE  air  bubbles  which^  in  fum- 
mer  time,  adhere  to  the  iniides 
of  decanters,  water  glalTes,  and  other 
vefiels  filled  with  water,  cannot  have 
efcaped  the  obiervation  of  any  ones 
-I  have  endeavoured  to  afcertain  the 
degree  of  heat  in  v/hich  thefe  bub- 
bles begin  to  be  formed. 

Into 


(     144     ) 

Into  a  water  glafs  filled  with  wa- 
ter I  immerfed  a  thermometer  -,  the 
heat  of  the  water  was  64  degrees ; 
the  water  was  fet  in  a  clofet,  where 
the  fun  never  fhone,  for  two  days  5 
the  heat  remained  much  the  fame 
during  that  period,  and  there  was  no 
appearance  of  bubbles.  The  glafs^ 
with  the  immerfed  thermometer, 
was  then  {(^t  in  the  fun,  and  when 
the  heat  amounted  to  about  90  de- 
grees, feveral  air  bubbles  were  found 
adhering  to  the  graduated  fide  of  the 
thermometer,  and  fome  wTre  begin?- 
ning  to  be  formed  on  the  bottom 
and  fides  of  the  glafs. 

Having  frequently  {ctn  the  in- 
fides  of  veiTels  containing  water, 
ftudded  with  bubbles,  when  the  heat, 
it  was  apprehended,  was  much  lefs 
than  90  degrees  ^  I  put  a  thermome- 
ter 


(    145     ) 

ter  into  a  water  glafs  at  a  time  when 
it  abounded  with  bubbles,  and 
found  that  the  heat  of  th^e  water 
was  not  above  64  degrees. 

The  refult  of  this  experiment  be- 
ing very  different  from  that  of  the 
preceding,  in  which  the  air  did  not 
begin  to  feparate  itfelf  from  the  wa- 
ter till  the  heat  was  about  90  de- 
grees, I  was  for  fome  time  at  a  lofs 
how  to  account  for  the  difference  5 
recollecting,  however,  that  the  water 
which  required  90  degrees  of  heat 
before  it  parted  with  its  air,  was 
pumped  from  a  well  fed  by  a  ftream, 
which  had  run  four  miles  in  the 
■open  air ;  and  that  the  other  water, 
which  let  go  its  air  at  64  degrees, 
was  pumped  from  a  well  fed  by 
fubterraneous  fprings,  I  attributed 
the  difference  in  the  degree  of  heat 

VOL.  III.  K  reaui-. 


(     '46     ) 

rcquifite  to  make  thefe  waters  part 
with  their  air,  to  the  diiTerent  qua- 
lities of  the  waters. 

In  order  to  try  thefe  waters  under 
fimilar  circumftances,  two  water 
glaflfes  were  filled,  one  with  common 
well  water,  another  with  that  which 
had  been  fupplied  by  the  ftream; 
on  being  expofed  to  the  air,  bubbles 
began  to  be  formed  in  the  well  wa- 
ter when  the  heat  amounted  to  60 
degrees,  the  other  did  Bot  part  with 
any  of  its  air  in  th€  fame  degree  of 
heat. 

I  v/as  at  firfl  difpofed  to  thirik, 
that  thefe  experiments  pointed  out  a 
general  difference  between  river  wa- 
ter and  well  water,  with  refpedb  to 
their  difpofition  for  retaining  or  part- 
ing with  their  air  ;  but  the  following 
experiment,  made  at  a  different  fea- 
I  foil 


(    U7     ) 
foil  of  the  year,  convrnced  me  tliat 
the  conjedure  was  not  well  founded. 

In  November,  when  the  heat  of 
the  air  had  been  for  fome  time  about 
JO  degrees,  I  took  three  water  glafles, 
one  was  filled  with  rain  water  imme- 
diately after  it  had  fallen,  another 
with  the  common  well  water,  the 
■third  with  the  water  which  came 
from  the  ftream  :  the  heat  of  thefe 
feveral  waters  was  the  fame,  namely 
48  degrees  ;  they  were  all  gradually 
warmed,  by  fetting  the  water  glafTes 
in  hot  water,  and  they  all  began  to 
exhibit  bubbles  when  the  heat  was 
about  60  degrees  ;  I  thought  the  rain 
waters  ihew*ed  the  moil  bubbles. 

Hence  it  is  plain^  that  the  flreia:m 

water  does  not  differ  from  rain  or 

well  water,  except  accidentally,  as  to 

the  degree  of  heat  in  v/hich  it  parts 

K  a  with 


(.148     ) 

with  its  air.  The  firft  experiment, 
ill  which  the  bubbles  were  not  form- 
ed till  the  heat  was  90  degrees,  was 
made  after  there  had  been  feveral 
days  of  very  hot  weather^  and  the 
water  in  being  expofed,  during  its 
courfe,  to  the  adion  of  the  fun,  had 
probably  loft  a  confiderable  portion 
of  its  air  before  it  arrived  at  the 
well.  All  river  water  has  a  vapid 
tafte  in  fummer  lime,  which  is  in 
part,  probably,  occafioned  by  having 
loft  fome  of  its  air,  in  confequence 
of  its  being  expofed  to  the  rays  of 
the  fun.  Water  drinkers  are  defirous 
of  having  water  frefti  from  the  well ; 
efpecially  in  fummer  time,  and  not 
without  reafon,  for  the  heat  in  that 
feafon  being  generally  above  60  de- 
grees at  our  principal  meal  time, 
the  water^  if  it  has  been  long  expofed 

to 


(     149     ) 

to  the  air,  muil  have  fuffered  a 
change  of  quality,  not  only  from  its 
increafe  of  heat,  but  from  a  confe- 
quent  lofs  of  a  portion  of  its  air. 
The  water  which  fupplies  the  warm 
bath  at  Matlock,  and  which  is  drunk 
by  invalids,  is  68  degrees  warm  i 
hence  it  has  loft  a  part  of  the  air 
which  it  would  naturally  contain, 
and,  except  in  very  hot  weather,  it 
does  not  exhibit  any  air  bubbles  in 
the  decanters. 

The  air  begins  to  be  mfihly  fepa- 
rated  when  the  heat  is  about  60  de- 
grees 5  but  it  begins,  probably,  to 
be  inviftbly  feparated  when  the  heat 
is  much  lefs  :  and  the  leaft  heat  will 
be  requifite  to  feparate  it,  when  the 
weight  of  the  atmoiphere  is  the  leaft. 

Phiiofophers  have  invented  vari- 
ous methods,  equally  cone  lu five,  of 
K  3  fhevv- 


r  150  _)  _ 

{lewing^  that  water  in  its  ordina^ 
ftate^  contains  diflblved  in  it  a  por- 
tion of  air.     And  they  have  fhewn^^ 
that  water  which  has  loil  a  portion 
of  this  air,  either  fey  hting  frozeny  or 
heated  J  or  by  longcontinued  agitation  y 
or  by  other  means,  has  the  property^ 
©f  re-abforbing  as  much  air  from  the 
atmofphere  as  it  had  loft ;  and  they 
have  fhewn,   th^t  this  abforption  is 
the  ftrongeft  at  firft,.  and  becomes 
lefs  and  lefs  r)Owerful,   as  the  water 
.becomes  more  and  more  impregnated 
with   air.     Thefe  and  fimiik-r  obfer- 
vations  renderitprobablcy  that  water 
is  as  capable  of  diiToiving  a  certain 
portion  of  air,  as  it  is  of  diiToiving  a 
certain  portion  of  any  particular  kind 
of  fait.     Thr  quantity  of  air,  vv^hich 
water  is  capable  of  diiToiving  and 
retaining  m  folutionj  depends  partly 


(     '5'     ) 

upon  the  temperature  of  the  water, 
partly  upon  the  weight  of  the  at- 
mofphere,  and  partly,  I  conceive, 
upon  the  water's  purity.  From  thefe 
circumftances,  as  well  as  from  fome 
others  which  might  be  attended  to 
in  making  the  experiment,  it  has 
happened,  that  authors  have  given 
very  different  accounts  of  the  quan- 
tity of  air  contained  in  water. 
Boerhaave  has  an  experiment*,  from 
which  he  infers,  that  there  may  be 
feparated.  from  v/ater  a  quantity  of 
air  equal  in  bulk  to  the  water  s  the 
experiment  is  ingenioufly  contrived, 
but  the  conclufion,,!  think,  is  liable 
to  fome  objedtions..  T\\t  Abbe  Nollet 
fays,  that  water  which  has  been  pre- 
vioufly  purged  of  air,  abforbs,  in  fix 
days,    one    thirtieth   of  its   bulk.f 

Docfor 

*  Boerh.  Chem.  Vol.  I.  p.  521, 

t  Hift,  del' Acad.  1743. 
k:4 


(  H^  ) 

Do5for  Hales  obtained  by  diftillation 
one  cubic  inch  of  air  from  fifty-four 
cubic  inches  of  water*.  Mr.  Eller 
is  of  opinion  that  the  portion  of  air 
contained  in  water  does  not  exceed 
the  150th  part  of  its  bulkf.  Dr. 
Prieftley  found  that  a  pint  of  his 
pump  water  contained  about  one 
fourth  of  an  ounce  meafure  of  air, 
that  is,  the  bulk  of  the  water  was  to 
that  of  the  air  it  contained,  as  64  to 
i§..  M.  Fontana  fays,  that  the  wa- 
ter of  the  Seine  at  Paris,  after  being 
long  boiled,  abforbs  in  forty  days 
one  twenty  eighth  of  its  bulk  of 
common  air  J.  Lailly,  M.  Cavallo 
obferves,  that  in  a  temperate  degree 
of  heat,  and  when  the  barometer  is 

about 

*  Veg.  Stat.  c.  6.     f  Berl.  Mem,  1750. 
§  Philof.  Tranf.  1772.  p.  248, 
I  Fhiiof.  Tranf.  1779.  P*  439* 


(     ^S3     ) 

about    29I    inches,    water  abforbs 

about  one   fortieth  of  its   bulk   of 
common  air*. 

It  has  been  remarked  in  another 
placet,  that  the  atmofpherical  air  con- 
fifts,  in  part,  o^ fixed  air ;  and  fome 
of  the  moll  ftriking  differences  be- 
tween fixed  and  atmofpherical  air 
were  there  mentioned.  If  a  bubble 
of  atmofpherical  air  of  a  definite 
bulk,  fuppofe  it  equal  to  eleven  pints, 
be  expofed  to  the  aftion  of  a  fulHci- 
ent  quantity  of  water,  which  has 
been  purged  of  its  air  by  boiling, 
the  zvhole  of  the  bubble  will,  in  a 
proper  length  of  time,  be  abforbed 
by  the  water  5  but  when  about  fevea 
pints,  or  even  a  lefs  portion,  have 
been  abforbed,  the  remaining  part 

will 

*  Cavalla  on  air.  p.  213. 
f  Vol.  II.  p*  247. 


(     154    ) 

will  refemble  fixed  air  in  this — that 

a  candle  will  not  burn  in  it*.  It  is 
very  probable  that  water  which  has 
not  been  boiled  may  have  a  fimilar 
efFedt  under  certain  circuinftances. 
— "  The  wells  at  Utrecht  are  from  8 
to  20  feet  in=  depth  ;  it  has  been  the 
cuftom  to  make  ufe  of  pumps  to 
raife  the  water,  and  they  are  then 
covered  over  with,  a  kind  of  arch. 
When,  after  a  certain  period  of  time> 
the  wells  are  opened,  on  any  account, 
it  is  necefifary  to  leave  them  un- 
covered for  12  hours,  before  any 
perfon  defcends  into  them  ;  whoever 
fhould  venture  to  go  down  into 
them  fooner,  would  expofe  himfelf 
to  immediate  death.  The  air  of 
thefe  wells  extinguilhes  candles  -like 
that  acquired  from  fermentation  or 

cffer- 
*  Philof.  Tranf,  1772.  p.  247, 


(     ^S5     > 

cffcrvefcence."*  —  Stagnatmg^    airj, 

which  has  brooded,  though  but  for 
a  fhort  time,  even  over  running  wa- 
ter^ is  found  to  be  fo  greatly  altered 
in  its  quality,  that  it  will  extinguifh 
flame,,  though  it  be  fufficiently  pure 
to  fupport  animal  life.     I  was  in- 
formed of  this  f^d  by  a  miner  in 
Perbyfhire,  who  had  frequently  ve- 
rified it  by  his  own  experience.     In 
order  to  free  a  mining  diftridt  from 
water,  they  frequently  dig  for  miles 
together  ftibterraneous    a<jueduds; 
fupporting  the  fides  and  roof  with 
timber  or  done.     The   mouths  or 
outlets  of  thefe  aqu^duds  or /oughs^ 
being  below  the  level  of  the  diftridt 
to  be  drained,  there-  is  a  conftant 
ilream    of  water   flowing    through 
them.     Thefe  Joughs   are   many  of 

thenai? 

*  LaY€>ifier''sEirays,  p,  ii8» 


(     156    ) 

them  high  enough  for  a  man  to 
walk  upright  in  them^  the  water 
reaching  to  his  middle  or  higher; 
and  men  with  lighted  candles  fre- 
quently walk  through  them  from  one 
end  to  the  other,  in  order  to  prevent 
obftru6lions ;  it  fometimes  however 
happens,  that  by  the  falling  in  of  the 
roof,  or  other  accidents,  the  fough  is 
in  part  dammed  up :  when  this  is 
the  cafe,  the  water  beyond  the  place 
where  the  obflru6lion  is,  rifes  to  the 
roof  of  the  fough,  and  thus  prevents 
a  circulation  of  air,  though  there  is 
ftill  a  difcharge  of  water  through 
the  mouth  of  the  fough.  When  an 
accident  of  this  kind  happens,  men 
are  fent  with  candles  in  their  hands 
to  find  out  and  remove  the  ob- 
ftru(5lion,  but  before  they  have  walk- 
ed fifty  yards  from  the  mouth  of  the 

fought 


C    157    ) 

fough,  the  candles  go  out,  though 
they  perceive  no  difficulty  in  breath- 
ing, and  this  extin6l!on  of  the  can- 
dles will  take  place  in  24  hours,  af- 
ter the  lloppage  of  the  water  has 
commenced^ 

Fahrenheit^  Boerhaav£y  and  other 
philofophers,  had  obferved  that  the 
degree  of  heat,  requifite  to  make 
water  boil,  was  variable  according  to 
the  purity  of  the  water  and  the 
weight  of  the  atmofphere.  Within 
the  ufual  limits  of  28  and  3 1  inches 
in  the  barometer,  Boerhaave  was  of 
opinion*,  that  there  would  be  a  va- 
riation in  the  heat  of  boiling  water, 
amounting  to  8  or  9  degrees.  This 
fubjed  ha«  of  late  been  examined 
with  great  accuracy  by  Mr.  de  LuCy 
and  Sir  George  Shuckhtirg ;  and  Mr. 

Cavallo 

^  Chem.  Vol.  I.  p.  171. 


(     i5«    ) 

t^avalto   has  given  us  the  refult  of 

their  experiments  in  the  annexed 
table,  which  is  formed  according 
to  the  fcale  of  Fahr£nheit'%  ther- 
mometer*. 

TABLE, 


Height  of  the 

Heat  of  boiling  water 
accordino;  to 

Barometer. 

Mr.de  Luc 

Sir  G.  Shuckburg 

Parts  of 

Parts  of  a 

aDeg.deg. 

Deg.  deg. 

26 

1 

205,17 
206,07 
206,96 
207,84 
208,69 

204,91 
205,82 
206,73 
207,63 
208,25 

29 

209»55 
210,38 

209,41 
210,28 

^9i 

210,2 

211,15 

30 

212 

212 

30I 

31 

212,79 

221,85 
213,69 

*  CavaUo  on  air,  p.  215, 


The 


(     '59    ) 

The  following  experiment  is  curi- 
ous in  itfelf,  and  it  illuftrates  both 
the  nature  of  boiling  in  general,  and 
what  is  here  advanced  relative  to 
the  heat  of  boiling  water  under  dif- 
ferent preiTures  of  the  atmofphere. 
I  hit  upon  it  many  years  ago,  when 
I  had  another  objecl  in  view.  My 
tdefign  was  to  exhibit  a  flriking  in- 
ftance  of  the  increafe  of  dimenfions 
produced  in  fluids  by  various  de- 
grees of  heat :  in  order  to  this,  I  took 
a  large  glafs  veflel,  refembling  in 
fhape,  fuch  mercurial  thermometers 
as  have  a  bulb  at  the  bottom*,  the 
hu\b  of  this  velTel  held  above  a 
gallon,  and  the  ftem  had  a  fmall  dia- 
meter, and  was  above  two  feet  in 
length.    Into  this  vefTel  I  poured 

boiling 

*  A  velTei  of  this  fhape  is  -ufually  called  a 
Maira/s, 


C    i6o    ) 

boiling  water,  and  having  filled  it 
up  to  the  very  top  of  the  ftem,  I 
corked  it  with  a  common  cork  as 
ciofe  as  I  could.  The  water  and 
the  cork  were  at  firft  contiguous  to 
each  other  ;  but  in  a  very  little  time 
the  water  began  to  grow  cold,  and  as 
it  grew'cold,  it  contracStcd  itfelf  and 
funk  very  vifibly  in  the  ftem ;  and 
thus  the  firft  intention  of  the  experi- 
ment was  fully  anfwered.  But  an 
unexpe6ted  phenomenon  prefented 
itfelf, — the  water,  though  it  was  re- 
moved from  the  fire, — was  growing 
cold, — and  had  for  fome  time  en- 
tirely ceafed  from  boiling,  began 
to  boil  afrefh  very  violently,  the 
bubbles  were  large  and  numerous, 
and  continued  to  afcend,  into  the 
fpace  between  the  furface  of  the  wa- 
ter in  the  ftem,  and  the  cork,  where 
2  the 


(     i6i     ) 

they  burfl,  for  above  two  hours. 
When  a  hot  iron  was  applied  to  that 
part  of  the  flem,  through  which  the 
water,  in  contradiing  itfelf,  had  de- 
fcended,  the  ebullition  prefently 
ceafed;  it  was  renewed  when  the  iron 
was  removed;  and  it  became  more 
than  ordinarily  violent,  when,  by  the 
application  of  a  cloth  dipped  in  cold 
water,  that  part  was  cooled.  There 
is  no  great  difficulty  in  accounting 
for  thefe  feveral  appearances  :  by 
the  finking  of  the  water  in  the  fleni 
a  kind  of  vacuum  is  left  between  its 
furface  and  the  cork  ;  water  and  other 
fluids  boil  with  lefs  degrees  of  heat, 
when  the  prefTureon  their  furface  is 
diminifhed  ;  here  the  preffure  of  the 
atmofphere  is  wholly  removed  by 
means  of  the  cork,  and  the  water 
continues  to  boil,  though  its  heat  be 
VOL.  Ill  L  con* 


C    r6i    ) 

eondantly  decrcaiing.  The  interval 
between  the  water  and  the  cork  U 
not,  as  will  be  ihewn  prefently,  a 
ferfe^  vacuum  ;  it  is  occupied  cither  ^ 
by  the  vapour  of  the  water^  or  hy  a 
filial  1  portion  of  r^ir,  or  by  both  ; 
heat  increafes  the  elaflicity  of  both 
air  and  vapour,  and  thus  augments 
the  preiTure  upon  the  fur  face  of  the 
water,  hence,  the  ceafir.g  of  the 
ebullition  on  the  application  of  the 
hot  iron;  cold  dim  inifhes  the  elalH- 
city  of  air,  and  condcnfes  vapour, 
and  thus,  the  preflure  upon  the  fur- 
face  being  Icffcned  by  the  applica- 
tion of  the  Goldcloth,  the  ebullition 
of  the  v^atcr  became  more  violent. 
When  the  water  ceafed  boiling  I 
poured  it  on  the  bulb  of  a  thermo- 
meter, and  found  that  its  heat  was 
only  130  degrees. 

-  Another 


(     »63    )  . 

Another  circumflance  defervirig  of 
notice  remains  to  be  mentioned* 
When  the  water  was  become  cold^ 
it  had  funk  through  the  whole  flem, 
and  through  part  of  the  bulb,  I  then 
inverted  the  veffei  which  contained 
it,  into  a  tub  of  water,  and  obferved 
upon  the  bottom  of  the  bulb  a  large 
circular  fpot  void  of  water,  I  con- 
fidered  this  fpot  as  a  perfed:  va- 
cuum, for  it  anfwered  to  the  fpace 
which  the  water,  in  contracting  it- 
felfj  had  deferted  ;  and  the  vapour 
which^  whilil  the  water  was  w^arm, 
might  have  been  fuppofed  to  occu- 
py that  fpace,  I  was  perfuaded,  was 
condenfed  by  the  cold  :  in  order  to 
fee  whether  it  was  a  vacuum  or  not, 
I  pulled  out  the  cork,  whilfl  it  was 
under  the  furface  of  the  water  into 
wiiich  the  veffei  w^s  inverted,  being 
L  %  certain 


(     i64    ) 

certain  that  if  it  was  a  vacuum,  it 
would  be  inftantly  filled  with  water, 
which  the  prelTure   of    the   atniof- 
phere  would  make  to  afcend  through 
the  ilem.     In  fad,  the  circular  fpot 
was  greatly  diminlihed  bytheafcent 
of  the  water,  but  never  (for  the  ex- 
periment w^as  often  repeated)  taken 
wholly   away  ?  what  remained  mufi 
have  contained  either  air,  or  fome 
other  fluid,  whofe    elaflicity  was  a 
counterpoize  to  the  preiTure  of  the 
atmofphere,   on   the  furface  of  the 
water  in  the  tub.     It  v.'ould  be  too 
haily  a  conclufion,  from  this  circum- 
ilancc,  to  attribute  the  formation  of . 
the   bubbles  to  the  particles  of  air, 
from  which  water  cannot  "be  fepa- 
rated  by  long  boiling'* ;  for  it  may 

be, 

*  Licet   diu  ebuUieriet  aq\ia  noa  erit  Reris 
cxpers.  Mufchen,  de  Aqua. 


_(     i65     ) 

be,  thnt  this  fmall  portion  of  air 
arofe  from  the  fubitance  of  the  cork, 
or  from  the  air  in  the  water  of  the 
tnb,  that  water  having:  not  been 
boiled  ;  or  it  may  have  been  intang- 
led  in  the  parts  of  the  boiling  water, 
as  it  was  poured  into  the  veiTel,  and 
not  have  had  time  to  efcape  before 
the  cork  was  inferted ;  or,  laftly, 
which  is  the  lead  probable  fuppofi- 
tion,  the  vapour  ariiing  from  the 
water  may  not  be  capable  of  being 
totallv  condenfed. 

The  phenomenon  of  the  boiling 
of  fluids  is  not  very  fatisfadtorily 
explained.  It  is  clear,  I  think,  from 
the  experiment  of  which  I  have  given 
an  account,  that  it  cannot  be  attri- 
buted, in  ail  cafes,  either  to  the 
efcape  of  air  from  the  interflices  of 
water,  or  to  the  matter  of  fire,  as  it 
L  3  is 


_  (     i66     ) 

is  called,  pervading  the  water ;  for 
the  water  continued  boiling  for  two 
hours  after  it  was  removed  far  from 
the  fire;  and  the  air,  if  it  contained 
any,  was  utterly  inadequate  to  the 
formation  of  the  numerous  bubbles* 
.Bc?(?;'^i3^'yd' has  remarked,  that  bubbles 
of  the  kind  here  fpoken  of  contain 
no  air,  but  he  has  not  affigned  the 
caufe  of  their  origin  ;  Dr.  Hooke  af- 
cribes  them  to  the  fubtle  parts  of 
the  water,  which,  when  the  prelTure 
of  the  air  is  removed,  (probably  by 
means  of  an  air  pump)  are  able  to 
-acquire  the  form  of  vapours,  by  thac 
fmall  degree  of  heat  which  is  left  in 
the  ambient  air  *:  and  other  philo- 
fophers  -f  have  adopted  this  idea, 
without  hinting,  at  what  Hooke  fup- 

pofed, 

^  See  Birch's  Hift.  of  the  Royal  Society. 
f  The  Abbe  Nollet  and  Dr.  Hamilton. 


(     i<J7    )' 
pafed,  a  different  degree  of  volatiliry 
in  the  parts  of  the  water. 

Froin  what  has  been  advanced  we 
may  conclude,  that  the  Ahnightyr 
when  he  feparated  the  chaotic  mafs 
into  air  and  water,  did  not  render 
ihefe  two  oceans  of  matter  fo  wholly 
heterogeneous  from  each  other,  as 
that  they  fliould  be  incapable  of 
Gontrad:lng  any  union  together ;  they 
have,  on  the  contrary,  fuch  a  difpo- 
fition  to  unite,  as  feems  t6  indicate 
their  having  had  a  common  origin; 
and  were  it  not  for  the  intervention 
of  heat,  they  would,  probably  unite 
and  again  compofe  a  common  mafs. 
The  water  on  the  fur  face  of  the  earth 
is  conftantly  replete  with  air,  and  the 
atmofphere  is  replete  with  water.The 
Bumerous  tribe  of  aquatic  animals, 
L  4  which 


(     i68     ) 

which  inhabit  the  ocean  of  water^, 
would  perilL,  if  it  contained  no  air ; 
and  it  it  is  not  an  improbable  conjec- 
ture, that  the  animals  which  exiil  in 
this  ocean  of  air,  would  pcrifn  if  it 
contained  no  water.  The  air,  more- 
over, b)^  being  abforbed  into  the 
w^ater,  and  afterwards  feparated  from 
it  by  the  ad:ion  of  the  fun,  to  which 
it  is  daily  expofed,  is  rendered  abun- 
dantly more  fit  fol*  animal  refpira- 
tion  than  common  air  ;  and  this 
purified  air  (the  quantity  of  which, 
confidering  the  great  extent  of  the 
furface  of  the  earth  which  is  covered 
v^'ith  w^ater,  muil  be  very  coniider- 
able)  cannot  but  be  one  great  means 
of  reftoring  to  the  whole  mafs  of  air, 
thofe  falubrious  qualities  of  which  it 
is  daily  deprived,  by  the  rejpration 

of 


(     i69     ) 

of  animals,  ihQ putrefaBicn  of  bodies, 
the  ccmbiiftion  of  fuel,  and  other 
caufes. 

*  Dr.  Prieftley  has  obferved,  '^  that  the 
fame  water,  which,  if  examined  immedi- 
ately, gives  only  a  fmall  quantity  of  bad 
air,  y\fiS.^%  fpontaneouJJy  about  ten  times  the 
quantity  of  pure  dephlogiilicated  air,  after 
ilanding  fome  time  expofed  to  the  funJ^^ 
Phil.  Tranf.  1779,  p.  377.  An  animal 
w'ill  live  five  times  as  long  in  what  is  called 
here  dephlogifticated  air,  as  it  v/ill  in  com- 
mon air  of  the  befl  quality. 


fiSSAY 


ESSAY      VI. 


OF  WATER  IN  A  SOLID  STATE;  OF 
THE  HEAT  OF  SPRING  WATER; 
AND  OF  A  PROBABLE  CAUSE  OF 
THE  IMPREGNATION  OF  SULPHU- 
REOUS WATERS. 


TH  E  mind  of  man  admits  with 
great  reluctance,  the  truth  of 
every  tellimony  concerning  matters 
of  fad,  which  happen  to  be  repug- 
nant to  the  uniform  experience  of 
his  fenfes ;  hence  the  general  back* 

wardnefs 


(     17^    ) 

wardnefs  to  believe  the  miracles  re- 
corded in  the  bible;  and  hence  the 
Dutchman  who  informed  the  king  of 
Siain,  that  water  in  his  country, 
would  fometimes,  in  cold  weather, 
be  fo  hard  that  men  walked  upon  it^ 
and  that  it  would  bear^an  elephant, 
if  he  were  there,  was  cfleemed  a  per- 
fon  unworthy  of  credit,  the  king,  as 
Mr.  £cfy^^  relates  the  flory,  faying  to 
him,  "  Hitherto  I  have  believed  the 
ftrange  things  you  have  told  me, 
becaufe  I  look  upon  you  as  a  fober 
man,  but  now  I  am  fure  you  lie,"-'^ 

Mahine,  the  native  of  Borahora^ 
could  fcarcely  be  perfuaded,  even  by 
the  information  of  his  fenfes,  of  the 
reality  of  the  fame  effedl.  The  ap- 
pearance of  "  white  flones,"  as    he 

called 

*  Locke's  ElTay  on  the  Hum.  Und.  B.  IVi 
C.  XV. 


(     173     ) 

colled  hail,  which  melted  in  his 
hand  was  altogether  miraciilous  to 
him  ;  and  when  he  had  been  with 
difficulty  convinced  that  an  exten- 
live  field  of  ice  was  not  common 
land,  he  was  determined  at  all  events 
to  call  it  ''  white  land,"  by  way  of 
dillineuiihine:  it  from  all  the  reil''^. 

This  dc term inatioii  of  the  favage 
was  made  in  the  true  fpirit  of  philo- 
lofophv,  for  ice  in  fm.all  particles  is 
afpecics  of  earth,  and  in  folid  maiTes 
it  may  be  conlidered  as  a  kind  of 
tranfparent  ftone.  The  waters,  fays 
Job,  "j-  fpeaking  of  the  eired  of  froil^ 
ere  hid  as  with  aftoiie^  that  is,  vs^a- 
ter  conceals  its  nature,  by  afluming  a 
Hone-like  hardnefs  and  conliftence 
when  it  becomes  ice.     The  Ruffians 

applied 

*  Forilei's  V^j.  Vol.  I,  p.  530. 
I  Chap.  >jcxviii.  30, 


c    174    ) 

applied  ice  to  the  fame  purpofes 
■with  flone,  at  the  whimficai  mar- 
riage of  Prince  Gallitzen^  in  1739; 
an  houfe,  conlifting  of  two  apart- 
ments, was  bnilt  with  large  blocks 
of  ice,  the  furniture  of  the  apart- 
ments, even  to  the  nuptial  bed,  was 
made  of  ice  ;  and  the  icy  cannon  and 
mortars,  which  were  iired  in  honour 
of  the  day,  perform.ed  their  office 
more  than  once  without  burilino;.  * 

Ice,  however,  differs  from  all 
other  earths  and  ftones,  not  only 
in  its  melting  in  a  much  lefs  degree 
of  heat  than  any  of  them,  but  in  its 
being  fubjedl  tOr  a  conftant  diminu- 
tion of  its  weight  when  expofed  to 
the  open  air,  in  the  greateil  degree 
of  cold.  It  generally  becomes  fluid 
in  the  33d  degree  of  heat,  as  indi- 
cated 

*  Manftein's  Mem.  of  Ruffia* 


(     '75     ) 

cated  by  Fahrenheit's  thermometer ; 
and  Mr.  Boyle,  by  expofing  in  a 
good  balance  fomewhat  lefs  than  two 
ounces  of  ice  to  a  fharply  freezing 
air,  a  little  before  midnight,  found 
it  in  the  morning  diminifhed  in 
weight  ten  grains.  *  It  is  probable, 
that  this  diminution  of  the  weight  of 
ice,  is  owing  to  the  abrafion  of  its 
parts  by  the  adlion  of  the  air.  The 
particles  of  air  are  thought  to  be 
larger  than  the  particles  of  water, 
and  may  by  their  motion  acquire 
force  enough  to  feparate  the  particles 
of  ice,  or  if  this  ihould  not  be  ad- 
mitted, it  muil  be  remembered,  that 
the  air  always  contains  a  great  quan- 
tity of  water,  the  particles  of  which 
when  converted  into  particles  of  ice, 
though  in  this  country  they  are  fel- 

doni 
*  Boyle's  Works,  Fob  Vol.  III.  p.  66. 


(     176    ) 

doni  large  enough  to  be  feen,  always 
make  themfelves  felt  by  impinging 
Upon  our  ikin  :  thefe  icy  particles 
wben  put  in  motion  may  abrade 
the  furface  of  a  mafs  of  ice,  and 
caufe  thereby  a  conRant  diminution 
of  its  weight.  In  confirmation  of 
this  explanation  it  may  beobferved, 
that  ice  fuiTers  no  lofs  of  its  weight 
in  a  velTel  devoid  of  air,  nor  in  a 
clofe  veffel  full  of  air.*  That  the 
icy  particles,  contained  in  a  freezing 
atmofphere,  ihould  be  able  to  a<5l 
upon  ice,  cannot  be  a  matter  of  dif- 
ircult  conception  to  thofe  who  recol- 
lect, that  the  hardeft  bodies  in  na- 
ture fuffer  a  diminution  of  their 
w-eight,  by  the  fridion  of  the  minute 
parts   of  the  fame  kind  of  liodies; 

dia- 

*  Hamilton  on  the  Afcent  of  Vspours,- 
p.  71. 


f  177  ) 

cFiamond  duft  being  eflentlally  ne- 
cefTary  for  the  cutting  or  polifhing. 
of  diamonds. 

That  water  was  diminifhed  in 
quantity  by  being  frozen  was  known 
to  Hippocrates;,  for  he  exprefsly  fays,, 
that  if  a  given  quantity  of  water  be 
frozen,  and  afterwards  thawed,  it 
will  not  fill  the  fame  vefTel  it  would 
have  done  before  it  was  frozen  *- 
Pliny  was  of  the  fame  opinion  with. 
Hippocrates,  and  they  both  of  them 
attribute  this  diminution  of  weight  ta 
the  feparation  of  the  more  fubtile 
parts  of  the  water  during  congela- 
tionf .  The  principal  caufe  of  the  lofs 
of  weight,:  fuflained  by  water  when : 
changed  into  ice,   feeras  to  be  the- 

inceffant 

*  Hippoc.  de  Aqua.> 

t  Plin.  Hifl.  Nat,  Lib.  II.  S.  61..  &  Lib,. 
JXXI.  S.  3. 

VOL.    IIU  M. 


(     178     ) 

incefTant  adion  of  air  upon  its  fur- 
face  'i  it  is  true,  however,  that  water 
is,  by  freezing,  deprived  of  the  great- 
eft  part  of  the  air  with  which,  in  its 
fluid  ftate,  it  is  ordinarily  faturated; 
and  this  feparation  of  its  air  may 
contribute  fomething  towards  the 
diminution  of  the  water's  bulk  -,  fince 
water  when  faturated  with  air,  is 
fomewhat  greater  in  bulk  than  when 
deprived  of  it. 

It  is  eafy  to  apprehend,  that  the 
lofs  of  weight  which  any  given  quan- 
tity, fuppofe  a  cubic  foot,  of  ice  will 
fuffer  by  expofure  to  the  air  in  a 
given  time,  will  depend,  partly  upon 
the  hardnefs  or  foftnefs  of  the  ice, 
partly  upon  the  temperature  of  the 
atmofphere,  with  refpedl  to  the  de- 
grees of  cold  and  humidity,  partly 
upon  the  velocity  of  the  wind  which 

bruihes 


(     179     ) 

brufhes  its  furface,  and  probably 
enough  upon  the  agency  of  other 
caufes  with  which  we  are  lefs  ac- 
quainted. Some  philofophers  have 
efbimated  in  general  terms^  the  lofs 
of  weight  fuftained  by  a  certain 
weight  of  ice,  without  fpecifying  the 
magnitude  of  the  ice's  furface  -,  others, 
with  more  accuracy,  have  mentioned 
both  the  weight  and  furface  of  the 
ice  expofed  to  the  air,  but  then  they 
have  either  omitted  to  fpeak  of  the 
ice's  confiftency  :  the  temperature  of 
the  atmofphercj  the  force  and  diredlion 
of  the  wind  ;  or  they  have  expreffed 
themfelves  in  very  indefinite  terms 
concerning  thefe  points,  fo  that  we 
cannot  be  faid  to  have  hitherto 
gained,  from  their  experiments^  any 
precife  information  upon  the  fubjedl. 
As  to  the  fad  itfelf,  the  moft  com- 
M  2  mon 


(     38o     )    _ 

mon  obfervation  is  fufficient  to  af-; 
certain  us  of  its  truth.  In  long  con- 
tinued frofts,  the  ice  formed  in  ponds 
and  other  fmall  colle6tions  of  water, 
is  fenfibly  diminifhed  every  day, 
and  often  v/liolly  evaporated ;  and  a 
flill  of  fnow  may  be  feen  confider- 
ably  wailed  in  a  few  days,  in  the 
fever  ell  feafon. 

Notwithflanding  this  diminution 
of  weight,  to  which  both  ice  and  fnow 
are  fubje6l  in  the  coldeil  weather, and 
the  thaw  v/hich  they  experience  in 
the  hottefl,  yet  fome  have  doubted 
whether  the  quantity  of  congealed 
water,  be  not  an  increafing  quantity 
upon  the  furface  of  the  earth  ;  and 
have  even  thought,  that  the  globe 
of  the  earth  mufl  in  procefs  of  time 
refemble  'an  egg,  having  its  diameter 
from  pole  to  pole,  longer  than  the 

equa- 


(     i8i     ) 

equatorial  diameter^  on  account  of 
the  conftant  accumulation  of  frozen 
water  at  the  two  poles. — '^  After  fo 
many  years  lapfe  it  cannot  be,  I 
think,  but  that  the  diameter  of  the 
earth  from  pole  to  pole,  from  the 
top  of  the  fnow  at  one  end  of  the 
earth,  to  the  top  of  it  at  the  other 
end,  is  much  longer,  than  in  any 
part  under  the  equator,  though  at 
the  creation  it  were  (as  I  believe) 
made  fpherical."* 

In  fome  mountainous  countries, 
the  proportion  between  the  fnow 
which  falls  at  one  feafon  of  the  year, 
and  that  which  is  diffolved  in  an- 
other, approaches  fo  near  to  an 
equality,  that  upon  the  fame  fpot, 
the  fnow  may  in  one  year  be  {gqti 
quite  through  the  year,  in  another, 

the 
*  Childrey's  Brit.  Bacon,  p,  148, 
M    3 


(      I82      ) 

the  laft  fpeck  of  it  will  vanilli  in  a 
few  weeks  or  days,  before  a  new 
fupply  is  brought  by  the  approach 
of  winter.  In  colder  climates,  the 
utmoft  power  of  the  fumn:ier  fun  is 
not  able  to  melt  all  the  fnow  which 
falls  in  the  winter.  In  afcending 
mount  Etna^  the  Jlps,  or  the  Andes y 
though  the  lower  parts  are  found  to 
be  rich  in  vegetation,  yet  you  foon 
come  to  a  region  covered,  as  it 
fhould  feem,  with  everlafting  fnow : 
the  height  at  which  this  region  com- 
mences, does  not  admit  much  varia- 
tion in  the  fame  latitude,  but  is  very 
different  in  different  latitudes.  It 
begins  at  the  diftance  of  near  three 
miles  above  the  level  of  the  fea,  un- 
der the  equino6lial  line  \  and  at  each 
pole,  probably,  it  is  not  removed 
from  that  level   fo   many  hundred 

feet ; 


(     i83     ) 

feet ;  it  is  found  to  be  600  yards 
nearer  to  the  level  of  xhc/ea  at  'Tene- 
riffe  than  under  the  equator  ^  and 
above  1 200  yards  nearer  in  Switzer- 
land  than  at  'Teneriffe^, 

Not  only  the  tops  of  high  moun- 
tains in  every  quarter  of  the  globe 
are  covered  at  all  feafons  of  the  year 
with  fnow,  but  the  ocean  both  in  the 
northern  and  fouthern  hemifphere  is, 
in  high  latitudes,  replete  with  im- 
menfe  mountains,  and  extenfive  plains 

of 

*  Hifto.  Nat.  des  Glaciers  Suifle the 

author  fays,  enlin  la  plupart  des  Montagnes 
volines  des  poles  font  convertes  jufqu'  a  leiir 
pied  de  neiges  perpetuelles.  This  obferva- 
tion  muft  not  be  admitted  without  reilridion, 
if  it  be  at  all  true,  lince  in  Greenland,  and 
in  the  latitude  79  degrees,  44  minutes  north, 
the  feet  of  the  mountains  are  in  certain  fea- 
fons freed  from  fnow.  See  Crantz  Hill,  of 
Greenland,  Vol.  I.  p.  30.  and  Phipps's  Voy, 
p.  52  and  70. 

M  4 


C     1 34     ) 

of  ice,  in  the  greateft  heats  of  fum- 
mer ;  and  hence  it  has  appeared  pro- 
bable to  many,  that  both  the  fnow 
upon  the  land,  and  the  ice  upon  the 
fea,  receive  an  augmentation  every 
year,  from  the  continued  agency  of 
the  fame  caufe  which  firfl:  produced 
'them. 

.A  philofopher,  well  acquainted 
with  the  natureof  the  Alps,  expreffes 
himfeif  upon  this  fubjed  in  the  fol- 
lowing manner,  "  one  cannot  doubt 
concerning  the  increafe  of  all  the 
Glaciers  of  the  Alps  :  for  their  very 
€xiftence  is  a  proof,  that  in  preced- 
ing ages  the  quantity  of  fnow  which 
has  fallen  during  the  winter^  has  ex- 
ceeded the  quantity  melted  during 
the  fummer.  Nov/  not  only  the  fame 
caufe  flill  fubfifls,  but  the  cold,  oc- 
cafioned  by  the.mafs  of  ice  already 

formed. 


(     i8s     ) 

formed,  ought  to  augment  it  ftill 
farther,  and  thence  both  more  fnow 
ought  to  fall,  and  a  lefs  quantity  of 
it  be  melted."*  If  this  be  admitted, 
the  time  will  undoubtedly  come 
when  the  fea  will  be  diminiflied  in 
depth,  if  not  dried  up  by  the  con- 
verfion  of  the  water,  which  is  daily 
raifed  from  it,  into  fnow  or  ice ;  and 
had  the  world  been  as  old,  as  fome 
are  fond  of  fuppofing  it  to  be,  we 
fhould,  probably,  have  had  no  wa- 
ter upon  its  furface  at  the  prefent 
day.  However,  it  mud  be  owned, 
that  no  argument  can  be  drawn  a- 
gainfl  the  antiquity  of  the  world, 
from  thisconfideration,  becaufe  there 
is  reafon  to  believe  that  the  ice  and 
fnow  upon  the  furface  of  the  ^arth, 
^re  not  annually  increafing  in  quan- 
tity. 
*  DeLuc  de  rAtmofphere,  Vol.  11,  p.  328. 


(     i86     ) 

tity.  For,  befides  the  heat  of  the  air 
in  fummer,  there  is  another  caufe 
which  tends  to  prevent  an  indefinite 
augmentation  of  congealed  water  — 
the  internal  heat  of  the  earth.  The 
general  heat  of  th€  fprings  of  water, 
fituated  deep  in  the  bowels  of  the 
earth,  is  48  degrees;  in  mountainous 
countries,  I  fufpefb  it  to  be  fome- 
what  lefs,  but  fufficient,  notwith- 
ftanding,  for  the  purpofe  here  men- 
tioned. When  the  fnow,  incum- 
bent on  any  fpot  of  ground,  is  but 
thin,  it  may  fo  far  cool  the  earth, 
that  its  internal  heat  may  not  be  able 
to  difToive  it ;  but  when  the  bed  is 
thick  enough  to  prote6t  the  earth 
from  the  influence  of  the  atmof- 
phericai  cold,  that  furface  of  the 
fnow  which  is  contiguous  to  the  fur- 
face  of  the  earth,  may,  even  in  the 

coldeft 


(    i87     ) 

coldeft  winters,  receive  more  heat 
from  the  earth  than  it  does  cold  from 
the  atmofphere,  and,  on  that  fuppo- 
fition,  I  fee  no  abfurdity  in  admit- 
ting, that  it  may  be  diffolved  at  all 
feafons  of  the  year. 

The  fadl  I  believe  is  certain,  that 
ftreams  of  water  iffue  from  the  bot- 
tom of  the  Glaciers  in  the  Alps^  in 
the  greatefl  feverity  of  winter;  fo 
that  whether  the  internal  heat  of  the 
earth  be  admitted  or  not,  as  a  caufe 
fufficient  to  explain  the  phenome- 
non, a  con  ft  ant  thaw  of  the  ice  or 
fnow,  which  is  contiguous  to  the 
furface  of  the  earth  in  the  Alps  can- 
not be  denied ;  and  this,  added  to 
other  caufes,  may  render  it  proba- 
ble, that  the  quantity  of  congealed 
water  has  its  limits  even  in  the  cold- 
eft  climates. 

The 


(     i88     ) 

The  ardinary  heat  of  fpring  water, 
which  does  not  feel  the  yiciflitudes 
of  the  temperature  of  the  atmof- 
phere,  is  here  faid  to  be  48  degrees 
of  Fahrenheit's  thermometer ;  it 
may  be  worth  while  to  add  a  few 
remarks  on  this  fubjedl. 

In  Auguft  1778,  when  the  heat  of 
the  air  was  7  2  degrees,  I  tried  on  the 
fame  day,  the  temperature  of  feveral 
fprings,  reputed  cold,  in  the  neigh- 
bourhood of  Matlock  5  and  I  found 
them  varying  in  heat  from  50  to 
54  degrees.  This  variation,  pro- 
bably, proceeds  from  their  fubterra- 
neous  pafTages  being  fituated  at  dif- 
ferent diflances  from  the  furface  of 
the  earth,  which  was  then  much 
warmed  by  the  heat  of  the  fummer. 
Or  it  may  proceed  from  the  fprings 
being  more  or  lefs  mixed  with  the 

water 


(     i89    ) 

water  which  fupplies  the  warm  baths^ 
the  heat  of  that  water  being  68  de- 
grees. There  is  a  fubterraneous 
pafTage  upon  the  fide  of  the  hill  near 
the  new/h2Lth  at  Matlock,  which  ter- 
minates in  a  large  cavern,  fituated 
under  one  of  the  fields  in  the  midway 
between  the  new  and  the  old  b3,th  ; 
and  from  this  cavern,  which  is  always 
full,  iflues  the  warm  water  which 
fupplies  both  the  baths  ;  and  it  may 
probably  ooze  out  in  different  direc- 
tions, and  in  different  quantities,  fo 
as  to  make  the  neighbouring  fprings 
participate  more  or  lefs  of  its  warmth. 
At  Lord  Godolphin's  houfe  on  Gcg- 
magog  hills,  near  Camhridgey  there  is 
a  well,  above  230  feet  in  depth, 
which  is  dug  through  a  ftratum  of- 
chalk  3  I  have  frequently  examined 
the  heat  of  the  water  of  this  well, 

and 


(     I90     ) 

and  conftantly  found  it  to  be   50 

.  degrees.  At  Cherry  Hint  on,  a  village 
fituated  at  the  bottom  of  thefe  hills, 
there  ifTues  from  the  chalk  a  very 
copious  fpring,  the  heat  of  this  water 
as  it  bubbles  out  of  the  earth,  is,  at 
all  feafons  of  the  year,  t^o  degrees. 
I  have  tried  the  heat  of  fome  deep 
wells  dug  in  chalk  at  Bury  St,  Ed- 
munds, and  found  it  variable  from 

50  to    52   degrees. «^  It   has 

been  long  and  generally  obferved, 
that  as  far  as  the  limeftone  extends, 
that  tra6t  of  ground  makes  the  fnow 
that  falls  on  it,  thaw  or  melt  fooner 
than  it  does  on  the  neighbouring 
lands."*  This  is  Mr.  Boyle's  ob- 
fervation  concerning  fome  limeftone 
land  in  Ireland,  and  he  fays  its  truth 
was  confirm-ed  to  him  by  a  Derby- 

fhire 

*  Boyle's  Works,  Vol.  IV.  p,  278. 


(     191     ) 

jfhire  miner,  who  aiTured  him,    that 

on  contiguous  diftrids  of  land,  fnow 
was  obferved  to  diiTolve  much  foon- 
er  on  the  foil  which  covered  lime- 
ftone,  than  on  that  which  covered 
freeftone.  If  thefe  obfervations 
may  be  depended  on,  we  may,  per- 
haps, in  general  infer,  that  the  heat 
of  calcareous  ilrata  is  greater  than 
that  of  other  kinds  of  Ilrata,  and 
this  would  furnilh  a  reafon  for  the 
fprings  in  chalk  countries  being  of 
the  v/armth  of  50,  though  the 
ordinary  heat  of  fprings  be  not 
above  48  degrees. 

In  the  middle  of  fummer,  v/hen 
the  air  was  7  2  degrees  hot,  I  tried 
the  heat  of  fome  fprings  at  Harrow- 
gate  in  Yorkfhire.  Pump  water  at 
the  Granby  Inn  48  degrees. — Old 
Spaw  48  degrees. — Pewit  or  ^ewit 

well 


(       ^92      ) 

well  48  degrees. — -Sulphur  well  50 
degrees.     The  cold  well  at  Buxtoriy 
examined  at  the  fame  tune  of  the  year^ 
was  48  degrees,  and  the  famous  Spaw^ 
at  Llanrbaid'r  in  Venhighjhire  was 
alfo  48  degrees;  St.  Winifred's,  well 
at  Holywell  in  Flintfhire,  was  con- 
fiderably  v/armer,  the  thermometer^, 
when  held  in  the  fpring  as   it  rofe 
out  of  the  earth,  (landing  at  54  de- 
grees.    I   have  tried  a  great  many 
other  fprings  in  different  parts   of 
Great-Britain,  and  found  the  heat  of 
moil  of  them  to  be  included  be- 
tween the  limits  of  48   and  54  de- 
grees,   the    mean  of  which    is   51. 
Springs  on  the  fides  of  high  moun- 
tains, may,  probably,  participate  of 
the  cold  which  is  found  to  be  greater 
in  elevated  than   in  low   fituations.. 
There  is  a  fpring  by  the  fide  of  the 

turn- 


C    m    ) 

•  turnpike  road  Icadmj^qser  the  high 
ground  called  Otky  Sk^vin  in  York- 
fliirci  I  obferved  the  heat  pf  this 
fpring  in  September,  when  the  air 
was  warmed  to  62  degrees,  to  be 
not  485  but  only  45  degrees.  The 
mean  heat  of  fprings  near  Edinburgh 
is  faid  to  be  47,  and  at  Lundo'd  51 
degrees :  f  this  diverfity  depends, 
probably,  on  the  different  elevations 
of  London  and  Edinburgh  above 
the  level  of  the  fea. 

I  have  mentioned  the  Sulphtir . 
well  at  Harrowgate^  according  to  its 
ufual  appellation  at  that  place,  with- 
out taking  upon  me  to  decide  the 
long  controverted  queftion,  concern- 
ing the  existence  of  fulphur  in  that 
and  other  waters  of  the  fame  kind. 
'^^  Sulfhur  has  been  long  efteem-ed  a 

mincrar 
t  Philof.  Tranf.  1775,  p.  46-cv. 
VOL.    III.  N 


(     ^94     ) 
niineral  body  very  common  to  be ' 
met  with  in  waters;   and  all  thofe 
waters    which  have  a  flrong    fetid 
fmell,  refembling  that  of  a  foul  gun, 
have  been  efteemed  to  be  more  or 
lefs     impregnated     with      fulphur.. 
However,     Dr.   Hoffman   feems    to 
doubt  much  of  its  exiftence  in  the 
greater  number  of  fuch  waters  ;  and 
Dr.  Lucas  has  affirmed,  that  it  is  not 
to  be  found  in  the  form  of  fulphur  in 
any  water  whatever;  not  even  in  that 
of  j^ix- la- Chape  Iky  where  a  true  and 
perfedl  fulphur  is  found  on  the  up- 
per parts  of  the  conduits  through 
which  the  water  pafles ;  for  he  fays, 
that,  flridiy  fpeaking,  thefe  waters 
do  not  contain  fulphur  fubftantially 
difiblved  in  them,  but  are  impreg- 
nated with  a  phlogiilon  and  an  acid, 
the  principles  of  fulphur ;  which  be- 
2  ing 


(     195     ) 

ing  in  a  volatile  ftate,  are  fublimed,, 
meet  on  the  furface  of  the  conduits,  ■ 
and  there  unite  into  a  true  and  per- 
fe6l  fulphur,  which  did  not  naturally 
exifl  in  the  water."  f  The  author, 
from  whom  I  have  made  this  ex- 
tradi  informs  us  that .  Dr.  Rutty 
maintains  the  exiilence  of  fulphur 
in  mineral  waters;  and  that  both  Dr. 
Shaw  and  Dr.  Short  found  fulphur  in 
Harrowgate  water.  Notwithftand- 
ing  the  teilimony  of  fuch  eminent 
phyficianSj  the  mose  recent  opinion 
of  a  phyfician,  whom  Dy,  Monro  con- 
fulted  on  the  fubje6l  iri  1768,  is 
againft  the  exiftence  of  fulphur  in 
fuch  w^aters.  "  I  have  taken  parti- 
cular notice  of  every  appearance  of 
the  Harrowgate  waters,   and  muft 

own 
f  Monro  on  Mineral  Waters,  Vol.  I.  p.  30. 
and  196. 

N   2 


(     196    ) 

own  I  never  obfcF-yed  any  appear- 
ance of  fulphur  floating  in  them,  nor 
any  fcum  at  the  top  of  the  well ;  nei- 
ther could  I  meet  with  any  perfon  in 
that  quarter,  who  remembered  the 
appearance  of  real  fulphur  fublimed, 
upon  taking  up  the  ftones  at  the 
bottom  of  the  well,  as  mentioned  by 
Dr.  NeaL^'X — I  beg  leave  to  add 
my  own  obfervation  on  the  fubjeft, 
which  I  made  in  1780.  The  v/ater 
in  the  well  rifes  into  a  circular  ftone 
bafon ;  a  whitifh  crull  adheres  to 
the  ftone,  where  it  is  contiguous  to 
the  furface  of  the  water  i  I  fcraped 
off  a  portion  of  this  cruft,  and  put- 
ting it  on  a  hot  iron,  I  found  that  it 
burned  with  the  flame  and  fmell  of 
Julphur,  I  do  not  think  that  this 
experiment  abfolutely  warrants  us  to 

conclude, 

%  Id.  p^  196. 


(     '97     ) 

c'o« elude,  that  a5fualjulphur  is  con- 
tained in  this  and  other  waters  ge- 
nerally denominated  fulphureous  |, 
we  juftly  infer  from  it,  that  fome- 
thing  is  fublimed  from  the  water, 
which  either  of  itfelf  is.  fulphur,  or 
which  in  conjundion.with  tne  air,  or 
fome  other  principle,-  conflitutes  ful- 
phur. 

The  profecution  of  this  fubje(ft 
would  lead:  to  fpeculations  too  ab- 
flrufe  for  mydefign;  the  following 
experiment,  however,,  which  I  have 
frequently  made,^  will,  I  hope,  throw 
no  inconfiderable  light  on  the  caufe 
of  the  impregnation  of  fulphureous 
waters  in.  general. 

The  acid  of  vitriol  does  not  afl: 

upon  the  common  Derbylliire  lead 

ore,  except   when  it  is   afiified  by 

.  heat,  it  then.  difTolves  it,  and  a. great 

N  3  efcape 


(     198     ) 

cfcape  of  air  is  obferved ;  I  made 
this  air,  as  it  was  difcharged  from 
ihe  ore,  pafs  through  a  high  bended 
tube  into  a  bottle  full  of  pump  wa- 
ter: the  water;,  in  a  very  littk  time,, 
acquired  the  fetid  Jmelloi  Harrow- 
gate  water, — its  tafte  was  the  fame 
as  that  of  fuch  fulphureous  waters 
as  contain  no  fait, — it  was  perfectly 
iranj^arenty  but  in  the  courfe  ©f  t\ 
hours  it  became  cloudy y  and  loft  moft 
of  its  fmell,— it  did  not  fufter  any 
'preclptaHon  by  the  addition  af  the 
acid  of  vitriol,— ^/^'^r  was  blackened 
both  hj  being  ,put  into  this  v/arer, 
and  by  being  expofed  to  the  vapour 
which  arofe  from  it ;  from  all  thefe 
cicumflances,  it  may  properly 
enough,  I  think,  be  called  an  ariifi^ 
cial fulphureous  water. 

I  have  obferved  the  fame  pheno- 
mena 


(     J99    ) 

mena  when,  inftead  of  lead  ore^  I 
iifed  black  jacky  and  I  remember 
that  once  having  placed  a  bottle, 
containing  black  jack  and  acid  of 
vitriol,  fo  that  its  neck  leaned  againft 
a  plaiftered  wall,  1  obferved  fome 
days  afterwards,,  that  the  wall  was 
flained,  to  the  diftance  of  above  a 
foot  from  the  mouth  of  the  bottle, 
of  a  purple  colour,  refembling  the 
purple  fediment  often  found  in  ful« 
phureous  wells. 

Air  of  the  kind  here  ipoken  of^ 
may  be  feparated  from  other  fub- 
flances,  as  well  as  from  lead  ore  and 
black  jack,  and  by  other  means,  as- 
well  as  by  the  acid  of  vitriol  j  and 
it  feems  very  probable,  that  the  wa- 
ters ufually  called  fulphureous,  are 
impregnated  with  this  kind  of  air,, 
which  has  been  feparated,  in  the 
N  4  bowels; 


(        2rOO       ) 

bowels  of  the  earthy  from  particular 
minerals  J  efpeciaily  fulphureousones. 
It  has  been  remarked  of  Harrowgate 
water;,  that  as  it  fprings  up  it  is  clear 
2iwdjfarkli7igy  and  throws  tip  a  quan- 
tity of  air  bubbles. 

During  the  procefs  of  impregnat- 
ing water  with  air,  by  difTolving  lead 
ore  in  the  acid  of  vitriol,  a  part  of 
the  glafs  tube  "was  coated  with  a 
thin  pellicle  of  falphur,  which  had 
accompanied  the  air  in  its  afcent : 
May  not  the  fulphur  fubiimed  from 
Harrowgate  waxer,  have  accompanied 
the  air  which -gives  it  its  fm.ell?  Is 
it  certain  that  this  kind  of  air  does 
not  confift  of  attenuated  parts  of  ful- 
phur,  which  have  acquired  an  elallic 
force,  and  which  cannot  be  con- 
denfed  in  v;ater?  Or  is  it  not  more 
probable^  that  this  kind  of  air  is  one 

of 


(       20£       ) 

of  the  conftituent  parts  of  fulphnrv 
than  fulphnr  itfelf?  Does  this  air^ 
and  the  inflammable  air  feparable 
from  fome  metallic  fubftances,  by 
folutioa  in  acidSjXonfift  o^ oleaginous 
partix:Ies  in  an  elaftic  ftate  I 

If  the  reader  wiflies  to  impregnate 
comiTion  water  with  the  fulphureons 
properties  of  Harrowgate  water,  he 
may  do  it  in  the  following  fimple 
manner. — Into  an  apothecary's  vial> 
holding  four  or  five  ounces>  put 
fome  pounded  lead,  ore,  and  pour 
upon  it  fome  acid  of  vitriol  j  (there 
is  no  occalion  to  be  foiicitous  about 
the  proportions  of  the  lead  ore  and 
acid,  for  if  there  be  more  or  lefs 
ore  thaathe  acid  can  difTolve,  ftill 
air  enough  for  the  purpofe  will  be 
difcharged  j.)  wrap  a.  fev/  folds  of 
wet  linen  round  one  end  of  a  bended 

tube^ 


(       202       ) 

tube,  infert  this  end  into  the  neck 
of  the  vial  fo  clofely,  that  no  air 
may  pafs  out  of  the  vial  except 
through  the  tube  -,  the  end  of  the 
tube  Ihould  be  at  fome  diftance 
from  the  fur  face  of  the  acid.  Put  the 
other  end  of  the  tube  into  a  bottle 
full  of  water,  then,  by  fetting  the  vial 
on  the  hot  bar  of  a  grate,  or  by  fome 
other  means,  heat  the  acid,  and  as 
foon  as  it  is  heated,  it  will  begin  to 
a6t  on  the  lead  ore,  and  a  great  quan- 
tity of  air  will  be  difcharged,  which 
will  pafs  through  the  tube  into  the 
water  in  the  bottle,  and  in  a  few  mi- 
nutes the  water  will  be  ftrongly  im- 
pregnated with  the  fulphureous  pro- 
perties of  Harrowgate  water.  Be- 
fides  its  fulphureous  impregnation, 
Harrowgate  water  contains  fea  fait ; 
and  moft  other  fulphureous  waters 

contain 


(  203  ) 
contain  fome  fait  or  otherj  fb  that^: 
to  make  a  complete  imitation  of 
them/the  falts  which  they  feverally 
hold  fhould  be  added  in  due  propor- 
tion, to  the  water  impregnated  with 
the  air  here  fpoken  oL 

Though  I  am  greatly  difpofed  tO' 
believe,  that  fdlphureous  waters  are- 
impregnated  with  their  peculiar 
fmell  and  taile,  after  the  manner  I 
have  defcribed ;  yet,  to  aifift  the  rea- 
der's conjedtures  concerning  the  ori-. 
gin  of  this  impregnatian,,  I  will  men- 
tion another  way  in  which  it  may  be 
fuppofed  to  arife,  and  which  will  ac-' 
caunt  for  the  faline  taile  as-  well  as 
the  Imell  of  the  water. 

I  know  not  whether  any  fpecies- 
of  maritime  plants,  containing  fea 
fait,  will  impregnate  water  with  a. 
fulphureous  fmell  by  means  ofpitre- 

fa^ion  y 


{     ^04     ) 

foMioriy  nor  whether  all  of  them  will 
do  it  by  means  of  combujlion^  but 
that  one  of  them  will  do  it  I  can 
haye  na  doubt :  I  allude  to  the 
bladder  fticus  or  Jea  wracks  which  is 
burned  on  our  coalls  for  the  makincj 
o{  Kelp..  It  has  been  mentioned  be- 
fore,* that  fe a  wrack  when  burned 
to  a  black  coal,  will  yield,  by  being 
boiled  in  v/ater,,  a  great  quantity  of 
common  fait;  and  I  would  now  re* 
mark,  that  the  water  extrads  from 
the  black  ai^es,  not  only  a  great 
quantity  of  common,  fait,  but  fome- 
thing  elfe  alfo,  by  which,  without 
lofing  its  tranfparency,:  it  aGq,uires 
both  the  fmell  and  fulphureous 
tafte  of  Harrowgate  water  -,  and  by 
which  it  is  enabled,  like  that  water, 
to  blacken  iilver  and  white  paint. 

This 

*  Vol.  L  p.  137. 


(      2G5       ) 

This  Jomething  I  am  fenfible  may 
be  what  chemifts  call  liver  of/ulphurf 
or  an  union  of  fulphur  with  fixed 
alkali,  and  it  would  not  be  difficult 
to  explain  its  formation  during  the 
combuftion  of  the  fea  wrack ;  no  ful- 
phur however  can  be  precipitated 
from  the  water  by  the  acid  of  vitriol, 
though  that  acid  turns  it,  as  is  the 
cafe  with  Harrowgatc  water,  a  little 
cloudy.  The  air  extra6led  from  iron 
by  the  acid  of  fea  fait,  impregnates 
water  with  a  fmell  fomewhat  refem- 
bling  that  of  Harrowgate  water,  but 
its  difference  both  from  the  natural 
and  the  artificial  fulphureous  waters, 
may  be  eafily  diftinguifhed,  efpecial- 
ly  after  the  water  has  Hood  a  few 
hours  expofed  to  the  air. 

ESSAY 


ESSAY      VII*. 


OF    DERBYSHIRE    LEAD    ORE. 


LEAD  ore,  as  dug  out  of  the 
mine,  is  generally  much  mixed 
with  ipar,  lime{lone,.and  other  fub- 
fiances,  bulk  for  bulk,  lighter  than 
the  ore  itfelf.  It  undergoes  various 
drefTings  before  it  becomes  a  mer- 
chantable commodity,  the  general 
tendency  of  which  is  to  free  it,  as 
much  as  poffible,  from  every  hetero- 
geneous impurity, 

Suppofe 

*  The  fubftance  of  this  EfTay  was  printed 
in  the  Philof.  Tranl".  1768. 


(       !208       ) 

Suppofe  that  a  cubic  foot  of  lead 
bre,  which  contained  no  fpar  or  other 
extraneous  matter^  wouldweigh  7  800 
ounces^  and  that  a  cubic  foot  of  fpar, 
which  contained  no  lead  ore  or  other 
foreign  fubflance,  would  weigh  2700 
ounces,  then  would  a  mixture,  con- 
fiftmg  of  a  cubic  foot  of  pure  lead 
ore,  and  a  cubic  foot  of  pure  fpar, 
weigh  10500  ounces,  and  one  cubic 
foot  of  fucli  a  mixture  would  weigh 
52 sO. ounces.  It  is  obvious  tliat 
according  to  the  different  propor- 
tions in  which  the  particular  kinds 
of  fpar  and  lead  ore  here  aiTumed, 
are  fuppofed  to  be  mixed  together,  a 
cubic  foot  of  the  mixture  will  have 
different  weights,  the  limits  of  which 
are  on  the  one  hand  7800,  and  on 
the  other  2700  ounces;  it  never  can 
weigh  fo  little  as   2700  ounces,  for 

then 


C    ^09    ) 

then  It  would  confid  intirely  of  fpar 
without  any  lead  ore  -,  nor  can  it 
ever  weigh  fo  much  as  7800  ounces, 
for  then  it  would  confift  intirely  of 
lead  ore  without  any  fpar. 

From  this  view  of  the  matter  it 
is  evident,  that  the  purchafing  of 
lead  ore  by  the  meafure,  which  is 
the  general,  though  not  the  univerfal 
cuftom  in  DerhyJIjire^  is  a  mode  lia- 
ble to  fome  exception  j  fmce  a  dilli, 
containing  any  definite  meafure,  muft 
have  d liferent  v/eights^  according  'as 
-the  ore  with  which  it  is  filled  is  more 
or  lefs  free  from  fpar.  And  it  is 
fcarce  poiTible,  by  repeated  dref- 
fings,  to  feparate  all  the  ipar  U'om.  an 
ore,  or  equal  portions  of  it  from 
equal  portions  of  ore. 

There  is  a  diverfity,  however,  in 
the  weights  of  equal  meafures  of  lead 

VOL.  HI,  .     O  ore. 


C      210      )' 

ore,  which,  probably,  does  not  arife 
from  fparry  or  other  heterogeneous 
accretions,  but  from  the  nature  of 
the  ore  itfclf.  I  have  carefully  cal- 
culated the  weight  of  a  cubic  foot  of 
many  of  the  Derbylhire  lead  ores ; 
the  weight  of  a  cubic  foot  of  the 
lighted  which  I  met  with  was  7051 
ounces,  and  the  weight  of  a  cubic 
foot  of  the  heavieft  was  7786  ounces  ; 
the  difference  amounting  to  between 
a  ninth  and  a  tenth  part  of  the  weight 
of  the  lighteil.  There  are,  proba- 
bly, other  ores  of  lead,  the  weights 
of  equal  bulks  of  which  differ  more 
than  thefe  here  mentioned  ;  but  the 
<lifference  between  thefe  is  fufhcient 
to  fliew  the  great  uncertainty  of  pur- 
chaiing  lead  ore  by  the  meafure, 
iince  ten  difhes  of  one  fort  of  ore 
may  not  weigh  more  than  nine  diflies 

of 


(  211  ) 

of  another  fort,  though  both  the 
forts  are  equally  well  drefled. 

Lead  ore  is  not  always  of  the  fame 
goodnefs  in  the  fame  min.c,  nor  even 
in  the  fame  part  of  the  fame  mine ; 
and,  what  is  more  remarkablej  the 
different  parts  of  the  fame  lump  of 
ore  have  in  equal  bulks  different 
weights.  I  could  not  eafily  have 
believed  this,  unlefs  a  variety  of  ex- 
periments had  convinced  me  of  the 
fad. 

They  wereemployed  lately  ^.tHoly- 
w^//infmelting  a  lead  ore  from  xh^IJle 
of  Man  \  the  ore  was  rich  in  filver. 
A  lump  of  this  ore,  weighing  about 
ten  ounces,  was  broken  into  fcveral 
pieces,  and  fuch  of  the  pieces  were 
fcleded  as  appeared  to  the  eye  to  be 
wholly  pure.  I  eftimated  the  weight 
of  a  cubic  foot  of  fix  of  thefe  pieces, 
o  a  and 


(       212      ) 

mnd  found  that  a  cubic  foot  of  the 
ilightefl  khid  would  have  weighed 
■^5^5  ounces,  and  a  cubic  foot 
^of  the  heavieft  kind  would  have 
-weighed  7636  ounces,  Suppofing 
(the  weight  of  a  cubic  foot  of  water 
to  be  denoted  by  1000,  the  mean 
weight  of  a  cubic  foot  of  the  fix 
'different  pieces  of  this  ore,  may  be 
vexpreffed  by  7 115  avoirdupoife 
ounces, 

A  very  pure  fpecimen  of  telTella- 
ted  lead  ore, from  a  mine  near  Ajhover 
in  Berhyjhirey  was  broken  into  fix 
pieces,  weighing  near  one  ounce 
each.  A  cubic  foot  of  the  lightefl 
of  thefe  pieces  would  have  weighed 
7326  ounces,  and  a  cubic  foot  of  the 
heavieft  would  have  weighed  7786 
ounces.  The  mean  weight  of  a  cu-' 
bic  foot  of  the  fix  pieces  was  7566. 
2  At 


C   213    ) 

At  the  fame  mine  they  frequently 
meet  with  fmall  quantities  of  fteel* 
grained  lead  ore.   Six  different  pieces' 
of  the  fame  lump  of  this  kind  of 
©re  were  chofen,    each  of  which  ap-- 
peared    quite    free    from    fpar   and^ 
every  other  impurity.    A  cubic  foot- 
of  the  lighten  of  thefe  pieces  would^ 
have  weighed   7188   ounces^  and  a 
eubic   foot   of  the   heaviefl  would, 
have  weighed  7442  ounces.      The- 
mean  weight  of  a  cubic  foot  of  the^ 
fix  pieces  was  7342. 

Other  lumps  of  ore,  from  different 
mines,  were  refpedtively  broken  into* 
different  pieces^  and  fcarcely  any 
two  equal  pieces  of  the  fame  lump^ 
were  obferved  to  agree  in  weighto^ 
This  diveriity  in  the  weights  of 
equal  bulks  of  the  feveral  pieces  oB 
the  fame  lump  of  ore  may  be  owinge,. 
o  3^  either: 


(  214  ) 
^either  to  the  different  proportions  in 
which  the  conftituent  parts  of  the 
pre  are  combined  in  the  fcveral 
pieces ;  or  to  the  different  quantities 
of  extraneous  fubilances  impercepti- 
bly mixed  with  them^ or,  which  feems 
iiK)ft  probable,  to  a  diveriity  in  the 
fize  or  configuration  of  their  pores. 

But  be  the  caufe  of  this  diveriity 
what  it  may,  the  fatt^  I  believe,  is 
certain,  and  by  no  means  fingular> 
for  not  to  mention  the  varieties  ob- 
fervable  in  the  weights  of  equal 
bulks  of  different  pieces  of  roll 
brimftone,  of  corrofive  fublimate,  of 
cad  ileel,  and  other  factitious  fub- 
fiances,  the  natural  fpars  generally 
found  along  with  lead  ore  are  fub- 
jedt  to  a  flmilar  diverfity,  though 
not,  perhaps,  in  an  equal  degree. 

A  piece-of  rhomboidal,  otberways 

called 


C   215    ) 

called  ref railing  or  lantern  fpary  waJJ 
broken  into  four  fm^ller  pieces, 
the  weights  of  a  cubic  foot  of  each 
of  which  were  2675,  2687^  2715, 
2723  ;  the  mediuin  of  the  four  is 
2700  ounces.  Mr.  Cotes  fixes  the 
weight  of  a  cubic  foot  of  Iceland 
cryftal  at  2720,  and  JVallerlus  fixes 
it  at  2700  ounces. 

The  weights  of  a  cubic  foot  of 
four  pieces  of  the  fame  lump  of  cu- 
bical fpar  were  3204,  3218,  3222^ 
3231  ;  the  medium  of  the  four  is 
3219  ounces. — Moil  of  the  fpars 
met  with  in  Derby/hire  are  either 
rhomboidal  or  cubical;  they  are  eafily 
diftinguiflied  from  each  other  by 
a  view  of  their  Ihape^  when  their  an- 
gles can  be  difcerned ;  and  when  the 
Ihape  cannot  be  cafily  feen,  the  na- 
^  ture  of  the  fpar  may  be  afcertained 
o  4  by 


(  2i6  ) 
by  touching  it  with  an  acid;  the 
rhomboidal  fpar  always  effervefcing 
with  an  acid,  and  the  cubical  refill- 
ing its  action.  The  lead  fnielters 
make  great -ufe  of  the  cubical  fpar  as 
a  flim  for  fuch  lead  ores  as  do  not 
readily  melt ;  it  is  curious  to  fee  its 
cifed:;  a  few  fhovels  full  of  ir,.. 
thrown  upon  a  heap  of  red  hot  ore,, 
immediately  melting  down  the  ore 
into  a  liquid,  though  the^  longed 
continuation  of  the  fame  degree  of 
heat^  without  the  addition  of  the 
fpar,  would  not  have  been  fufficienC 
for  the  purpofe. 

Six  ounces  of  fine  teffellated  lead 
ore  were  put  into  a  crucible  and  ex- 
pofed,  at  firil,  to  a  gentle,  and  after- 
wards to  a  flrong  fire  :  the  ore  grew 
red,  and  emitted  fumes  which  fmel- 
led  of  fulphur ;  ac  length  it  melted, 

and 


(    2^7     ) 
and  the  fumes  became  very  copious  *; 

they  were  accompanied  with  a  yel- 
lowifh  flame  upon  the  furface  of  the 
melted  ore,  and  when  collected  had: 
a  whitiih  appearance.  The  crucible,, 
after  the  ore  had  continued  a  full 
hour  in  perfect  fuiion  was  taken 
from  the  fire,  and  when.it  was  cold 
it  was  broken.  The  mafs  which  it 
contained  weighed  five  ounces  and, 
an  half;  there  was  no  fcoria  obferv- 
able  on  its  furface,  nor  were  any 
particles  of  metal  formed^  it  was^ 
ftill  an  ore  of  lead.. 

The  mafs  remaining  from  the  lafl: 
experiment  was  put  into  a  freih  cru- 
cible, and  expofed  to  a  flrong  melt- 
ing heat;,  the  fumes  which  arofe 
from  ir  feemed  to  be  heavy;  they 
brooded  over  the  furface  of  the: 
melted  mafs  in  undulating  flames^. 

which 


(      2l8      ) 

which  now  and  then  appeared  like 
burning  zinc*  The  lead  was  now 
formed,  and  many  particles  of  it 
were  fublimed  to  at  leafl  fix  inches 
above  the  furface  of  the  liquid  in 
the  crucible.  After  letting  the  cru- 
cible continue  two  hours  in  this 
Itate,  I  poured  out  its  contents,  and 
found  them  confifting  partly  of  lead, 
partly  of  lead  ore,  and  partly  of  a 
very  minute  portion  of  brownifh 
fcoria.  I  repeated  this  experiment 
with  the  fame  fuccefs. 

Thefe  experiments  prove,  that 
fome  fubftance  or  other  is  contained 
in  lead  ore,  which  muft  be  difperfed 
before  the  ore  can  be  formed  into 
lead  ;  and  they  fhew  too,  that  it  re- 
quires 

*  It  may  deferve  to  be  inquired  whether 
zinc  may  not  be  contained  in  lead,  iron  and 
©ther  ores,  more  frequently  than  is  fuppofed. 


C    219    ) 

quires  a  coniiderable  lime  to  effedl: 
the  difperfion  of  this  fubflance^fince 
fix  ounces  of  ore,  though  kept  three 
hours  or  more  in  complete  fufion, 
were  not  wholly  brought  into  the 
form  of  lead ;  they  inflrud:  us  alfo  to 
believe  that  the  lead  in  this  kind  of 
ore  is  in  its  metallic  ftatc,  as  the  ore 
was  changed  into  lead  without  the 
addition  of  any  fubllance  containing 
the  inflammable  principle;  and,  laft- 
ly,  they  render  it  probable,  that  the 
fumes,  arifing  from  melted  ore,  carry 
off  with  them  no  inconiiderable  por- 
tion of  the  lead  itfelf.  At  the  great 
fmeking  houfes  in  Derbylhire,  they 
put  a  ton  of  ore  at  a  time  into  the 
furnace,  and  work  it  off  in  eight 
hours ;  the  ore  might  be  wholly 
melted  in  one  hour,  but  the  lead, 
perhaps,  is  not  formed  in  the  great- 


(       220       } 

ell  poflible  quantity  in  eight  h(mm 
Some  fine  teifellated  lead  ore  from 
Derbyfhire  was  pounded  into  fmall 
lumps,  each  about  the  fize  of  a  pea,, 
and  carefully  picked  from  fpar  and 
other  impurities.  Sixteen  ounces^ 
of  this  ore,  thus  previouily  cleanfed,, 
were  diililled  in  an  earthen  retort;. 
as  foon  as  the  ore  felt  the  fire,  the 
ftopple  of  the  quilled  receiver  had  a. 
ftrong  fmell,  refembling  that  of  the- 
inflammable  air,  feparable  from  fome:^ 
metals  by  folution  in  acids ;  foon  af- 
ter a  fmall  portion  of  a  liquid  came 
over  into  the  receiver ;  the  fire  was- 
then  raifed  till  the  retort  v/as  of  a 
white  heat,  when  a  black  matter  be- 
gan to  be  fublimed  into  the  neck  of 
the  retort ;  the  operation  was  then 
difcontinued'..  This  experiment  was 
undertaken  with  a  view  of  feeing, 

wLe- 


(       221       ) 

•whether  fulphur  could  be  feparatecl 
from  lead  ore,  as  it  may  be  from 
fome  fpecles  of  the  pyrites,  by  diilil- 
lation,  and  it  appears  from  the  iffue 
of  the  experiment  that  it  cannot,  at 
leaft  in  the  degree  of  heat  which  is 
requifite  for  fubliming  the  ore.  Up- 
on breaking  the  retort  I  found,  that 
the  ore  had  been  melted  during  the 
operation,  for  there  was  a  confident 
cake  of  ore  of  the  figure  of  the  bot- 
tom of  the  retort ;  the  weight  of  this 
cake  was  fifteen  o  unces  and  an  half, 
the  weight  of  the  liquid  in  the  re- 
ceiver, and  of  the  black  matter 
which  had  been  fublimed,  did  not 
together  amount  to  one  quarter  of 
an  ounce,  fo  that  a  quarter  of  an 
ounce  or  more  had  been  difperfed, 
probably,  in  the  form  of  air,  or  fome 
elaftic  fluid.     The  ore  by  this  pro- 

cefs 


(       222       ) 

cefs  had  loft  one  thirty-fecond  part 
of  its  weight.     The  liquid  did  not 
cffervefce  with  either  acids  or  alka- 
lies ;  nor  did  it  produce  any  change 
in  the  colour  of  blue  paper,   yet  I 
am  certain,   from  experiment,    that 
one  drop  of  oil  of  vitriol,    though 
diluted  with    two  ounces  of  water, 
would  have  produced  a  fenfible  red- 
nefs  on  the  blue  paper  which  I  ufed. 
The  liquid,  notwithftanding,  had  an 
acid  tafte,  and  a  pungent  fmell,   re- 
fembling  that  of  the  volatile  vitriolic 
acid.     The  black  matter  which  had 
been  fublimed  ii^to  the  neck  of  the 
retort,  was  examined  with  a  microf- 
cope,   and   it  appeared  to  be  pure 
lead  ore.     The   melted    ore    which 
was  found  at  the  bottom  of  the  re- 
tort,   had    not   any    appearance    of 
fcoria,  or  of  lead^  upon  its  furface. 

Some 


(       223       )  ^ 

Some  phenomena  attending  this 
experiment  deferved,  I  thought,  a 
further  invelllgation,  I  therefore 
diftilled  another  i6  ounces  of  ore, 
but  with  a  fire  flronger  and  continu- 
ed for  a  longer  time,  than  in  the  pre- 
ceding experiment  :  the  quantity  of 
liquid  was  much  the  fame,  there  was 
a  fmell  of  fulphur,  and,  perhaps,  to 
the  amount  of  half  a  grain  of  ful- 
phur  was  found  in  the  receiver  ;  the 
ore  was  in  this  experiment  fublimed 
into  the  neck  of  the  retort,  to  the 
thicknefs  of  one  fourth  of  an  inch. 
There  was  found,  as  before,  a  cake 
of  melted  ore  at  the  bottom  of  the 
retort,  but  no  fenlible  portion  of 
either  lead  or  f  carta ;  '^  fo  that  we  may 

fafely 

*  I   have  faid  no   fenlible  portion ;    there 

^vas,  however,    an   appearance  of  fcoria  ad- 

liering  to  the  fide,  and  an  appearance  of  lead 

adhering 


X  ■^24  ) 
fafely  conclude,  that  lead  ore  cannot 
'be  decompofed  by  the  ftrongeil  fires 
in  clofe  velTels,  but  that  it  may  be 
fublimed  in  them.  The  ore  had 
loll  near  an  ounce  of  its  weight. 

Though  the  experiment  is  fuffici- 
ently  troublefome,  I  was  not  deter- 
red from  making  it  once  more  ;  for 
I  wanted  to  fee  whether  lead  ore 
could  be  wholly  fublimed  ;  as  I 
thought  that  philofophers  might 
'thereby  form  fome  conjedturcs  of 
the  efhcacy  of  fubterraneous  fires  in 

fubliming 
^adhering  to-  the  bottom  of  the  retorf;  but 
the  quantity  of  each  vvus  exceedingly  fmall, 
and  they  were  both,  probably,  produced 
from  that  minute  decompofition  of  the  ore 
i^hich  produced  the  fulphur,  and  which 
would  not,  I  think,  have  taken  place  in  any 
degree,  had  there  been  no  communication 
with  the  external  air ;  but  the  orifice  of  the 
quilled  receiver  was  not  always  clofely  flop- 
ped during  the  difdllation. 


(       225       ) 

in  lead  ores,  and,  perhaps,  ores  of 
other  metallic  fubftances.  The  event 
of  this  third  experiment  was  perfect- 
ly correfpondent  to  that  of  the  two 
former,  with  refpedt  to  the  produc- 
tion of  liquid,  and  the  reparation  of 
air,  which  w^as  caught  in  a  bladder, 
but  was  not  found  to  be  inPiamma-' 
ble :  the  lead  ore  too  was  fo  plenti- 
fully fublimed  into  the  neck  of  the 
retort,  that  it  quite  plugged  it  up 
for  above  three  inches  in  length. 
Upon  difcontinuing  the  fire,  which 
had  been  raifed  to  a  degree  of  heat 
exceedingly  great,  I  found  the  retort 
was  cracked,  and  that  the  cake  at 
its  bottom  was  very  different  from 
v/hat  was  found  at  the  bottom  of  the 
other  retorts,  which  had  flood  the 
fire  without  cracking ;  for  this  cake 
was  covered  with  a  black  glaffy  fco- 
VOL.  III.  P  ria 


(  ii6  ) 
iria  ^  of  an  inch  in  thicknefs,  -and  the 
ore  which  laid  under  it,  was  in  part 
changed  into  lead,  and  the  whole  of 
the  ore  did  not  weigh  quite  ten 
ounces,  fo  that  above  6  ounces  had 
been  loft  by  efcaping  through  the 
crack.  By  a  communication  with 
the  air  through  the  crack,  the  ore 
was  decompofed,  and  thus  both  lead 
znd/coria  were  formed,  which  in  the 
other  experiments,  for  want  of  fuch 
a  decompofition,  could  not  be  form- 
ed. There  was  a  thin  coat  of  ful- 
phur  aifo  which  lined  the  infide  of 
the  receiver,  and  this  fulphur,  pro- 
,bably,,  arofe  from  the  decompofition 
of  the  ore,  fince  none,  or  next  to 
none,  was  obferved  in  the  other  di- 
ftillations  of  the  ore.  I  found  that 
the  weight  of  a  cubic  foot  of  the 
ore,  which  had  been  fublimed  into 
3  the 


(  ^^7  ) 
the  neck  of  the  retort,  was  7500 
ounces ;  which  fuificiently  agrees 
with  the  weight  I  had  before  afcer^ 
tained  of  this  kind  of  ore.  A  cubic 
foot  of  the  black  glafly  fcoria  Vv^eigh- 
ed  3233  ounces ;  and  the  metailiG 
cake  which  laid  under  it,  and  which 
confifled  partly  of  lead,  and  princi- 
pally of  ore  not  quite  changed  into 
lead,  gave  87 38  ounces  to  the  cubic 
foot. 

Finding  that  fulphur  could  not  be 
feparated  from  lead  ore  by  diflilling 
it  in  clofe  veffels  without  addition,, 
and  yet  being  much  difpofed  to 
think,  that  it  contained  a  confidera- 
ble  portion  of  fulphur,  I  firil  thought 
of  diftilling  it  with  charcoal  dull:, 
iron  filings,  fand,  and  other  addi- 
tions; but  recolle6ting  that  fulphur 
might  be  feparated  from  antimony 
p  ^  by 


(       228       ) 

by  folution  in  acids,  I  thought  it 
not  improbable,  that  it  might  be 
feparated  from  lead  ore  by  the  fam.e 
means,  and  the  luccefs  of  the  follow- 
Lng  experiment  abundantly  juflified 
the  conje6]:ure. 

Upon  ten  ounces  of  lead  ore, 
cleanfed  as  in  the  preceding  experi- 
ments, I  poured  five  ounces  of  the 
ilrongeft  fuming  fpirits  of  nitre  ;  this 
ftrong  acid  not  feeming  to  a6l  upon 
the  ore,  I  diluted  it  with  five  ounces 
of  water  ;  a  vfolent  ebullition,  ac- 
companied with  red  fumes,  immedi- 
ately took  places  the  folution  of  the 
ore  in  this  meyiftruu77i  becam.e  mani- 
feit,  and  when  it  was  finifhed,  there 
rem.ained  floating  upon  the  furface 
of  the  menftruum  a  cake  of  fine  yel- 
low fulphur,  perfedly  refembling 
common  ililphur. 

I  re- 


(  ^29  ) 
I  repeated  this  experiment  a  great 
many  times,  in  order  to  afcertain  the 
quantity  of  fulphur  contained  in  lead 
ore,  and  feparable  therefrom  by  fo- 
lution  in  acid  of  nitre.  The  refults 
of  different  experiments  were  feldom 
the  fame  i  the  matter  feparable  from 
the  ore  by  folution,  after  being  re- 
peatedly wafhed  in  large  quantities 
of  hot  water,  in  order  to  free  it  from 
every  faline  admixture,  fometimes 
amounted  to  more,  fometimes  to 
lefs  than  one-third  of  the  weight  of 
the  ore.  This  matter  may,  for  the 
fake  of  diffin6lion,  be  called  crude 
fulphur*  Its  apparent  purity  might 
induce  a  belief  that  it  contained  no 
heterogeneous  mixture,  yet  the  fol- 
lowing experiments  (hew  how  much 
we  fliould  be  deceived  in  forming 
p  3  fuch 


(    ^30    ) 
ftich  a  conje6lure,  and  how  rightly  it 
is  denominated  crude  fulphur. 

From  one  hundred  and  twenty 
parts,  by  weight,  of  lead  ore,  I  ob- 
tained, by  folution  in  acid  of  nitre, 
fubfequent  walhing  in  hot  water,  and 
drying  by  a  gentle  fire,  forty  parts  of 
a  fubftance  which  looked  like  ful- 
phur :  thefe  forty  parts  were  put  on 
a  red-hot  iron,  the  fulphur  was  made 
manifefc  by  a  blue  flame  and  pun- 
gent fliiell.  "When  the  flame  went 
out,  there  remained  upon  the  iron 
unconfum.ed  twenty-fix  parts  of  a 
greyifh  calx-,  the  weight  of  the  ful- 
phur which  was  confumed  muil  there- 
fore have  amounted  to  fourteen  parts, 
or  between  one  eighth  and  one  ninth 
part  of  the  weight  of  the  ore.  It 
has  been  obferved,  that  the  weight  of 
the  matter,  feparable  from  lead  ore 

by 


c  m  1 

by  folutlon  in  acid  of  nitre,  fome- 
times  exceeded,  and  fometimes  fell 
fhort  of,  one  third  part  of  tlie  weight 
of  the  ore  -,  this  variety,  as  far  as  I 
have  been  able  to  obferve,  does  not 
extend  to  the  quantity  of  fulphur 
contained  in  a  given  quantity  of  ore, 
it  depends  upon  the  quantity  of  calx 
remaining  after  the  burning  of  the 
fulphur.  Different  lead  ores  will 
doubtlefs  contain  different  quantities 
of  fulphur  i  but  that  the  fulphur 
contained  in  the  lead  ore  which  I 
examined,  conilitutes  between  one 
eighth  and  one  ninth  part  of  the 
weight  of  the  ore,  is  a  conclufion 
upon  which,  from  a  variety  of  expe- 
riments, I  am  difpofed  to  rely. 

There  are  faid  to  b^  annually  fmelted 

inDerhyJlme  about  ten  thaufand  tons 

p  4  of 


(  232  ) 
of  lead  ore  j*  now  if  means  could  be 
invented  (which  I  think  very  pofTi- 
ble)  of  faving  the  fulphur  contained 
in  ten  thoufand  tons  of  ore^  fuppof- 
ing  that  the  ore  fhould  only  yield 
one  tenth  of  its  weight  of  fulphur, 
though  it  unqueilionably  contains 
more^  Derhyjhire  alone  w^ould  furnifh 
annually  one  thoufand  tons  of  ful- 
phur, the  value  of  which  would  an- 
nually be  about  fifteen  thoufand 
pounds.  ]  mention  this  circum.ftance 
thus  publicly3  in  hopes  that  the  lead 
fmelters  rnay  be  induced  to  profe- 
cute  the  fubjeft.  If  the  fulphur 
contained  in  the  lead  ore  could  be  col- 
le6led^  it  would  not  only  be  a  lu- 
crative bufmefs  to  the  fmelters,  but 
a  great  faving  to  the  nation.    We  at 

prefent 

*  This  efliii^ate  is  I  have  resfon  to  think 
too  high. 


(     ^33     ) 

prefcnt  import  the  fulphur  we  nfe, 

and  the  confumption  6f  this  com- 
modity is  exceeding  great^  in  the 
making  of  gunpowder,  in  form- 
ing the  mixture  for  covering  the 
bottom  and  fides  of  fhips,.  *  and 
in  a  great  variety  of  arts.  The 
fmelters  need  not  be  apprehenfive 
lefb  the  quality  of  the  ore  Ihould  be 
injured  by  extra6ling  the  fulphur. 
Eighteen  hundred  weight  of  ore, 
from  which  the  fulphur  has  been 
extracted,  will  certainly  yield  as 
much  lead  as  twenty  hundred  weight 
of  ore,  from  which  the  fiilphur  has 
not  been  extracted,  and  it  will,  pro- 
bably, yield  more.  Arfenic  is  ex- 
traded 
*  This  mixture  is  made  of  one  part  of 
tallow,  of  one  part  of  brimflone,  and  of  three 
.parts  nearly  of  rolin.  The  tallow  and  rofin 
are  melted  together,  and  the  brimftone  is 
llirred  into  them  ;  140  pounds  of  brimftone 
i§  enough  for  a  veffel  of  1 40  tons. 


(     234     ) 
trafted   from   a  particular  ore    in 

Saxony,  by  roafting  the  ore  in  a  fur- 
nace, which  has  a  long  horizontal 
chimney ;  the  chimney  is  large,  has 
many  windings  and  angles,  thai  the 
arfenical  vapour  which  arifes  from 
the  ore  may  be  the  more  eafily  con- 
denfed  :  the  arfenic  attaches  itfelf 
like  foot  to  the  chimney,  and  is  from 
time  to  time  fwept  out.  It  is  very 
probable,  that  by  fome  fuch  con- 
trivance the  fulphur  contained  in 
lead  ore  might  be  colle6ted.  The 
fmelters  call  every  thing  fulphur 
v/hich  is  volatilized  during  the 
roafting  or  fluxing  of  an  ore  -,  but 
none  of  thofe  with  whom  I  have 
converfed,  had  any  notion  that  com- 
mon fulphur  could  be  feparated 
from  lead  ore. 

The  greyifh  calx  which  remained 

upon 


(     ^3S     ) 
upon  the  iron  after  the  fulphur  was 

confumed,  was  put  upon  a  piece  of 
lighted  charcoal ;  the  heat  of  the 
charcoal  being  quickened  by  blow- 
ing upon  itj  a  great  nunnber  of  glo- 
bules of  lead  were  formed  upon  its 
furface.  From  hence  it  appears, 
that  this  calx  is  not  an  unmetallic 
earth  contained  in  the  ore,  which 
the  acid  of  nitre  could  not  diffolve  -, 
but  a  calx  of  lead,  probably  pro- 
duced by  the  violent  a6lion  of  the 
acid,  and  which,  by  the  addition  of 
phlogifton,  may  be  exhibited  in  its 
metallic  form.  The  quantity  of  this 
calx  depends  much  upon  the  adion 
of  the  acid  upon  the  ore  -,  if  that 
a6lion  is  violent,  the  calx  is  in 
greater  abundance  than  if  it  be  mo- 
derate ;  and  I  am  not  certain  whe- 
ther the  experiment  might  not  be  fo 

managed. 


(   ^36  y 

managed,  that  there  would  be  little: 
or  no  calx  remaining;  that  is,  a 
given  quantity  of  ore  might  be  io 
dilTolved  in  the  acid  of  nitre,  that 
nothing  would  remain  undilTolved 
except  the  fulphur.  But  I  have  not 
yet  perfectly  fatisfied  myfeif  as  to 
the  conftituent  parts  of  lead  ore.  I 
am  certain  that  it  contains  lead,  and 
Julphur,  a  liquid,  ^,nd  air  :■  of  the  ex- 
iftence  of  the  three  firft  there  can  be 
no  doubt,  from  what  has  been  faid, 
and  the  air  is  rendered  beautifully 
apparent  by  the  following  experi- 
ment. 

Let  fome  lead  ore  be  reduced  into 
a  fine  powder,  put  it  into  a  narrow- 
bottomed  ale  glafs,  fill  the  glafs 
three  parts  with  water,  drop  into  the 
water  a  portion  of  the  ftrong  acid  of 
nitre,   you  may  judge  of  the  requi- 

lite 


(     ^37     ) 
fite  quantity  by  feeing  the  folution 

commence,  and  you  will  obferve  the 
ore  univerfally  covered  with  bubbles 
of  air,  thefe  will  buoy  the  ore  up 
in  large  tufts  to  the  furface,  and  the 
air  will  continue  to  be  feparated 
from  the  ore  till  the  acid  becomes 
faturated  with  the  lead.  The  fait 
arifing  from  the  union  of  the  nitrous 
acid  to  the  lead  often  appears  cry- 
ftallized  upon  the  furface  of  the 
menftruum  in  this  experiment;  and 
if,  when  the  menftruum  is  in  that 
ftate,  a  little  frelh  acid  be  added,  the 
fait  inftantly  cryftaliizes  and  falls 
down  to  the  bottom  of  the  glafs,  the 
acid  having  abforbed  the  water  which 
held  it  in  folution.  When  lead  is 
difiblved  in  the  m^anner  here  menti- 
oned, by  a  very  diluted  acid  of  ni- 
tre, there  is  no  appearance  of  ful- 

phur 


(     233     ) 

phur  upon  the  furface  of  the  men- 
ftruum,  there  is  found  at  its  bottom 
a  black  matter,  which  is  the  fulphur. 
But  though  lead,  and  fulphur,  a 
liquid,  and  air*,  are  unqueilionably 
conftituent  parts  of  lead  ore,  I  do 
not  take  upon  me  to  fay,  that  they 
are  the  only  conflituent.  parts  :  it  is 
well  known,  that,  during  the  foelt- 
ing  of  lead  ore,  a  third  part  or  more 
of  its  weight  is  fome  how  or  other 
loft,  fince  from  one  and  tw^enty  hun- 
dred weight  of  ore,  they  feldom  ob- 
tain above  fourteen  hundred  weight 
of  lead.  What  is  loft  partly  confifts 
of  a  fcoria  which  floats  upon  the 
furface  of  the  lead  during  the  opera- 
tion of  fmelting,  and  partly  of  what 

is 

*  I  have  feparated  inflammable  air  from 
lead  ore,  by  diflTolving  it  in  the  acid  of  lea 
fait. 


(   n9   ) 

is  fublimed  up  the  chimney  and  dif- 
fipated  in  the  air.  The  fcoria,  I  ap- 
prehend, would  be  very  little,  even 
from  a  ton  of  ore,  if  the  ore  was 
quite  free  from  fpar  :  it  is  the  fpar 
which  is  mixed  with  the  ore  that  con- 
ftitutes  the  main  portion  of  the  fco- 
ria*.  I  have  in  my  poiTefTion  a  folid 
mafs  of  fcoria,  which  accidentally 
flowed  out  from  a  fmelting  furnace, 
and  which  in  colour  and  confiftency 
perfedly  refembles  grey  lime-ilone, 
it  receives  a  polifli  as  fine  as  marble, 
and  it  might  perhaps  with  advan- 
tage be  cad  into  moulds  for  paving 
ftones,    chimney  pieces,    and  other 

matters. 

*  The  fpar  without  queflion  augments 
the  quantity  of  the  fcoria,  yet  the  lead  ore, 
which  appears  to  the  eye  to  be  quite  free  from 
fpar,  yields  a  conliderable  portion  of  a  black 
glafly  fcoria,  when  urged  with  a  liifficient 
fire. 


(  240  ) 
matters.  It  arifes  from  the  fpar  mix- 
ed with  the  ore^  and,  by  the  addition 
of  cubical  fpar  to  the  ore  during  its 
fufion,  its  quantity  might  be  increaf- 
ed  at  no  great  expence,  in  any  pro- 
portion. That  part  of  the  ore  which 
is  fubiimed  and  difperfed  in  the  air^ 
confiils  partly  of  the  fulphur  which  is 
decompofed,  and  partly  of  lead  j  this 
fubiimed  lead  attaches  itfelf  in  part 
to  the  fides  of  the  chimney  of  the 
fmelting  furnace  ;  the  reft  of  it  flies 
lap  into  the  air,  from  whence  it  falls 
upon  the  ground,  poifoning  the  wa- 
ter and  herbage  upon  which  it  fet- 
tles. This  fubiimed  lead  might  be 
collected  either  by  making  it  meet 
with  water,  or  with  the  vapour  of 
water,  during  its  afcent,  or  by  iriak- 
ing  it  pafs  through  an  horizontal 
chimney  of  a  fufficient  length. 

It 


(     ^41     ) 

It  is  not  eafy  to  determine  with 
precifion  the  quantity  of  this  fublim- 
ed  lead  ;  a  general  guefs,  however, 
may  throw  fome  light  upon  the  fub- 
jed.  They  ufually  at  a  fmelting 
houfe  work  ofF  three  tons,  or  fixty 
hundred  weight,  of  lead  ore  every 
twenty-four  hours  ;  the  fulphur  con- 
tained in  fixty  hundred  weight  of  ore, 
we  will  fuppofe  to  be  feven  hundred 
weight,  and  the  lead  to  be  forty 
hundredweight;  the  air,  liquid,  fco- 
ria,  and  fublimed  lead  muft  toge- 
ther, upon  this  fuppofition,  amount 
to  thirteen  hundred  weight  -,  now, 
admitting  three  hundred  weight  of 
the  thirteen  to  be  fublimed  lead,  it  is 
evident  that,  could  it  be  colleded, 
there  would  be  an  annual  faving  at 
^ach  fmelting  houfe  of  above  fifty 
tons,    which,    fuppofing    it   to   be 

VOL.  III.  Q^  worth 


(       242      ) 

>worth  four  pounds  per  ton,  would 
amount  to  above  two  hundred 
pounds  a  year.  The  price,  if  not 
the  quantity  of  lead  fublimate,  here 
-afiTumed,  is,  probably,  below  the 
truths  but  my  end  is  anfwered  in 
giving  this  hint  to  perfons  engaged 
in  the  fmelting  bufinefs. 

The  following  experiments, 
though  upon  a  different  fubjedt,  may 
;not  be  unacceptable  to  the  lovers  of 
chemiftry,  as  I  do  not  remember  to 
have  any  where  met  with  them. 

It  is  commonly  known,  that  the 
furface  of  melted  lead  becomes  co- 
vered with  a  pellicle  of  various  co- 
lours. I  undertook  fome  experi- . 
ments  in  the  courfe  of  laft  winter, 
with  a  view  to  afcertain  the  order  in 
which  the  colours  fucceeded  each 
.other.      The  lead  which  lines  the 

.boxes 


(  243  ) 
boxes  in  which  tea  is  imported  from 
China  happening  to  be  at  hand,  fome 
of  it  was  melted  in  an  iron  ladle;  but 
I  was  much  furprized  to  find  that 
its  furface,  though  it  was  prefently 
covered  with  a  duiky  pellicle,  did 
not  exhibit  any  colours.  Imagining 
that  the  heat  was  not  fufHciently 
ftrong  to  render  the  colours  vifible, 
the  lire  was  urged  till  the  ladle  be- 
came jed  hot,  the  calcined  pellicle 
upon  the  furface  of  the  lead  was  red 
hot  alfo,  but  it  was  ftill  without  co- 
lour. The  fame  parcel  of  lead  was 
boiled  in  a  crucible  for  a  confider- 
able  time ;  during  the  boiling  a  co- 
pious fteam  was  difcharged,  and  the 
furface  of  the  lead,  as  is  ufual,  be- 
came covered  with  a  half  vitrified 
fcoria.  The  lead  which  remained 
unvitrified  was  then  examined,  and  it 
ct,  2  had 


(     244     ) 

had  acquired  the  property  of  form-' 
ing  a  fucceflion  of  coloured  pellicles, 
during  the  whole  time  of  continuing 
in  a  ftate  of  fufion. 

Another  portion  of  the  fame  kind 
df  lead  v/as  expo  fed  to  a  llrong  cal- 
cining heat  for  a  long  time ;  the  part 
which  rem,ained  uncalcined  did,  at 
length,  acquire  the  property  of  ex- 
hibiting colours  fufiiciently  vivid. 

Thefe  experiments  induced  me  to 
conclude,  that  the  Chinefe  lead  was 
mixed  with  fome  fubftance  from 
Vv^hich  it  was  neceflary  to  free  it  ei- 
ther by  fublimation  or  calcination, 
before  it  would  exhibit  its  colours. 
It  would  be  ufelefs  to  mention  all 
the  experiments  which  I  made  be- 
fore I  difcovered  the  heterogeneous 
fubflance  with  which  I  fuppofed  the 
Chinefe  lead  was  mixed.     At  laft  I 

hit 


(  245  ) 
hit  upon  one  which  feems  fully  fuf- 
ficient  to  explain  the  phenomenon. 
Into  a  ladle  full  of  melted  Derby- 
fhire  lead,  which  manifefted  a  fuc- 
cefTion  of  the  mod  vivid  colours, 
I  put  a  fmall  portion  of  tin,  and  ob- 
ferved,  that  as  foon  as  the  tin  was 
melted,  and  mixed  with  the  lead, 
no  more  colours  were  to  be  feen.  I 
do  not  know  precifely  the  fmalleft 
poffible  quantity  of  tin,  which  will 
be  fufficient  to  deprive  a  given 
quantity  of  lead  of  its  property  of 
forming  coloured  pellicles,  but  I 
have  reafon  to  believe  that  it  does 
not  exceed  one  five  thoufandth  part 
of  the  weight  of  the  lead. 

Derby  (hire  lead,   which  has  lofb 

its  property  of  exhibiting  colours  by 

being  mixed  with  tin,    acquires   it 

again,  as  is  mentioned  of  the  Chinefe 

0^3  lead. 


lead,  by  being  cxpofed  to  a  calcining 
heat  for  a  fi^f^cient  time  3  the  tin,  it 
is  fappoiedj  being  feparated  from  the 
lead  by  calcination,  before  all  the 
lead  is  reduced  to  a  calx. 

Some  calcined  Chinefe  lead  was 
reduced  to  its  m.etallic  form  by  burn- 
ing fomiC  taliow  over  it.  The  re- 
duced lead  gave,  when  melted^  co- 
loured pellicles  ; '  the  calx  of  tin, 
which  we  fuppofe  to  have  been  mix- 
ed with  the  calcined  lead,  not  being 
fo  eafily  reducible  as  that  of  lead. 

I  find  that  %inc  is  another  mxetallic 
fubftance  which  has  the  fame  pro- 
perty as  tin  v^ith  refped  to  the  de- 
priving lead  of  its  power  of  forming 
coloured  pellicles  3  but  it  does  not, 
I  think,  pofiefs  this  power  in  fo 
eminent  a  degree  as  tin.  I  put  fmall 
portions  of  hifmuth  alfo  into  melted 

lead, 


'  (  m  f 

lead,  but  the  lead  ftill  retained  its  ■ 
quality  of  forming  colours.  I  melted 
together  fome  filver  and  lead,  but 
the  lead  did  not  thereby  lofe  its 
power  of  forming  colours.  A  little 
tin  added  to  a  mixture  of  lead  and 
bifmuth,  or  to  a  mixure  of  filver 
and  lead,  immediately  takes  away 
from  the  refpediive  mixtures  the  fa- 
culty of  forming  coloured  pellicles. 

This  quality  of  tin  has  hitherto,, 
as  far  as  I  know,  been  unobferved  -, 
but  every  new  fa6l,  relative  to  the 
actions  of  bodies  one  upon  another, 
ought  to  be  recorded.  The  change, 
produced  in  lead  by  the  admixture 
of  a  fmall  portion  of  tin  is  much 
felt  by  the  plumbers,  as  it  makes 
the  metal  fo  hard  and  harfli,  that  it 
is  not  without  difficulty  they  can 
eaft  it  into  Iheet  lead.  If  their  old 
0^4  lead 


lead  does  not  work  fo  willingly,  nof 
exhibit  colours  fo  readily,  as  new 
lead,  they  may  refer  the  difference 
to  the  fmall  quantity  of  tin  contained 
in  the  folder,  from  which  old  lead 
can  feldom  be  thoroughly  freed. 

With  refpe6l  to  the  order  in 
v/hich  the  colours  fucceed  one  an- 
other upon  the  furface  of  melted 
lead,  it  feems  to  be  the  following 
one ;  yelloWy  purple,  hluey  — yellow^ 
'purple y  green y  — pink^  green,  — pinky 
green.  Upon  exhibiting  the  bright 
furface  of  melted  lead  to  the  air,  I 
have  often  obferved  thefe  ten  changes 
to  follow  one  another  in  a  more  or 
lefs  rapid  fuccefiion,  according  to  the 
degree  of  heat  prevailing  in  the  lead. 
If  the  heat  is  but  fmall,  the  fuccef- 
fion  flops  before  it  has  gone  through 
all  the  changes  5  but  v/ith  the  great- 
eft 


(     249     ) 

eft  heat  I  did  not  obferve  any  fur- 
ther variation.  All  the  colours  are 
very  vivid,  and  each  feems  to  go 
through  all  the  fhades  belonging  to 
it  before  it  is  changed  into  the  next 
in  order. 

The  formation  of  thefe  colours 
may  be  explained  from  what  has 
been  advanced  by  Sir  Ifaac  Newton^ 
and  illuftrated  by  the  very  ingenious 
experiments  o^yiwDelavaly  relative 
to  the  fize  of  the  particles  confti- 
tuting  coloured  bodies. 


ESSAY 


ESSAY      VIII. 


OF    THE    SMELTING     OF    LEAD    ORE, 
AS  PRACTISED  IN  DERBYSHIRE. 


THERE  IS  a  certain  ftandard 
of  perfedtion  in  the  exercife  of 
every  art,  which  is  not  always  well 
undcritood ;  and  after  men  do  fuffi* 
ciently  comprehend  it,  many  ages 
often  pafs  away  before  they  are  for-  j 
tunate  or  ingenious  enough  to  attain 
it.     To  extract  the  greatcfl  poffible 

quantity 


(       252       ) 

quantity  of  metal,  from  any  parti- 
cular kind,  and  any  definite  quantity 
of  ore,  is  a  problem  of  great  iPxi- 
portance,  whether  it  be  confidered  in 
aphilofophical  or  a  commercial  light; 
yet  he  who  fliould  apply  himfelf  to 
the  folution  of  it,  v^nth  an  expedta- 
tion  of  being  ufeful  to  mankind, 
muft  take  into  confideration  another 
circumflance,  of  as  much  importance 
as  the  quantity  of  metal  to  be  ex- 
traded,— the  expence  attending  the 
procefs.  For  it  is  obvious,  that  a 
great  quantity  of  metal  extrad:ed  at 
a  great  expence,  may  not  produce  fo 
much  clear  profit,  as  a  lefs  quantity 
procured  at  an  eafier  rate  ;  there  is  a 
beneficial  limit  between  the  quantity 
to  be  obtained,  and  the  expence  at- 
tending the  operation,  which  nothing 
but  experience  can  afccrtain. 

It 


(  253  ) 
It  has  been  proved,  by  experi- 
ments made  in  France^  *  that  lead  ore 
when  fmelted  by  a  fire  made  of  wood, 
yielded  one  tenth  more  lead,  than  in 
the  ordinary  method  of  fmelting  by 
means  of  piccoal ;  yet  pitcoal  is  fo 
much  cheaper  than  wood,  in  Derby- 
ihu-e,  and  moil  other  parts  of  Great 
Britain,  that  the  lofs  of  a  tenth  of 
the  lead,  is  probably,  more  than 
compenfated,  by  the  ufe  of  pitcoal 
inftead  of  wood  or  charcoal.  It  is 
pollible,  ^perhaps,  even  with  the  ufe 
of  pitcoal,  by  an  alteration  in  the 
procefs  of  fmelting,  to  cxtra(ft  from 
every  twenty  tons  of  ore,  one  ton 
more  of  lead  than  is  any  where  ex- 
traded  at  prefent ;  but  whether  the 
price  of  one  ton  of  lead,  would  be 

more 

*  Effais  des  Mines,  par  M.  Hellot,  Vol. 
:H.  .p.  114, 


(  154  ) 
moi-e  than  fufficient  to  defray  the 
extraordinary  expence  attending  the 
alteration  of  the  procefs,  muft  be 
left  to  the  decifion  of  thofe  who  are 
interefted  in  the  fuccefs  of  fuch  in- 
quiries. 

The  art  of  fmelting  the  ores  of  all 
metallic  fubflances,  was,  probably, 
at  firfl  very  imperfe6t  in  every  part 
of  the  world  ;  and  this  doubtlefs  has 
been  a  reafon,  why  the  ufe  of  iron 
has  every  where  been  of  a  more  re- 
cent date,  than  that  of  the  other 
metals,  fince  it  requires  the  applica- 
tion of  a  much  ftronger  fire  to  fmelt 
the  ores  of  iron,  than  thofe  of  any 
other  mietal. 

We  have  no  certain  account  when, 

or  by  whom,  the  feveral  metals  were 

<lifcovered  3   Wdllerius  fays,  that,  as 

far  as  he  knew,  Pliny  was  the  fir  ft 

3  who 


(     255     ) 

who  enumerated  the  fix  metals:"^ 
Pliny  may,  probably,  be  the  firft 
Natural  Hiftorian  who  mentioned 
them,  but  they  were  certainly  known 
long  before  the  age  of  Pliny,  and 
were  mentioned  both  by  Horner^  "ssidi 
by  an  author  far  more  ancient  than 
Homer — Mojes. — "  Only  the  goldy 
and  the^/ter,  the  brafs  {cofper)^  the 
irony  the//;^,  and  the  lead^  every  thing 
that  may  abide  the  fire,  ye  fhall  make 
it  go  through  the  fire,  and  it  fhall  be 
clean."  f  From  this  tcflimony  we 
are  certain  that  all  the  metals  were 
known,  at  leafl  in  the  country  of  the 
Midianites,  above  1450  years  before 
the  birth  of  Chrift,  or  near  900  years 

after 

*  —  Primus  (fcil  Plliiius)  quantum  mihi 
conftat,  fex  metalla  enumeravit.  Waller,  de 
Syf.  Minera.  p.  10. 

f  Numb.  xxxi.  22, 


(    2J6    ) 

after  the  deluge.  When  I  fay  all 
the  metals,  I  mull  be  underftood  to 
mean,  all  thofe  which  were  anciently- 
known  ',  for  plalina,  the  feventh  me- 
tal, has  been  but  recently  difcovered, 
and  is  not  yet  brought  into  general 
ufe  ;  and  quickfilver  or  mercury  is  not 
admitted  by  mineralogifts  into  the 
clafs  of  metals  i  though  it  has  a  good 
right  to  be  admitted,  fince  in  a  fuffi- 
cient  degree  of  cold,  it  poflefTes  the 
great  charaderiftic  property  of  a 
metal,  as  diftinguillied  from  zfemi- 
metal — malleability.  This  property 
of  malleability,  as  conftituting  the 
x:riterion  by  which  metals  differ  from 
femimetals,  is  not  over  rigidly  to  be 
infifted  on,  fince  iron,  when  firfl 
fluxed  from  its  ore,  or  when  con- 
averted  into  fleel,  and  hardened  by 
being  fuddenly  immerfed  when  red 

hot 


(  m  ) 

hot  in  water,  is  lefs  malleable  than 
]zincy  which  is  always  clafled  amongft 
the  fern i metals. 

It  has  been  contended,  that  copper 
Was  one  of  the  firft  metals  which  was 
ufed  as  money,  and  that  gold  and 
filver  were,  in  very  remote  ages,  of 
little  account  in  that  view.  In  many 
inftances  the  greatnefs  of  the  Roman 
name  has  made  us  forget  the  sera 
when  that  people  began  to  be  di- 
itinguifhed  in  hiilory,  and  induced 
us  to  confider  their  cuftoms,  as  the 
firfl  which  prevailed  amongft  man- 
kind. It  is  granted,  that  Servius 
Tullius  firft  coined  copper,  and  that 
the  Romans  ufed  no  other  currency 
till  the  four  hundredth  and  eighty- 
fifth  year  of  their  city,*  when  filver 
began  to  be  coined  3   but  from  this 

con* 
*  Plin.  Hift.  Nat.  Lib.  XXXIII,  S,  13. 

VOL.    Ill,  R 


(     2s8     ) 

concefTion,  no  argument  can  be  de- 
duced for  the  foie  ufe  of  copper  as  a 
currency,  in  the  firft  ages  of  the 
world.  We  know,  from  undoubted 
authority,  that  filver  was  ufed  in 
commerce,  at  ieafl:  eleven  hundred 
years  before  even  the  foundation  of 
Rome.  —  And  Abraham  weighed  to 
Ephroriy  theftlver  which  he  had 'named 
in  the  audience  of  the  Jons  ofHeth^  four 
hundred fljekels  of  filver^  current  money 
with  the  merchant^.  About  60  years 
before  Abraham  paid  this  fum  for  a 
piece  of  land  in  Canaan ^  he  is  faid, 
upon  his  return  from  Egypt ^  to  have 
been  rich,  not  in  copper  and  iron, 
but  in  filver  and  gold  f. 

Iron  and  copper  were  certainly. 
knovv'n  before  the  deluge ;  and  it  is 
probable,   that  ail  the  other  metals,. 

every 
*     Gen.xxHK  16,  f  Gen.  xiii.  2, 


C  ^59  ) 
every  one  of  which  is  more  eafily 
€xtraded  from  its  ore  than  iron  and 
copper  are  from  their's,  were  known 
slIio  to  the  Antediluvians ;  we  have 
proofs  how^ever,  that  in  the  time  of 
Abraham,  gold  and  filver  were 
cfleemed;,  as  they  are  at  prefent^  pre- 
cious metals ;  and  hence  it  feems 
reafonable  enough  to  conclude,  that 
Noah  was  able  to  inilru61:  his  de- 
fcendants  in  the  art  of  fmelting  me- 
tallic ores  :  but,  though  this  be  ad- 
m.itted,  we  need  not  be  furprized  at 
the  ignorance  of  many  barbarous  na- 
tions in  this  particular.  For  the  va- 
rious colonies  which,  either  by  com- 
pulnon  or  choice,  quitted  the  plains 
Q^Afidy  in  fearch  of  fettlements,  may 
not  always  have  had  in  their  compa- 
ny men  who  had  been  indrudled  in 
the  art  of  fmelting ;  and  thofe  who 
R  2  did 


(     26o     ) 

did  underftand  it,  when  the  colony 
firft  migrated,  may,  in  many  in- 
llances,  have  died  before  any  ores 
were  difcovered,  upon  which  they 
might  have  exerted  their  Jkill  -,  and 
thus  the  art  of  fmelting  being  once 
loft,  it  is  eafy  to  conceive  that  many 
nations  may  have  remained  for  ages 
without  the  ufe  of  metals,  or  with 
the  u{e  of  fuch  only  as  are  found 
ready  formed  in  the  earth,  or  are 
eafily  fluxed  from  their  ores. 

The  earth  in  a  little  time  after 
tht  deluge,  and  long  before  it  could 
have  been  peopled  by  the  pofterity 
of  Noah,  mull  have  become  covered 
Tvithwood;  tlie  moft  obvious  me- 
i.hod  of  clearing  a  country  of  its 
wood,  is  t:l:e  flatting  if  on  fire  :  nov/ 
in  m.oft  mineral  countries  there  are 
veins  of  metallic   ores^    wliich   lie 

con- 


(    a6i     ) 

contiguous  to  the  furface  of  the 
earth,  and  thefe  having  been  fluxed 
whilft  the  woods  growing  over  them 
were  on  fire,  probably,  fuggefled  to 
many  nations  the  firil  idea  of  fmelt- 
ing  ores. 

Powerful  gold  firfl  raifed  his  head. 

And  brafs,  and  lilver,  and  ignoble  lead. 
When  iliady  woods,  on  lofty  mountains  grown^ 
Felt  fcorching  fires  ^    whether  from  thundeir 

thrown, 
Or  elfe  by  man's  defign  the  flames  arofe* 


Whatever  'twas  that  gave  thefc  flames  t^r 

birth, 
Which  burnt  the  tov/ering  trees  and  feorch^d 

the  earth, 
Hot  flreams  of  filver,   gold,   and  lead,  and 

brafs,   (copper) 
As  nature  gave  a  hollow  proper  place, 
Defcended    down,    and    form'd   a    glitt'^ring; 

mafs*.. 

There 
*  Lucretius  by  Creech,  VoLII.  p.  572^ 
^   3 


(      262      ) 

There  is  no  natural  abfurdity  in 
this  notion  of  the  poet;  and  indeed 
it  is  confirmed  by  the  teilimony  of 
various  ancient  hiftorians,  who  fpeak 
of  filver  and  other  metals  being 
melted  out  of  the  earth,  during  the 
burning  of  the  woods  upon  the  Alps 
and  the  Pyrenees,  A  fimilar  circum.-- 
ftance  is  faid  to  have  happened  in 
Croatia  in  the  year  176 1  ;  a  large 
mafs  of  a  mixed  metal,  compofed  of 
copper,  iron,  tin  and  filver,  having 
been  fluxed,  during  the  conflagra- 
tion of  a  wood,  which  v/as  acciden- 
tally fct  on  fire.  * 

The  putting  a  quantity  of  ore  up- 
on a  heap  of  wood,  and  fctting  the 
pile  on  fire,  in  conformity  to  the 
manner  in  which  ores  were  melted 
during  the  burning  of  foreits  was, 

it 
*  Annual  Repiflerj  1761,  p.  138. 


J 


(     ^62     ) 

it  may  be  conje^lured,  the  firfl  rude 
procefs  by  which  metals  were  ex- 
tra6ted  from  their  ores.  But  as  the 
force  of  fire  is  greatly  diminiflied, 
when  the  flame  is  fuffered  to  expand 
itfelf,  and  as  the  air  a6ls  more  forci- 
bly in  exciting  fire,  when  it  rufheg 
upon  it  with  greater  velocity,  it  is 
likely,  that  the  heap  of  wood  and 
ore  would  foon  be  furrounded  with 
a  wall  of  ftone,  in  which  fufiicient 
openings  would  be  left  for  the  en- 
trance of  the  air,  and  thus  a  kind  of 
furnace  would  be  conftruded.  The 
Peruvians  we  are  told  "  had  difcover- 
ed  the  art  of  fmeltinc-^  and  refininor 
filver,  either  by  the  fimple  applica- 
tion of  fire,  or  ^yhere  the  ore  was  more 
ftubborn  and  impregnated  v/ith  fo- 
reign fubllances,  by  placing  it  in 
fmall  ovens  or  furnaces  on  high 
R  4  e-rounds^ 


(     s64    ) 

grounds,  fo  artificially  conflru6led 
that  the  draught  of  air  performed 
the  fundlion  of  a  beU4)wS;,  a  maGhiiie 
with  which  they  were  totally  unac- 
quainted." * 

This  method  of  fmelting  ores  on 
high  grounds>  without  the  affiftance 
of  a  bellows,  at  lead  of  a  bellows 
moved  by  water,  feems  to  have  been 
formerly  prad:ifed  in  other  countries 
as  v/ell  as  in  Peru,  When  M.  Belon 
travelled  into  Greece^  he  found  the 
furnaces  placed  on  the  fides  of  ri- 
vuletSj  and  obferves,  that  all  their 
bellows  played  with  v/heels  turned 
by  flream^s  ^f  v/ater,  yet  formerly 
they  had  fmelted  their  ores  in  a  dif- 
ferent manner :  for  upon  the  m.oun- 

tains 

*  Robertfon's  Hill,  of  America. — Alonfo 
Barba,  Treatife  of  Metals,  French  Tranf- 
Vol,  I,  p.  272, 


(     265     ) 

ta^ins  of  Macedonia^  where  mines  had 
been  wrought  in  the  time  of  Philip 
tlie  father  of  Alexander y  great  heaps 
of  flag  have  been  difcovered,  which 
are  fituated  fo  far  above  any  river  of 
the  country,  that  the  furnaces  from 
which  they  were  formed,  muft,.  pro- 
bably, have  been  wrought  by  the 
wind.  There  are  feveral  places  in 
Derby/hire  called  Boles  by  the  inha- 
bitants, v/here  lead  has  been  ancient- 
ly fmelted,  before  the  invention  of 
moving  bellows  by  water.  Thefe 
places  are  difcovered  by  the  flags  of 
lead,  which  are  found  near  them ; 
there  is  no  certain  tradition  concern- 
ing the  manner  in  which  the  ore 
v/as  fmelted  at  thefe  boles,  it  was, 
probably,  as  fimple  as  that  of  the 
Peruvians ;  for  in  Berhyjhirey  as  well 
'Ss  in  Pe-ru^  they  feem  chiefly  to  have 

relied 


(  a66  ) 
relied  upon  the  ftrength  of  the  wind 
for  the  fuccefs  of  the  operation;  the 
boles  being  always  fituatedupon  high 
grounds,  and  moflly  upon  that  fide 
of  a  hill,  which  faces  the  weft.  This 
fituation  was  not  fixed  upon  with- 
out defign,  fmce  the  wind  blows  in 
England,  in  the  courfe  of  a  year, 
near  twice  as  many  days  from  that 
quarter  as  from  any  other.*  A  me- 
thod is  mentioned  by  Ercker7t  f  of 
fmelting  bifmuth  ore  by  the  wind, 
and  it  feems  as  if  the  ore  of  lead 
might  have  been  fmelted   at  thefe 

boles, 
*  As    may    appear    from    the    following 
abridged  Hate  of  the  winds  at  London  in  the 
years  1774  and  1775. 


N 

s 

E        W 

NWJ  8E     NE 

sw 

^774 

25 

;Tr 

21 
21.^ 

anf. 

171^4 
II     i8|- 
1774—5 

43i  30    74 
391-13^1172 

126.^ 

148" 

dys 

f  See  Fleta  Minor,  by  Sir  John  Pettus, 

p.  30 

(     ^67     ) 
boles,  after  the  fame  manner.    This 
method  confifls  in  putting  the  bif- 
murh  ore,  when   beat  to  a  proper 
fize,    into  fmall  flat  iron  pans,  thefe 
are  fee  in  a  row  contiguous  to  each 
other,  in  an  open  place  -,  and  when 
there  is  a  flrong  wind,   a  fire  of  dry 
wood  is  made  clofe  to  the  pans,  and 
on  that  iide    of  them  from  which 
the  wind  blows,  by  this  contrivance, 
t\\t  wind  driving  down  the  flame  of 
the  w^ood  upon  the  pans,   the  ore 
contained  in  them  is  quickly  melted, 
A  pig  of  lead  was  dug  up  at  one  of 
the  boles  in  the  year  1766  on  Crcm- 
ford  moor  near  Matlock^  upon  its  un- 
der furface  there   is   an   infcription 
in  relievoy  from  which  it  appears  to 
have  been  fmelted  in  the  age  of  the 
Emperor  Adrian ;  it  is  not  very  dif- 
ferent in  fn.ape  from  the  pigs  which 

arc 


(  268  ) 
are  caft  at  prefent ;  it  confifls  of  fe- 
veral  horizontal  layers  of  unequal 
thicknefies,  and  there  is  an  irregular 
hole  in  it  running  from  the  top  to 
near  the  middle  of  its  fubftance  5 
from  thefe  appearances  it  feems  as  if 
it  had  been  formed  by  pouring  into 
a  mould,  at  different  times,-  feveral 
quantities  of  lead  ^  and  if  lead  had 
been  fmelted  after  the  manner  before 
mentioned  of  fmelting  bifmuth  ore, 
the  feveral  pans  being  emptied,  at 
different  times  as  they  became  ready, 
into  the  fame  mould,  would  have 
yielded  a  mafs  of  lead  divided  into 
layers  of  unequal  thickneffes,  and 
refemblingthis  Roman  pig;  for  the 
hole  in  its  furface  was,  probably, 
made  accidentally,  from  the  unequal 
cooling  of  the  lead,  or  from  fome 
extraneous  matter  being  lodged  in  it. 

The 


(     269     ) 

The  boles  in  Derbyfhire  are,  pro- 
•bably,  many  of  them  of  high  anti- 
quity, as  appears  from  the  pig  of 
lead  before  mentioned  -,  yet  I  have 
met  with  a  pafTage  in  a  writer  of  the 
lail  century^  from  which  it  is  evident, 
that  the  method  of  fmelting  lead  on 
high  grounds  was  then  pradlifed  in 
the  Peak.  "  The  lead-ftones  in  the 
Peak  lye  but  juft  within  the  ground 
next  to  the  upper  cruil  of  the  earth. 
They  melt  the  lead  upon  the  top  of 
the  hills  that  lye  open  to  the  weft 
wind  i  making  their  fires  to  melt  it 
as  foon  as  the  weft  wind  begins  to 
blow  3  which  wind  by  long  experi- 
ence they  find  holds  longeft  of  all 
others.  But,  for  what  reafon  I  know 
not,  fmce  I  ihould  think  lead  were 
the  eafieft  of  all   metals   to  melt, 

they 


(     270     ) 
they  make  their  fires  extraordinary 

great."  * 

The  fmelting  of  ore  by  the  varia- 
ble and  uncertain  a6lion  of  the  wind, 
mull  have  been  a  troublefome  pro- 
cefs.  It  has  therefore  been  univer- 
faliy  difufed,  and  the  more  regular 
blail  of  a  bellows  has  been  intro- 
duced in  its  fcead.  The  invention  of 
the  bellows  is  attributed  by  Straho  to 
Anacharfis  the  Scythian  :  j  but  it  is 
more  probable,  that  he  was  the  in-. 
ventor  of  fome  improvement  of  this 
machine,  than  of  the  machine  itfelf; 
for  Horner^  v/ho  lived  long  before  the 
age  oi Anacharfis^  defcribes  Vulca7C2j^ 
employing  twenty  pair  of  bellows  at 
once,  in  the  formation  of  Achilles^ 

fnield. 


*  Childrey's  Britan.  Bacon,  i66i« 
f  Strab.  Geog.  Lib.  VII, 


(     27.     ) 

Ihield.  *  It  is  difficult  to  fay  when 
the  art  of  moving  bellows,  by  means 
of  a  water  wheel,  was  firft  difcovered; 
it  is  pretty  certain,  that  the  ancients 
did  not  know  it;  and  that  it  was 
very  generally  known,  amongil  the 
Germans  at  leafc,  in  the  time  of 
i^gricola,  one  of  the  firft  of  our 
metallurgic  writers,  for  he  fpeaks  of 
it  in  feveral  places  without  any  hint 
of  its  being  a  recent  invention,  f 
The  heat  of  the  fire  in  a  furnace  de- 
pending much  upon  the  force  of  the 
blaft  of  air  impelled  againft  the  fuel ; 
and  that  force,  other  circumftances 
remaining  the  fame,  being  in  pro- 
portion to  the  quantity  and  velocity 
of  the  air  ;  the  application  of  a  power 

able 
*  Iliad.  Lib.  XVIIT.  V.  470. 
t  Agric,  de  Re  Metal,  pubiiflied  in  1550, 
p.  165.  33S. 


(       2/2      ) 

able  fuddenly  to  comprefs  the  largeft 
bellows  when  fwelled  with  air,  could 
not  fail  of  being  confidered  by  nie- 
tallurgifts,  as  an  invention,  whenever 
it  was  niade,  of  the  1  aft  importance. 
The  moderns  accordingly  have,  in 
many  ihftantes,  worked  over  again, 
with  confiderable  profit,  the  heaps  of 
iron  and  other  kinds  of  flag,  from 
which  the  metal  had  been  but  im- 
perfectly extraded,  before  the  mov- 
ing of  bellows  by  water  was  difco- 
vered. 

It  is  not  fifty  years  fince  the  hlafl 
or  hearth  furnace,  was  the  only  one 
in  ufe  for  fmelting  lead  ore  in  Der- 
hyjhire.  In  this  furnace  ore  and 
charcoal,  or  ore  and  what  they  call 
white  coal,  which  is  wood  dried  but 
not  charred,  being  placed  in  alter- 
nate layers,  upon  a  hearth  properly 

con- 


(    ^73     ) 
conllrudied,   the  fire  is  raifed  by  the 

blail  of  a  bellows,  moved  by  a 
water  wheel ;  the  ore  is  foon  fmelt- 
ed  by  the  violence  of  the  fire,  and 
the  lead  as  it  is  produced  trickles 
down  a  proper  channel,  into  a  place 
contrived  for  its  reception.  There 
are  not  at  prefent,  I  believe,  above 
©ne  or  two  of  thefe  ore  hearths  in  the 
whole  county  of  Derby;  this  kind 
of  furnace,  however,  is  not  likely 
to  go  entirely  out  of  ufe,  fince  it  is 
frequently  applied  to  the  extracfling 
lead  from  the  flag  which  is  produc- 
ed, either  at  the  ore  hearth ,  or  the 
cupola  furnace,  and  it  is  then  called 
2.  flag  hearth  I  and  the  lead  thus  ob- 
tained is  CcxWtdi  flag  lead':  the  fire  in 
a  ilag  hearth  is  made  of  the  cinder 
of  pitcoal  inftead  of  charcoal. 

The  furnace  called  a  cupol  or  cu- 
VOL.  111.  S  pola^ 


I     ^74    ) 

'pohy  in  which  ores  are  fmelted  by 
the  flame  of  pitcoal,  is  faid  to  have 
been  invented,  about  the  year  1698, 
by  a  phyfician  named  TVright^  * 
though  Beecher  may,  perhaps,  be 
thought  to  have  a  prior  claim  to  its 
invention  or  introdudion  from  Ger- 
many. -\'  But  whoever  was  the  firfl 
inventor  of  the  cupola,  it  is  now  in 
general  ufe^  not  only  in  Derbyfhire 
and  other  countries  for  the  fmelting 
of  the  ores  of  lead,  but  both  at  home 
and  abroad,  where  it  is  called  the 
Engliih  furnace,  for  the  fmelting  of 
copper  ores.  This  furnace  is  fo 
contrived,  that  the  ore  is  melted,  not 
by  coming  into  immediate  contad; 
with  the  fuel,  but  by  the  reverbera- 
tion of  the  flame  upon  it.  The 
•bottom  of  the  furnace  on  which  the. 

lead 
■^'  ElTais  dcs  Mines,  Vol.  II.  p.  114. 
'i   See  Vol.  I.  p.  3% 


(  ^75  _) 
lead  ore  is  placed,  is  fomewhat  con- 
cave, flielving  from  the  fides  towards 
the  middle;  its  roof  is  low  and  arch* 
ed,  rcfembling  the  roof  of  a  baker's 
oven ,  the  fire  is  placed  at  one  end 
of  the  funtace^  upon  an  iron  grate, 
to  the  bottom  of  which  the  air  has 
free  accefs  ;  at  the  other  end^  oppo- 
fite  to  the  fire  place,  is  a  high  per- 
pendicular chimney ;  the  dirediion 
of  the  flame,  when  all  the  apertures 
in  the  fides  of  the  furnace  are  clofed 
up,  is  neceifarily  determined,  by 
the  fi:ream  of  air  which  enters  at 
the  grate,  towards  the  chimney, 
and  in  tending  thither  it  fi:rikes 
upon  the  roof  of  the  furnace,  and 
being  reverberate4  from  thence 
upon  the  ore,   it  foon  melts  it. 

It  is  not  always  an  eafy  matter  to 

meet  with  a  current  of  water,  fuffi- 

s  2  cient 


(    ^76    ) 

clent  to  move  the  bellows  required 

in  fmelting  on  an  hearth    furnace; 
and  to  carry  the  ore  from  the  mine 
where  it  is  dug,  to  a  confiderablc 
difiance  to  be  fmelted,  is  attended 
with  great  ex  pence ;  this  expence  is 
faved    by    fmelting    in    the    cupola 
furnace,    which   not   requiring    the 
life  of  bellows,  may  be  conflrudied 
any  where.    Wood  is  very  fcarce  in 
every  mining  country  in  England, 
and  though    pitcoal    cofls   ten     or 
twelve  Ihillings    a    ton    in    Derby- 
ihire,  yet  they  can  fmelt  a  definite 
quantity  of  ore  in   the  cupola,  at  a 
far  lefs  expence  by  means  of  pit- 
coal,   than    of  wood.— The   flame^ 
which  plays  upon  the  furface  of  the 
.  ore  and  fmelts  it  in  a  cupola  fur- 
nace, is  not  driven  againll  it  with 
much     violence ;    by    this    means 

fmall 


I 


(  277  ) 
jinall  particles  of  ore,  called  beU 
land,  may  be  fnielted  in  a  cupola 
furnace  with  great  convenience, 
which  would  be  driven  away,  if 
expofed  to  the  fierce  blait  of  a 
pair  of  bellows  in  a  hearth  furnace. 
— Thefe  are  fome  of  the  advantages 
attending  the  ufe  of  a  cupola  in  pre- 
ference to  a  hearth  furnace ;  and  to 
thefe  may  be  added  one  fuperior  to 
all  the  reft, — the  prefervation  of 
the  workmen's  lives ;  the  noxious 
particles  of  lead  are  carried  up  the 
chimney  in' a  cupola,  whilft  they  are 
driven  in  the  face  of  the  hearth 
fmelter  at  every  blaftof  the  bellows. 
They  generally  put  Into  the  cu- 
pola furnace  a  ton  of  ore,  previoufly 
beat  fmall  and  properly  dreifed,  at 
one  time;  this  quantity  they  call  a 
charge ;  if  the  ore  is  very  poor  in  lead 
they  put  in  fomevvhat  more^and  they 
s  3  work 


(    278    > 

work  off  three  charges  of  ore  in 
every  twenty -four  hours.  In  about 
fix  hours  froLB  the  time  of  charg- 
ing, the  ore  becomes  as  fluid  as 
milk.  Before  the  ore  becomes  fluid^ 
and.  even  whiift  it  continues  in  a 
flate  of'iufion,  a  confiderable  por- 
tion of  its  weight  is  carried  off 
through  the  chimney  ;  what  remains 
in  the  furnace  con  fills  of  two  dif- 
ferent fubilancts, — of  the  lead^  for 
the  obtaining  of  which  the  procefs 
was  commenced^ — -and  of  the  Jlag 
ox  Jcorla,  The  proportion  between 
thefe  parts  is  not  always  the 
fame,  even  in  the  fame  kind  of 
ore;  it  depending  much  upon  the 
management  of  the  fire.  The  lead, 
being  heavier  than  the  flag,  finks 
through  it  as  it  is  formed,  and  fet- 
tles into  the  concavity  of  the  bot- 
tom of  the  furnace.    The  pure  flag, 

accord- 


<  279  ) 
according  to  the  idea  here  given,  is 
that  part  of  the  ore  of  lead  which  is 
neither  driven* oif  by  the  heat  of  the 
furnace,  nor  changed  into  lead.  In 
order  to  obtain  the  lead  free  from 
the  flag  which  fwims  over  it,  the 
'  fmelters  ufually  throw  in  about  a 
bufhel  of  lime;  not,  as  is  ufually 
fuppofed,  in  order  to  contribute  to- 
wards the  more  perfedt  fulion  of  the 
ore.,  but  to  dry  up  the  flag  which 
floats  upon  the  furfaee  of  the  lead, 
and  which,  being  as  liquid  as  lead, 
might  otherwife  flow  out  along 
with  it.  The  flag  being  thus  thick- 
ened by  an  admixture  of  lime,  is 
raked  up  towards  the  fides  of  the 
furnace,  and  the  lead  is  left  at  the 
bottom.  There  is  a  hole  in  one  of  the 
fides  of  the  furnace,  which  is  pro-. 
perly  flopped  during  the  fmelting^ 
s  4,  of 


(     aSo     ) 
©fthe  ore;  when  the  Hag  is  raked 
off,   this  hole  is  opened,  and   being 
iitu-ated  lower  than  the  lead   in   the 
furnace,    the  lead  gufhes  through  it 
into  an  iron   pot  placed  contiguous 
to  the  nde  of  the  furnace  ;  from  this 
pot  it  is  laded  into  iron  mouMs^  each 
containing  what  they  call  a  pig  of 
lead,  the  |)lgs  when  cold,  being  or- 
dinarily flamped   with  the  maker's 
name,  are  fold  under  the  name  of  ore 
lead,.    After  the  lead  has  all  flowed 
«aut  of  the  furnace,  they  Hop  up  the 
lao    hole,    and  drawins:   down    the 
Hag  and  liQ:te  into  the  middle  of  the 
furnace,  they  raife  the  fire  till  the 
mixture   of  flag   and  lime,   which 
they  limply  term  flag,    is  rendered 
very  liquid,  upon  this  liquid  mafs, 
they    throw     another    quantity    of 
lime  to  dry  it  up  as  in  the  former 

part 


(  '^8i  ) 
part  of  the  procefs.  This  fecond 
mixture  of  flag  and  lime  is  then 
raked  out  of  the  furnace,  and  the 
fmall  portion  of  lead  feparated  from 
the  fufion  of  the  firfl,  generally  to 
the  amount  of  twenty  or  thirty 
pounds,  being  Let  out  of  the  fur- 
nace, a  nev7  charge  of  ore  is  put  in,, 
and  the  operation  re-com.menced. 
In,  order  to  fpare  the  lime,  and  the 
expence  of  fuel  attending  the  fiiix- 
ing  of  the  mixture  of  lime  and  flag, 
they  have  in  fome  furnaces  lately 
contrived  a  hole,,,  through  which 
they  fuffer  the  main  part  of  the  li- 
quid flag,  to  flow  out,  before  they 
tap  the  furnace  for  the  lead  -,  upon 
the  little  remaining  fl.ag  they  throw 
a  fmall  portion  of  lime,  and  draw 
the  mixture  out  of  the  furnace 
without  fmelting  it.     This  kind  of 

fur- 


(       282       ) 

fiitnace    they    have   nick-named   a 
Maccaroni, 

The  procefs  of  fmelting  here'de-. 
fcribed,  appears  to  be  defeftive  iii 
fonne  points,  which  I  will  take  the 
liberty  to  mention,  and  at  the  fam© 
time  fuggeft  the  means  of  improve- 
ment; without,  however,  prefuming 
to  fay,  how  far  it  may  be  expedient 
to  adopt  the  propofed  alterations  ; 
being  fenfible  that  what  m^ay  appear 
very  feafible  in  theory,  or  m^ay 
even  anfwer  in  fmall  affays,  may 
not  be  practicable  in  large  works. 

The  firft  alteration  which  I  v/ould 
propofe  to  the  confideration  of  the 
lead  fmelters,  is  to  fubilitute  an  ho- 
rizontal chimney  of  two  or  three 
hundred  yards  in  length,  in  the^ 
place  of  the  perpendicular  one  now 
in   ufe.      In   the   preceding   EfTay, 

which 


(     583     ) 

which  was  firft  publiHied  in  177^^^ 
mention  is  made  of  the  probability 
of  faving  a  large  quantity  of  fub- 
limed  lead,  hj  making  the  fmoke, 
which  rifes  from  the  ore,  pafs 
through  an  horizontal  chimney, 
with  various  windings  to  condenfe 
the  vapour.  I  have  fmce  converfed 
with  fome  of  the  principal  lead 
fmelters  in  Derhyjhirey  and  find  that 
I  had  over-rated  the  quantity  of  this 
fublim.ed  lead  3  the  weight  of  the 
Jcoria  from  a  ton  of  ore,  amounting 
to  m^ore  than  I  had  fuppofed  ;  they 
were  all  of  them,  however,  of  opi- 
nion, that  the  plan  I  had  propofed 
for  faving  the  fublimate,  was  a  very 
rational  one.  But  fo  difficult  is  it 
to  wean  artifls  from  their  ancient 
ways  of  operating,  that  I  queftion 
very  much   whether   any  of  them 

would 


(     2§4     ) 

would  ever  have  adopted  the  plan 
they  approved^  if  an  horizontal 
Ghimney,  which  was  built  a  iittk 
time  ago  in  Mid  die  ton  dale^  for  a 
quite  different  purpofe^  liad  not 
given  them  a  full  proof  of  the 
pra(5l:iGability  of  faving  the  fubli- 
mate  of  lead,  which,  is  lofi:  in  the 
ordinary  method  of  fmelting.  This 
chimney  was  built  on  the  fide  of  an 
hill,  to  prevent  fome  adjoining  paf- 
tures  from  Being  injured  by  the 
fmoke  of  the  furnace.  It  not  only 
anfwers  that  end,  but  it  is  found 
alfo  to  colle£l  confiderable  quanti- 
ties of  the  lead,  which  is  fublimed 
during  the  fmelting  of  the  ore  \  this 
fublimed  lead  is  of  a  whitifh  cafr, 
and  is  fold  to  the  painters  at  ten  or 
twelve  pounds  a  ton  s  it  might  per- 
haps be  converted  into  red  lead  with. 
ftill  more  profit, 

A  f€.- 


C     ^«5     ) 

A  fecond  circumftance  to  ht  at- 
tended to  in  the  fmelting  of  lead  ore, 
is  the  faving  the  fulphur  contained  in 
it.  The  pure  lead  ore  of  Derbylliire 
contains,  between  an  eighth  and  a 
ninth  part  of  its  weight  of  fulphur; 
but  as  the  ore  which  is  fmelted  is 
never  pure,  being  mixed  with  par- 
ticles o(/par,  cawky  limeftone^  brazily 
and  other  fubftances,  which  the  mi- 
ners call  deads y  we  fhali  be  high 
enough  in  our  fuppofition,  if  we  fay 
that  the  ordinary  ore  contains  a  tenth 
'  of  its  weight  of  fulphur ;  it  may  not, 
probably,  contain  fo  much,  but 
even  a  twelfth  part,  could  it  be  col- 
le6led  at  a  fmall  expence,  v/ould  be 
..an  obje6h  of  great  importance  to  the 
fmelter.  In  the  common  method  of 
fmelting  lead  ore  there  is  no  ap- 
|)earance  of  the  fulphur  it  contains, 

it 


(  286  ) 
it  is  confumed  by  the  flame  of  the 
furnace,  as  foon  as  it  is  feparated 
from  the  ore  ;  an  attentive  obferver 
may,  indeed,  by  looking  into  the 
furnace  diflinguifn  a  diverfity  in  the 
colour  of,  the  flame,  at  diflferent  pe- 
riods of  the  procefs ;  during  the  flrfl: 
three  or  four  hours  after  the  ore  is 
put  into  the  furnace,  the  flame  has 
a  bluifli  tint,  proceeding  no  doubt 
from  the  fulphur  which,  in  being 
fublimed  from  the  ore,  is  inflamed  ^ 
after  all  the  fulphur  is  feparated 
fromi  the  ore,  the  flame  has  a  whi- 
tifn  call,  and  then  and  not  before 
the  fire  may  be  raifed  for  flnifliing 
the  operation ;  for  if  the  fire  be  made 
flirong  before  the  fulphur  be  difperf- 
ed,  the  quantity  of  lead  is  Icfs,  pro- 
bably, for  two  reafons;  the  fulphur 
unites  itielf  in  part  to  the  lead  which 


(     237     ) 

is  formed,  and  by  this  union  be* 
comes  infeparable  from  it ;  for  the 
fulphur  cannot  without  much  diffi- 
culty be  feparated  from  an  artificial 
mixture  of  lead  and  fulphur,  when 
the  two  ingredients  have  been  fufed 
together  -, — 2.  The  fulphur,  whilil 
it  continues  united  to  the  lead  in 
the  natural  ore,  renders  the  ore  vo- 
latile, ib  that  in  a  flrong  heat  a  great 
portion  of  it  is  driven  off.  Hence, 
very  iulphureous  ores  fhouid  be 
roailed  for  a  long  time  with  a  gen- 
tle heat,  and  in  this  proper  mianage- 
ment  of  the  lire,  principally  confifbs 
the  fuperiority  of  one  fmelter  above 
another. 

An  old  lead  fmelter  informed  me 
that  he  had  often  reduced  a  ton  of 
ore  to  16  hundred  weight  bjy  roafl- 
ing  it;,   but  that  he  did  not  obtain 

more 


(  283  ) 
more  metal  from  it  by  a  fubfequent 
fufion,  than  if  he  had  fluxed  it  with- 
out a  previous  roafting.  This  may 
be  true  of  fome  forts  of  ore,  but  it 
is  not  true  of  very  fulphureous  ores. 
Indeed  the  lire  may  be  fo  regulated 
in  a  cupola  furnace,  as  to  make  it 
anfwer  the  purpofe  of  a  roafting  and 
a  fmelting  furnace  at  the  fame  time  : 
I  have  feen  much  lead  loft  by  fmelt- 
ing a  ton  of  fulphureous  ore  in  eight 
hours,  which  might  have  beenfaved, 
if  the  fire  had  at  firft  been  kept  fo 
gentle  as  to  have  allowed  twelve 
hours  for  finifhing  th€  operation. 

Sulphur  cannot  be  feparated  from 
lead  ore  in  clofe  vefTels,  and  the  lead 
ore  melts  with  fo  fmall  a  degree  of 
heat,  that  there  may  be  more  diffi- 
culty in  procuring  the  fulphur  from 
the  ores  of  lead,   than  from  thofe  of 

copper 


(    289     ) 

copper  or  iron,  however,  I  am  far 
from  thinking  the  matter  impra6:i- 
cable,  though  I  have  not  yet  hit  up- 
on the  method  of  doing  it ;  and  the 
following  refiedions  may,  perhaps, 
tend  to  fuperfede  the  neceffity  of 
colledling  the  fulohur  in  fubftance. 

When  it  is  faid  that  the  fulphur  is 
confumed  by  the  flame  of  the  fur- 
nace as  fooTi  as  it  is  feparated  from 
the  ore,  the  reader  Vv^iil  pleafe  to  re- 
colled,  that  fulphur  coniiils  of  two 
parts,  —  of  an  inflammable  part 
hy  which  it  is  rendered  combuflible, 
—  and  of  an  acid  part  which  is  fet 
at  liberty,  in  the  form  of  vapour, 
during  the  burning  of. the  fulphur. 
Now  this  acid,  though  it  may  be 
driven  out  of  the  furnace  in  the 
form  of  a  vapour,  yet  it  is  incapable 
of  being  thereby  decompofed  ;  it  Hill 
vol.  HI.  T  con- 


(      290      ) 

continues  to  be  an  acid ;  and,  could 
the  vapour  be  condcnfed,  might  an- 
fwer  all  the  fame  purpofes  as  the 
acid  of  vitriol ;  iince  all  the  acid  of 
vitriol,  now  ufed  in  commerce,  is 
adrually  procured  from  the  burning 
of  fulphur.  That  the  faft,  with 
refpedt  to  the  acid  not  being  decom- 
pofed,  is  as  I  have  ftated  it,  may  be 
readily  proved.  The  fmoke  which 
iiTues  out  of  the  chimney  for  fom.e 
hours  after  each  freili  charge  of  ore 
has  a  fufFocating  fmell,  perfectly  re- 
fembling  the  fmell  of  burning  brim- 
ilone,  and  if  a  wet  cloth,  or  a  wet 
hand  be  held  in  it  for  a  very  ihort 
fpace  of  time,  and  afterwards  appli- 
ed to  the  tongue,  a  Urong  acid  will 
be  feniibly  perceived.  Various  me- 
thods may  be  invented  for  conden- 
iing  this  acid  vapour,  and,  probably, 

more 


(      291       ) 

more  commodious  than  the  follow- 
ing one,  which,  however,  I  will  juft 
take  the  liberty  of  mentioning,  as, 
if  it  fhould  not  fucceed,  the  trial  will 
be  attended  with  very  little  expence. 
Suppofing  then  an  horizontal 
chimney  to  be  built,  let  the  end  far- 
thefl  from  the  fire  be  turned  up,  by 
a  tube  of  earthen  ware,  or  otherwife, 
fo  that  the  fulphureous  acid  may 
ilTue  out  in  a  direction  parellel  to  the 
£ue  of  the  chimney,  and  at  the  dis- 
tance of  about  a  foot  and  an  half  a- 
bove  it.  Let  a  number  of  large 
globular  veffels  be  made  of  either 
glafs  or  lead,  each  of  thefe  globes 
muft  have  two  necks  fo  as  to  ba 
capable  of  being  inferted  into  one 
another ;  let  thefe  veiTels  be  placed 
on  the  flue  of  the  chimney,  the 
neck  of  the  firft  beins:  inferted  into 
T  2  the 


(      292       ) 

'the  tube  through  which  we  have 
fuppofed  the  fulphureous  acid  to 
-iffue,  and  the  neck  of  the  lad  being 
left  open,  for  fear  of  injuring  the 
draught  of  the  furnace.  Let  each  of 
thefe  globular  veflels  contain  a  fmall 
quantity  of  water,  then  it  is  con- 
ceived, that  the  heat  of  the  flue  will 
raife  the  water  into  vapour,  and  that 
this  watery  vapour  will  be  the  means 
of  condeniing  the  fulphureous  acid 
vapour,  if  not  wholly,  at  lead  in 
fuch  a  degree  as  may  render  the  un- 
dertaking profitable.  When  the  ful- 
phur  is  all  confumed,  the  draught 
of  the  furnace  may  be  fufiTered  to 
have  its  ordinary  exit  at  the  end  of 
the  horizontal  chimney,  by  a  very 
ilight  contrivance  of  a  moveable 
damper.  Since  the  firll  publication 
of  the  preceding  Effay,  I  have  feen 


C    293    >,. 

an  horizontal  chimney  at  the  copper 
works  near  Liverpool,  where  every- 
thing J  had  faid  concerning  the  pro- 
bability of  faviiTg  fulphur  by  roail- 
ing  lead  ore,  is  verified  with  refpedt 
to  copper  ore-:  and  I  believe  a  patent 
has  been^  granted  to  fome  individual 
for  this  mode  of  collediing  fulphur. 
Sulphur  might  be  obtained  witb 
equal  facility  from  the  fyrites  which 
is  found  amongil  coal,  and  this  ap- 
plication of  the  pyrites  might,  pro- 
bably, be  more  lucrativ^e  than  the 
prefent  one — -making  green  vitriol/^ 
A  third  circumftanee,  which  re- 
quires the  utmoft  care  of  the  lead 
fmelter,  is  the  leaving  as  little  lead 
aS'  poffible  in  the  flag.  Near  ever3r 
fmelting  houfe  there  are  thoufands- 
of  tons  of  flagjVvhirGh,  when  properly^ 
T-3,  allayed^ 

*  Vol.  I.  p.  229, 


(  294  ) 
aflayed,  are  found  to  yield  from  one 
eighth  to  one  tenth  of  their  weight 
of  lead  ;  though  no  perfon  has  yet 
difcovered  a  method  of  extrad:ing, 
fo  much  from  them  when  fmelted 
in  large  quantities  ;  and  indeed  the 
fmelters  are  fo  little  able  to  obtain, 
all  the  lead  contained  in  them,  that 
in  many  places  they  never  attempt 
to  extradt  any  part  of  it :  in  fome 
places,  where  they  do  attempt  it,  I 
have  known  the  proprietor  of  the 
Hag  allow  the  fmelters  20s.  for  every 
pig  of  lead  they  procured  of  the  va- 
lue of  38s.  befides  furnifliing  them 
with  fuel  J  and'  yet  the  men  employ- 
ed in  fuch  an  unwholefome  bufinefs, 
feldom  made  above  ys.  a  week  of 
their  labour.  This  fufion  of  the 
Hag  of  a  cupola  furnace  is  made,  as 
has  been  mentioned,  at  a  hearth  fur- 
"^  nace ; 


C   295    ) 

nace ;  the  coal  cinder,  which  they  ufe 
as  fuel,  and  the  flag  are  foon  melted 
by  the  ftrong  blaft  of  the  bellows- 
into  a  black  mafs,  which,  when  the 
fire  is  very  ftrong,  becomes  a  pcrfedt 
glafs ;  this  black  mafs,  even  in  its 
moll  liquid  ftate,  is  very  tenacious, 
and  hinders  many  of  the  particles  of 
lead  from  fubfiding,  and  ic  being 
from  time  to  time  removed  from  the 
furnace,  a  coniiderable  quantity  of 
lead  is  left  in  it^  and  thereby  loll^ 
A  principal  part  of  the  lead  con-- 
tained  in  the  flag  of  the  cupola  fur- 
nace, is  not,  I  apprehend,  in  the 
form  of  a  metal,  but  in  the  form  of  a, 
litharge  or  calcined  lead  ;  a  portion 
of  the  lead,  in  being  fmelted  from  its 
ore,  is  calcined  by  the  violence  of 
the  fire ;  this  calcined  lead  is  not 
only  very  vitrifiable  of  itfelf,  but  it 
T  4  helps: 


(     296    ) 

helps  to  vitrify  the  fpar  which  k 
mixed  with  the  ore,  and  thus  eonfli- 
tutes  the  liquid  fcoria ;  might  it  not 
be  ufeful  to  throw  a  quantity  of  char- 
coal duft  upon  the  liquid  fcoria  in 
the  cupola  furnace,  in  order  that  the 
calcined  lead  might  be  converted 
into  lead,  by  uniting  itfelf  to  the 
iniiammable  principle  of  the  char- 
coal ?  —  Iron  will  not  unite  with 
lead,  but  it  readily  unites  with  ful- 
phur,  and  when  added  to  a  mixture 
of  lead  and  fulphur,  it  will  abforb 
the  fulphur,  leaving  the  lead  in  its 
metallic  form ;  might  it  not  be  ufe- 
ful to  iiux  fulphureous  lead  ores  in 
conjund:ion  with  the  fcales  or  other 
xefufe  pieces  of  iron,  or  even  with 
fome   forts   of  iron  ore  ?  ■  The 

fmelter's  great  care  ihould  be  to  ex- 
trad  as  much  lead  as  pofTible  at  the 

firft 


(     297     ) 
firft  operation  of  fmelting  the  ore, 
and  to  leave  the  flag  as  poor  as  pof- 
fible;  but  if  he  fliould  ilill  find  either 
the  flag  of  the  cupola  furnace,  or 
that  of  the  hearth  furnace,  contain- 
ing much  lead,  (as  that  even  of  the 
hearth  furnace  certainly  does),,  he 
may,  perhaps,  find  it  v/orthhis  while 
to  reduce  the  flag  into  a  powder  by 
a  (lamping  mill,  or  by  laying  it  in 
highways  to  be  ground  by  the  carts, 
or  by  fome  other  contrivance^  and 
then  he  may  feparate  the  ftony  part 
of  the  flag  from  the  metallic,  by 
waflii-ng  the  whole  in  water,  inafmuch 
as  the  metallic  part  is  far  heavier 
than  the  other. 

I  eftimated  the  weights  of  feveral 
pieces  of  flag,  and  found  them  to 
differ  very  much  from  each  other ; 
this  difference  is  principally  to  be 

at- 


(     29S     ) 

attributed  to  the  different  quantities 
of  lead  left  in  them. 

Weight  of  a  cubic  foot  of 

Avoir,  oz. 
Slag  from  a  cupola  furnace,   where  1 

no  lime  was  ufed     -      -     -       J  ^ '  ^ 

Black  flag  from  a  hearth  furnace      -  3652 

Another  piece         -         «         -        -  3612 
Black  flag  from  another  hearth  fur-  I  g 

nace  —  ftruck  fire  with  fleel      J  ^^' 

Blafs  glafs  flag      -       -     -      -      -,  3371 

This  may  not  be  an  improper 
place  to  add  a  word  or  two  concern- 
ing the  Derhyjhire  'Toadfioney  which- 
conftitutes  one  of  the  principal  flrata 
in  the  mining  country,*  and  which 
is  fuppofed  to  have  been  in  its  origin 
a  flag  thrown  out  by  a  volcano.  It 
perfedtly  refembles  fome  of  the  fpe- 
cimens,  I  have  feen,  of  one  of  the 
forts  of  the  lava  of  Vefuvius,  not  only 

in- 
*  See  Vol.  II.  p.  2o6r 


C     ^99     ) 

m  the  hardnefs  of  its   texture,  and 

blacknefs  of  its  colour,  but  in  its 
weight ;  a  cubic  foot  of  fome  forts 
of  Derbyihire  toadllone  weighing 
more,  and  of  other  lefs  than  a  cubic 
foot  of  the  Vefuvian  lava,  which  it  - 
refennbles.  The  ftreets  of  London 
have  fome  of  them  been  paved,  of 
late  years,  with  a  toadftone  from  Scot^ 
land,  of  the  fame  nature  as  the  Der- 
byihire toadftone  ;  and  the  ftreets  of 
Naples  have  for  many  centuries  paft^ 
been  paved  with  the  lava  from  Ve- 
fuvius  which  refembles  toadftone^ 
Neither  the  Derbyihire  toadftone, 
nor  that  fort  of  Vefuvian  lava  which 
refembles  it,  feem  to  have  experienced 
in  their  formation  any  great  degree 
of  heat,  they  are  but  in  a  half  vitri- 
fied ftate ;  the  toad-Hone  I  have  fre- 
quently  melted  in  a  fmith's  forge 

inta 


(  300  ) 
into  a  black  glafs,  and  the  Vefuvian 
lava  gives  a  glafs  of  the  fame  kind. 
The  air  has  a  manifeft  adtion  upon 
tlie  Derbyfhire  toadftone,  for  it  not 
only  waftes  away  the  fpar  which  is 
found  in  the  blebs  of  fonfie  forts  of 
toadftone,  but  it  reduces  into  a 
browniih  mouldy  fit  for  vegetation, 
the  moil  hard  and  compad:  forts  i 
the  Vefuvian  lava  is  fubjcdt  to  the 
fam.e  change  from  the  optcration  of 
the  fame  eaufe. 

Weight  of  a  cubic  foot  of 

Avoir.  oXi 

Toadllone  hard  and  free  from  blebs  2884 

Vefuvian  la\'^  refembhng  toadftone  2865 

Iron  flag,   a  greenilh  glafs    -    »    -    -  2843 

Iron  flag,  a  brov^'nilh  glafs   -    -    -    -  2729. 

Iceland  cryflal —-- Mr.  Cotes    -    -    -  2720 

Toadllone,  decaying    -    -    -    -    -    -  2680 

Another  piece --  2662 

Another  piece   -    -    -    ^    -    -    -    -  2558 

ESSAY 


E  S  S  A  Y       IX. 


^OF  SILTERXXTRACXEID    FROM  LEAD, 


WE  have  no  filver  mines,  pro- 
perly fpeaking,  in  Great  Bri- , 
■tain^    but  we  have  plenty  of  lead, 
from  which  filver  is,  in  fome  places, 
.extra6led  with  much  profit.     If  the 
method  of  doing  this  had  been  known 
to  the  2inc\ent  Britons,  it  might  have 
freed  our  country  from  the  reproach 
of  Cicero,  who  tells  his  friend  Jtticus, 
that  there  was  not  a  fc-rupie  of  filver 
2.  in 


(      302       ) 

in  the  whole  ifland ;  *  and  in  another 
place^  he  fays,  that  he  had  heard 
there  was  neither  gold  nor  filver  in 
B7'itain.,  f  The  Romans  had  a  very 
imperfecc  knowledge  of  this  country 
in  the  time  of  Cicero ^  fo  that  his  ac- 
count of  the  matter  may  not,  per- 
haps, deferve  to  be  much  relied  on  ; 
we  are  certain,  at  leail,  that  about 
fifty  or  fixty  years  afterwards,  both 
gold  and  filver  were  reckoned  by 
Strnho  amongft  the  products  of  Bri- 
tain-,%  hence,  if  the  Britons  did  not 
tinderftand  the  art  of  extracting  fil- 
ver from  lead  at  the  firfl  invafion  of 

the 

*  ., —  etiam  illud  jam  cognitum  eft,  ne 
cfae  argenti  fcrupulum  effe  ullum  in  ilia  infula 
(Britann.)  Epifl^adAtt.  L.  IV.  E.  XVII. 

t  Epift.  Fam.  L.  VII.  E.  VII. 

:*:  L.  IV.  p.  305, .--  See  alfo  Tacitus'  Life 
^f  Agricola. 


(     3^3     ) 

the  Romans,  they  foon  learned  it 
from  their  conquerors,  and  this  be- 
comes more  probable,  if  it  be  ad- 
mitted, that  filver  v/as  coined  in  Bri- 
tain in  the  time  oi  Auguftus.^ 

Silver  is  fo  commonly  contained  in 
lead,  that  it  is  eileem^d  a  very  great 
curiofity  to  meet  with  lead  which  is 
entirely  free  from  it:  it  has  even  been 
afTerted,  that  there  is  no  lead  in  the 
world,  except  that  of  Villach  in  Ca- 
rinthia^  which  does  not  contain  fil- 
ver. t 

The  more  ancient  alchemifls,  not 
knowing,  probably,  that  fiiver  was 
fo  generally  contained  in  lead,  and 

yet 

*    Sir  John  Pettiis  Fod  Reg. 

f  II  n'y  point  de  plomb  au  monde,  hor- 
mis  celui  de  Villach  que  ne  contienne  de  V 
argent.  Lehmao  fur  les  Mines,  Vol.  I.  p. 
174.  —See  alio  Philof,  Tranf,  for  1665.  p. 


10* 


(     304     ) 

yet  obferving,  that  lead,  when  treated 
according  to  their  procefTes,  often 
gave  a  portion  of  filver,  were  of 
opinion,  that  they  could  convert  lead 
into  filver.*  This  was  an  eafy  miilake, 
and  if  they  had  obtained  a  portion  of 
gold,  they  would,  no  doiibt,  have 
concluded,  that  they  had  tranfinuted 
the  lead  into  gold ;  fince  there  is  no 
metal,  perhaps,  which  does  not  coii- 
tain  a  fmall  quantity  of  gdld,  or  from 
which  gold  may  not  h^  feparated  hj 
long  calcination. 

Lifler  had  long  ago  obferved,  that 
all  thfC  Englifh  lead  contained  filver; 
and  he  fpeaks  as  having,  by  his  own 
experiments,  proved  the  exiflence  of 
filver  in  the  lead  of  at  leafl  thirty 
difiTerent  mines  3  f  nor  has  any  per- 

fon 

*  GebriChem.  L.  1.  C.  XIX. 

f  Lifler  de  Fontibus,  Cap.  11.  S,  9,  10. 


(  305  ) 
Ion  fince  his  time,  found  lead  wholly 
free  from  filver.  The  Z)^r^jvy^/>d' lead 
has  been  faid  to  contain,  two  grains 
of  filver  in  a  pound  of  lead.  * 
Every  general  obfervation  of  this 
kind  is  liable  to  much  contravention 
from  particular  fafe ;  becaufe  the 
quantity  of  filver  contained  in  lead,, 
is  not  only  different  according  as  the 
lead  is  fluxed  from  the  ore  of  differ- 
ent mines,  but  it  is  very  poflible  in 
an  affay  of  the  ore  of  the  fame  mine,, 
to  meet  with  one  piece  of  ore  which 
Ihall  afford  a  lead  yielding  eight  or 
ten  times  as  much  filver,.  as  another 
piece  would  do<  This  diverfity  arifes 
from  the  ore  itfelf  being  variable  in 
quality  indifferent  parts,  of  the  fame 
mine ;  and  even  different  lumps  of 
ore,  though  contiguous  to  each  other^ 

,   will 
*  Oper.  Min,  Explicata,  p.  263, 

'^ol.  III.  U 


(    3o6    ) 

^ill  often  yield  very  diiferent  quaft^ 
titles  of  filver,  from  the  fame  quan- 
tity of  lead.  This  obfervation  may- 
explain  the  reafon  of  the  very  oppo* 
iite  teflimonies,  which  have  been 
fometlmes  given  in  courts  of  juflice^ 
concerning  the  richnefs  of  a  mine 
from  particular  allays ;.  the  plainriffs 
and  defendants^  where  the  iffue  to 
be  tried  was  the  quantity  of  filver^ 
having  been  fevcrally  interefted  in 
getting  the  beft  and  the  worfl  pieces 
of  ore  aifayed,  in  order  to  fupport 
their  refpedive  claims.  There  was  a 
notable  ini^ance  of  this  with  refped: 
to  the  lead  mine  of  EJi-kyr-kyr  in 
Cardigar/JIjirey  which  was  dlfcovered 
in  1690.  The  law  at  that  time  ad- 
judged every  mine  to  be  a  royal  mine 
the  metal  of  which  contained  enough 
of  gold  or  filver  to  compenfate  the 

charges 


C   307    ) 

charges  of  refining,  and  the  lofs  of 
the  bafer  metal  in  which  they  were 
contained.  In  confequence  of  this 
law  the  patentees  of  royal  mines 
laid  claim  to  the  mine  of  EJi-kyr-kyr 
which  was  rich  in  fllver,  and  they 
produced  proof  in  Weftmtnfter-hallj 
thai  the  lead  of  that  mine  contained 
to  the  value  of  (ixty  pounds  of  iilver 
in  every  ton,  whilil  the  proprietor, 
produced  proof  that  it  only  contain- 
ed to  the  value  of  four  pounds  of 
Iilver  in  a  ton.  * ' 

I  have  been  informed  by  an  in- 
telligent perfon,   that  there  are  fome 
lead  ores  in  Great  Britain^  which,  . 
though  very   poor  in  lead,  contain  ' 
between   three    and   four    hundred' 
ounces  of  filver  in  a  ton  of  the  lead. 
It  is  not  to  be  expeded  that  the  pro-  - 

prietors  > 
*  Some  Account  of  Mines,  p.  27. 
U   2 


C  3oS  ) 
pEietors  of  thefe^  or  of  any  othsr 
mines  rich  in  iilver^  Ihould  be  for- 
ward  in  declaring,  to  the  world  the 
quantity  of  lilver  which  they  con- 
tain. The  proprietor  indeed  of  a 
lead  mine  containing  filver,  may 
work  the  fame^  without  any  appre- 
henlion  of  its. being  taken  from  him^ 
under  the  pretence  of  its  being  a 
royal  mins;  yet  the  crown^  and  pep- 
fons  claiming  under  it,  have  the  right 
of  pre-emption,  of  all  the  ore  which 
may  be  raifed.  There  was  an  adt  of 
parliam.ent  paiTed  in  the  fixth  year 
of  JVilliam  and  Mary^  intitJed,— An 
adt  to  prevent  difputes  and  contro- 
verfies  concerning  royal  mines. — 
This  ad:  gave  great  quiet  to  the  ful> 
ied  by  declaring,  that  every  propri- 
etor of  a  mine  of  copper,  tin,  iron^ 
or  leadj^  Ihould  continue  in  pofleffion 

of 


(    309     ) 

of  the  faid  mine,  notwithflanding  its 

being  claimed  as  a  royal  mine,  from 
its  containing  gold  or  filver :  but  it 
.further  enadted,  that  their  majeflies, 
their  heirs  and  fucceffors,  and  all 
claiming  under  them,  fhould  have 
the  privilege  of  purcliaiing  all  the 
ore  whicii  fhould  be  raifed  out  of 
fuch  a  mine,  at  the  following  prices; 
this  is  to  fay,  paying  for  all  ore 
wafhed,  made  clean  and  merchant- 
able, wherein  is  copper,  after  the 
rate  of  fixteen  pounds  a  ton  ;  for  tin 
ore  (except  that  raifed  in  Devonlhire 
and  Cornwall)  forty  fhillings;  for 
iron  ore  forty  fhillings  ;  and  for  lead 
ore  nine  pounds  a  ton.  This  ftand- 
ard  price  of  nine  pounds  a  ton  for 
lead  ore  was,  at  the  time  it  was  fix- 
ed, much  higher  than  the  ordinary 
price  of  ore^  ^n  which  there  was  no 
u  3  filver 


(     310     ) 

filver  worth   extradlng ;    the   beft 
kind  of  Derbyfhire  lead  ore,  being 
at  prefent,  generally  worth  no  more 
than  feven  pounds  a  ton.     It  may 
deferve  however  the  coniideration  of 
the  legiilature,  whether  the  elaufe  in 
the  forementioned  at3:  refped:ing  the 
right  of  pre-emption  ihould  not  be 
wholly  repealed;   as  there  may  be 
many  lead   mines  in  England  very 
rich  in  filver,  but  which,  on  account 
of  the  difficulty  of  working  them., 
cannot.be  entered  upon  with  advan- 
tage, whilft  this  right  fubfifts.     At 
many  lead  mines,  moreover,  there 
are  large,  quantities  of  fteel-grained 
ore  raifed  together  with  the  ordinary 
fort,  now  it  generally  happens  that 
the  fteel-grained  ore  is  much  richer 
in  filver  than  the  ordinary  diced  ore 
-of  Derbyfhire  ;  and  it  might,  if  fepa- 

ratcd 


(    311     ) 

rated  from  the  reft,  be  worked  for 
filver ;  but  whether  from  an  appre- 
-henfion  of  the  operation  of  the  claufe 
we  are  fpeaking  of,  or  from  mere 
ignorance  or  inattention,"  all  the 
forts  of  ore  are  mixed  and  fmelted 
together. 

Silver  has  formerly  been  cxtradted 
from  lead  in  a  great  many  places  ia 
this  iiland.  In  the  reign  of  Edward 
I.  near  1600  pounds  weight  was  ob- 
tained, in  the  courfe  of  three  years, 
from  a  mine  in  Devon/bire,  which  had 
been  difcovered  towards  the  begin- 
ning of  his  reign ;  this  mine  is  called 
a  lilver  mine  by  the  old  writers,  but 
it  appears  to  have  been  a  mine  of 
lead  which  contained  lilver.*     The 

lead 

*  Hollingfhed's  Chron.   Vol.  II.  p.  316. 

See  alfo  in  the  fame  author  a  further  account 

of 
XJ  4 


lead  mimes  in  Cardiganjhire  have  at 

different     periods     afforded      great 

quantities  of  filver  :   Sir  Hugh  Mid- 

4leton  is  faid  to  have  cleared  from 

them     two     thoufand     pounds     a 

month,  '^  and  to  have  been  enabled 

thereby  to  undertake  the  great  work 

of  bringing  the  new  river  from  Ware 

to  London  ;  and  in  allufion,  probably, 

to  thefe  two  great  circumftances  of 

his  life,  there  are  painted  upon  fome 

of  his  piiftures  the  two  termS'—fonfes 

— -fodin^,     Thefe  fame  mines  yield- 

^d^  in  the  time  of  the  great  rebellion, 

eighty  ounces  of  iilver  out  of  every 

ton  of  lead,   and  part  of  the  king's 

:army  was  paid  with  this  Iilver,  which 

was 
loF  filver  extraded  from  the  lead  in  Devonfhire 
•and*  Corn vvali  'in  the  time  of  Edward  I'll.  p« 

^13. 

*  .Oper,  Min.  explic.  p.  245. 


(     313    ) 

ivas  minted  at  Shrewjhury*  -f-  A  minit 
for  the  coinage  of  Welch  filver  had 
before  that  time  been  eftabliihed  in 
i6'^y  at  AheryftwHh\  the  indenture 
was  granted  to  "Thomas  Bujhel  for  the 
coining  of  half-crowns,  Ihillings, 
fix-pences,  two-pences,  and  pennies, 
and  the  monies  were  to  be  ftamped 
with  the  oftrich  feathers  on  both 
fides*.  In  the  year  1604  near  three 
thoufand  ounces  of  this  Welch  bul- 
lion were  minted,  at  one  time,  at  the 
tower  if.  Wehfter  in  his  hiftory  of 
metals,  publiihed  in  1671,  makes 
mention,  from  his  own  knowledge, 
of  two  places  in  Craven^  m  the  weft- 
riding  of  Torkjhhe,  where  formerly 
good  filver  ore  (lead  ore  abounding 

ia 

-f-  Sir  J.  Pettus,  Effay  on  Metal.  Works, 
*  Rym.  Faed.  Tom.  XX.  164. 
%  Some  Account  of  iviiues.  p.  6. 


(    3H    ) 

in  filver)  had  been  gotten.    One  .of 

the  places  was  Brunghill  moor  in  the 
pariih  of  iS/^/W^«r;/,  the  ore  of  which 
held  about  the  value  of  fixty^feven 
pounds  of  filver  in  a  ton :  the  other 
was  Skelkorn  field  within  the  townlhip 
oi  Rimmington  in  the  parilh  of  Gif- 
hum  I  it  had  formerly  belonged  to 
one  Pudfey^  who  is  fuppofed  to  have 
coined  the  filver  he  got  out  of-  his 
mine,  there  being  many  ihillings 
in  that  country  which  the  common 
people  called  Pudfey 'schillings.* 

There  is  not  at  prefent  any  place 
in  Derhyjhire  where  filver  is  extradled 
from  lead.  A  work  of  this  kind 
was  eftabliihed  a  few  years  ago  not 
far  from  Matlock^  and  the  lead  yield- 
ed fourteen  ounces  of  filver  from  a 
ton;  but  the  mine  which  afforded 

the 
f  Webfler's  Metal,  ^lu 


(    3^5    ) 

the  ore  was  foon  exliaufted,  or  be- 
came too  difficult  to  be  worked  with 
profit.      There  is   a   lead  mine  in 
Patierdale  ne^v  Kefwick^  which  yields 
between  fifty  and  fixty  ounces  of  fil- 
ver  from  a  ton  of  the  lead,  the  ore  of 
this  mine  is  reckoned  to  be  poor  in 
lead;  and  indeed  it  is  very  common- 
ly obfervedj  that  the    pooreft  lead 
ores  yield  the  moft  ftlver,    fo  that 
much   filver     is    probably    thrown 
away,  for  want  of  having  the  ores 
of  the  pooreft  fort  properly  affayed. 
The  quantity  of  lead  fmelted  an- 
nually in  Derbyfhire,  may  be  efti*^ 
mated  at  7500  tons  upon  an  average,; 
fifty  years  ago  the  average  was,  pro- 
bably   1 0000   tons  a  year,  but  we 
put  it  high  enough  in  fuppoiing  it, 
at  prefent,  to  amount  to  7500  tons : 
I  have  never  been  able  to  get  any 
I  proper 


(    31^    ) 

iproper  information,   concerning  the 

quantity  of  lead  annually  fmelted  in 
other  parts  of  Great  Britain,  but  for 
the   illuftration   of  the  fubjedt   we 
are  upon,  let  us  fuppofe  that  in  the 
whole  kingdom  30000  tons  of  lead 
are  annually  fmelted,  and  that  at  a 
medium   each    ton    of  lead  would 
yield  12  ounces  of  filver  ;  then  would 
there  be,  if  all  the  lead  was  refined, 
a   faving  of  three  ounces  of  filver 
from  each  ton  of  lead,  or  ninety  thou- 
fand  ounces  in  the  whole  ;  our  Eng- 
lifh  workmen  reckoning   that  nine 
ounces  of  filver  are  full   adequate 
to  the  expence  of  refining  a  ton  of 
lead,    added   to   that    of   the   lead 
which  is  loft  during  the  operation. 
^    The  general  manner  of  extrading 
lilver  from  lead  is  every  where  the 
fame ;   it  is  very  fimple,  depending 

upon 


C   317    )  ^ 

upon  the  different  effential   proper- 
ties of  the  two   metals. — It   is   an^ 
effential    property     of   lead,    when 
melted  in  the  open  air^  to>  lofe  its 
metallic    appearance,   and   to-  burn 
away  into    a  kind  of  earth.-— It  is- 
an  effential  property  of  filver  not  to:^ 
burn  away,  or  to  lofe  its  metallic  ap-- 
pearance  when  expofed  to  the  adtion 
of  the  ftrongeft  fires,  in  the  open  air.. 
Hence,,  when  a  mafs  of  metal  con- 
fining of  lead  and  filver,  is  melted^ 
in    the- open    air,   the  lead  will  be 
burned  to   afhes,  and  the  filver  re- 
maining unaltered,    it  is  eafy  to  un- 
derftand  how  the  filver  may  be  es- 
tradted  from  the  lead;  for  being  hea- 
vier than  the  afhes  of  the  lead,  and 
incapable    of  mixing    with    them,, 
(fince  no  metal  is  mifcible  with  an 
earth),  it  will  fmk  to  the  bottom  of 

tha: 


(    3^8    ) 

the  veffel  in  which  the  mafs  is  melt- 
ed. Iron,  tin,  and  copper,  refera- 
ble lead,  in  being  convertible  into 
a  kind  of  aihes,  when  t  xpofed  to  the 
adtion  of  air  and  fire,,  and  gold  re- 
fembles  filver  in  not  undergoing  any 
change  from  fueh  adlion  ;  hence  ei- 
ther gold  or  filver,  or  a  mafs  con- 
lifting  of  both,  may  be  purified  from 
any  or  all  of  thefe  metals  by  the 
mere  operation  of  fufion  ; .  for  thefe 
metals  will  rife  to  the  top  of  the 
vefFel,  in  which  the  fufion  is  made, 
in  the  form  of  an  earth  or  drofs,  leav- 
ing the  gold  or  filver  pure  at  the 
bottom. 

The  ancients  certainly  knew  that 
filver  could  be  purified  from  the 
bafe  metals  by  the  force  of  fire.— 
^e  houfe  of  IJrael  is  to  me  become 
drojs :  all  they  are  hrqfsy  (copjier)  and 

titiy 


(    319    ) 

tiHy  and  iron^  and  lead^  in  the  tnidfl  of 
the  furnace ;  they  are  even  the  drofs  of 
filver:-^  And  as  we  read  of  filver 
being  purified  feven  times  in  a  fur- 
nace of  earth,  "i-  it  may,  perhaps,  jbe 
inferred,  that  the  method  of  refining 
filver  which  was  then  in  ufe,  con» 
fifled  in  reducing  the  bafe  metals 
into  earth,  by  a  repetition  of  the 
procefs  of  fufion.  This  inference^, 
it  mufl  be  owned,  is  rendered  doubt- 
ful by  a  paffage  in  Jeremiah  \—the 
lellows  are  burned i  the  lead  is  confumed 
of  the  fir  e^  the  founder  melteth  in  vain.^ 
— This  paffage  is  fomewhat  ambi- 
guous, and  interpreters  tranfiate  the 
original  Hebrew  differently,  buc 
inoil  of  them  coHed:  from  it,  that  the 

founder 

*  Ezek.  xxii.  i8.  f  Pf,  xii.  6, 

%  Jerem.  vi.  2^ 


C       ?20       ) 

founder  added  lead    to  the  mixetf 
mafs  which  he  wanted  to  refine.. 

Lead,  when  reduced  to  an  eartk 
by  being^  burned  in  the  open  air^ 
may,  in  a  ftronger  degree  of  heat, 
be  converted  into  a  yellowilh  glafs,  * 

which 

*  Other  metallic  fubftances  yield  coloured 
glafles,  either  when  vitrified  alone,  or  in- 
conjundion  with  pure  glafs.  In  enamel  and 
china  painting  they  prepare  rofe  red  and 
purple  colours  from  gold ;  fcarlet  reds  from 
iron,  or  vitriols  that  partake  of  it ;  greens 
from  copper ;  blues  from  cobalt ;  blacks 
from  magnefia,  zafTer,  and  fcales  of  iron  ;  yel- 
lows from  filver  antimony,  Naples  yellow, 
and  crocus  martis  j  white  from  tin.  Tb^ 
fame  fubftance  yields  different  colours,  ac- 
cording to  the  degree  of  heat  to  which  it  is 
expofed ;  thus,  the  green  colour  of  common 
glafs  bottles,  which  proceeds  from  the  iron, 
contained  in  the  fand  and  vegetable  alhes 
from  which  the  glafs  is  made,  is  changed, 
into  a  blue  by  a  Wronger  degree  of  heat. 


C    321    ) 

•which  has  the  property  of  greatly 
contributing  to  the  eafy  vitrification 
of  all  earthy  fubftances ;  hence, 
when  gold  or  filver  are  mixed  with 
iron,  copper,  or  tin,  it  is  ufual  to 
add  to  the  mixed  mafs  a  quantity  of 
lead,  in  order  to  accelerate  the  purifi- 
cation; for  the  lead  will  be  converted 
into  glafs,  and  this  glafs  will  vitrify 
all  the  extraneous  fubftances  with 
which  the  gold  or  filver  are  polluted, 
v/ithout  exerting  the  leaft  adion  upon 
the  precious  metals  themfelves. 

I  do  not  know  upon  what  grounds 
one  of  the  moft  diftinguifhed  cho- 
mifts  of  the  age  has  afferted,  '^  that 
the  refining  of  gold  and  filver  mere- 
ly by  the  adion  of  the  fire  was  the 
only  method  anciently  known  ;  "  f 

and 

>t  Chem.  Did.    by  M.  Macquer.    artic. 
Refining. 

VOL.  irr.  X 


(        0^2       ) 

and  that  the  doing  it  by  the  addition 
of.  lead,  is  a  difcovery  with  which 
the  ancients  were  unacquainted. 
Not  to  inlift  upon  what  has  been 
quoted  from  Jeremiah  -,  in  Diodorus 
Skulus  there  is  a  very  minute  de- 
scription of  the  m.anner  of  working 
fome  gold  mines  in  the  confines  of 
Egypt  and  Arabia  \  this  defcription 
was  probably  written  on  the  fpot 
¥/hen  he  vlfitcd  that  country,  but 
the  mode  of  operation  feems  to  have 
been  derived  from  a  more  early  pe- 
riod 5  as  the  difcovery  of  the  mines  is 
attributed  by  him  to  fome  of  the  moft 
ancient  JEgyftian  kings  ;  amongft 
other  particularities,  he  takes  notice 
of  their  melting  the  mineral  in  con- 
jun6lion  with  a  little  tin,  fome  fmall 
portion  of  fait,  and  a  lump  of  lead,  *. 

Strabo 
•  Diod,  Sic.  Lib,  HI.  p.  183 — ^^189, 


C     3^5    ) 
Straho  quotes  Poly  bins  as  fpeaking  of 
•a  filver  ore,  which,  after  being  five 
times  waihed,  was  melted  with  lead^, 
and  became  pure  filver.     Unfortu- 
nately this  part  of  the  works  of  Po- 
lybius  is  loft,  or  we  might  have  had 
a  more  circumftantial  knowledge  of 
the  proceffes  by  which  the  ancients 
extraded   filver   from   its  ores,    as 
Strabo  fays,   that  he  omitted  Poly- 
bius^  account  of  this  matter,  becaufe 
of  its  prolixity,  f     PJiny  probably 
has  an  allufion  tx)  the  ufe  of  lead  in 
refining  filver,  when  he  fays,  that  a 
filver  ore  in  the  form  of  an  earth 
could  not  be  melted  except  in  con- 
jun6lion  with  lead  or  the  ore  of  lead.* 
a  more  diligent  fearch  into  the  writ- 
tings  of  the  ancients,  would,  doubt- 

lefs, 
f   Strab.  Geo.  Lib.  II.  p,  221, 
*  Plin,  Hifl,  Nat.  Lib,  XXXIIL  C.  VI. 
X  2 


(     3^4     ) 

lefs,  jfurniili  more  authorities  upon 
the  pointy  but  thefe  may  be  fuffi- 
cient  to  induce  us  to  believe^  that 
they.were  not  unacquainted  with  the 
ufe  of  lead  in  refining  gold  and  fil- 
ver. — But  to  return  to  the  manner 
of  extracting  filver  from  lead. 

The  veiTel  in  which  the  work- 
men melt  the  mafs  of  filver  and  lead 
is.  of  a  fhallow  form,  that  a  large  fur- 
face  of  the  melted  mafs  may  be  ex- 
pofed  to  the  air,  it  is  made  ufually  of 
four  meafures  of  the  ajQies  of  calcined 
^bones,  and  of  one  meafure  of  un- 
i^^afh.ed  fern  afhes,  and  is  called  a 
4eft-.^     This  vefTel  is  very  porous^ 

but 

*  Tefts  are  fometimes  made  of  clay  and 
other  materials,  and  tnetaliurgic  writers  of- 
ten order  the  wood  afhes  to  be  wafhed,  left 
the  alkaline  falts  which  they  contain  fhould 
.tend  -to  nitrify  the  tefl  j  but  a  very  good  re- 
finer 


C    J^5    ) 

but  not  fo  much  as   to  imbibe  the 
metal,  whilft  it  continues  in  the  form 
of  a  metal  -,   but  as  the  earth,  into 
which  the  lead  is  foon  reduced  by 
the  adlon  of  the  fire,  becomes  melt- 
ed,  the  tefl  imbibes  a  portion  of  it 
in  that  liquid  ftate,    the  other  por- 
tion is  driven  off  (as  cream  is  blown 
off  from  mxilk)  from  the  furface  of 
the  melted  mafs,   by  the  blaft  of  a. 
bellows.    The  liquid,  half  vitrified^, 
earth  of  lead,  which  is  thus  driven, 
off,  concretes  into  hard,  maffes  of  a- 
fcaly  texture,   and  is  called  in  that 
flate  litharge,  or  filver  ftone,^  from, 
the  manner  of  its  being  produced,, 
or  from  an  idle  notion  of  its   con- 


taining 


finer  at  Holywell  informed  me,  that  he  al- 
ways ufed  the  aflies  without  wafhing  them, 
as  the  velTel  became  thereby  lefs  apt  to  crum- 
ble into  pieces-. 

X  3 


(      J26       ) 

faining  much  filver.  The  litharge 
which  is  nril  fomned  is  whitiih,  that 
which  experiences  a  greater  degree 
of  heat  is  red  3  the  colour  of  the 
litharge  is  aifo  influenced  by  that  of 
the  other  metals;,  v/hich  may  chance 
to  be  mixed  with  the  mafs  of  lead 
and  iilver.  When  the  furface  of  the 
melted  mafs  becomes  white,  and 
throws  up  no  more  litharge,  the  ope- 
ration is  finiilied;  but  as  the  re- 
maining filver  is  not  quite  pure,. 
fmce  it  contains  a  fmall  portion  of 
lead,  from  whicli  the  degree  of  heat 
re  qui  free  fljr  melting  the  mixed  m.afs 
cannot  readily  fi^ee  it^  it  is  taken  to  a 
refining  furnace,  and  r'endered  quite 
pure,  at  leafl  fi-om  lead,  by  cup  ell  a- 
tion.  This  procefs  confiils  in  miclt- 
ing.  the  iilver  obtained  from  the  firft 
operation^  in  a  vefTel  made  of  the 

fame 


(     3^7     ) 

fame  materials  as  the  teft,  and  which, 
from  its  refemblance  to  a  wide 
mouthed  cup^  has  been  called  a 
cupel.  The  cupel  being  expofed  to 
a  ilronger  heat  than  the  tefl:,  the  lead 
which  had  efcaped  the  a6lion  of  the 
fire  on  the  tell,  is  now  driven  out 
from  the  filver,  and  being  converted 
into  litharge,  is  abforbed  by  the  cu- 
pel, and  by  this  means  the  filver'is 
purified  from  every  mictal  except  gold; 
for  it  is  not  neceffary,  on  this  occa- 
fion,  to  remark,  that  a  minute  por- 
tion of  copper,  when  there  happens 
to  be  any  in  a  mafs  of  filver  and 
lead,  probably  efcapes  the  a6lion  of 
the  fire  in  cupelling  gold  or  filver. 

There  are  feveral  fmelting  houfes 
at  Holywell  in  Flintjhirej  where  filver 
is  extraded  from  leads  Mr.  Fenncnt^ 

has 

*   Tour  through  Wales. 

X4 


(     3^8     ) 

has  given  the  following  account  of 
the"  quantity  of  filver  extra6t€d  at 
one  of  the  largeft  of  thefe  houfes  in 
the  courfe  of  fix  years. 

ounces.  ounces. 

Year  1754  -  12160    Year  1774  -  5693 
3755  -     1276  1775  -  6704 

^756  -     7341  1776  -  4347 

The  filver  obtained  from  lead  at 
Holywellj  is  chiefly  fold  to  the  ma- 
nufadurers  at  Birmingham  and  Shef- 
field, Much  filver  is  alfo  extradled 
from  lead  in  Northutnherland. 

At  Holywell  they  ufually  work  off 
three  tons  of  lead  at  one  operation, 
the  quantity  of  filver  which  they 
procure^  is  variable  according' to  the 
richnefs  of  the  leadj  a  few  years 
ago  they  were  refining  lead  from  an 
ore  found  in  the  Ifle  of  Man^  and  it 
gave  them  about  60  ounces  at  every 

ope- 


(     3^9    ) 

operation,  or  20  ounces  in  a  ton  of 
the  lead..  The  litharge  ordinarily 
obtained  from  three  tons  of  lead 
amounts  to  58  hundred  weight;  this 
litharge  may  either  be  changed  into 
red  lead  by  calcination,  or  it  may  be 
reduced  into  lead  again  by  being 
fluxed  with  charcoal,  or  any  other 
m.atter  containing,  the  inflammable 
principle  ;  *  but  when  it  is  reduced 
they  feldom  obtain  more  than  52 
hundred  weight  of  lead,  f  fo  that  by 

ex- 

*  Lead  from  litharge  is,  generally  fpeak- 
ing,  worth  five  fhillings  a  ton  more  than  ore 
lead,  as  the  plumbers  elleem  it  fofter  and 
litter  for  making  fheet  lead;  yet  the  litharge 
lead  from  the  ore  of  the  Ifle  of  Man  here 
mentioned,  was  found  quite  unfit  for  making 
fheet  lead,  on  account,  probably,  of  the  ore 
having  held  other  metals  belides  iilver  and 
lead. 

f  In  the  foreign  works  they  eflimate  the 
lofs  of  weight,  which  the  litharge  fuflains  in 

being: 


(     SS'^     ) 
extradling  the  filver^   there  is  a  lois 

of  eight  hundred  weight  in  three 
tons  of  lead.  It  has  been  faid  that 
the  Dutch  can  extradl:  the  filverfrom 
three  tons  of  lead>  and  not  lofe  above 
G.ii-  hundred  weight  *  upon  convert- 
ing the  litharge  into  lead,  and  that 
this  fuperior  fkill, :  aided,  probably, 
by  their  fuperior  induflry,  enabled 
them  to  purchafe  our  lead,  and  to 
extra 61  the  filver  from  fuch  as  could 
not  be  refined  here  with  advantage  : 
I  have  been  informed^  however,  by 
an  experienced  refiner  in  Derbyfhire, 
that  he  could  extract  the  fdver  with- 
out ioling  quite  fo  much  as  fix  hun- 

being  reduced  into  lead,  at  a  lixth  part  of  the 
weight  of  the  litharge,  or  9I  hundred  weight 
from  53  hundredweight  of  litharge.     Ellais 
des  Mines,   Tom.  II.  p.  401. 
*  Webller's  Metal,  p.  233. 

I  dred 


C   331    ) 

drcd  weight  in  three  tons  of  lead;  I 
make  no  queftion  that  the  lofs  de- 
pends, in  fome  meafure,  on  the  qua- 
lity of  the  lead.  It  has  been  re- 
marked before,  that  lead,  which  does 
not  contain  nine  ounces  of  filver  in 
a  ton,  is  not  thought  v/orth  the  re- 
fining ;  the  fmailefi:  quantity  which 
can  be  extradbed  .with  profit,  m^uil 
depend  much  upon  the  price  of  lead, 
all  expences  attending  the  feveral 
proceiTes  being  the  fame.  For  eight 
hundred  weight  of  lead,  which  may 
be  aiTumed  at  a  medium  as  the  lofs 
fuftained  during  the  operations  of 
refining  and  reducing^  is  worth  6L 
when  lead  is  at  15I.  a  ton,  and  it  is 
worth  only  4L  16s.  when  it  is  at 
12I.  a  ton.  The  value  of  27  ounces 
of  filver,  which  we  fuppofe  to  be  the 
quantity  feparable  from  three  tons 

of 


C    3J2     3 

of  lead,   is  7I.  los.  9d.  at  5s.  yd. 

an  ounce;  hence^  the  difference  be- 
tween the  value  of  the  filver  obtain- 
ed, and  that  of  the  lead  loft,  would, 
when  lead  is  at  15I.  a  ton,  be 
il.  I  OS.  9d.  and  when  lead  is  as  low 
as  12I.  a  ton,  it  would  amount  to 
al.  14s.  pd.  In  the  times  of  Sir 
John  FettuSy  the  ufual  allowance  for 
wafte  in  refining  and  reducing  of 
lead,  was  three  hundred  weight  in  a 
ton,  or  nine  hundred  weight  in  three 
tons,,  and  the  lead  was  valued  at 
12I.  a  ton,*  fo  that  lead  has  altered 
very  little  in  its  price  in  the  courfe 
of  above  one  hundred  years. 

Silver  is  here  valued  at  5s.  yd. 
an  ounce;  this  requires  fome  ex- 
planation. A  pound  of  fiandard 
filver   in   England,    confifts   of  i.i 

ounces 

*  Fodinae  Reg.  p.  10, 


(  333  ) 
•ounces  and  2  penny weigb-ts  ^i  fine 
filver,  and  of  18  pennyweights  of 
copper  \  in  other  words,  every  mafs 
of  ftandard  filver  confiiling  of  40 
parts  by  weight,  is  compofed  of  37 
parts  of  fine  filver,  and  of  3.  parts  of 
copper ;  the  copper  is  called  the  al- 
loy. All  nations  ufe  fome  alloy  both 
in  their  gold  and  lilver ;  partly  with 
a  view  of  rendering  thefe  metals 
harder,  -and  partly  becaufe  it  would 
require  much  labour  and  expence  to 
free  them  wholly  from  that  fmall 
portidh  of  copper,  which,  in  their 
ordinary  flate,  as  fluxed  from  their 
ores,  they  are  generally  found .  to 
contain. .  A  pound  of  ftandard  {A^^v 
is  coined  into  62  fhillings,  hence  the 
Mint  price  of  an  ounce  oi. ftandard 
filver  would  be  a  twelfth  part  of  62 
Ihillings,   or  55.  izd.     From  hence 

. '      it 


(  334  ) 
it  might  be  lliev/n,  by  the  rule  of 
proportion,  that  the -^z/?ri^^/  price  of 
an  ounce  of  fine  filver,  which  con- 
tains no  copper,  will  be  5s.  yd.  at 
the  lead.  The  market  price  of  fil- 
ler bullion  does  not  wholly  depend 
on  the  mint  price^  it  can  never  be 
lower  than  that,  but,  from  the  ope* 
ration  of  various  caufes,  it  may  ex- 
ceed it.  •\— -Standard  gold  with  us 
confifts  of  1 1  parts  o^  fine  gold,  and 
.of  I  part  of  copper^  or  of  a  mixture 
of  filver  and  copper  -,  and  a  pound 
or  12  ounces  of  Handard  gold,  is 
^coined  into  44I  guineas  3  hence  the 
price  of  an  ounce  of  ftandard  gold  is 
^1.  17s.  lofd.  and  the  prke  of  an 
ounce  Q^ fine  gold  is  4I.  4s.  iijd. 
Foreign  gold  trinkets  llain  the 
liand^  more>  and  have  a  more  cop- 
pery 
f  EfTay  on  Money  and  Coins,  p.  2.  &  55, 


(     33S     ) 
pcry  look  than  Englilli  ones;    and 

in  fa6t  they  are  made  of  gold  which 
is  alloyed  with  a  much  greater  pro- 
portion of  copper,  than  the.ftand- 
ard  gold  of  England ;  yet,  when  an 
enamel  is  to  be  fixed  on  gold,  one 
of  the  mofb  experienced  of  the  fo~ 
reign  enameilers,  f  recommends  the 
•ufe  of  gold,  which  has  the  fame  al- 
>loy  as  the  Englijfh  ftandard  gold,  or 
two  parts  alloy,  and  twenty-two 
parts  of  fine  gold. 

Copper  communicates  a  fmell 
both  to  gold  and  filver.  Tht  Ro- 
.man  fpecula,^  which  they  ufed  as  look- 
ing glaffes,  in  Fltny^.%  time  wer^ 
commonly  made  of  filver,  but  the 
fdver  was  alloyed  with  much  cop- 
per; for  we  find  a  cunning  waiting 
.maid  in  Plautus  advifing  her  mif- 

trefs 

.f  M.  de  Montamyj  Traite  des  CoLeurao 


i    S36    ) 

tre{s  to  wipe  her  fingers  after  hav- 
ing handled  a  fpeculum^,  left  her 
paramour  from  the  fmell  of  her 
fingers  fhould  fufpedt  her  of  having 
received  filver  from  fome  other 
lover. 

Ut  fpeculum  tenuifli,  metuo  ne  oleant  argene 

turn  manus. 
Ne  ufque  argentum   te  accepifle  fufpicetur 

Philolacles.  * 

*  Plant,  Mofl.  Aa.  I. 


ESSAY 


ESSAY      X. 


OF    RED    AND    WHITE    LEAD, 


IF  the  reader  does  not  know  what 
minium  or  red  lead  is,  I  v/ould 
wifh  him  to  fend  for  a  few  ounces 
of  it  to  his  painter  or  apothecary. — 
Suppofing  him  to  have  a  parcel  of 
••ed  lead  before  his  eyes,  the  firft 
tning  which  will  fl-rike  him  is  its  vi- 
vid colour  .verging  a  little  towards 
oranges  if  he  crumbles  it  betwceu 
VOL.  III.  Y  b.i^ 


(    33^     )   _ 
his  fingers,  he  will  find  it  to  be  an 

almoft  inapalpable  powder ;  if  he 
poizes  it  in  his  hand,  he  will  per- 
ceive it  to  be  much  heavier  than 
either  brick  dufl  or  red  ochre, 
with  which  fubftances  it  is  fomc- 
times  adulterated ;  if  he  compares 
it  with  a  piece  of  lead,  he  will  be 
aftonifhed  how  it  can  be  either  pro- 
duced from  lead,  or  be  capable  of 
being,  by  a  very  flight  operation^ 
reduced  into  lead  again. 

It  has  been  mentioned  in  the  pre- 
ceding EfTay,  that  red  lead  is  made 
from  litharge  at  Holywell :  this  red 
lead  which  is  made  from  litharge  is 
not  perhaps,  in  all  its  properties,  of 
quite  the  fame  kind  with  that  which 
is  made  diredly  from  lead;  at  leaft 
I  have  been  informed,  that  the  mak- 
ers cf  flint  dafs,  who  ufe  much  red 

lead 


(     339    ) 

lead  in  the  compofition  of  that  glafs, 
are  of  opinion,  that  the  litharge  red 
lead  does  not  flux  fo  well  as  that 
which  is  made  from  the  dired  calci- 
nation of  lead,  as  is  praftifed  in 
Derhyjhire,  There  are  in  that  county 
nine  red  lead  mills  or  furnaces,  all 
of  which  are  much  upon  the  fame 
conflru6lion. 

The  furnace  is  very  like  a  baker's 
oven,  its  vaulted  roof  is  not  at  a  great 
diilance  from  the  bottom  or  floor,  on 
each  fide  of  the  furnace  there  are 
two  party  v/alls,  rifing  from  the 
floor  of  the  furnace,  but  not.  reach- 
ing to  the  roof;  into  the  intervals 
between  thefe  walls  and  the  fides  of 
the  furnace  the  pit- coal  is  put,  the 
flame  of  which  being  drawn  over 
the  party  walls  and  firiking  upon 
the  roof,  is  from  thence  refleded 
y  2  down 


(  340  ) 
down  upon  the  lead,  which  is  placed 
in  a  cavity  at  the  bottom,  by  which 
means  the  lead  is  foon  melted.  The 
furface  of  melted  lead,  when  expofed 
to  the  open  air,  inilantly  becomes 
covered  with  a  dufky  pellicle  ;  and 
this  pellicle  being  removed  another 
is  formed,  and  thus  by  removing  the 
pellicle,  as  faft  as  it  forms,  the  great- 
c^  part  of  the  lead  is  changed  into 
a  yellowifh  green  powder.  This 
yeilowifh  powder  is  then  ground  ve- 
ry fine  in  a  mill,  and  being  wafhed, 
in  order  to  feparate  it  from  fuch  parts 
of  the  lead  as  are  ftill  in  their  m,e- 
tallic  ftate,  it  becornes  of  an  uni- 
form yellow  colour,  and,  when  it  is 
dried  to  a  proper  confiftency,  it  is 
thrown  back  again  into  the  furnace, 
and  being  conftantly  llirred,  fo  that 
all  its  parts  may  be  expofed  to  the 

adlion 


(     34t      ) 

adlion  of  the  flame  of  the  pit  coal, 
in  about  48  hours  it  becomes  red 
leady    and  is  taken  out  for  ufe. 

The  colour  of  the  red  lead  admits 
fome  variety,  which  is  occafioned  by 
the  different  degrees  of  heat.  If 
the  heat  is  too  fmall,  inftead  of  red 
it  is  yellow  or  orange  coloured  j  if  it 
is  too  great  the  red  colour  is  changed 
into  a  dirty  white,  between  thefe  tv/o 
extremes  it  is  fubjed  to  fome  diver- 
fity  of  fhades  of  red,  which  cannot 
well  be  noticed  or  defcribed,  except 
by  thofe  who  are  engaged  in  the 
making  of  it. 

It  has  been  alTerted,  that  the  re- 
verberation of  the  flame  and  fmoke 
upon  the  furface  of  the  lead,  is  not 
&    a  neceflary  circumftance  in  giving  it 
■jka  red  colour,*  but  that  it  will  ac- 

i 


quire 
*  Infllt,  de  Chym.  par  M.Demachy,  p.  522, 
Y  3 


(  M^  ) 
quire  t!iis  colour  by  a  long  calci- 
nation without  coming  into  contact 
with  the  flame-  The  truth  of  this 
-afiertion  I  think  may  be  doubted.  I 
have  more  than  once  calcined  lead 
for  above  60  hours^  without  fuffer- 
ing  the  flame  of  the  fire  to  touch  it 
during  any  part  of  the  procefs,  but 
by  this  method  I  could  never  obtain 
any  thing  better  than  a  dirty  red, 
refem.bling  the  red  of  brickduil, 
which  is  very  different  from  the 
colour  of  red  lead;  and  even  this 
dirty  red  was  changed  into  a  yellow 
colour,  by  augmenting  the  degree  of 
heat  with  which  the  lead  had  been 
calcined.  The  method  of  making 
red  lead  is  very  well  underftood  in 
England  and  Holland y  but  not  in 
France;  and  the  French  workmen  are 

of 


(     343     ) 
of  opinion,  that  it  cannot  be  made 
by  the  flame  of  wood  fires.  * 

During  the  making  of  red  lead, 
part  of  it  is  volatilized,  there  rifes 
up  from  it  a  vapour,  which  attaches 
itfelf  to  the  roof  of  the  furnace,  and 
forms  folid  lumps.  Thefe  lumps 
arc  of  a  yellowifh  white  colour  mix- 
ed with  pale  green  and  fome  reddilli 
itreaks,  wherein  are  frequently  fmall 
red  cryftals,  refembling  fuch  as  may 
be  artificially  formed  by  fubliming 
fulphur  and  arfenic  together.  The 
workmen  call  the  whole  of  what  is 
feparated  from  the  lead  in  the  form 
of  fmoke,  fulphur  :  when  this  fub- 
limed  matter  is  detached  from  the 
roof  of  the  furnace,   the  red  parts 

*  Mem.  de  I'Acad.  des  Scien.  1770.— 
Elemens  de  Mineral,  par  M,  Sage.  Vol.  II. 
p.  248. 

y  4  are 


(  344  ) 
are  converted,  by  a  fubfequent  pro- 
cefs,  into  red  lead  ;  and  the  yellow 
ones  are  fent  to  the  fmelting  fur- 
naces, to  be  run  down  again  into 
lead.  The  quantity  of  this  fubli- 
mate  announts  to  about  five  hundred 
weight  in  making  one  hundred  tons 
of  red  lead.  The  proportion  here 
afiigned  is  not  wholly  to  be  relied 
on,  fince  the  frnoke  arifing  from  the 
lead  forms  itfelf  into  larger  mafTes, 
and  in  lefs  time,  when  it  is  not  con- 
flantly  fwept  from  the  roof  of  the 
furnace  than  when  it  is  -,  and  the 
workmen  endeavour  to  keep  the 
roof  as  free  from  it  as  they  can,  be- 
caufe  a  fmall  portion  of  it  injures 
the  colour  of  a  large  quantity  of  the 
red  lead  with  which  it  happens  to 
be  mixed^ 

A  ton  or  twenty  hundred  w^eight 

of 


(     345     ) 

of  lead  generally  gives  twenty- two 
hundred  weight  of  red  lead,  notwith- 
flanding  the  lofs  of  fubftance  which 
the  lead  evidently  fuftains  from  the 
copious  fmoke  which  arifes  from  it 
during  the  operation.  Some  authors 
tell  usj  that  the  increafe  in  the  v/eight 
of  the  red  lead  is  double  what  I  have 
here  mentioned :  thus,  Or/iri^^Z/fpeak- 
ing  of  the  red  lead  made  at  Nurem- 
berg^ alTures  us,  that  loo  pounds  of 
lead  yield  120  pounds,  and  fome- 
times  even  more,  of  red  lead.*  It 
is  not  impofTible  that,  according  to 
the  different  manners  of  condudins; 
the  procefs,  there  may  be  a  differ- 
ence in  the  quantity  of  weight  v/hich 
the  red  lead  acquires :  I  had  my  in- 
formation from  fome  of  the  mofl 

expe- 

*  Orfch.  Metal.  French  Tranf.  p.  ico. 

M.  Sage's  Mine.  Vol.  II.  p.  384, 


(     346     ) 

experienced  makers  of  red  lead  in 
Derbyiliire.  There  have  been  great 
difputes  amongil  philofophers,  to 
vvhat  principle  this  increafe  of  weight 
fhould  be  afcribed^  fome  have  attri- 
buted it  to  what  they  call  the  matter 
of  fire;  others  are  upon  good  grounds 
convinced,  that  it  is  owing  to  the 
abforption  of  the  air  itfelf,  or  of 
fome  of  the  principles  of  which  the 
air  confiils.  This  hypothefis  con- 
cerning the  fixation  of  air  during  the 
calcination  of  metals,  is  faid  to  have 
been  firft  advanced  by  John  Rey,  a 
French  phyfician,  ini630j  Dr, Hales 
was  partly  of  the  fame  opinion;* 
and  Dr.  Pemherton  very  exprefsly  af- 
firms, that  calcined  metals  receive 
their  increafe  of  weight  from  the  air, 
-which  "  by  a6ting  on  the  inflamma- 

able 
*r  Veget.  Stat, 


(     347     )      ' 
able  fubilance^    either^  in  metals  or 
other  bodies,   expels  its  from  them, 
and  unites  itfelf  (in  part  at  leaft)  to 
the  remains  of  the  body."  *     The 
ingenious  labours  of  Dr.  Prieftley  and 
of  M.  Lavoifier  have  confirmed  the 
conje6tures  and  experiments  of  for- 
mer   philofophers,    for    they   have 
clearly    proved    two    points — firft, 
that  a  large  portion  of  air  may  be 
JeparaUd  from  red  lead,  by  reducing 
it  to  the   ftate    of  a    metal  ^ — and 
fecondly,    that   a   large   portion  of 
air  is  ahjorhed  by  lead  during   the 
calcination,   by  v/hich  it  is  reduced 
to  the  ftate  of  red  lead.f 

During  the  calcination  of  lead,  it 
is  certain,  from  what  has  been  faid, 

that 

*  Pember.  Chem,  p.  24^. 
f  Prieflley's  Exper.  and  Lavoifier's  EiTays, 
franilated  by  Renry, 


(     34^    ) 

that  much  of  its  fubftance  is  difperf- 
ed  into  the  air  -,  this  fubftance  may 
indeed  be  feen  afcending  as  a  fmoke 
from  the  furface  of  the  lead,  if  the 
heat  be  fo  great  as  to  make  it  boil ; 
and  in  a  lefs  degree  of  heat,  the  va- 
pour which  afcends  from  it,  may  be 
rendered  vifible,  by  holding  over  it 
a  wet  iron  ladle  to  condenfe  it.  But 
at  the  fame  time  that  the  lead  lofes 
confiderably  of  its  weight  by  the 
voladlization  of  part  of  its  fubftance, 
it  receives  fuch  an  accellion  of  new 
matter  from  the  air,  as  renders  the 
v/eight  of  the  part  which  remains, 
much  greater  than  that  of  the  whole 
lead  which  was  expofed  to  calcina- 
tion. This  accefiion  of  aerial  matter 
may  be  driven  off  from  red  lead,  by 
reftoring  to  it  the  inflammable  prin- 
ciple which  was  confumed  during 
3  the 


(  ^49  ) 
the  calcination  -,  but  after  this  extra- 
neous matter  is  driven  otT,  by  re- 
ducin^r  the  lead,  Vv'e  ought  not  to 
cxpe6l  that  the  lead,  which  is  thus 
.brought  back  to  its  former  Rate, 
fhould  weigh  as  much  as  it  did  be- 
fore it  was  calcined  j  becaufe  that 
part  of  it  which  was  volatilized  anvi 
difperfed  into  the  air  cannot  be  reco- 
vered. And  in  fact,  it  was  obferved 
in  the  laft  ElTay,  that  three  tons  of 
lead,  when  converted  by  calcination 
into  litharge,  had  loft  two  hundred 
weight ;  this  quantity,  and,  probably 
much  more  than  this,  had  been  vo- 
latilized and  loft,  for  the  rem.aining 
fifty-eight  hundred  weight  confifted 
partly  of  the  earth  of  lead,  and  partly 
of  the  air  which  had  been  fixed  in  it 
during  the  calcination  J  and  hence, 
when  it  was  reduced,  it  did  not  give 

above 


(     3S0     ) 

above  fifty-two  hundred  weight.  In 
calcining  then,  and  reducing  fixty 
hundred  weight  of  lead,  there  is  a 
lofs  of  eight  hundred  weight :  a  great 
part  of  this  lofs  is  rightly  referred  to 
the  volatilization  of  the  lead,  but  a 
part  alfo  may  juftly  enough  be  re- 
ferred to  the  fcoria  which  remains 
after  the  reduction  of  the  litharge 
into  lead,  that  operation  being  fel- 
dom  performed  fo  accurately  as  not 
to  leave  fome  part  of  the  litharge 
unreduced.  I  have  here  fpoken  of 
the  lofs  of  weight,  fuflained  during 
the  redudion  of  litharge,  as  if  it 
was  the  fame  as  that  which  red  lead 
fuilains ;  there,  probably,  may  be 
fome  difference  between  them,  but 
the  general  inference  is  the  fame  s 
and  I  have  been  informed  moreover, 
that    there   is  neither  increafe    nor 

decreafe 


(     3S^     ) 

decreafe   in  weight,    in  converting 
litharge  into  red  lead.  * 

In  making  red  lead  in  Derbyfhire, 
the  workmen  mix  one  hundred 
weight  o(  flag  lead  with  about  eigh- 
teen hundred  weight  of  ore  lead  f 
and  they  are  perfuaded  that  this  flag 
lead  has  a  great  efixct,  in  accelerating 
the  converfion  of  the  other  lead  into 
an  earth.  5"/;/,  when  mixed  with 
lead,  very  much  promotes  its  calci- 
nation 5    and  the  flag  lead  has  this 

property 

*   This  obfervation  does  not  accord  with 
that  of  the  author  of  the  Familiar  Difcourfe 

concerning  Mines,    p.  34. "20  hundred 

weight  of  this  litharge  will  produce.  22  hun- 
dred weight  of  red  lead."  Another  author 
informs  us  that  20  pounds  of  lead  will  by 
a  long  calcination  give  25  pounds  of  allies, 
and  that  thefe  25  pounds  of  alhes  will,  when 
]-educed,  give  19  pounds  of  lead,  Lemery 
Cours  de  Chym.  p,  145. 


(  3S^  ) 
property  In  coiriinon  with  a  mixture 
of  tin  and  lead,  that  it  does  not, 
when  melted,  exhibit  any  colours  on 
its  furface  :  may  not  its  properties, 
by  which  it  is  diftinguifhable  from 
ore  lead,  arife  from  its  containing 
zinc  or  tin  ?  We  are  too  apt,  I  think, 
to  look  upon  the  ores  of  lead  as  con- 
taining only  one  metal;  fince  we  are 
certain  that  they  all  contain  two, 
namely,  lead  and  filver ;  and  it  may 
be,  that  they  contain  other  metallic 
fubftances,  particularly  zinc  and  tin. 
In  converting  a  ton  of  lead  into 
red  lead,  the  workmen  obferve,  that 
towards  the  end  of  the  operation, 
a  few  pounds  of  lead  are  always 
found  to  remain,  which  cannot  be 
changed  into  red  lead,  with  the  fame 
facility  with  which  ordinary  lead  is 
changed.  When  I  was  firil  inform- 
ed 


(  353  ) 
cd  of  this  circumltance,  I  confidered 
it  in  the  following  manner.  —  Der- 
bylhire  lead,  though  it  does  not  con- 
tain filver  enough  to  render  the  ex- 
traction of  it  profitable,  yet  it  gene- 
rally contains  five  or  fix  ounces  in  a 
ton  :  filver  is  not  capable  of  being 
converted  into  an  earth  by  the  ac- 
tion of  air  and  fire,  when  therefore 
a  ton  of  lead  is  converted,  as  to  its 
greatefl  part,  into  red  lead,  why  may 
not  the  fix  ounces  of  filver  contained 
in  that  lead,  be  left  unaltered  ?  and 
may  not  the  fuperior  difficulty  of 
reducing  the  laft  portion  of  the  lead 
into  red  lead,  proceed  from  hence, 
that  it  is  much  more  impregnated 
with  filver,  than  ordinary  lead  is  ? 
Under  the  influence  of  this  conjec- 
ture, I  procured  from  Derbyfliire, 
fome  of  the  lead  which  remained 
VOL,  III.  Z  un- 


(     354   1 

uncalcined  in  the  making  of  reki 
lead,  and  I  afTayed  it  for  filver  j 
but  it  did  not  contain  more  filver, 
than  many  fpecimens  of  ore  lead 
contained. 

It  has  been  remarked,  more  than 
once,  that  red  lead  may  be  reduced 
into  lead,  by  being  melted  v/ith  roiin, 
tallow,  charcoal,  or  any  fubftance 
containing  the  inflamimiable  princi- 
ple. The  proof  of  this  is  very  eafy ; 
a  few  grains  of  red  lead  being  fcat- 
tered  on  a  piece  of  red  hot  charcoal, 
will  be  changed  into  globules  of 
kadi  or  if  the  reader, burns  a  com- 
mon red  wafer  in  the  ilamiC  of  a 
candle,  holding  a  piece  of  v/hite 
paper  under  it;  he  will  fee  many 
red  hot  globules  falling  upon  the 
paper,  and  thefe  globules  he  will  find 
to  be  lead  :   this  lead  proceeds  from 

the 


(     3S5     ) 

the  red  lead  with  which  ordinary 
wafers  are  coloured^  being  reduced 
into  the  ftate  of  a  metal,  by  uniting 
itfelf  with  the  inflamnaable  principle. 
The  beil  wafers  are  coloured  with 
vermilion — powdered  cinnabar.  * 

Having  been  difappointed  in  the 
cxpeftation  of  finding  a  large  pro- 
portion of  filver;,  in  the  fm.all  refidue 
of  lead  remaining  after  the  conver- 
fion  of  ordinary  lead  into  red  lead  \ 
and  being  unwilling  to  give  up  the 
notion,  I  v/as  defirous  of  convincing 
myfelf  that  I  had  not  been  guilty  of 
any  miftake  in  the  allay  that  I  had 
made,  by  trying  whether  red  lead  it- 
felf did  not  contain  filver  -,  for  if  red 
lead  contained  filver,  I  faw  no  reafon 

to 

*  Cinnabar  is  an  ore  of  quickfilver ;  it  is 
compofed  of  quickfilver  and  fulphur ;  gene- 
rally of  7  parts  of  quickfilver  to  i  of  fulphur. 

Z  2 


(  35^  ) 
to  be  furprifed  at  the  refidue,  before 
mentioned,  not  containing  more 
than  I  found  it  to  do.  I  therefore  re- 
duced a  quantity  of  red  lead  into 
the  Hate  of  a  metal,  by  melting  it 
with  rofm;  this  reduced  lead  was 
carefully  afTayed  more  than  once, 
and  It  always  afforded  a  portion  of 
filver.  Hence  we  may  conclude, 
that  the  filver  contained  in  lead, 
though  it  be  not  fubje6l  to  calcina- 
tion during  the  procefs  of  making 
red  lead,  iSf  neverthelefs  mixed  with 
the  calcined  lead  in  fuch  a  commi- 
nuted ilate,  as  to  efeape  our  fenfes ; 
the  filver,  probably,  is  ftill  in  the 
form  of  filver,  but  its  particles  are 
fo  indefinitely  fine,  that  they  can- 
not be  diflinguifhed  in  the  mafs  of 
red  lead,  which  contains  them. 
The  method  of  making  flag  lead 

has 


(    357     ) 

has  been  defcribed  before  ;  I  affayed 

this  kind  of  lead  feveral  times,  and 
I  fometimes  obtained  from  it  a  glo- 
bule of  filver,  at  other  times  there 
was  no  appearance  of  filver.  This 
difference  in  the  refult  of  the  afTays, 
is  not  to  be  attributed  to  any  differ- 
ence in  the  quality  of  the  flag  lead 
which  was  affayed^  for  all  the  pieces 
which  I  tried  were  cut  from  the 
fame  lump,  but  to  the  different  de- 
grees of  heat  ufed  in  the  aperation  ; 
when  the  fire  was  too  ilrong,  the 
filver,  I  conceive,  was  volatilized. 
Silver  I  know  is  looked  upon  as  a 
fixed  metal,  and  not  capable  of  being 
volatilized  ;  and  the  lofs  of  filver 
when  the  fire  is  too  flrong,  has  been 
attributed  to  its  being  not  volatiliz- 
ed, but  abforbed  by  the  cupel-,  I 
have  no  objedion  to  this  account; 
z  3  but 


(    35§     ) 

but  that  the  volatilization  of  filver 

on  the  cupel  is  no  unwarranted  con- 
je6bure,  appears  from  hence^  that  in 
the  iail  procefs  of  refining  lead  for 
filver  at  Holyv/ell,  fo  much  of  the 
filver  is  carried  into  the  chimney  of 
the  furnace,  that  they  have  pro- 
cured a  filver  cup  from  melting  the 
fweepings. 

A  great  quantity  of  lead  is  annu- 
ally imported  in  the  tea  boxes  from 
China,  a  Congo  box  contains  about 
lo  pounds,  and  an  Hyfon  box  about 
4  pounds  of  lead  j  I  have  frequently 
allayed  this  lead,  and  always  found 
that  it  contained  filver,  but  not  in 
quantity  fufficient  to  quit  the  ex- 
pence  of  extrading  it. 

Pure  lead  is  heavier  than  pure  fil- 
ver, and  the  purer  the  lead  the  great- 
er is  its  weights    I  calculated   the 

weight' 


(     359     ) 

weight  of  a  cubic  foot  of  five  differ- 
ent forts  of  lead  : 

Weight  of  a  cubic  foot  of 

Avoir,  oz. 

Lead  from  the  reduclion  of  red  lead  1 1460 

Lead  uncalcined  in  making  red  lead  11331 

Lead  fmelted  from  an  ore     -     -     -  11262 

Lead  from  the  flag  of  a  cupola  furn.  11212 

Lead  from  a  tea  box     -      -      -     -  11 176 

The  experiments  from  which  I  form- 
ed this  table^  were  repeated  at  dif- 
ferent tim.es,  and  the  m.ean  of  feve- 
ral  trials  in  the  refpedlive  forts  is 
expreffed.  A  cubic  foot  of  fine 
filver  weighs  1 1091  ounces,  * 

The  following  aiTays  of  the  feveral 
leads  here  mentioned,  were  made  by 
an  experienced  afiayer  in  London  -, 
they  are  very  little  different  from 

thofe 
*  Cotes. 

z  4 


(    36o    )       , 

thofe  which  I  myfelf  had  made,  but 
I  was  defirous  that  the  reader  might 
rely  upon  the  authority  of  a  peribn 
verfed  in  the  particular  bufmefs  of 
allaying,  rather  than  upon  mine. 

Fine  filver  in  a  pound  of 

Grains. 

Lead  from  the  redu6lion  of  red  lead  1 1 

Lead  uncalcined  in  making  red  lead  1 1- 

Lead  fmelted  from  an  ore   -    -    -    -  i  J 

Lead  from  the  flag  of  a  cupola  furn.  i| 

Lead  from  a  tea  box    -----  jl 

From  comparing  the  two  tables 
together,  we  fee  that  the  heavieft 
lead  contains  the  lead  filver.  I  do 
not  think,  that  perfons  interefted  in 
knowing  the  quantity  of  filver  con- 
tained in  any  particular  fpecimen  of 
lead,  ihould  reft  fatisfied  with  affay- 
ing  fo  fmall  a  portion  as  a  pound, 
efpecially  if  no  notice  is  taken  of 

any 


(    36i     ) 

any  weight  lefs  than  one  fourth  of 
a  grain. 

White  lead  or  cerufe^  is  lead  cor- 
roded by  vinegar.  Thin  plates  of 
lead  are  rolled  up  in  a  fpiral  form, 
and  placed  in  earthen  pots  contain- 
ing vinegar ;  thefe  pots  being  ranged 
on  proper  llages,  and  their  mouths 
being  covered  in  fuch  a  manner,  as 
to  permit  the  vapour  of  the  vinegar 
to  efcape,  and  at  the  fame  time  to 
prevent  any  impurity  from  falling 
into  them,  a  quantity  of  horfe  dung 
is  thrown  in  amongft  them  ;  by  the 
heat  of  which,  as  it  grows  putrid, 
the  vinegar  is  raifed  in  vapour,  and 
this  vapour  attaching  itfelf  to  both 
fides  of  every  fpiral  of  the  lead, 
which  is  fo  placed  as  not  to  touch 
the  vinegar,  it  corrodes  the  lead  into 
white  fcales,  which  being  beat  off 

from 


(     3^2     ) 

from  the  plates,  wafhed  and  ground 
in  a  mill,  conftitute  the  white  lead 
of  the  fhops,  excepting  that  this  is 
generally,  even  before  it  gets  into 
the  hands  of  the  painters,  adulterat- 
ed with  chalk.  Cerufe  was  for- 
merly made  by  the  vapour  of  putrid 
urine  inflead  of  vinegar.  The  time 
when  this  preparation  of  lead  v/as 
firil  difcovered  is  wholly  uncertain  i 
Diqfcorides  fpeaks  of  its  being  made 
in  great  perfedion  ^t  Rhodes^  Corinth 
and  Lacedemon^  and  of  an  inferior  fort 
of  it  at  Puteoli',  *  and  Pliny  defcribes 
two  ways  of  condu6ting  the  opera- 
tion, both  of  v/hich  are  now  in  ufe  J. 
The  Roman  ladies  were  well  ac- 
quainted with  the  ufe  of  cerufe  as  a 
cofmetic :  Plautus  introduces  a  wait- 


ing 


*  Diof.  Lib.  V.  C.  103, 
{  Lib.  XXXIV,  S.  54, 


(     3^3     ) 

ing  woman  refufing  to  give  her  mi- 
ftrefs  either  cerufe  or  rouge ^  becaufe, 
forfoothj  in  the  true  fpirit  of  a  flat- 
tering Abigail,  Ihe  thought  her  quite 
handlbme  enough  without  them.  * 
I  fuppofe  the  Chriftian  ladies  in  the 
days  oi  St, Jerome  J  were  given  to  this 
pagan  cuftom,  for  the  venerable  fa- 
ther inveighs  very  forcibly  againil 

the 

*  — —  non  do,   fcita  es  tu  quidem, 
Nova   pidura  interpolare   vis   opus   lepidiffi- 

mum, 
Non  iflanc  ^tatem  oportet  pigmentum  allem 

attingere, 
Neque  cerufam,  neque  melinum,  neque  alium 
ullam  ofFuciam. 

Plaut.  ]\Ioft.  Acl.  I. 
Quid  facial  in  facie  Chriftianae  purpurilTus 
ct  cerufa,  quorum  alterum  ruborem  genarum, 
labiorumque  mentitur,  alterum  candorem 
oris  et  colli,  ignis  juvenum,  fomenta  libidi- 
num,  impudicse  mentis  judicia.  Hieron,  ad 
Fufcum. 


(  364  ) 

the  life  of  rouge  for  the  lips  and 
cheeks,  and  of  cerufe  for  the  face  and 
neck,  as  incentives  to  luft,  and  indi- 
cations of  unchafte  defires.  With- 
out prefunning  to  explore  the  arcana 
of  a  lady's  toilet,  or  to  reveal  the 
arts  by  which  my  fair  countrywo- 
men endeavour  to  improve  charms 
naturally  irrefiftible,  I  would  add 
to  the  admonition  of  St.  Jerome,  a 
caution  more  likely,  in  thefe  dege- 
nerate times,  to  be  attended  to — 
the  certain  ruin  of  the  complexion, 
to  fay  nothing  of  more  ferious  mala- 
dies, which  muft  ever  attend  the 
conftant  application  of  this  drug. 
Nor  is  the  magiftery  of  bifmuth  or 
SpaniJIj  white^  as  it  is  called,  much 
lefs  pernicious  than  cerufe,  notwith- 
ftanding  its  being  in  fuch  repute  in 
London,  that  the  chemifts  can  hardly 

pre- 


(    365    ) 

prepare  it  faft  enough  to  fupply  the 
demand  for  it.*  But  if,  as  is  moft 
probable,  they  will  negle6b  this  cau- 
tion, I  warn  them,  however,  to  for- 
bear the  ufe  of  fuch  wafhes  at  Har- 
rowgate,  Moffat,  and  other  places  of 
the  fame  kind,  left  they  fhould  be  in 
the  ftate  of  the  unlucky  fair  one, 
whofe  face,  neck,  and  arms  were 
fuddenly  defpoiled  of  all  their  beau- 
ties, and  changed  quite  black  by  a 
fulphureous  water.  Indeed,  all  phlo- 
giftic  vapours,  and  even  the  fun  it- 
felf,  tends  to  give  both  the  magiftery 
of  bifmuth,  and  cerufe,  a  yellow  co- 
lour :    this  obfervation  may  explain 

a  line 

*  The  magiftery  of  bifmuth  is  made  by 
dilTolving  that  femimetal  in  aqua  fortis,  and 
precipitating  the  dilTolYed  bilmuth  from  the 
acid,  by  water. 


(    366     ) 

a  line  in  Martial ^  where  a  cerufed 
lady  is  faid  to  fear  the  fun.* 

Other  fluidsj  befides  the  vapour 
of  vinegar^  corrode  lead  into  a  kind 
of  cerufe.  When  plumbers  ftrip 
the  roofs  of  churches,  or  other  build- 
ings covered  with  lead,  which  has 
lain  undiilurbed  for  many  years, 
they  ufuaily  find  that  fide  of  the  lead 
which  is  contiguous  to  the  boards, 
covered  with  a  vvhite  pellicle,  as 
thick  fometimes  as  an  half  crown; 
this  pellicle  is  corroded  lead,  and  is 
as  ufeful  for  painting,  and  other 
purpofes,  as  the  beil  white  lead.  The 
lead  on  the  fouth  fide  of  any  build- 
ing is  found  to  abound  mofl  with 

this 

*  .- cretata  timet  FabuUa,  nimbum, 

Cerufata  timet  Sabelia,  folem. 

Mar.  Ep.  Lib.  11.  E.  XLL 

3 


(     367     ) 

this  white  crufl  -,   that  on  the  nortfl 

fide  having  very  little,  or  none  at  all 
of  it.  It  is  believed  alfo,  that  lead 
which  lies  on  deal  boards,  is  not  fo 
apt  to  be  covered  with  this  white  in- 
cruftation,  as  that  which  lies  upon 
oak  ;  if  there  be  any  truth  in  this 
obfervation,  it  may,  perhaps,  be  ex- 
plained from  hence,  that  oak  con- 
tains a  much  ilronger  acid  than  deal, 
and  this  ftrong  acid  being  diililled, 
as  it  were,  by  the  heat  of  the  fun  in 
fummer,  attaches  itfelf  to  the  lead 
and  corrodes  it :  or  this  ccrrofion 
may  be  the  effedt  of  the  fun  and  air, 
v/hich,  by  their  conilant  adion,  cal- 
cine or  corrode  the  lead;  and  this 
calcined  lead  not  being  wafhed  off 
by  the  rain,  may,  in  the  courfe  of  a 
great  many  years,  form  the  cruft 
here  fpoken  of.     It  might  be  worth 

v/hile 


(     368     ) 

while,  in  a  philofophical  view,  to 
examine  more  minutely  than  has 
been  done,  the  difference  between 
old  lead  which  has  loft  fome  of  its 
parts  by  long  expofure  to  the  air, 
and  new  lead.  The  plumbers  have 
affured  me  that  if  a  pig  of  old  lead, 
and  an  equal  pig  of  new  lead,  be 
put  together  into  the  fame  iron  pot, 
and  expofed  to  the  fame  degree  of 
heat,  the  new  lead  will  be  melted 
much  fooner  than  the  old  lead.  An- 
other difference  betwixt  them,  re- 
Ipedts  the  quicknefs  with  which  they 
may  be  reduced  to  a  calx,  the  new 
lead  being  obferved  to  calcine  much 
f after  than  the  old. 

Neither  cerufe,  nor  litharge,  nor 
minium,  have  any  tafte,  but  any  of 
thefe  fubftances  being  boiled  in  di- 
ftilled  vinegar,  which  has  an  acid 

tafte. 


(3%     ) 

tafte,  will  be  diffolved  in  it ;  and  the 
folution  being  cryflallized  will  give 
one  of  the  fweeteft  fubftances  in  na- 
ture, called  Saccharum  Satiirnij  or 
fugar  of  lead.  It  is  this  property 
which  lead  has  of  acquiring  a  fv/eet 
tafle  by  folution  in  an  acid,  that  has 
rendered  it  fo  ferviceable  to  thofe 
wine  merchants  who,  refpecling  their 
own  profit  more  than  the  lives  of 
their  cuflomers,  have  not  fcrupled 
to  attempt  recovering  v/ines,  v/hich 
had  turned  four,  by  putting  into 
them  large  quantities  of  cerufe  or  li- 
tharge. I  believe  this  adulteration 
is  puniihed  with  death  in  fome  parts 
of  Germany  5  and  it  is  to  be  wifhed 
that  it  met  with  that  puniihment 
every  where.  In  1750  the  farmers 
general  in  France  being  aftonifhed  at 
the  great  quantities  de  v in  gate  which 
VOL.  Ill,  A  A  were 


(  370  )  ^ 
were  brought  into  Paris y  in  order  to 
be  made  into  vinegar,  redoubled 
their  refearches  to  find  out  the  caufe 
of  the  great  increafe  in  that  article  ^ 
for  near  thirty  thoufand  hoglheads 
had  been  annually  brought  in  for  a 
fev/  years  preceding  th€  year  i75o> 
whereas  the  quantity  annually  brought 
in  forty  years  before,  did  not  exceed 
1200  hoglheads.  They  difcovered, 
that  feveral  wine  merchants,  aiTum- 
ing  the  name  of  vinegar  merchants, 
bought  thefe  four  wines  (whicPi  were 
ilill  rendered  more  four  by  the  cuf- 
torn  of  pouring  into  each  hogfhead 
iix  pints  of  vinegar  before  it  was 
fold,)  and  afterwards,  by  means  of 
litharge,  rendered  them  potable,,  and 
fold  them  as  genuine  wines,* 

Our 
*  Exam.  Chy,    de  Differ.  Subf.  par.  M. 


(    37^     ) 

Our  Englifh  vintners,  there  Is  rca- 
fon  to  fear,  are  not  lefs  fcrupulous 
in  the  ufe  of  this  poifon  than  the 
French  wine  merchants  ;  for  it  not 
only  corre£ts  the  acidity  of  four 
•wines,  but  it  gives  a  richnefs  to 
meagre  ones>  and  by  this  property 
the  temptation  to  ufe  it  is  much 
increafed. 

The  reader  may  foon  furnifli  him- 
feif  with  the  means  of  detecting  lead 
when  dilToived  in  viiHQ,  Let  him 
boil  together  in  a  pint  of  water,  an 
ounce  of  quicklime  and  half  an 
ouTice  of  flowers  of  brim.llone,  and 
when  the  liquor,  which  will  be  of  a 
yellow  colour,  is  cold,  let  him  pour 
it  into  a  bottle,  and  corking  it  up, 
referve  it  for  ufe.  A  few  drops  of 
this  liquor,  being  let  fall  into  a  glafs 
of  wine  or  cyder  containing  lead, 

A  A    2  Will 


(  372  ) 
will  change  the  whole  into  a  colour 
more  or  lefs  brown^  according  to  the 
quantity  of  lead  which  it  contains; 
if  the  v/ine  be  wholly  free  froni  lead, 
it  v/ill  be  rendered  turbid  by  the  li- 
quor, but  the  colour  will  be  rather 
a  dirty  white  than  a  blackiih  brown. 
Van  Helmo?it^  was  of  opinion,  that 
Varaceljus  made  no  vain  boail,  in 
faying  that  he  could  cure  r^vo  hun- 
dred difeafes  by  preparations  of  lead; 
but  he  does  not  tell  us  of  x\it  many 
hundred  perfons  he,  probably,  fent 
to  their  graves  by  his  attempt.  But 
it  is  beyond  m.y  ability,  and  falls 
not  within  my  defign,  to  difcufs  ei- 
ther the  falubrious  or  poifonous 
qualities  of  lead  ;    efpecially  as  the 

labours 

*  Adeo  lit  non  friillra  Paracelfus  glorietiir 
Iblo  pliimbo  forte  ducentas  morborum  clalTes 
{iiperare  polTe.      Helm.  Op.  p.  561. 


(     373     ) 
labours  of  Sir  G.  Baker  *  and  Dr. 
Per  civ  al  f  have  fo  fully  illuilrated 
that  fubjed. 

Having  accidentally  heard,  during 
the  printing  of  this  volume,  that 
Dr.  Prieftley  had  difcovered  a  method 
of  reducing  red  lead  to  its  metallic 
form,  by  melting  it,  in  conta6t  with 
inflammable  air,  by  means  of  a 
burning  glafs,  I  was  very  defirous  of 
having  lb  remarkable  a  fad:  confirm- 
ed by  other  experiments.  But  being 
prevented  by  a  bad  ftate  of  health 
from  venturing  into  an  elaboratory 
myfelf,  I  communicated  my  wifhes 
and  ideas  to  an  ingenious  gentleman 
of  this  univerfity>  ^  who  has  for  fome 
years  been  cultivating  chemiftry  with 

a  pro- 

*  Med.  EfT.     f  Eir.  on  the  Poifon  of  Lead. 
:   Rev.   Mr.  Milner,    A.   M.    Fellow   of 
Queen's  College. 


(    374    ) 

a  proper  degree  of  enthufiafm,  and 
he  has  fucceeded  in  reducing  red 
lead  by  means  of  inflammable  air  in 
the  following  manner.  To  one  end 
of  a  glafs  tube,  into  the  middle  of 
which  fome  red  lead  had  been  put, 
an  empty  bladder  was  tied  ;  to  the 
other  end  a  bladder  full  of  inflam- 
mable air,  obtained  from  a  folution 
of  iron  in  the  acid  of  vitriol,  was 
lailened  very  clofe :  that  part  of  the 
tube,  in  which  the  red  lead  was 
principally  lodged,  being  heated  al- 
mofl  red  hot,  by  being  held  over  a 
fmall  crucible  full  of  burning  char- 
coal, the  inflamimiable  air  was  preiTed 
out  of  the  bladder;  at  its  flrft  paffage 
through  the  tube  the  red  lead  be- 
came brown,  as  if  it  had  been  mixed 
v/ith  fome  oleaginous  particles;  and  by 
prelfing  the  bladders  alternately  for 

a  (hort 


(  37S  ) 
a  fhoft  fpace  of  time,  the  red  lead 
was  reduced  into  fmall  globules  of 
lead;  the  quantity  of  inflammable 
air  was  fenfibly  diniiniilied,  a  part  of 
it  having  been  abfbrbed  by  the  red 
lead,  when  it  became  a  metal. 

Occafion  v/as  taken  in  another 
place  to  remark,,  the  inflammable 
air,  as  a  conftituent  part  of  ccxn- 
bufbible  bodies,  bore  a  great  refem- 
blance  to  phlogiilon,  *  and  a  doubt 
alfo  has  been  expreflfed,  whether  the 
phlogiflion  of  metallic  fubllances  be 
not  an  elailic  inflammable  fluid  -,  this 
experiment,  in  which  lead  is  reduced 
by  abforbing  inflammable  air,  tends 
very  much  to  fcrengthen  that  hypo- 
thefls,  and  I  doubt  not  we  fhall  fee 
reafon  to  adrniit  it  without  hefitation,, 
when  the  fubjed:  has  been  more  in- 

vefliigated 
*  VoLIL  p.  35U 


(     376     ) 
veftigated  -,     at    prefent    I    do   not 
know  whether  it  has  been  proved 
that  the  whole  of  any  definite  quan- 
tity of  inflammable  air  can  be  ab- 
forbed  by  a  metallic  earth  -,   nor,  if 
it  cannot,  what  the  nature  of  the 
remainder  is :    but  the    removal  of 
thefe,  and  other  doubts,  will  be  beft 
accomplifhed  by  the  ability  of  him, 
to  whom  we  owe  the  firfl  fuggef- 
tion,   of  the  phlogiflon   of  metallic 
fubftances,  being    an    inflammable 
air. 


END   ©F    VOL.  III.