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A New View of the Origin 


Dalton's Atomic Theory 



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A New View of the Origin 


Dalton's Atomic Theory 

A Contribution to Chemical History 










All rights reserved 



Introduction vii 


On the Genesis of Dalton*s Atomic Theory . , . . i 


Dalton's Scientific Diary^ 1802-1808 .... 52 


Dalton^s Atomic Weight Numbers . . . . .81 


Notes of Lectures delivered at Royal Institution in London^ 

December and January 1 8 1 o . . . . .99 


Letters written and received by D alt on . . . . 1 30 


It may seem remarkable that, after the lapse of 
nearly a century since John Dalton first applied the 
atomic theory of matter to chemical phenomena, it 
should be possible to find anything new respecting 
the genesis of his ideas. And this is the more 
remarkable when we remember that the life and 
scientific labours of the great Manchester chemist 
have formed the subject of independent memoirs 
at the hands of two such able contemporaries as 
Charles Henry and Angus Smith. The explana- 
tion is to be found in the unlooked-for discovery, 
in the rooms of the Literary and Philosophical 
Society of Manchester, where the whole of 
Dalton's experimental work was carried out, of his 
laboratory and lecture notebooks contained in a 
number of manuscript volumes. A careful study 
of these has led us to conclusions concerning the 
origin of the atomic theory of chemistry which 
differ widely from those which have been generally 
accepted. It has hitherto been supposed that it 
was the experimental discovery of the law of com- 

viii New View of Daltons Atomic Theory 

bination in multiple proportions which led Dalton, 
seeking for an explanation of this most remarkable 
fact, to the idea that chemical combination consists 
in the approximation of atoms of definite and 
characteristic weight, the atomic theory being thus 
adopte^o explain the facts ascertained by chemical 
analysis. This prevailing view is found on ex- 
amination to rest upon the authority of contem- 
porary chemists rather than on any explicit state- 
ment on the part of the author himself ; for, strange 
as it may appear, no attempt to explain the 
genesis of his ideas is to be found in any of Dalton's 
published writings. Among these newly-discovered 
manuscript notes, which have hitherto escaped 
the attention of his biographers, we have found 
an account in Dalton's own handwriting of this 
very subject. It is of course well known that he 
was an ardent adherent of the Newtonian doctrine 
of the atomic constitution of matter, and that he 
was thus led to that realistic conception of the 
structure of gases, which forms so characteristic 
a feature of his speculations. It now appears that 
it was from this physical standpoint that Dalton 
approached the atomic theory, and that he arrived 
at the idea that the atoms of different substances 
have different weights from purely physical con- 
siderations. This at once led him to conceive 
of chemical combination as taking place between 
varying numbers of atoms of definite weight, a 
position which he then succeeded in confirming 

Introduction ix 

by the results of analyses made both by other 
chemists and by himself. 

The actual relations are, therefore, precisely the 
inverse of those which are usually accepted. It 
was the theory of the existence of atoms of different 
weights which led Dalton to the discovery of the 
facts of combination in multiple proportions. 

The first portion of this work contains a de- 
tailed account of the evidence upon which the 
above conclusion is founded. This is followed by 
a short epitome of Dalton's daily laboratory notes 
from 1802 up to the publication of the first part 
of the New System of Chemical Philosophy in 
1808, showing the line of thought and of experi- 
mental work which he followed during the period 
when the atomic theory was being elaborated. 
Next will be found a discussion of the successive 
and varying series of numbers given by Dalton as 
representing the atomic weights of the elements, 
showing how far these were derived from the 
analyses of others and how far from his own work. 
The notes for his lectures, delivered at various times 
and places, have also been reproduced in full, to- 
gether with a collection of hitherto unpublished 
letters, which serve to indicate the great reputation 
which he enjoyed among his contemporaries. 

Our thanks are due to the Council of the 
Literary and Philosophical Society of Manchester 
for the readiness with which they granted access 
to the manuscripts in their possession. 




The first published indications of Dalton's atomic 
theory are, as is well known, appended to a paper 
" On the absorption of Gases by Water and other 
Liquids " read before a select audience of nine 
members and friends in the rooms of the Literary 
and Philosophical Society of Manchester on 21st 
October 1803, and printed in the Manchester 
Memoirs with the date of November 1805. 

In the concluding paragraph of this paper, 
Dalton remarks : — " The greatest difficulty attend- 
ing the mechanical hypothesis, arises from the 
different gases observing different laws. Why does 
water not admit its bulk of every kind of gas alike ? 
This question I have duly considered, and though 
I am not able yet to satisfy myself completely, I 
am nearly persuaded that the circumstance depends 
upon the weight and number of the ultimate 
particles of the several gases : Those whose par- 
ticles are lightest and single being least absorbable, 
and the others more according as they increase in 


2 New View of Baltons Atomic Theory chap. 

weight and complexity. An enquiry into the 
relative weights of the ultimate particles of bodies 
is a subject, as far as I know, entirely new : I have 
lately been prosecuting this enquiry with remark- 
able success. The principle cannot be entered 
upon in this paper ; but I shall just subjoin the 
results, as far as they appear to be ascertained by 
my experiments. 

" Table of the relative weights of the ultimate particles 
of gaseous and other bodies. 





Carbone .' 


Amnionia . 


Oxygen . 


Water . . 




Phosphuretted hydrogen . 


Nitrous gas 




Gaseous oxide of carbone 


Nitrous oxide 


Sulphur . 


Nitric acid 


Sulphuretted hydrogen 


Carbonic acid 


Alcohol . 


Sulphureous acid . 


Sulphuric acid 


Carburetted hydrogen from stagnant water 6.3 

Olefiant gas 


An outline of the new theory was included in 
the course of lectures which Dalton delivered at 

I The Genesis of Daltons Atomic Theory 3 

the Royal Institution in London during December 
1803 and January 1804, and at Edinburgh in 1807, 
but the general public first became acquainted with 
it through the medium of a short account which 
appeared in Dr. Thomas Thomson's System of 
Chemistry^ pp. 424-451 of vol. iii. of the third 
edition, published in 1807. Dalton himself after- 
wards published a detailed account of the theory, 
accompanied by another and more extended table 
of ^ atomic weights in the first part of his New 
System of Chemical Philosophy (Manchester, 1808), 
of which it forms the third chapter, entitled 
" On Chemical Synthesis." The second part of 
the first volume of this work, published in 18 10, 
contained the application of the theory to the 
chemistry of the elements and the compounds 
of two elements, as well as a " New Table 
of the relative weights of atoms" (pp. 352- 


The first published table of weights is of such 

a character as to show that its author clearly 

recognised the facts generally expressed in the laws 

of combination in definite and multiple proportions. 

This is seen very distinctly in the cases of the two 

carburets of hydrogen, and the oxides of sulphur, 

of carbon, and of nitrogen. The numbers given 

for nitrous gas and nitrous oxide are obviously 

misprints for 9.7 and 13.9. 

Much interest attaches to the question whether 

Dalton was led to this mode of interpreting the 


4 Klew View of Daltons Atomic Theory chap. 

facts by the results of his analytical experiments, 
or whether it was the corpuscular theory of the 
constitution of matter which induced him to draw 
theoretical conclusions as to the nature of chemical 
combination, which he afterwards found were in 
accordance with fact. In other words, was the 
atomic theory founded on an experimental know- 
ledge of the law of combination in multiple pro- 
portions, or did Dalton arrive at this law as a 
necessary consequence of the atomic structure of 
matter ? 

The evidence to be gathered on this point 
from the various biographers of the great 
Manchester chemist and from the historians of » 
chemical science is unsatisfactory, and rather 
calculated to disturb than settle our minds upon 
the question. 

The most definite evidence is that afforded by 
Thomson, who spent a day or two with Dalton in 
August 1804, and carried away with him the very 
clear and accurate idea of the nature of the new 
theory published three years later in his System of 
Chemistry, He says : — " Mr. Dalton informed 
me that the atomic theory first occurred to him 
during his investigations of olefiant gas and 
carburetted hydrogen gas, at that time imperfectly 
understood, and the constitution of which was first 
fully developed by Mr. Dalton himself. It was 
obvious from the experiments which he made 
upon them that the constituents of both were 


I The Genesis of Daltons Atomic Theory 5 

carbon and hydrogen and nothing else ; he found, 
further, that if we reckon the carbon in each the 
same, then carburetted hydrogen contains exactly 
twice as much hydrogen as olefiant gas does. 
This determined him to state the ratios of these 
constituents in numbers, and to consider the 
olefiant gas a compound of one atom of carbon 
and one atom of hydrogen ; and carburetted 
hydrogen of one atom of carbon and two atoms 
of hydrogen. The idea thus conceived was 
applied to carbonic oxide, water, ammonia, etc., 
and numbers representing the atomic weights of 
oxygen, azote, etc., deduced from the best analy- 
tical experiments which chemistry then possessed " 
[History of Chemistry^ vol. ii. p. 291). 

To this statement Henry, in his Life of Dalton^ 
p. 80, appends the following note : — 

" In a subsequent biographical account of 
Dalton, read before the Glasgow Philosophical 
Society, 5th November 1845, ^^' Thomson repeats 
the same statement ; but in his notice of Wollaston, 
read November, 1850, he states: — 'Mr. Dalton 
founded his theory on the analysis of two gases, 
namely, protoxide and deutoxide of azote. . . . 
The first of these he considered as a compound of 
one atom of azote with one atom of oxygen, and 
the second of one atom of azote united with two 
atoms of oxygen.* There is no doubt that the 
earlier statement is the more correct one. For 
Dalton never regarded nitrous oxide as a ' binary 

6 New View of Daltons Atomic Theory chap. 

compound,' but as constituted of two atoms azote 
and one of oxygen, and nitrous gas as one and 
one. See all his successive atomic tables, and 
his letter to Dr. Daubeny. Atomic Theory^ p. 


The account given by Thomson in his History . 

has been generally accepted by chemists, and 
it is usually held to be confirmed by Dalton's 
own remarks concerning the composition of car- 
buretted hydrogen. In the New System^ vol. i. 
p. 444, he says, " No correct notion of the con- 
stitution of the gas about to be described ^ seems 
to have been formed till the atomic theory was 
introduced and applied in the investigation. It 
was in the summer of 1804 that I collected, 
at various times and in various places, the inflam- 
rnable gas obtained from ponds. . . ." 

* It now appears, as has been already suggested 
by Dr. Debus in a brochure recently published in 
German, " On some of the Fundamental Laws of 
Chemistry," ^ that the meaning of this passage is 
quite the reverse of that which has been attached 
to it by Henry, Kopp, and other historians of the 
science. It was, according to this new view, the 
atomic theory which helped to clear up the exist- 
ing confusion about the composition of carburetted 
hydrogen, and not the analysis of the gas which 
led to the atomic theory. 

1 Marsh gas. 
2 Cassel. Hofbuchhandlung von Gustav Klaunig, 1894. 

I The Genesis of Baltotis Atomic Theory 7 

Henry adduces further evidence on the question 
in the shape of two memoranda of conversations 
held v^ith Dalton, one by his father, the other by 
himself The first of these notes is dated 13th 
February 1830, and is as follows: — "Mr. Dalton 
has been settled in Manchester thirty-six years. 
His volume on Meteorology^ printed but not 
published before he came here. At p. 132 ^/ seq. 
of that volume, gives distinct anticipations of his 
views of the separate existence of aqueous vapour 
from atmospheric air. At that time the theory of 
chemical solution was almost universally received. 
These views were the first germs of his atomic 
theory, because he was necessarily led to consider 
the gases as constituted of independent atoms. 
Confirmed the account he before gave me of the 
origin of his speculations, leading to the doctrine of 
simple multiples, and of the influence of Richter's 
table in exciting these views " (Henry, Life of 
Dalton^ pp. 62-63). '^h^ second conversation is 
reported in Henry's journal in the following 
words: — "5th February 1824. The speculations 
which gave birth to the atomic theory were first 
suggested to Mr. Dalton by the experiments of 
Richter on the neutral salts. That chemist 
ascertained the quantity of any base, as potash for 
example, which was required to saturate 100 
measures of sulphuric acid. He then determined 
the quantities of the different acids which were 
adequate to the saturation of the same quantity of 

8 New View of D alt on s Atomic Theory chap. 

potash. The weights of the other alkahne bases 
entering into chemical combination with loo parts 
of sulphuric acid were then obtained ; and these it 
is obvious (?) would be equivalent to the saturation 
of the quantities of the different acids before deter- 
mined. On these principles a table was formed, 
exhibiting the proportions of the acids, and the 
alkaline bases constituting neutral salts. It im- 
mediately struck Mr. Dalton that if these saline 
compounds were constituted of an atom of acid 
and one of alkali, the tabular numbers would 
express the relative weights of the ultimate atoms. 
These views were confirmed and extended by a 
new discovery of Proust. He maintained that 
the compounds of iron and oxygen are strictly 
definite ; in other words, that i oo parts of iron 
combine either with twenty-eight or forty-two 
parts of oxygen, but with no intermediate quantity. 
He did not, however, discover the existence 
of multiple proportions. This law was first 
developed by Mr. Dalton, and contributed in a 
great degree to establish his theory of atomic 

Remarking on the somewhat contradictory 
nature of the various statements just detailed, 
Henry {Life^ p. 85) sums up the evidence very 
judiciously. " My own belief," he says, " is, that 
during the three years (i 802-1 804) in which the 
main foundations of the atomic theory were laid, 
Dalton had patiently and maturely reflected on all 

I The Genesis of Daltons Atomic Theory 9 

the phenomena of chemical combination known to 
him, from his own researches or those of others, 
and had grasped in his comprehensive survey, as 
significant to him of a deeper meaning than to his 
predecessors, their empirical laws of constant and 
reciprocal proportion, no less than his own law of 
multiple proportion, and his own researches in the 
chemistry of aeriform bodies. On reviewing in 
conversation, after the lapse of twenty years, the 
labours of the past, Dalton himself may have failed 
in recalling the antecedents of his great discovery 
in the exact order of sequence. His fresh utter- 
ances to Dr. Thomson in 1804, when fervently 
engaged in the investigation, are more likely to be 
accurate, especially as they are confirmed by the 
special direction of all his previous researches. At 
all events it is the obvious duty of a conscientious 
historian to record faithfully all documents in his 
possession." In a footnote to this passage he adds : 
"This view that Dalton's acquaintance with the 
writings of Richter was posterior, in the order of 
time, to his experiments on the two carburetted 
hydrogens and other gases, and that those writ- 
ings rather confirmed than originally suggested his 
atomic doctrine, is strengthened by the following 
decisive words of Dr. Thomson : — I do not know 
when he adopted these notions, but when I visited 
him in 1804, at Manchester, he had adopted them ; 
and at that time both Mr. Dalton himself and 
myself were ignorant of what had been done by 


lo New View of Dal ton s Atomic Theory chap. 

Richter on the same subject " [Proc, PhiL Soc. of 
Glasgow^ 1 845-1 846, p. 86). 

Angus Smith came to very much the same 
conclusion as Henry : — " From the earhest period of 
his scientific Hfe," he writes, " Dalton had been 
accustomed to think carefully on the constitution 
of the atmosphere ; this is seen as early as 1793, in 
his Meteorology, This subject continued to be a 
favourite one, and led him to gases generally. The 
experiments quoted at p. 43, on nitrous gas and 
oxygen, and those mentioned afterwards in a 
quotation from Dr. Thomson, show the method by 
which he came to believe, and to prove experi- 
mentally, the existence of definite and constant 
proportion" [Memoir of Dalton^ p. 231). . 

Debus, on the other hand, in the pamphlet 
already referred to " On some of the Fundamental 
Laws of Chemistry, especially the Dalton- Avogadro 
Law," has arrived at quite a different conclusion. 
As mentioned above he interprets Dalton's own 
remarks about the discovery of the relations between 
olefiant gas and carburetted hydrogen in a different 
and certainly a more natural way than had hitherto 
been done. From the fact that Thomson in his 
account of the atomic theory (1807) uses the 
expression relative density or density of the atom 
as synonymous with weight of the atom^ whilst 
Dalton only uses the latter expression. Debus 
further argues that when Dalton communicated 
his theory to Thomson, he must have held the 

The Genesis of Daltons Atomic Theory ii 

opinion that these two relations, the relative 
density and the relative weight of the atoms, were 
identical, or what Debus appears to consider to be 
the same thing, that the relative densities of the 
gases were identical with the relative weights of 
their atoms. This view he seeks to confirm by 
quoting in support of it a passage from the New 
System^ p. i88, in which Dalton says: "At the 
time I formed the theory of mixed gases, I had a 
confused idea, as many have, I suppose, at this 
time, that the particles of elastic fluids are all of the 
same size ; that a given volume of oxygenous gas 
contains just as many particles as the same volume 
of hydrogenous ; or if not, that we had no data 
from which the question could be solved." On 
the strength of this argument, which appears to 
rest on a confusion between the relative density of 
the atoms and the relative density of the gases made 
up of those atoms, between which, by the way, 
Thomson expressly distinguishes in the case of 
nitrous gas (NO), Debus concludes (loc, cit, 58) that 
Dalton endeavoured to determine the atomic 
weights according to the theory laid down in the 
chapter on " Chemical Synthesis," in order to 
obtain facts which would either confirm or dis- 
prove this law, the law of equal gas volumes. The 
atomic weights were not proportional to the gas 
densities, and Dalton, therefore, abandoned the law 
of equal atomic or molecular volumes for gases. 
Debus also considers that the passage just quoted 

1 2 New View of Daltons Atomic Theory chap. 

from Dalton entitles him to rank equally with 
Avogadro as the co-discoverer of what is termed by 
him throughout the pamphlet in question, " The 
Dalton-Avogadro Law." 

An unexpected light is thrown on these vexed 
questions by the contents of a number of MS. 
volumes which have recently been found among the 
Dalton papers in the possession of the Manchester 
Literary and Philosophical Society. These com- 
prise, in the first place, an extensive series of labora- 
tory notes, commencing in the year 1802, and going 
down to Dalton's latest years, containing an almost 
unbroken record of the experimental work to which 
he so entirely devoted himself throughout his life, 
and which supplied him with the materials em- 
bodied in his great work, A New System of 
Chemical Philosophy, These notes are bound up 
in twelve volumes, each of these " compound " 
volumes being made up of a number of " simple " 
notebooks of unruled paper, which have been taken 
out of their original covers and bound together. 
They have often been commenced at toth ends ; 
some of them have been begun, then left un- 
used for a considerable interval, and finally again 
brought into requisition. Moreover, several of 
them seem to have been in use at the same time, 
appropriated to the experiments on different sub- 
jects in progress at the moment. 

In addition to these very valuable and interest- 
ing laboratory records, there is also a notebook 

I The Genesis of 'Daltoris Atomic Theory 1 3 

dated 3rd February 18 10, in which are contained 
the notes of the last six lectures of the course of 
twenty delivered in that year by Dalton at the 
Royal Institution in London. 

The fifteenth and sixteenth lectures deal with 
heat, but the next one, delivered on 27th January 
1 8 10, is of such great interest and importance in 
connection with the genesis of the atomic theory, 
that it will be convenient here to quote it in full. 

Lecture 17. — Chemical Elements 

" As the ensuing lectures on the subject of chemical 
elements and their combinations will perhaps be thought 
by many to possess a good deal of novelty, as well as im- 
portance, it may be proper to give a brief historical sketch 
of the train of thought and experience which led me to 
the conclusions about to be detailed. 

Having been long accustomed to make meteorological 
observations, and to speculate upon the nature and con- 
stitution of the atmosphere, it often struck me with 
wonder how a compound atmosphere, or a mixture of 
two or more elastic fluids, should constitute apparently 
a homogeneous mass, or one in all mechanical relations 
agreeing with a simple atmosphere. 

Newton had demonstrated clearly, in the 23rd Prop. 
of Book 2 of the Principia^ that an elastic fluid is con- 
stituted of small particles or atoms of matter, which repel 
each other by a force increasing in proportion as their 
distance diminishes. But modern discoveries having ascer- 
tained that the atmosphere contains three or more elastic 
fluids, of difl^erent specific gravities, it did not appear to 

r>* 'I' 

14 New View of Dal ton s Atomic Theory chap. 

me how this proposition of Newton would apply to a case 
of which he, of course, could have no idea. 

The same difficulty occurred to Dr. Priestley, who 
discovered this compound nature of the atmosphere. He 
could not conceive why the oxygen gas being specifically 
heaviest, should not form a distinct stratum of air at the 
bottom of the atmosphere, and the azotic gas one at the 
top of the atmosphere. Some chemists upon the Con- 
tinent, I believe the French, found a solution of this 
difficulty (as they apprehended). It was chemical affinity. 
One species of gas was held in solution by the other ; and 
this compound in its turn dissolved water ; hence evapora- 
tion^ rain^ etc. This opinion of air dissolving water had 
long before been the prevailing one, and naturally paved 
the way for the reception of that which followed, of one 
kind of air dissolving another. It was objected that there 
were no decisive marks of chemical union, when one kind 
of air was mixed with another — the answer was, that the 
affinity was of a very slight kind, not of that energetic 
cast that is observable in most other cases. 

I may add, by the bye, that this is now, or has been 
till lately, I believe, the prevailing doctrine in most of the 
chemical schools in Europe. 

In order to reconcile or rather adapt this chemical 
theory of the atmosphere to the Newtonian doctrine of 
repulsive atoms or particles, I set to work to combine 
my atoms upon paper. I took an atom of water, another 
of oxygen, and another of azote, brought them together, 
and threw around them an atmosphere of heat, as per 
diagram ; I repeated the operation, but soon found that 
the watery particles were exhausted (for they make but 
a small part of the atmosphere). I next combined my. 
atoms of oxygen and azote, one to one ; but I found in 

I The Genesis of Daltons Atomic Theory 1 5 

time my oxygen failed ; I then threw all the remaining 
particles of azote into the mixture, and began to consider 
how the general equilibrium was to be obtained. 

My triple compounds of water ^ oxygen^ and azote were 
wonderfully inclined, by their superior gravity, to descend 
and take the lowest place ; the double compounds of 
oxygen and azote affected to take a middle station ; and 
the azote was inclined to swim at the top. I remedied 
this defect by lengthening the wings of my heavy par- 
ticles, that is, by throwing more heat around them, by 
means of which I could make them float in any part of 
the vessel ; but this change unfortunately made the whoJe 
mixture of the same specific gravity as azotic gas — this 
circumstance could not for a moment be tolerated. In 
short, I was obliged to abandon the hypothesis of the 
chemical constitution of the atmosphere altogether, as 
irreconcilable to the phenomena. 

There was but one alternative left, namely, to sur- 
round every individual particle of water^ of oxygen^ and 
of azote^ with heat, and to make them respectively centres 
of repulsion, the same in a mixed state as in a simple state. 
This hypothesis was equally pressed with difficulties ; for, 
still my oxygen would take the lowest place, my azote 
the next, and my steam would swim upon the top. 

In 1 801 I hit upon an hypothesis which completely 
obviated these difficulties. 

According to this, we were to suppose that the atoms 
of one kind did not repel the atoms of another kind, but 
only those of their own kind. This hypothesis most 
effectually provided for the diffusion of any one gas 
through another, whatever might be their specific gravities, 
.and perfectly reconciled any mixture of gases to the 
Newtonian theorem. Every atom of both or all the gases 

1 6 New View of Baltoris Atomic Theory chap. 

in the mixture was the centre of repulsion to the proxi- 
mate particles of its own kind, disregarding those of the 
other kind. All the gases united their efforts in counter- 
acting the pressure of the atmosphere, or any other pres- 
sure that might be opposed to them. 

This hypothesis, however beautiful might be its 
application, had some improbable features. 

We were to suppose as many distinct kinds of repul- 
sive powers, as of gases ; and, moreover, to suppose that 
heat was not the repulsive power in any one case ; 
positions certainly not very probable. Besides, I found 
from a train of experiments, which have been published 
in the Manchester Memoirs^ that the diffusion of gases 
through each other was a slow process, and appeared to be 
a work of considerable effort. 

Upon reconsidering this subject, it occurred to me 
that I had never contemplated the effect of difference of 
size in the particles of elastic fluids. By size I mean the 
hard particle at the centre and the atmosphere of heat 
taken together. If, for instance, there be not exactly the 
same number of atoms of oxygen in a given volume of 
air, as of azote in the same volume, then the sizes of the 
particles of oxygen must be different from those of azote. 
And if the sizes be different, then on the supposition that 
the repulsive power is heat, no equilibrium can be estab- 
lished by particles of unequal sizes pressing against each 
other. (See Diagram.) ^ 

This idea occurred to me in 1805. I soon found 
that the sizes of the particles of elastic fluids must be 
different. For a measure of azotic gas and one of 
oxygen, if chemically united, would make nearly two 
measures of nitrous gas, and those two could not have 

1 The diagrams here referred to are not reproduced in the notes. 

I The Genesis of Dalton s Atomic Theory 17 

more atoms of nitrous gas than the one measure had of 
azote or oxygen. (See Diagram.) Hence the suggestion 
that all gases of different kinds have a difference in the 
size of their atoms ; and thus we arrive at the reason for 
that diffusion of every gas through every other gas, 
without calling in any other repulsive power than the 
well-known one of heat. 

This then is the present view which I have of the 
constitution of a mixture of elastic fluids. 

The different sizes of the particles of elastic fluids 
under like circumstances of temperature and pressure 
being once established, it became an object to determine 
the relative sizes and weights^ together with the relative 
number of atoms in a given volume. This led the way 
to the combinations of gases, and to the number of atoms 
entering into such combinations, the particulars of which 
will be detailed more at large in the sequel. Other bodies 
besides elastic fluids, namely liquids and solids, were 
subject to investigation, in consequence of their combin- 
ing with elastic fluids. Thus a train of investigation was 
laid for determining the number and weight of all chemical 
elementary principles which enter into any sort of com- 
bination one with another. 

1. Divisibility of matter considered. Atoms — see 

Newton's ideas. 

2. Elastic fluids exhibit matter in extreme division. 

Newton, B. 2 ; Prop. 23. See Diagram. 

Hydrogen and oxygen cannot be broken down 
into finer kinds by electricity. Like flour, 
etc. ; sugar, etc. 

Compound gases, as nitrous, carbonic acid, are 
separated into their ulterior elements by elec- 
tricity. . . . See Diagram atmosphere. 

1 8 New View of D alt on s Atomic Theory chap. 

3. Other bodies constituted of atoms as well as 

elastic fluids — charcoal, sulphur, phosphorus. 
Metals by combining with atoms of elastic 
fluids show that they have atoms. 

4. All atoms of the same kind alike in wt. bulk. 

5. Atoms of diff^erent kinds unequal in wt., etc. 

See Newton, 2. 

6. Bodies deemed simple till they are decomposed. 

7. Chemical synthesis. Exhibit two particles. See 

also Newton, 3. 

8. Table of arbitrary marks. 
Gay-Lussac's notion." 

The operation of combining the atoms upon 
paper as described in these notes is a little difficult 
to follow. Only the proportion of the constituents 
of the atmosphere by weight and volume being 
known, some theory as to the relative number of 
particles was necessary before Dalton could write : 
" I soon found that the watery particles were 

• No doubt at this time he still entertained the 
" confused idea," to which he confesses in the 
New System^ p. 188, "that the particles of elastic 
fluids are all of the same size ; that a given volume 
of oxygenous gas contains just as many particles as 
the same volume of hydrogenous," and he, therefore, 
made the number of particles of each constituent 
directly proportional to its pressure in the atmo- 
sphere. He thus, of course, found (the necessity 
for a trial on paper being, indeed, hardly obvious) 


I The Genesis of Daltons Atomic Theory 19 

that after using all the water particles to form 
triple compounds with an atom of nitrogen and 
one of oxygen, the number of nitrogen atoms left 
was far too large to simply provide a companion 
atom for each one of oxygen, and he was, there- 
fore, left with a surplus of nitrogen atoms on 
hand, which were of course free. 

It may be well to remember that, according to 
Dalton's view, which is a modification of that of 
Newton and Lavoisier, each atom or particle of a 
gas consisted of an exceedingly small central nucleus 
of solid matter surrounded by an enormously more 
bulky elastic atmosphere of heat, of great density 
next the atom, but gradually growing rarer accord- 
ing to some power of the distance. To this 
atmosphere of heat was ascribed the power of 
repulsion by means of which the elastic state of 
the gas was maintained. By increasing the amount 
of heat round each atom the density of the gas 
would, therefore, be diminished. 

In Dalton's paper atmosphere, however, the 
lightest particles were those of unaltered nitrogen, 
with which Dalton evidently felt a delicacy in 
interfering ; he, therefore, had no alternative but, 
as he says, " to make the whole mixture of the 
same specific gravity as azotic gas, a state of things 
which could not be for a moment tolerated." 
Precisely the same difficulties assailed him when 
he imagined the atmosphere as a simple mixture 
of repulsive atoms of nitrogen, oxygen, and water ; 

20 New View of Daltons Atomic Theory chap. 

there was apparently nothing to prevent the gases 
from arranging themselves in the order of their 
specific gravities. 

The way in which Dalton surmounted this 
difficulty by means of his celebrated theory that 
gases behave as- vacua towards one another is suffi- 
ciently clear, but the view which finally replaced 
that theory, and gave the inspiration which led to 
the atomic theory, may perhaps not be quite so 
readily understood. The complete account of the 
idea, as given in the New System, pp. 1 87-191, 
may, therefore, be helpful on this point : — 

" I shall now proceed to give my present views 
on the subject of mixed gases, which are somewhat 
different from what they were when the theory 
was announced, in consequence of the fresh lights 
which succeeding experience has diffused. In 
prosecuting my enquiries into the nature of elastic 
fluids, I soon perceived it was necessary, if possible, 
to ascertain whether the atoms or ultimate particles 
of the different gases are of the same size or volume 
in like circumstances of temperature and pressure. 
By the size or volume of an ultimate particle, I 
mean, in this place, the space it occupies in the 
state of a pure elastic fluid ; in this sense the bulk 
of the particle signifies the bulk of the supposed 
impenetrable nucleus, together with that of its 
surrounding repulsive atmosphere of heat. At the 
time I formed the theory of mixed gases, I had 
a confused idea, as many have, I suppose, at this 


I The Genesis of Daltons Atomic Theory 21 

time, that the particles of elastic fluids are all of 
the same size ; that a given volume of oxygenous 
gas contains just as many particles as the same 
volume of hydrogenous ; or if not, that we had no 
data from which the question could be solved. 
But from a train of reasoning, similar to that 
exhibited at p. 71,^ I became convinced that 
different gases have not their particles of the same 
size : and that the following may be adopted as 
a maxim, till some reason appears to the contrary ; 
namely, — 

" T'hat every species of pure elastic fluid has its 
particles globular and all of a size ; hut that no two 
species agree in the size of their particles^ the pressure 
and temperature being the same. 

" There was another thing concerning which 
I was dubious ; whether heat was the cause of 
repulsion. I was rather inclined to ascribe repulsion 
to a force resembling magnetism, which acts on 
one kind of matter, and has no effect on another. 
For, if heat were the cause of repulsion, there 
seemed no reason why a particle of oxygen should 
not repel one of hydrogen with the same force as 
one of its own kind, especially if they were both 
of a size. Upon more mature consideration, I see 
no sufficient reason for discarding the common 
opinion, which ascribes repulsion to heat ; and I 
think the phenomena of mixed gases may be still 

^ The formation of two volumes of nitrous gas from one of nitrogen 
and one of oxygen. 


22 New View of D alt on s Atomic Theory chap. 

accounted for, by repulsion, without the postulatum, 
that their particles are mutually inelastic, and free 
from such of the preceding objectiony as I have left 

" When we contemplate upon the disposition of 
the globular particles in a volume of pure elastic 
fluid, we perceive it must be analogous to that of a 
square pile of shot ; the particles must be disposed 
into horizontal strata, each four particles forming a 
square : in a superior stratum, each particle rests 
upon four particles below, the points of its contact 
with all four being 45° above the horizontal plane, 
or that plane which passes through the centres of 
the four particles. On this account the pressure 
is steady and uniform throughout. But when a 
measure of one gas is presented to a measure of 
another in any vessel, we have then a surface of 
elastic globular particles of one size in contact with 
an equal surface of particles of another : in such 
case the points of contact of the heterogeneous 
particles must vary all the way from 40° to 90° ; 
an intestine motion must arise from this inequality, 
and the particles of one kind be propelled amongst 
those of the other. The same cause which pre- 
vented the two elastic surfaces from maintaining an 
equilibrium, will always subsist, the particles of 
one kind being from their size unable to apply 
properly to the other, so thlt no equilibrium can 
ever take place amongst the heterogeneous particles. 
The intestine motion must therefore continue till 


ll}'cfio e.'en gc'i s Ni t ro (J s ovi s (Carbonic aci cf ga s 


X \ 




^ A^<>^ 


/ / ' \v\ 











I The Genesis of Daltons Atomic Theory 23 

the particles arrive at the opposite surface of the 
vessel against any point of which they can rest 
with stability, and the equilibrium at length is 
acquired when each gas is uniformly diffused 
through the other. In the open atmosphere no 
equilibrium can take place in such case till the 
particles have ascended so far as to be restrained by 
their own weight ; that is, till they constitute a 
distinct atmosphere." 

The idea does not appear to have been . very 
carefully thought out, and although the conditions 
of equilibrium would certainly be disturbed, it is 
doubtful whether the intestine motion of which 
Dalton speaks would have been set up in a vessel 
filled with his atoms. The point of importance, 
however, for our purpose is to understand what 
Dalton thought about the subject, not whether he 
was justified in so thinking. The theory may be 
further illustrated by the diagrams (Plates i and 2) 
reproduced from the second part of the New System^ 
p. 548, the description of which is as follows: — 

"Plate 7. Figs, i, 2, and 3 represent pro- 
file views of the disposition and arrangement of 
particles constituting elastic fluids, both simple and 
compound, but not mixed ; it would be difficult to 
convey an adequate idea of the last case, agreeably 
to the principles maintained, p. 190. The principle 
may, however, be elucidated by the succeeding 

" Fig. 4 is the representation of four particles 

24 New View of Daltoris Atomic Theory chap. 

of azote with their elastic atmospheres, marked by- 
rays emanating from the soHd central atom ; these 
rays being exactly alike in all the four particles 
can meet each other, and maintain an equilibrium. 
" Fig. 5 represents two atoms of hydrogen drawn 
in due proportion to those of azote, and coming in 
contact with them ; it is obvious that the atoms of 
hydrogen can apply one to the other with facility, 
but can not apply to those of azote, by reason of 
the rays not meeting each other in like circum- 
stances ; hence, the cause of the intestine motion 
which takes place on the mixture of elastic fluids, 
till the exterior particles come to press on some- 
thing solid. 

; " Plate 8. The first sixteen figures represent 
^the atoms of different elastic fluids, drawn in the 
centres of squares of different magnitude, so as to 
be proportionate to the diameters of the atoms as 
they have been herein determined. Fig. i is the 
largest ; and they gradually decrease to Fig. i6, 
which is the smallest ; namely, as under : — 



I. Superfluate of silex 

1. 15 


Oxymuriatic acid 


2. Muriatic acid 

1. 12 


Nitrous gas 


3. Carbonic oxide 



Sulphurous acid . 


4. Carbonic acid 



Nitrous oxide . 


5. Sulphuretted hydrogen . 

1. 00 


Ammonia . 


6. Phosphuretted hydrogen 



defiant gas 


7. Hydrogen . 



Oxygen . 


8. Carburetted liydrogen . 





The method employed by Dalton in calculating 
these numbers is a very simple one. The number 




^^'■■■^ - 

I The Genesis of 'Daltons Atomic Theory 25 

of particles in unit volume of a gas is proportional 
to the weight of that volume, or the density of the 
gas, divided by the weight of a single particle, its 
atomic weight. The diameter of a particle is, of 
course, inversely proportional to the cube root of 
the number present in 2l given volume. Taking 
hydrogen as the standard atomic weight, the 
diameter of the particle of any gas compared with 
that of one of hydrogen is therefore given by the 

expression </ = \/— , in which j- is the relative 

density of the gas, and w the relative weight of its 
ultimate particle. 

It may be observed that no less than live out of 
the sixteen gases tabulated above have their particles 
of the same diameter, and it does not appear how 
Dalton reconciled this anomaly with the experi- 
mental facts. 

As we have seen (p. 16) Dalton states in his 
lecture notes that the idea that the uniform 
diffusion of gases might be explained by the 
different sizes of their constituent atoms occurred 
to him in 1805, and led to the determina- 
tion of the relative size, number, and weight of 
these atoms. This date must be a clerical error for 
1803, since he communicated an account of the 
atomic theory to Thomson in 1804, and, as we 
shall see, he had worked out a table of the 
diameters of the atoms in September 1803. 

The account of the origin of the atomic theory 

26 New View of Daltons Atomic Theory chap. 

here presented to us strikingly confirms the opinion 
expressed by his sagacious biographer in the 
passage already quoted (p. 8). 

It shows us very clearly how Dalton, starting 
from the Newtonian doctrine of repulsive atoms or 
particles, had been brought face to face with the 
problem of determining the relative size and weight 
(for, as we have seen, the one involved the other) 
of these small and almost infinitesimal particles. 
The method he adopted, and at all events some of 
his reasons for adopting it, become plain when we 
refer to the laboratory notes. 

One of the small " constituent " notebooks of 
the first volume (pp. 244-289) was reserved by him 
for this subject and contains matter of the highest 
historical interest. The portions of it which bear 
upon the point under discussion are printed verbatim, 
and some of the most important of these (viz. from 
pp. 244, 248 and 249) are reproduced in facsimile 
(Plates 3 and 4) from photographs taken from the 
original manuscripts. 

Vol. I. Page 244 

Observations on the ultimate particles of bodies and 

their combinations. 

6//? September 1803 

Characters of elements — 

O Hydrogen. 


CD Azote. 

# Car bone, pure charcoal. 



I The Genesis of Baltons Atomic Theory 27 

The characters on this page constitute the very 
earliest set of atomic symbols with which we are 
acquainted ; it is interesting to note that the signs 
for oxygen and hydrogen are not those used in 
the later tables, but were interchanged (see Plate 3 
for facsimile reproduction). 

Page 245 

N.B. — The ultimate atoms of bodies are those particles 
which in the gaseous state are surrounded by heat ; or 
they are the centres or nuclei of the several small elastic 
globular particles. 

Page 246 

Enquiry into the specific gravity of the ultimate 
particles or elements. 

Though it is probable that the specific gravities (j/V) of 
different elastic fluids has some relation to that of their 
ultimate particles, yet it is certain that they are not the 
same thing ; for the ult. part, of water or steam 
are certainly of greater specific gravity than those of 
oxygen, yet the last gas is heavier than steam. 

Dalton here, at the very first conception of the 
atomic theory, touches on the great difficulty which 
was to prove a stone of offence to so many of his 
successors. The fact that steam, the ultimate par- 
ticle of which contains both oxygen and hydrogen, 
is specifically lighter than oxygen, is proof to him 
that the specific gravities of gases and the relative 
weights of their ultimate particles are not identical. 


New View of Daltons Atomic Theory chap. 

and that, therefore, the diameters of the atoms are 
not the same for all substances. 

Page 247 

From the composition of water and ammonia we may 
deduce ult. at. azot i to oxygen 1.42 : — 

Ult. atom of nit. gas should therefore weigh 2.42 azot. 
Ult. atom of oxygen . . . 1.42 oxygen. 

According to this i oxygen will want 1.7 nitrous. 

Sulph. Oxy. 

Chenevix — 61 J + 38 J = sulphuric A. 
Then 61 J + 19 J should be sulphureous. 

This gives ult. part, of sulphur to oxy. 3.2 : i nearly. 

Sulph. Oxy. 

Thenart 56 +44 

56 + 22 sulphureous. 
Fourcroy says 85 + 15 = sulphureous. 

Page 248 

Ult. at. Hydrogen 
Oxygen . 

Carbon (charcoal) 
Water . 
Nitrous gas 
Nitrous oxide 
Nitric acid 
Sulphur . 
Sulphureous acid 
Sulphuric acid 
Carbonic Acid 
Oxide of carbone 












The most important matter with respect to the 
history of the origin of the atomic theory is to 

Plate 3 

' J2JW/ 


CMi^it-^^^^ -t fr-> -_ , r- jtjhr 

I The Genesis of Baltons Atomic Theory 29 

be found on these two pages. Page 248 contains 
a table of atomic weights (see facsimile repro- 
duction Plate 3) written out on 6th September 
1803, two years before the one published in the 
Memoirs (i. 287) in 1805, and about a year before 
the verbal communication made to Thomson in 
the summer of 1804, which formed the basis of 
the account of the atomic theory published in 
the latter's System of Chemistry, In this table 
it will be seen that the law of combination 
in multiples is as clearly recognised as in any 
of the subsequent ones, but no mention what- 
ever is made of carburetted hydrogen, either 
light or heavy. The experiments on carburetted 
hydrogen from stagnant water were in fact not 
made until the summer of 1804, nearly a year 
after this table of atomic weights had been drawn 
up, and this date is trebly attested (i) by the 
statement of Dalton {New System^ p. 444), (2) 
by Thomson {History , ii. p. 291), and (3) by the 
evidence of the Notebook, in which the first ex- 
periments on this substance are found under date 
of 6th August 1804. 

This disposes once and for all of the opinion 
commonly held, founded on Thomson's statement, 
that the atomic theory was suggested by a com- 
parison of the analyses of marsh gas and olefiant 
gas, and this conclusion is in full agreement with 
the record already quoted from the lecture notes. 

On p. 247, opposite to the table, we find the 

30 New View of Daltons Atomic Theory chap. 

clue to the reasoning which had led Dalton to 
these numbers. The weights of hydrogen, oxygen, 
and azot, it will be seen, are derived from the 
composition of water and ammonia (the actual 
numbers will be afterwards separately discussed), 
whilst the weight of an atom of sulphur is 
calculated from an analysis of sulphuric acid by 
Chenevix. No information is actually given as 
to the source of the number for carbon, but it 
appears certain that this was derived from the 
usually accepted composition of carbonic acid 

In determining the relative weights of these 
atoms, Dalton has rigidly followed the law of greatest 
simplicity, which he afterwards laid down in his 
chapter on " Chemical Synthesis," single com- 
pounds of two elements being considered as binary 
(in the sense of containing two atoms only), and 
the lighter of two compounds having ascribed to it 
the simpler structure. All the numbers in this 
earliest table, it is interesting to note, are derived 
from analyses performed by chemists of reputation, 
and generally accepted by the chemists of the 
time ; not one of them appears to be due to Dalton 
himself It is from the analyses of water, ammonia, 
sulphuric acid, and carbonic acid, that all the 
numbers are calculated, the law of combination in 
multiple proportions being, as far as can be seen, 
assumed as the only one according to which atomic 
combination could possibly occur. 


Ax^ . 

do ^ 

i^'^iT^S^Xs^ /k>^-My^TM-f /^^i^^.tyM^^ J 


I The Genesis of 'Daltons Atomic Theory 31 

We may here refer to a fact of some im- 
portance, viz. that the mention of carburetted 
hydrogen, derived from stagnant water, in the 
paper read 1803, but pubHshed in 1805, the ex- 
periments having been performed in 1804, proves 
that the statements contained in the paper 
pubHshed in the above year were brought up to 
date by their author, who, as secretary of the 
Society at the time, would of course have ample 
opportunity of doing so. 

Page 249 
(X)GXD Nitrous oxide. 
dXD Nitrous gas. 

0CD0 Nitric acid. SSp Nitrous acid. 

00 Water. 

00 Ammoniac 

00 Gaseous oxide of carbon. 

0#0 Carbonic acid. 

#0 Alcohol ? ether ? 

00 Sulphureous acid. 

000 Sulphuric acid. 

#0# Alcohol ? #0« Alcohol. 

•0# Ether ? 

Carbonated hydrogen gas #0 

^0 Gas. oxide of carb. and hydrogen. 

Nitrat ammoniac = i acid i am. i water. 


This page (reproduced in facsimile on Plate 4) 


32 New View of Daltons Atomic Theory chap. 

contains the symbols corresponding with the sub- 
stances mentioned on the preceding page of the 
Notebook. Symbols of a few compounds are added 
of which the composition is not given in the table. 
These are of nitrous acid, alcohol, and ether, the 
gaseous oxide of carbon and hydrogen, and nitrat 
ammoniac, and 'they have probably nearly all been 
subsequently inserted. The most important of these 
is no doubt nitrous acid, the formula for which 
is composed in accordance with Dalton's famous 
experiment on the combination of nitrous gas 
with the oxygen of the air. 

The account of this experiment is contained in 
his paper entitled " Experimental Enquiry into the 
Proportions of the several Gases or Elastic Fluids 
Constituting the Atmosphere," read 1 2th November 
1802, and published in 1805, in the same volume 
of the Memoirs with his later paper on the " Absorp- 
tion of Gases." The account there given {Memoirs^ 
i. p. 249) is as follows : — 

" 2. If 100 measures of common air be put to 
36 of pure nitrous gas in a tube -jV^hs of an inch 
wide and 5 inches long, after a few minutes the 
whole will be reduced to 79 or 80 measures, and 
exhibit no signs of either oxygenous or nitrous 

"3. If 100 measures of common air be ad- 
mitted to 72 of nitrous gas in a wide vessel over 
water, such as to form a thin stratum of air, 
and an immediate momentary agitation be used. 

I The Genesis of Daltons Atomic Theory 33 

there will, as before, be found 79 or 80 measures 
of pure azotic gas for a residuum. 

" 4. If, in the last experiment, less than 72 
measures of nitrous gas be used, there will be a 
residuum containing oxygenous gas ; if more^ then 
some residuary nitrous gas will be found/' 

The conclusion to which the experiment led 
him is stated in the significant words : " These facts 
clearly point out the theory of the process : the 
elements of oxygen may combine with a certain 
portion of nitrous gas, or with twice that portion, 
but with no intermediate quantity. In the former 
case nitric acid is the result ; in the latter nitrous 
acid : but as both these may be formed at the same 
time, one part of the oxygen going to one of nitrous 
gas, and another to two^ the quantity of nitrous gas 
absorbed should be variable." 

These results have been much discussed, but at 
present the interesting question is not how did 
Dalton manage to obtain these numbers, but when did 
he obtain them ? It is obvious that this statement, 
if made by Dalton at the date on which the paper 
was read, November 1802, would indicate that he 
had recognised the experimental fact of com- 
bination in multiple proportions long before he 
had adopted the atomic theory of chemical com- 
bination. The evidence of the laboratory note- 
books on this point is unfortunately not quite 
conclusive, as the earliest record contained in 
them is dated November 1802, and may possibly 

34 New View of Daltons Atomic Theory chap. 

have been preceded by some other containing an 
account of the experiments in question. The 
evidence which can be gathered, however, goes to 
show that both the experimental results and the ex- 
planation, as in the case of the carburetted hydrogen, 
are of a later date than that upon which the paper 
was read. EXalton certainly became aware at an 
early date that the proportions in which the two 
gases unite depend a good deal on the circumstances 
of the experiment. Thus on p. 122 (Notebook, i.), 
2 1 St March 1803, we read in connection with 
some experiments on the solubility of nitrous gas 
in water: "Nitrous gas — 1.7 or 2.7 may be 
combined with oxygen, it is presumed." On 
p. 129 of vol. i. of the Notebook, under the in- 
auspicious date of ist April 1803, is a list of 
experimental results obtained with nitrous gas and 
common air. In nearly every case a note is added 
as to whether the mixture of the two gases has 
been made rapidly or slowly, and the numbers 
show that more nitrous gas is absorbed when the 
mixture is rapidly made. Near the bottom of the 
page there is a note ; " Query, is not nitrous air 
decomposed by the rapid mixture ? " 

This certainly seems to indicate that Dalton 
at that date, nearly six months after the reading 
of the paper, had not arrived at the conclusion so 
definitely expressed therein. 

The actual numbers quoted in the Memoirs 
are found unaccompanied by any explanation on 

I The Genesis of D alt on s Atomic Theory 35 

p. 305, in a part of the book dated somewhere 
between loth October and 13th November 1803, 
a month or so after the first atomic weight table 
had been drawn up. The passage is as follows : — 

Notebook, vol. i. p. 305 
Nitrous Gas. 
It appears that 100 com. air 

+ 36 nit. gas 
give 79 or 80 azot, 
and that 100 com. air 

to 72 nit. gas, in a broad vessel, and 
suddenly mixed, also give 79 or 80 azot, 

and if 100 com. air be put to 100 nit. gas 
as above, and just agitated, there will be 24 or 25 nit. gas left, 
supposing 2 or 3 per cent azot in the nit. gas. 

That this particular experimental result was 
not prominently before Dalton*s mind during the 
very earliest stages of the development of his 
theory is further shown by several striking facts. 
In the first place, we have a little piece of indirect 
evidence afforded by the following calculation found 
on p. 246 of the Notebook (September 1803) : — 

"Cavendish, 10 Az. + 26 Oxy. gave acid by spark. If this 
was nitrous, then 10 Az. + 39 Oxy. = nitric acid. 
Lavoisier says : — 

By weight. 
A. Oxy. 

20J + 43^ = 64 nit. gas. 

20 J + 79J = nit. acid. 
This will perfectly agree with Mr. Cavendish." ^ 

1 This last remark is scored out in the manuscript. 

36 New View of Baltons Atomic Theory chap. 

Lavoisier's Elements of Chemistry must have been 
one of the sackload of books to which Dalton is 
said to have confined his reading, for it is there 
that is to be found the clue to the meaning of this 
calculation. On p. 286 of the English transla- 
tion of that work (2nd edition, 1793) we find the 
following passage dealing with the composition of 
nitric acid : — " Mr. Cavendish, who first showed 
by synthetic experiments that azote is the base of 
nitric acid, gives the proportions of azote a little 
larger than I have done ; but as it is not improbable 
that he produced the nitrous acid and not the 
nitric, that circumstance explains in some degree 
the difference in the results of our experiments." 
In the passage cited above Dalton is obviously 
testing the truth of this suggestion by calculation 
from Cavendish's numbers, and immediately below 
the passage quoted he gives Lavoisier's own num- 
bers, which agree pretty closely with the amended 
result of Cavendish. 

It will be seen that Dalton has converted 
nitrous into nitric acid by adding to the former 
half as much oxygen as it already contains. 
If we calculate the amount of oxygen from 
Dalton's own results, however, the number arrived 
at is quite a different one. Taking nitrous acid as 
two atoms of nitrogen and three of oxygen, whilst 
nitric acid is one of nitrogen and two of oxygen 
(his own assumption), it will be seen that the 
amount of oxygen to be added is not one-half but 


I The Genesis of Daltons Atomic Theory 37 

one-third of that already present in the nitrous 
acid. The same conclusion is reached if the calcula- 
tion be based not on the theoretical view, but 
on the actual numbers obtained by Dalton, as 
quoted on p. 35. Allowing for the specific 
gravity of nitrogen, oxygen, and nitrous gas, as 
given in the table (p. 41), 72 volumes of nitrous 
gas and 20 of oxygen correspond with 79.3 and 
22.5 parts by weight; 101.8 parts by weight of 
nitrous acid therefore require 22.5 parts by weight 
of oxygen to convert them into nitric acid. 
Cavendish's acid made up of 10 of nitrogen and 
26 of oxygen by volume, or 9.7 and 29.3 by 
weight, would then require, according to Dalton's 

experiment, ^^^^^^g'^ — 8.6 parts by weight, or nearly 

8 volumes of oxygen instead of the 1 3 which have 
been added in the notes. It appears from this, 
therefore, that in September 1803, the date of the 
first atomic weight table, Dalton had not adopted 
his well-known view as to the relation of nitrous 
to nitric acid. The conclusion that Cavendish's 
numbers could by this supposition be brought into 
agreement with Lavoisier's has afterwards been 
crossed out, perhaps after the very experiment 
which we are discussing had been made. 

At the same time it is certain that Dalton, 
before the composition of his first atomic weight 
table in September 1803, had noticed that in 
some experiments a simple ratio was found 
between the amounts of nitrous gas with which a 

38 New View of D alt on s Atomic Theory chap. 

given volume of oxygen combined under different 
circumstances. This is seen from the following 
extract from the Notebook, i. p. 132, dated 
4th August 1803 : — "It appears, too, that a very- 
rapid mixture of equal parts com. air and nitrous 
gas, gives 11^ or 1 20 residuum. Consequently 
that oxygen joins to nit. gas sometimes 1.7 to i, 
and at other times 3.4 to i." 

It by no means follov^s, however, that he had 
at that time devised the explanation that in one 
case nitrous acid, and in the other nitric acid, was 
formed. It seems rather as though this were 
another instance in which " no correct notion " of 
the actual relations was formed " until the atomic 
theory was introduced and applied in the investiga- 
tion." However this may be, Dalton did not 
include the quantitative composition of nitrous 
acid in any of the earlier atomic weight tables, 
although nitrous oxide, and nitrous gas, about 
the composition of which he had made no experi- 
ments, both found a place in all of them, and this 
of itself renders it very unlikely that the atomic 
theory was suggested by this particular experiment 
about nitrous gas and oxygen. 

The formula of nitrous acid does indeed occur, 
as we have seen, on p. 249 of the Notebook, 
but its position on that page, by the side of the 
column of symbols, gives some colour to the view 
that it may have been added later. 


The Genesis of Bait on s Atomic Theory 


Page 250 

On the position 
other compounds of 

of the other 
azote be such 


if nitric acid and 

then Nitrous oxide 

Nitrous gas 
and Nitric acid 





Cavendish . 
Lavoisier . 




The theory above gives i .43 for Priestley's test. 

N.B. — 9/A September. Tried Cavendish's experiment 
in I hour constant turning the machine in good order — 
about 20 grs. measure of air were reduced to 16 ; 
remainder 2^ oxygen. 

This extract contains a calculation of the com- 
position of the oxides of nitrogen from the numbers 
given for oxygen and nitrogen v^hich had been 
obtained by the analysis of v^ater and ammonia, an 
independent check of great value on the validity 
of the atomic theory of combination, and on the 
accuracy of the numbers adopted. The received 
numbers for nitric acid are quoted, and, as will be 
seen, the results of different chemists differ more 
from one another than from the calculated ones. 

Although the numbers contained in the first 
table w^ere not due to Dalton himself, he lost no time 
in endeavouring to confirm them by experiments 
of his own. On 9th and again on i oth September 

40 New View of Daltons Atomic Theory chap. 

he repeated Cavendish's experiment on the com- 
position of nitric acid. The experiment of the i oth 
is described as follows (Notebook, i. p. 213) : — 

" I oth September, Composition of nitric acid. — Mr. Cavendish's 
experiment. Took 17 grain measures of air J azotic, and f 
oxygenous, in a glass tube -J inch diameter : electrified it almost 
incessantly for four or five hours. It w^as gradually reduced to 4 
grain measures, 2J of which were oxygen. It was confined by 
water having no oxygen, but f impregnated with azot. The 
spark was taken principally, but sometimes small shocks were 




17 grains 



Residue 4 grains 



Disappeared . 



Relative wts. 



I az. to 2 oxy. \ 
individual particles/ 



Are as 

. 24 



The Genesis of Bait on s Atomic Theory 


Page 258 

19M September 1803 

Table of the Specific Gravities, etc. 

Wt. of ult. 

Diameters of particles 
elastic, to water i. 

Hydrogen gas 
Oxygen gas 
Azotic gas . 


1. 127 



Nitrous oxide 2 A. i O. 
Nitrous gas i A. + i O. . 

Nitric acid 




Phosphuretted hydrogen . 
Gaseous oxyd. carb. i C. 

I O 

Carbonic acid . . . . 
Carbonated hydrog. i to i 
Ammoniac gas .... 
Sulphureous acid . . 
Sulphuric acid . . . . 
Sulphuretted hydrog. . . 
Water vapour .... 
Ether 2 Carb. + i H. . 
Alcohol 2 Carb. + 2 H. i 


1. 102 


1. 000 




1. 106 




















II + 


10 + 


7 + 

The table on this page shows that Dalton lost 
no time in applying his results to the solution of the 
problem which had suggested them. The weights 
employed differ to some extent from those used 
a fortnight earlier, and are applied in conjunction 


New View of Daltons Atomic Theory chap. 

with the specific gravities of the gases to ascertain 
the relative diameters of the particles, by the method 
already described (p. 25). In this particular table 
the particle of standard diameter is not that of 
hydrogen but that of liquid water, so that the 
specific gravities of the gases have to be divided by 
833^, the density of liquid water compared with 
that of air, and the weight of the ultimate particles 
by 6.66, the weight of the atom of water. 

The value for hydrogen should be 11.7. The 
results show that, with a few exceptions, the 
diameters of the different atoms are diff^erent, and 
Dalton was, therefore, so far justified by facts in 
supposing that the uniform mixture of gases might 
be brought about by a diflFerence in the sizes of 
their particles. 

Page 260 

Ultimate atoms of gases in the order of their Specific 
Gravities : — 

. r Hydrogen . 
t Azot 



Carbonated hyd. gas . 
f Oxygen 

Phosphorated hydrogen 
^ Nitrous gas . . . 
Gaseous oxide of carbone 



^Carb. aqueous vapour 


Nitrous Oxide 
Sulphurated hyd. gas 
Carbonic Acid gas . 

• 13-5 

• 15.4 
. 15.4 

I The Genesis of Daltons Atomic Theory 43 

Here we find the atomic numbers used to test 
the theory suggested in Dalton's paper on the 
absorption of gases, viz. that the solubiHty of a gas 
depends on the weight of its ultimate particle. If 
this table be compared with the table of solubilities 
given in the paper on the absorption of gases we 
see that the order is nearly the same [Memoirs^ i. 
p. 272). 

"Bulk Absorbed, the Bulk of Water being Unity 

-^ Azotic gas, hydrogenous gas, carbonic oxide. 

r Oxygenous gas, nitrous gas, carburetted hydrogen gas, 
2^ ( from stagnant water. 
\ defiant gas of the Dutch chemists. 
I Carbonic acid gas, sulphuretted hydrogen, nitrous oxide." 

As already noticed carburetted hydrogen gas 
from stagnant water has been inserted some time 
after the reading of the paper. 

The carbonated hydrogen gas of the table in the 
Notebook is olefiant gas, whilst carbonated aqueous 
vapour (11=5.5 + 4.4+1) is the gas which was 
afterwards proved to be a mixture of carbonic 
oxide and hydrogen. 

Page 262 

lind December 1803 

Proportions of compounds according to theory : — 

Azote. Oxy. 

Nitrous oxide . . . 62 38 

Nitrous gas . . . 42.1 57.9 

Nitric acid . . . 26.7 73.3 

44 iVif-o; View of D alt on s Atomic Theory chap. 





Nitrous oxide 





Nitrous gas 





Nitric acid 





Dalton here recurs to the agreement between 
theory and experiment with regard to the oxides 
of nitrogen, the atomic weights of the last 
table in which oxygen is taken as 5.5 being 
used. This entry is of particular interest, because 
the date which it bears, 22nd December 1803, 
is that of Dalton's first lecture at the Royal 
Institution. There seems to be no doubt that 
Dalton utilised the various tables just discussed 
in these lectures and took the notebook containing 
them with him to London. We may even imagine 
that this special comparison arose from a personal 
challenge from Davy, who, with regard to the 
atomic theory, sustained the part of the " sceptical 
chymist," to test Dalton's latest results. The 
calculations are given on the opposite page of the 
Notebook (261), and it is interesting, and perhaps 
consoling, to observe that the composition of 
nitrous oxide is quite wrongly calculated, the 
atomic weight of nitrogen having been, by a slip, 
taken as 4.5 instead of 4. The real numbers should 
be azote 59.2, oxygen 40.8, which, by the way, 
do not agree with the experimental figures nearly 
so well. 

.Of nearly the same date as the tables quoted 

The Genesis of Dalton's Atomic Theory 


above, is a classified list of formulae (pp. 361-353, 
1 2th October 1803), which presents some points of 
interest. The alternative symbols here proposed are 
interesting in view of Dalton's great repugnance to 
the alphabetic symbols afterwards introduced by 
Berzelius. This list is marked by the same char- 
acteristics as the preceding ones. Olefiant gas is 
mentioned as carbonated hydrogen gas, but marsh 
gas is not referred to. 

Page 361 

l^th October 1803 

New theory of the constitution of the ult. atoms of 



(H) Hydrogen 


® Azote . 

. (D 



% Carbon or charcoal 


© Sulphur . 

. e 


. ® 

P^g^ 359 Binary Compounds. 

00 Water. 

0(D Ammonia. 

03 Gaseous oxide of carbon. 

(DO Nitrous gas. 

#0 Carbonated hydrogen gas. 

00 Sulphureous Acid. 

©O Sulphurated Hydrogen. 

®0 Phosphorous acid. 

®0 Phosphorated Hydrogen. 

46 New View of Baltons Atomic Theory chap. 

Ternary Compounds. 

000 Nitrous oxide. 
000 Nitric acid. 
0#0 Carbonic acid. 
000 Sulphuric acid. 
•0# Ether. 
OSO " Phosphoric acid. 

P^g^ 355 Compounds of 4 Particles. 

•© Alcohol ? ■ 

8§ Sugar. 

P^g^ 353 Compounds of 5 Particles. 


^O Nitrous acid. 

One point still remains for discussion, the influ- 
ence of Richter's work on Dalton's ideas. At 
what exact period Dalton became acquainted with 
this work it is difficult to say, but that his theory- 
was in any way suggested by it can hardly be 
seriously maintained in view of the fact that the 
early tables contain no trace of it, whilst it would 
have been extremely easy for Dalton, if possessed 
of Richter's tables, to have worked out the weights 
of the ultimate particles of the chief bases. This 
matter is more fully treated on p. 91, in the 
discussion of the special numbers used by Dalton 
in his various atomic weight tables. 

I The Genesis of D alt oris Atomic Theory 47 

The view expressed by Debus (p. 10) that the 
use of the term " specific gravities " by Thomson 
in his account of the atomic theory impHed the 
acceptance of the law of equal volumes by Dalton 
in 1804 is also seen to be incorrect. Dalton ex- 
pressly states \n 1803 (see extract from Notebook, 
p. 246), quoted on p. 27, that the specific gravities of 
different elastic fluids and the specific gravities of 
their particles are not the same thing. He never 
appears to have believed in the " law of equal 
volumes," and this only occurred to him as a 
possible alternative, at once shown to be inconsist- 
ent with fact, to the statement which he recognised 
as the true one, viz. " that no two elastic fluids 
agree in the size of their particles." 

Dalton's attitude towards the law of com- 
bination by volume, which, enunciated by Gay- 
Lussac in 1808, has since become of such funda- 
mental importance in chemical theory, is more 
easily understood when we perceive how firmly he 
had been led to believe in the unequal size and 
number of the particles in different gases. So long 
as we hold the view that the atomic theory was 
inspired by the experimental discovery of the law 
of combination in multiple proportions, it remains 
almost incredible that its founder should have 
denied his adherence to such a brilliant extension 
of the same principle. Gay-Lussac's law, inter- 
preted by the atomic theory, leads at once to the 
conclusion that the numbers of particles in equal 

48 New View of Daltons Atomic Theory chap. 

volumes of the different gases are either equal or 
stand in some simple ratio to each other. This con- 
clusion seemed to Dalton to be contradicted both by 
experimental, and, as we have seen, by theoretical 
considerations. The results of his own experiments, 
and those of many other chemists, tended to show 
that the proportions by volume in which gases 
enter into combination are neither exactly equal 
nor in simple multiples, but only approximately 
so. With regard to the special gases, Dalton's 
opinion fluctuated with the results of his experi- 
ments. Hydrogen and oxygen were at one time 
supposed to combine in the proportion of 2 : i 
{New System^ ii. p. 275) ; at another as 1.97 : i 
{New System^ ii. p. 560) ; again as 1.85 : i. 00 
(August 1804). His view is well expressed in a 
letter to Berzelius, dated 20th September 18 12 
(see p. 159). "The French doctrine oi equal 
measures of gases combining, etc., is what I do not 
admit, understanding it in a mathematical sense. 
At the same time I acknowledge there is some- 
thing wonderful in the frequency of the approxi- 

To this opinion he adhered until the close of 
his life, and in the Appendix to the last part of 
the New System^ p. 349, he says : " The combina- 
tions of gases in equal volumes, and in multiple 
volumes, is naturally connected with this subject. 
The cases of this kind, or at least approximations 
to them, frequently occur ; but no principle has 

I The Genesis of Daltons Atomic Theory 49 

yet been suggested to account for the phenomena ; 
till that is done I think we ought to investigate 
the facts with great care, and not suffer ourselves 
to be led to adopt these analyses till some reason 
can be discovered for them." 

It is interesting to note that, although Dalton's 
experiments were less accurate than those of Gay- 
Lussac, yet his conclusion was " in a mathematical 
sense " the more correct. Accurate determinations 
of density have shown that the molecular volumes 
of gases are not exactly equal, but that the 
nearer a gas is to its critical temperature the 
smaller is its molecular volume. In the case of 
gases like ammonia, chlorine, and sulphur dioxide, 
this difference amounts to from i to 2 per cent. 

The evidence afforded by the foregoing 
extracts as to the origin of the atomic theory of 
chemical combination, may be briefly summed 
up as follows : — Dalton's own statement, made 
after an interval of seven years, attributes a 
purely physical origin to the theory, and this is 
confirmed by the fact that in the earliest table 
of atomic weights (6th September 1803) the 
relationships exhibited between the several oxides 
of nitrogen, sulphur, and carbon, are not founded 
upon direct experimental evidence, but upon an 
assumption derived from the physical theory. On 
the other hand, it is equally clear that a month 
before the compilation of the first atomic weight 
table, Dalton had performed an experiment which 

50 New View of D alt on s Atomic Theory chap. 

showed him that oxygen could be made to combine 
with quantities of nitrous gas represented by the 
numbers i and 2. If, however, this experiment 
had inspired Dalton with the idea of the atomic 
theory, it is scarcely credible that in the table 
drawn up only a month afterwards, the atomic 
weight of nitrous acid, upon which the whole 
question turns, should not have been included. 

The balance of evidence is, therefore, strongly 
in favour of the statement made in London by 
Dalton himself in 18 10, that he was led to the 
atomic theory of chemistry in the first instance by 
purely physical considerations, in opposition to the 
view, hitherto held by chemists, that the discovery 
by Dalton of the fact of combination in multiple 
proportions led him to devise the atomic theory as 
an explanation. 

It, therefore, becomes necessary for us to 
modify our view as to the foundation of the 
atomic theory. There seems to be no doubt 
that the idea of atomic structure arose in Dalton's 
mind as a purely physical conception, forced 
upon him by his study of the physical pro- 
perties of the atmosphere and other gases. Con- 
fronted, in the course of this study, with the 
problem of ascertaining the relative diameters of 
the particles, of which, he was firmly convinced, all 
gases were made up, he had recourse to the results 
of chemical analysis. Assisted by the assumption 
that combination always takes place in the simplest 

1 The Genesis of Daltons Atomic Theory 51 

possible way, he thus arrived at the idea that 
chemical combination takes place between particles 
of different weights, and this it was which differ- 
entiated his theory from the historic speculations 
of the Greeks. The extension of this idea to 
substances in general necessarily led him to the 
law of combination in multiple proportions, and 
the comparison with experiment brilliantly con- 
firmed the truth of his deduction. Once dis- 
covered, the principle of atomic union was found 
to be of universal application. Nothing essential 
has since been added to our knowledge of the laws 
of chemical combination by weight. To Dalton 
must be ascribed the rare merit of having, by the 
application of a single felicitous idea to a whole 
class of the facts of chemistry, so completely com- 
prehended the prevailing relations, that his general- 
isations have sustained without alteration the 
labours and changes of almost an entire century. 


dalton's scientific diary, 1 802-1 808 

An examination of the record of Dalton's experi- 
mental work during the period in which he was 
elaborating the atomic theory, and which culmin- 
ated in the publication of the first part of the 
New System of Chemical Philosophy in 1808, entirely 
confirms the non-chemical origin of his great con- 
ception. It is at once apparent that his attention 
was at first directed almost entirely either to purely 
physical phenomena, or to those lying on the 
borderland of physics and chemistry. The solu- 
bility of gases in water and the diffusion of gases, 
together with the laws of heat, were the main 
subjects of investigation, chemical work being 
restricted to the analyses which these researches 
rendered necessary. 

Immediately after the appearance of the first 
table of atomic weights in his Notebook, however, 
purely chemical research begins. In the year 
1803 chemical analysis had attained but a low 
standard of accuracy, especially in its application 

CHAP. II Daltons Scientific Diary 53 

to gases, and the results obtained by different 
observers, all of repute, differed among themselves 
by many units per cent. Nitric acid, for example, 
contained, according to Cavendish, 72.3 per cent 
of nitrogen, according to Lavoisier 79.5, and 
according to Davy 70.5, w^hilst the statements 
as to the composition of sulphuric acid were 
even more discrepant. 

In order to test the application of the theory of 
atoms of different sizes and v^eights to chemical 
phenomena, Dalton therefore at once set to v^ork 
to repeat the analyses both of his predecessors and 
contemporaries, and to institute new ones of his 
own. Only three days after he had written in his 
Notebook the first atomic symbols with which we 
are acquainted, he repeated Cavendish's celebrated 
experiment on the composition of nitric acid 
(p. 39), and in the following autumn he began 
the series of researches on the gaseous compounds 
of carbon, which enabled him to recognise the 
simple relation between olefiant gas and stagnant 

As Dalton advanced in this direction the plan 
of the New System of Chemical Philosophy gradually 
developed in his mind, and we find him turning in 
1806 to the composition of salts, to the chemistry 
of the metals, and to general systematic work. 

It is especially in the investigations on heat 
that Dalton's characteristic mental attitude is laid 
open. A few experiments suggest a sweeping 

54 New View of Daltoris Atomic Theory chap. 

generalisation, which is at once written down in 
the form of a query and then tested by a further 
series of experiments. Nearly all the fundamental 
laws of heat which are stated in the New System 
appear in the notebooks in this form, together 
with many other conjectures, which failed to stand 
the test of experiment. 

In the following pages a general account is 
given of the nature of the work done during the 
successive months of each year, accompanied by 
a few quotations of passages which illustrate 
the author's characteristic methods of work and 

The earliest date to be found in the notebooks 
is September 1802, so that the work embodied in 
the papers entitled " The Power of Fluids to 
conduct Heat" (read 12th April 1799), "The 
Heat and Cold produced by the Mechanical Con- 
densation and Rarefaction of the Air " (read 27th 
June 1800), and "Experimental Essays on Gases" 
(read during October 1801), all of which were 
published in the Memoirs of the Literary and Philo- 
sophical Society of Manchester^ vol. v. part ii. (1802), 
and " On the Tendency of Elastic Fluids to Dif- 
fusion through each other," read 28th January 
1803, and published in vol. i. of the second series 
of the same Memoirs (1805), is not to be found 
among these manuscript records.^ 

^ References [ ] are to the successive volumes of the notebooks. 

II Daltons Scientific Diary ^^ 


The last four months of this year were 
occupied with experiments on lime water, on 
the carbonic acid in air [Manchester Memoirs 
(2), i. 253), and on the solubility of carbonic 
acid, air, and other gases in water. 

2()th October 1802. — On this date Dalton read 
a paper before the Society " On the Proportion of 
the several Gases or Elastic Fluids constituting the 
Atmosphere ; with an Enquiry into the Circum- 
stances which distinguish the Chymical and 
Mechanical Absorption of Gases by Liquids " 
(published in Manchester Memoirs (2), i. 244 ; the 
date appended to the printed paper is 12th 
November 1802). 

[i. 90, 91]. 26th December. — Boiling points of 
sulphuric and nitric acids of different strengths. 


January^ February^ and March were chiefly 
occupied with work on the solubility of gases in 

[i. 81]. — " 2600 grs. water may be said to take 

35 Azotic gas . . 1.35 1.6 

38 Hydrogenous gas . 1.46 1.7 

60 Oxygenous gas . 2.31 3.0 

^ \ Nitrous gas . . If *[ 8 or jL- nearly." 

The numbers of the first column represent the 

56 New View of Daltons Atomic Theory chap. 

solubility per hundred vols, of water ; those of the 
second column have been added later on, and are 
the results of experiments which Dalton considered 
to be more accurate. 

[i. 96-120]. — These pages are entirely filled 
with speculations as to the arrangement of the 
particles of a gas dissolved in water, especially at 
its surface, the nature of which may be judged 
from the following extract, dealing with the equi- 
librium of the exterior gas with that dissolved 
in the water : — 

[i. 99, 100]. — "Query, is it not two atmo- 
spheres pressing one against the other : both being 
constituted of geometrical progressions of very 
different ratios t One slowly and the other very 
rapidly running off in density ? 

" To investigate the preceding query it will be 
proper to consider what kind of geometric series 
will take place at the surface of the water. 

" Let the particles of air to water at the surface 
of contact be i to 100, and let F(29^ inch M.) 
= force exerted by the whole on the surface, the 
whole force of atmosphere being 30 inches. 
Thence the first surface of particles will press 
with F/ioo force, and all the rest must press with 
the same Force. 

" If we take the whole force of the atmosphere 
on the water, then the diminution of the series 
= 1/100 in force, or each particle below must be 
i/ioo farther of the upper one, the original dis- 



Daltons Scientific Diary 


tance being unity : the distances at different points 
may therefore be found as under : — 

Diameter of 

Whole distance 

Sum of 

Remr. of sum 



from surf. 


to infinity. 


1. 1046 














1. 01 150 














5 + 

[i. 112]. 6th March, — "It now appears more 
than probable that in all cases 

" Hydrogen and azotic gases in water have 
their particles 4 times the distance that they 
have incumbent = 1/64 or 1.5625 per cent, and 
oxygen gas 3 times =1/27 density = 3.7." (Com- 
pare Manchester Memoirs (2), i. 272.) 

A few experiments on diffusion, and a number 
on the combination of nitrous gas with oxygen, 
were also carried out during these months, a paper 
being read on 14th January before the Manchester 
Society on the " Spontaneous Intercourse of 
Different Elastic Fluids in Confined Circum- 
stances," no account of which has been published. 

[i. 133]. 1st to 6th April, — Experiments on the 
combination of nitrous gas with oxygen, and on the 
solubility of gases. April 6th is noted as " End of 
Expts. of this sort till after midsummer 1803." 
The remainder of the month of April, and the 

58 New View of Daltons Atomic Theory chap. 

whole of May and June were devoted to researches on 
the phenomena of heat, expansion of liquids, expan- 
sion of water in different vessels, force of steam, etc. 

[i. 161]. 5//z May, — "It appears more than 
probable that the expansion of all liquids (bulk for 
bulk), from /reezing to boiling, is reciprocally as 
their specific heat, — and that all liquids require 
(bulk for bulk) the same quantity of heat to be 
added to them in their lowest state to make them 
boil under the atmospheric pressure." 

6th. — " Tried a saturated solut. of com. salt 
in water in the same bulb as the pure water. It 
gave 348 parts of expansion from ^j° to boiling 
water ; to which add 2 1 for the glass, we have 
369. Now about 1 10 more should be allowed for 
salt and water by reason of 57"" or more below and 
1 2° above. This makes 479 for salt and water in 
all. The expansion of pure water for the same is 
363. This gives the capacity of water to sat. salt 
and water nearly as 10 to 7.5. Gadolin makes it 
.7926 ; but it is probable he is too much by taking 
the zero too high." 

yuly of this year was given up to the annual 
holiday, no entries being found for it after the 5th, 
whilst the next date recorded is 

[i. 188]. yd August, — "It appears from the 
recent observations on Helvellyn that the vapour 
point falls about 1° in 200 yards ascent nearly." 

August, — Experiments on the solubility of 
gases, a few observations ,on the combination of 

II Daltons Scientific Diary 59 

nitrous gas with oxygen, and some experiments on 
diffusion, the last of these being carried out by 
exposing a phial filled with the gas, and sometimes 
provided with a tube, to the air for a few minutes, 
and then examining the residual gas. 

[i. 244-260]. September, — Here occur the tables 
of atomic weights, etc., as already quoted (pp. 26- 


[i. 2 1 5-2 1 9] . — These pages contain the diagrams 

of gases dissolved in water, published in the Man- 
chester Memoirs (2), i. 285, Plates 2 and 3 (1805). 
In the Notebook the two diagrams of particles at 
a distance of 3 to i (density 1/27) are ascribed to 
oxygenous and nitrous gas, whilst in the Memoirs 
carburetted hydrogen has been added, this gas 
having been, as we have already seen, first examined 
in 1804 (p. 29). 

A few analyses of air were also done during the 

October. — Absorption of nitrous gas by water 
and combination of this gas with oxygen (see p. 35). 
In this month Dalton commenced his work on the 
gaseous compounds of carbon, experimenting on 
the gases obtained by the incomplete combustion 
of ether and alcohol vapours, and by heating wood, 
wet charcoal, etc. No less than seventy experi- 
ments on ether vapour are recorded during the 
month, and new formulas for ether and alcohol 
continually recur in the notes, devised to explain 
the results of special experiments. 

6o New View of Daltons Atomic Theory chap. 

An account of the state of knowledge on this 
subject and the reasons which induced him to com- 
mence the investigation is given by Dalton in his 
notes for the lectures at the Royal Institution 1 8 1 o 
(p. ii6). 

The following passage written in October 
summarises the results at which Dalton had 
arrived at that date. The " carb. hyd." of this 
table is shown by the contents of the preceding 
pages in the Notebook to be some product obtained 
from ether vapour : — 


[^ , -\ Ox. Carb. acid. upon 

1. 294J. original. 

1 00 pure carb. hyd. should take 1 86 and make 120 i .56 
100 pure gaseous oxid. carb. 50 100 .5 

C 42 hyd. -^ com. A. 1.4 

100 pure hydrogen I or 

( 50 hyd. yV com. A. 1.5 

100 pure carb. aqueous vap. 60 56 1.04 

21 St October, — Paper on Absorption of gases, 
read before the Manchester Society. This paper 
contained the first published intimation of the 
atomic theory. 

4^ November. — Paper on the " Law of Expan- 
sion of Elastic Fluids, Liquids, and Vapours " (not 

This paper embodied the results and specula- 
tions recorded in the Notebook during April, May, 
June, and July. 

The only entry for November of this year is of 
some interest. 

II 'Daltoris Scientific Diary 6i 

[i. 306]. 13/^ November. — "Query, does not 
hydrogen retain the same density in hydrogen gas, 
carb. hydrogen gas, oxy. hydrogen gas (aqueous 
vapour), sulph. hyd. gas, azotated hyd. gas (vol. 
alkali), phosphuretted hyd. gas." 

December. — The only work recorded consists of 
a few analyses of air, some experiments on the 
latent heat of fusion of ice, and a repetition of Hope's 
experiment, dated i6th December, together with 
the entry dated 22nd December, to which refer- 
ence has already been made (p. 44). 

Towards the close of the month Dalton went 
to London to deliver a course of lectures at the 
Royal Institution, the first of which was given on 
22nd December. 


loth 'January. — Letter written from London 
to the editor of Nicholson s Journal expressing the 
opinion that the maximum density of water occurs 
at 32° (see p. 139). 

February., March., April. — Experiments on the 
temperature of greatest density of water. 

[i. 381, 382]. March. — On these pages is to be 
found the first application of the atomic theory to 
the compounds of the metals (p. 97). 

May and June. — Diffusion, solubilities, com- 
bination of oxygen with hydrogen, and of oxygen 
with nitrous gas. 


62 New View of D alt on s Atomic Theory chap. 

yuly, — On the 28th is found the usual " holi- 
day " entry, dealing with air from Helvellyn. 

August, — Experiments on the gaseous com- 
pounds of carbon, from ether and alcohol vapours, 
and from stagnant water. 

[i. 269]. — -"New carb. hyd. from stagnant 
water. Contains no oxygen, and 7 or 8 per cent 
carbonic acid till cleared." 

This is followed by a number of eudiometric 

analyses, of which the following may be taken as 

an instance : — 


78 oxy. 

80 fired. 
67 washed. 

[i. 271]. — "New carbonated from stag, water. 

" It appears by a most decisive set of experi- 
ments, direct and indirect, that this gas is absorbed 
-2^5 and therefore differs from the olefiant gas and 
oxy. carb. gas." 

[i. 2j2a\, — " Query, is not ether after all i 
carbon and i hydrogen ? 

00 ether ? G)#0 olefiant gas. q^ oxy. carbonate. 

Or is ^ ether. #0 olef. G)#0 carb. hyd. 

^Y oxy. carb." 

[i. 278]. — " N,B, — The carb. hyd. in water 
formed thus 

II Baltons Scientific Diary 63 

2 oxy. + I carb. = carb. acid. 
2 hyd. + I carb. = gas in quest. 

from the decomp. of 2 particles of water. 

Thus O O 0#0 
or thus g • O^ become {OJO» 

This is one of very few symbolic equations to 
be found in the notes. 

[i. 282]. 24M August. — " It now appears highly 
probable that the gas called oxy, carbonate in these 
notes is in reality a compound oi gas oxid, of car bone 
and hydrogen in equal parts." 

[i. 283]. 2\th August. — This page contains a 

statement showing that by this time the relation 

between olefiant gas and stagnant gas had become 


Olefiant gas. 

Meas. Acid. Oxy. Dimin. 

100 200 300 200 

100 100 200 200 

All gases containing olefiant are distinguished by the smell : 
the oxycarbonate and stagnant not. 

[i. 287, 288]. — These pages contain a list of the 
equivalents of the alkalis and earths, to be discussed 
later (p. 92). 

The following " Remarks on sulphurated hydro- 
gen, etc.," are interesting : — 

64 New View of Daltons Atomic Theory chap. 

[i. 324-326]. — I. " Sulph. hyd. gas cannot be 
sulphur and water because in firing with oxy. 
sulphur is thrown down and oxy. spent. 

2. The gas may then be i hyd. + i sulphur, or 
2 hyd. + I sulphur. It seems formed from hydro- 
gen and sulphur by passing hyd. through melted 

3. It seems probable that the oil which Ber- 
thollet calls sulphur hydrogenated is i sulphur and i 
hydrogen, analogous to the olefiant gas of carbone 
and hyd. 

000 Sulphuretted hydrogen. 

^^'^^^ Hydrosulphure of lime. 
^ Sulphure of lime. 
^ hydrogenated sulphur. 
^^ hydrogenated sulphure." 

September. — Experiments with Volta's eudio- 
meter and on ether vapour, etc. Expansion of 

[i. 318]. — Theory of oxides of metals (p. 97). 

[i. 329]. I 3//^ September, — " It seems very pro- 
bable that azotic and oxygen gases condensed 
moderately would fire by the electric spark and 
become nitric acid." 

[ii. 107] \\th September. — More correct tables 
of the sp. gr. etc. of certain gases. 



II Daltons Scientifi 

k Diary 


Sp. Gr. 


Wt. of 

ult. par. 

Diam. of 
part, elas- 

air I 

Hyd. being 

tic to 

Hydrogen gas .... 


hyd. I. 




Oxygen gas .... 




Azotic gas ..... 





Nitrous oxide (2 A + i ox.) 




Nitrous gas (i A + i ox.) 

1. 102 



Nitric acid (i A + 2 ox.) 




Carbonic oxide (i C + i ox.) 




Carbonic acid (i C + 2 ox.) 



1. 00 

defiant gas (i C + i H) 




Carb.hyd. from water ( I C + 2 H) 



1. 00 

Sulphuretted hyd. (i S + 2 H ?) 

1. 106 ? 



Aqueous vap. (i H + i ox.) 




Ether (2 carb. + i hy.) 




Alcohol (2 carb. + i wat.) 




Ammon. gas (i A + i H) 




It will be seen that the numbers in the last 
column generally differ very considerably from 
each other, and must have been considered by 
Dalton as in very satisfactory agreement with his 
theory of the structure of gases. 

October, November and December, — These months 
were occupied with experiments on heat, the 
rate of cooling of bodies and the expansion and 
temperature of maximum density of water. Papers 
were read by Dalton before the Manchester Society 
on 5th October, " On Heat," and on 30th 
November " Review of Dr. Hope's paper on 
the Contraction of Water by Heat.'* 

66 New View of Daltons Atomic Theory chap. 


'January, — Determination of the temperature 
of maximum density of water by expansion in 
thermometers of different materials, and by Hope's 
experiment under various conditions. 

No entries are to be found for February ^ March^ 
Aprils and May, We learn from Henry {Life of 
Dalton^ p. 63) that in February Dalton went to 
London to purchase apparatus, and in the summer of 
the year delivered a course of lectures in Manchester 
to an audience of about 120 at two guineas each. 

The last section of vol. ii. of the Notes is made 
up of about half a dozen of spare copies of the 
prospectus of these lectures, the printed side being 
often covered with notes as well as the blank pages. 

The prospectus runs as follows : — 

" Prospectus 

of an intended course of 

Lectures on Natural Philosophy 

in Manchester 

by John Dalton 

" In a populous town like this, where the Arts 
and Manufactures are so intimately connected with 
various branches of Science, it may be presumed 
that public encouragement will not be wanting to 
a person qualified to exhibit and illustrate the truths 


II Daltons Scientific Diary 67 

of experimental philosophy upon a liberal and 
extensive scale. 

" Notwithstanding this it would be imprudent 
for one of limited resources to purchase a large and 
expensive apparatus adequate to the object, upon a 
mere presumption. Something like a certainty of 
remuneration in a degree may fairly be expected. 

" With this view I propose, if a competent 
number of subscribers at two guineas each be pro- 
cured, to extend the apparatus already in my 
possession, so as to give a course of twenty lectures 
on the various branches of experimental philosophy 
in the ensuing spring. Having for many years 
been engaged in the cultivation of the sciences of 
Mathematics and Natural Philosophy, and having 
lately delivered a course of Lectures similar to the 
one proposed in the Royal Institution at London, 
I may perhaps have some claim upon public 

" Each subscription ticket will admit a Gentle- 
man and a Lady or two Ladies. The Lectures 
will be delivered twice if the number of subscribers 
exceed sixty, in order to their greater accommoda- 

" Those who wish to favour the undertaking will 
oblige me by putting down their names as early as 
may be on papers left for the purpose at Messrs. 
Clarkes' or Messrs. Thomson and Son's, book- 

Falkner Street, Jan, 2, 1805. 

68 New View of Daltotis Atomic Theory chap. 

yune. — Composition of nitrous oxide. Solu- 
bility of olefiant gas, nitrous oxide and nitrous gas. 

[ii. 36]. t^th July, — " It appears that stag. 
Gas requires ^ of its share of oxigen, namely 
cent per cent before it will fire. It then becomes 
same bulk of gas without any acid, that is gas. 
oxid. of carb. and hyd. 

" It again appears that olefiant gas requires its 
bulk of oxigen to fire — i measure then becomes 
nearly 4, and requires \ its bulk of oxigen and 
produces half its bulk of acid. No oxigen or 
acid after the first firing." 

Composition of nitrous oxide, gas from boxwood, 
from chalk and iron, ether gas, olefiant gas, etc. 

[ii. 41]. — Composition of sulphuretted hydrogen 
by explosion with oxygen. 

" It seems clear that sulph. hyd. takes twice 
its bulk of oxigen, and is therefore 4 times the 
density of com. hydrogen." 

(This refers to the density of the hydrogen in 
the compound, see p. 61.) 

July, — Sp. gr. of air, ether vapour, carbonic 
acid, and stagnant gas. 

August, — Solubility of gases, composition of 
nitrous oxide, ether gas, etc. 

September, — Alcohol vapour. 

Nitrous gas and oxygen. 


??■' -■■- 

II Daltons Scientific Diary 69 

Two or three pages are occupied with an 
account of the colour of the precipitates produced 
by mercuric nitrate and lead acetate with lime- 
water, sulphuretted hydrogen, and alkalis, showing 
that Dalton was now beginning to take an interest 
in general chemistry. 

October, — The only entry during this month is 
as follows : — 

[ii. 123]. 6th October 1805. — "It appears from 
sundry expts. that hyd. fired with oxigen gives 
100 ox. for 190 hyd.: — it seems too that when the 
combustion is very rapid there is some trace of oxig. 
left in hydrogen. In slow combustion it should 
seem as if 100 ox. required 200 hyd. At least 60 
seems right for atmos. air. 

" Again repeated and 60 seems the nearest num- 
ber — 


185. This may be said to be 190." 

60 here is the diminution produced by firing air 
containing 21 per cent of oxygen with hydrogen. 

November. — Cooling of a thermometer in 
difi^erent gases. 

Heat of combustion of tallow. 

Dalton seems to have commenced his work on 
the New System at about this time (Henry's Life^ 
p. 64), and this no doubt accounts for the small 
amount of experimental work recorded during 
these months. 

70 New View of 'DaltorCs Atomic Theory chap. 

December, — Experiments on rate of cooling, etc. 

Experiments on diabetic urine. 

[ii. 137]. 1st December, — "It seems probable 
that the Radiation of heat is either a constant 
quantity, or rather perhaps increases as the density 
decreases : — that the Abduction depends upon the 
proper capacity of the medium. The abduction 
cannot therefore decrease exactly as the density^ 
because the capacity is greater in rarefied air, 
proved by the cold produced. It cannot be as the 
cube root of density or diameter of particles, because 
experience is against it. It may be as the square 
root of the density, as that nearly agrees with 
experiments. The square of cube root of density 
does not seem to agree — nor ought it." 

Note (added at a later date). 

" Probably the sq. of cubic root of density 
multiplied by capacity." 

In the New System^ i. p. 120, Dalton states his 
final conclusion that it varies " nearly or accurately 
as the cubic root of the density." 


January, — Temperature of maximum density of 

February, — No entries. 

March, — Experiments on the efi^ect of breathing 
and combustion on air (Paper " On Respiration 
and Animal Heat" read 7th March 1806. Pub- 

II Daltons Scientific Diary 7 1 

lished, Manchester Memoirs^ ii. (Second Series), p. 


The remainder of this month, together with 
the whole of April and May and the greater part 
of June, was entirely occupied (the notes extend 
to about fifty pages) with experiments and specula- 
tions on heat, the final results of which are em- 
bodied in the New System^ part i. 

The following extract from a short article 
" On heat," extending to five pages of manuscript 
[ii. 287-292], 2yd May 1806, is of interest 
as giving a very clear account of Dalton's ideas 
about the atmospheres of heat with which his 
atoms were provided. 

"... According to this view of the subject, 
every atom has an atmosphere of heat around it, in 
the same manner as the earth or any other planet has 
its atmosphere of air surrounding it, which cannot 
certainly be said to be held by chemical affinity, 
but by a species of attraction of a very diff^erent 
kind. Every species of atoms or ultimate particles 
of bodies will be found to have their peculiar powers 
of attraction for heat, by which a greater or less 
quantity of that fluid will be conglomerated around 
them in like circumstances : this gives rise to what 
has been called the different capacities of bodies for 
heat or their specific heat. Any two bodies, the 
atoms of which have difl?erent capacities for heat, 
being placed in any medium will acquire the 
same temperature. This state consists in the several 

72 New View of T) alt on s Atomic Theory chap. 

individual atmospheres of heat acquiring the same 
density at their exterior surface^ or where they 
become contiguous. The virtual diameters of 
atoms of matter will therefore vary in like circum- 
stances according to their attraction for heat ; those 
with a strong a^ttraction will collect a large and 
denser atmosphere around them, whilst those 
possessing a weaker attraction will have a less 
atmosphere, and consequently the virtual diameter, 
or that of the atom and its atmosphere together, 
will be less, though the atmospheres of both have 
precisely the same disposition to receive or to part 
with heat upon any change of temperature. 

" Temperature may perhaps be best conceived of 
from a vacuum surrounded by any solid body : heat 
will flow into the vacuum till an atmosphere of 
uniform density is established within it. If more 
heat be added to the solid body a part of it will be 
given off to the vacuum ; the density of heat within 
the vacuum is to be understood as the proper 
measure of temperature, provided it could be 

" Every atom of matter possesses the same at- 
traction for heat, whether it is situated in a dense 
or rare atmosphere of that fluid ; the quantity 
collected therefore must depend primarily on the 
temperature of the medium." 

[ii. 208]. — "Query, does not the quantity of 
heat in a given volume of gas vary as the diameter 
of the atoms under like pressure ? No." 

Plate 5 



I' •"'^ 

Plate 6 

^ ,^^^^::zix^* yY—£<^ v,^w^^ r>^ 

. /■^ 

II Daltoris Scientific Diary 73 

[ii. 209]. 1st June, — "I. It seems clear that 
the attraction of any atoms for heat must be as 
their diameters in an elastic state, whatever be the 
law of attraction. 

" II. It seems also true that the law of attrac- 
tion, whatever it may be, will not affect the relative 
quantities of heat around different kinds, in like 

" III. Further, the absolute quantities of heat 
around different atoms must be as the cubes of 
the diameters of these atoms. Consequently all 
elastic fluids of given pressure and temperature contain 
the same heat in the same bulk'' 

This conclusion is stated in the New System^ i. 
p. 70, to be untenable. 

[ii. 218, 219]. ijth June. — These pages are 
reproduced in facsimile in Plates 5 and 6. 

" Thoughts on atmospheres of caloric." 

" I. It is probable that on the coalition or 
chemical combination of two atoms of air, the 
caloric between them is partly given out and is 
(partly) thrown on to the new general atmosphere, 
but that the quantity thrown out is always greater 
than the quantity so collected. 

"2. It is probable that the distances of the 
particles so combined varies by heat the same 
in the simple as the compound, in like circum- 

" 3. The figures of compound particles cannot 
be globular if one simple has a greater attraction 


74 New View of Daltofis Atomic Theory chap. 

for caloric than another. The difference, however, 
will be small. 

" 4. Whenever three units form a particle, or two 
particles, one double and the other single, caloric 
is given out so that the compound is of greater 
specific gravity than would arise from the simple 

[ii. 220-2]. 2\st June. — Experiments on the 
explosion of gaseous mixtures, of oxygen and car- 
bonic oxide, leading to the conclusion " that both 
oxygen and the gas in plenty may be left after 

July, — Analysis of air and oxygen. 

[ii. 224]. yuly 26th, — "It seems to strike 
with peculiar force that with respect to heat there 
ought to be found two Analogies — one for the 
absolute quantity of heat — the other for tempera- 
ture ; the measures of the former will be some- 
what resembling a cylinder in capacity — the other 
probably resembling a cone,''' 

August^ Septembery and October, — During these 
months Dalton was busy with the composition of 
salts and the revision of his atomic weights (see 

PP- 83, 93)- 

[ii. 241]. 9M September, — '' N,B, Sulphuretted 

hydrogen and sulphuric acid ought to be formed 

from water as carburetted hyd. and carbonic acid 

(p. 63) by decomposing as under : — 




II Dahons Scientific Diary 75 

Therefore the sulphuretted hyd. ought to be i 
sulphur and 2 hydrogen." 

[ii. 245]. "Sulphuretted Hydrogen. — From 
a carefully repeated trial it seems confirmed that 
20 of this gas takes 30 oxygen as near as may 
be. The hydrogen therefore is three times the 
density of com. hydrogen. 

" If therefore sulphur =12 

Sulphuretted hyd. = 15= r^^. 
If sulphur = 8 
Then sulphuretted hyd. = 10 = 000." 

(Compare p. 64.) 

[ii. 269]. 2jth September. — "Found that ^r^ 
damp of coal mines is carb, hyd, pure." 

November and December 1806. — The only entry 
is as follows : — 

[ii. 258]. 2nd November, — It appears almost 
demonstrable that ammonia is 2 particles of azot 
and 2 of hydrogen united ; also that a particle of 
nitric acid weighs 38, and is made of what I have 
formerly conceived to be two particles, whence 
they will be marked thus — 

§0000 Nitric Acid. 

QCD00 Nitrous vapour. 

O^P-^O Oxynitric acid formed by mixing nitrous gas with 
^ O an excess of oxygen. 

76 ISIew View of Daltons Atomic Theory chap. 


In March and April of this year Dalton 
delivered and repeated a course of lectures at 

During the ^earlier part of the year he was 
almost entirely engaged with experiments on heat 
and on the specific gravity and boiling points of 
acids. One or two new tables of atomic weights 
are also found, probably drawn up for the Edinburgh 

[ii. 306]. 2()th January, — "Heat. The densities 
of the exterior surfaces of elastic atoms depend 
entirely on the pressure and no ways on the 
temperature : this last influences the bulk of the 
atom only." 

[ii. 318-322]. February, — Determination of the 
heat of combustion of hydrogen, etc. The results 
are practically identical with those given in the 
New System^ i. 'jj^ but the volume of gas used 
and the capacity of the vessel heated are only 
one half of those mentioned in the latter. 

[ii. 330]. February, — "Does not the capacity 
increase as the volume reckoning from absolute 
solidity or from the volume at absolute cold ? " 

[ii. 331]. Theory of the formation of ice as 
given in the New System^ i. p. 137. At foot of 
page, " This is a most satisfactory explanation." 

On tth February Dalton read before the 
Manchester Literary and Philosophical Society a 


II Daltons Scientific Diary 77 

paper on " The Constitution and Properties of 
Sulphuric Acid," which was not printed in the 
journal of the Society. The alternate blank pages 
of this paper were utilised later on (in 181 1) by 
the author for notes, and the paper is therefore 
found bound up in vol. iv. of the Notebook 
[pp. 192-156]. 

The paper consists of a critical discussion of 
the various authoritative analyses of the acid and 
of barium sulphate, accompanied by the author's 
own views, which are practically the same as those 
expressed in the New System^ ii. 398. 

The remainder of the paper treats of the 
density of the acid and some of its mixtures with 
water and the heat evolved on dilution, the latter 
being used to calculate the absolute amount of heat 
in the acid. 

The following extracts are of some interest : — 

" Upon the whole I think we may safely 
conclude from the experience already had on this 
subject that the quantity of sulphur in real sul- 
phuric acid is not less than 40 nor more than 
45 per cent ; and consequently the oxygen not 
less than 55 nor more than 60 per cent." 

" In corroboration of the above conclusion I 
might add the results of my own investigation on 
this subject. My enquiries not only respect the 
weighty but the number of particles of sulphur and 
oxygen which constitute an atom or smallest 
particle of sulphuric acid. Having found from 

78 New View of Daltons Atomic Theory chap. 

a comparison of the several sulphates and other 
neutral salts, that a particle of sulphuric acid 
weighs 34 times as much as i of hydrogen ; 
and that one of oxygen weighs nearly 7 times 
as much as i of hydrogen : it seemed almost 
certain that to constitute an atom of sulphuric 
acid, either 2 or 3 atoms of oxygen must 
join to I of sulphur ; if 2 atoms of oxygen, 
then one of sulphur must weigh 20 ; if 3 atoms 
of oxygen then one of sulphur must weigh 
13 or 14; the latter supposition seemed most 
coincident with the facts in general. According 
to my view of the subject, therefore, sulphuric acid 
must be composed of 39 or 40 sulphur and 60 or 
61 oxygen. It is remarkable that sulphuretted 
hydrogen gas seems likewise to be constituted of 
I atom of sulphur and 3 of hydrogen." 

[ii. 334]. ^th March, — "Boiled some nitric 
acid with a view to condense it ; it began about 
240°, and having boiled a few minutes the greater 
part was vaporised or decomposed in a moment, 
throwing the rest about the room, breaking the 
phials, burning nearly all my cloaths, hands, etc., 
thighs and legs marked through breeches and 
stockings, etc. This acid was dark coloured, but 
gave no elastic vapour of consequence before 

[ii. 342]. — Specific gravity of sulphuric acid. — 
" OHF^y? is not the geometric mean of any two specific 
gravities correspondent to the arithmetic mean of 

II Daltons Scientific Diary 79 

the two ingredients ? If so it will be a most 
important fact. Try 10 A + 5 W and see if it 
come 1.58. Also is not alcohol and water the 
same ? Also is not the quantity of heat given out, 
proportionate to the difference between the arith- 
metic and geom. means of the densities ? " 

[ii. 343]. — " It seems clear that the geometric 
mean of the two sp. gr. must be right, for it is 
airways less than the arith. mean as it ought 
to be ; and it agrees with direct expt. This 
regards sulphuric acid. But if it apply to alcohol 
we must be wrong in supposing alcohol of .82 
to be pure; it probably contains considerable 

[ii. 347]. Edinburgh^ 2%th March. — " It is 
probable the purest alcohol of .791 sp. gravity is 
still more than half water." 

1 9M April, — " Is not sulphureous acid sul- 
phuric and sulphur? Thus q©0' ^^^ weight 


[ii. 348]. "Oxalic acid is probably 088 — S^* 

" Tartaric acid seems to be 50 by Richter. 

" Citric acid is about 50 by Richter and Vau- 

This is the first reference to Richter which 
has been found. Richter's numbers for these acids 
were — Tartaric 1694, citric 1583 (sulphuric = 

On his return from Edinburgh, Dalton was 


New View of Daltons Atomic Theory chap, n 

engaged during May, June, and July in the study 
of the oxides and salts of the metals. 

The notes include his own analytical results 
and observations, together with numerous com- 
pilations and comparisons of the results of others. 

[ii. 421]. July, Metals. 












After July, Dalton was probably much occupied 
with preparing and passing through the press the 
first part of the New System^ as the entries for the 
remaining part of the year and the whole of 1808 
are very scanty, and for the most part consist of 
tables, etc., which are reproduced in that work. 

The following passage is perhaps as character- 
istic of its author as any hitherto quoted : — 

[ii. 495]. July 1808. — "A quire of paper 
such as part i. oi New System of Chemistry weighs 
14 oz. at a medium." 

Sp. gr. 

Ult. atom. 

Sp. heat. 


37 ^' 50 ? 40 






















1. 00 








dalton's atomic weight numbers 

In seeking to determine the weight of the ulti- 
mate particle or atom of a substance, Dalton at 
once perceived that a simple knowledge of the 
proportion in which the substance combined with 
a fixed weight of some standard substance was 
not sufficient, but that it was also necessary to 
ascertain the number of atoms of each between 
which the combination ensued. He was unable 
to perceive any more definite way of deciding this 
all important question than the assumption of the 
" Law of greatest simplicity," according to which 
the simplest possible formula is most probably 
the correct one. Admitting the uncertainty of 
this method of reasoning, but finding himself 
unable to replace it by any more trustworthy, 
Dalton in his first table of atomic weights, as 
well as in his last, remained true to the prin- 
ciples laid down in the celebrated chapter on 
" Chemical Synthesis." ^ 

^ Neza System^ part i. p. 214. 

82 New View of Daltons Atomic Theory chap. 

The actual numbers chosen by Dalton to repre- 
sent the atomic weights of the elements and their 
compounds, varied considerably in the various 
tables w^hich he published from time to time, 
and they are in many cases marked by wide 
divergence from the numbers which are now 
accepted, so that it becomes a matter of interest 
to ascertain the reasons which led him to the 
choice of each special number, and to see how far 
he depended for his data upon the analyses of 
others, and how far upon his own work. The 
attempt has been already made,^ but the additional 
information now supplied by the laboratory records 
renders a much more complete treatment of the 
matter possible, and shows that some of the con- 
clusions previously arrived at are not quite 

It will be convenient in dealing with the 
atomic weights to divide the substances concerned 
into the three classes of non-metals, earths and 
alkalis, and metals. 

Dalton's attention was at first directed almost 
entirely to the non-metals, their gaseous compounds, 
and the acids derived from them, and the laboratory 
notebooks contain several provisional lists of atomic 
weights in addition to those which have hitherto 
been made known. 

The following table contains in chronological 
order all the lists drawn up by Dalton before the 

1 Roscoe, Manchester Memoirs (1875), [3] 5» 269. 



Daltons Atomic Weight Numbers 


publication of the first part of the New System in 
1808, together with those published in the first two 
parts of that work, and the list supplied by Dalton 
to Thomson, and printed by the latter in his System 
of Chemistry in 1807 : — 

Table A 













Hydrogen . 












Azote . . 











Sulphur . 














9 + 






(i) Notebook, i. 248, 6th September 1803. 

(2) Notebook, i. 258, 19th September 1803. 

(3) Notebook, i. 260, September 1803. 

(4) Manchester Memoirs (2), i. 287 (1805). 

(5) Thomson's List (1807), probably given to Thomson by Dalton 
in 1804, or perhaps later. 

(6) Notebook, ii. 282, 23rd August 1806, and ii. 284, 14th 
August 1806. 

(7) Notebook, ii. 247, i6th September 1806 ; and ii. 256, 
22rid October 1806. 

(8) New System^ part i. p. 219. 

(9) New System, part ii. p. 352. 

(10) The numbers of (9) calculated to 0=i6, and assuming the 
modern formulae. Two numbers are given for nitrogen and phosphorus, 
one calculated from Dalton's formula of the hydride, the other from 
that of the oxide. 

(11) The modern numbers, 0= 16. 

84 New View of Daltons Atomic Theory chap. 

I. Oxygen 

Dalton uniformly adopted the atomic weight 
of hydrogen as unity and determined the relative 
weight of oxygen from the composition of water, 
assuming that the atom of the latter was made up 
of one atom of oxygen and one of hydrogen. 

Columns (i) and (2), Table A. — The number 
5.66 is calculated from Lavoisier's analysis of water, 
according to which it contains — 

85 Oxygen. 
15 Hydrogen. 


Columns (3) and (4). — The reason for the 
change from 5.66 to 5.5 is to be found in the 
Notebook, i. 257. 

" Note relative to the wt. of oxygen : — 

"If we take 84J to 15J it gives 5.5 oxy. to i hyd. ; but i 
measure oxy. seems to combine w^ith 2 hydrogen : if sp. gr. of 
hydrogen be -^ of oxygen it gives 5 to 

» 5.5 „ 

55 6.5 „ 
55 7 )) 

Column (5). — The number 6 is probably given 
by Thomson from recollection as the nearest whole 

Columns (6), (7), (8), and (9). — After the 
appearance of Gay-Lussac and Humboldt's memoir 
in 1805, Dalton [New System^ i. 274) adopted their 













Ill 'DaltoYis Atomic Weight Numbers 85 

analysis for water, according to which it contains 
87.4 oxygen to 12.6 hydrogen, or nearly 7 to i 
(6.93 to i). 

II. Nitrogen 

Columns (i), (2), (3), Table A. — The number 

4 for nitrogen is derived from an old analysis of 
ammonia (Notebook, i. 247, September 1803) by 
Austin (Phil 'Trans, 1788), according to which this 
gas is composed of 121 parts of nitrogen to 32 of 
hydrogen, or about 80 per cent nitrogen to 20 per 
cent hydrogen. 

Column (4). — Berthollet [yourn, de Phys, xxix. 
177) obtained the more correct numbers, 121 of 
nitrogen to 29 of hydrogen, or 4.2 to i. 

Columns (5) to (9). — The reasons for adopting 

5 as the atomic weight of nitrogen are explained 
in the New System^ i. 319. From Davy's analysis 
of the oxides of nitrogen it appeared to be 5.6 
(0 = 7), whilst from the analysis of ammonia it 
seemed to be 4.7. The reason for this great 
divergence does not lie in the experimental work, 
but in the fact that Dalton formulated the oxides 
of nitrogen as we do, but looked upon ammonia 
as NH. The correct numbers would, therefore, 
have been from the oxides, N = 6. i (0 = 7) and 
from ammonia, N = 4.7 (H=i). Dalton himself 
considered that 5.1 more nearly represented the 
atomic weight of nitrogen as derived from the 
analysis of the oxides. 


86 New View of Daltons Atomic Theory chap. 

III. Carbon 

Dalton seems to have adhered throughout 

to Lavoisier's analysis of carbonic acid gas, 

according to which it contains 72 of oxygen 

and 28 of carbon per cent. If this be so, 

and the atomic weight of oxygen be 5.66, then, 

the formula of carbonic acid being assumed as 

COg, the atomic weight of carbon must be 

28 X C.66 _- , . . 1 
^ — =4-4- ihe number 4.5 given m the 

first list is probably a miscalculation. When the 
atomic weight of oxygen was changed to 5.5, 

that of carbon became ^'^ =4-3? ^i^d finally 

with O = 7, carbon became 5.4. In lists 6-8, how- 
ever, it is made equal to 5, this being most probably 
simply an approximation, which Dalton, in view 
of the great uncertainty attaching to the numbers 
for the other elements, considered to be sufficiently 
accurate. In any case there does not seem to have 
been any more authoritative analysis of carbonic 
acid which would account for the change, and in 
the New System^ i. 237, we find the statement : — 

" From the various combinations of charcoal 
with other elements, hereafter to be mentioned, 
the weight of its ultimate atom is deduced to 
be 5, or perhaps 5.4, that of hydrogen being de- 
noted by unity." 


III Daltons Atomic Weight Numbers 87 

IV. Sulphur 

The great variation in the numbers chosen for 
sulphur at various times is to be attributed to the 
uncertainty which existed as to the composition of 
sulphuric acid. The results of different observers 
differed so much that the choice of numbers was 
very difficult, and we find accordingly that several 
of the numbers selected are compromises between 
differing analyses. 

The earliest number, 17 (column (i), Table A), 
is derived from Chenevix's analysis of sulphuric 
acid, Nicholsons yournal^ v. 126 (1803), on the 
assumption that the acid consists of i atom of 
sulphur combined with 2 of oxygen. Thus we 
find the following passage (Notebook, i. 247) : — 

Sulph. Oxy. 

"Chenevix 61 J + 38 J = sulphuric A. 

then 61 J + 19 J should be sulphureous." 

"This gives the ult. part, of sulphur to oxy. 3.2 : i, nearly." 

The number next employed (columns (2) and 
(4) ), 14.4, corresponds with Thenard's analysis of 
sulphuric acid, according to which it contains — 

56 Sulphur. 
44 Oxygen. 


The number 22 given in column (6) (August 
1806) corresponds with the composition 61. i 
sulphur and 38.9 oxygen, and, therefore, indicates 

88 New View of DaltorCs Atomic Theory chap. 

an approximation to Chenevix's number. The 
further development of Dalton's views on this 
matter may be traced by the following passages : — 

[ii. 243]. " N.B. — The mean of all expts. on sulphuric acid 
is 59 sulph., 41 oxygen. Chenevix is 61 J, 38 J. Probably we 
may be safe in saying 60 to 40, which gives sulphur 21." 

This number does not actually find a place in 
any of the lists. 

[ii. 246]. i6th September 1806. — "It seems that Kirwan and 
Klaproth will agree in sulphuric acid if we take sulphur 12, oxy. 7 
and make real sulphuric acid = O0O ^^id sulphuric acid of 1.85 = 

" Mr. Chenevix will agree in the composition of sulphuric acid 
if we adopt Kirwan on sulphate of lime, instead of him — also in 
giving sulphate of barytes 33 per cent acid." 

Kirwan and Klaproth differed as to the amount 
of water with which the real acid combined to 
form the most concentrated liquid sulphuric 
acid, the former stating it as 21 water to 79 acid, 
and the latter as 25 water to 75 acid. Adopting 
Dalton's view, 34 of concentrated acid contains 
8 of water, or 23.5 per cent. We accordingly 
find in column (7), Table A (September 1806), 
that sulphur is taken as 12, real sulphuric acid 
being 124-2x7 = 26, and liquid sulphuric acid 
12 + 2x7 + 8 = 34. 

In comparing the composition of the various 
salts of the alkali and alkaline earth metals, how- 
ever (Notebook, ii. 248 et seq,^ see p. 94), Dalton 

Ill Baltons Atomic Weight Numbers 89 

found that the same amounts of the various bases 
(i atom) were saturated by 38 parts of nitric acid 
(2 atoms), 23 parts of muriatic acid (i atom), 19 
parts of carbonic acid (i atom), and 34 parts of 
sulphuric acid. He, therefore, seems to have 
somewhat inconsistently assumed that the 8 parts 
of water contained in 34 parts of liquid sulphuric 
acid entered into the composition of the salts of the 
acid. This inconsistency was finally removed in 
the lists published in the New System^ columns (8) 
and (9), in which Dalton, making the atomic 
weight of sulphur 13, takes real sulphuric acid 
as made up of 3 atoms of oxygen and i of 
sulphur, the compound atom therefore weigh- 
ing 34 = 3 X 7 + 13- This corresponds with 
the composition 38.3 sulphur and 61.7 oxygen, 
whilst liquid sulphuric acid becomes 34+8 = 42, 
containing 17.7 per cent of water (see also p. jj). 
The actual numbers for sulphur trioxide are 40 of 
sulphur to 60 of oxygen, whilst liquid sulphuric acid 
contains 1 8.4 per cent of water, an agreement which 
Dalton would have thought " very satisfactory." 

V. Phosphorus 

The numbers given for phosphorus correspond 
almost exactly with the composition of phosphoric 
acid as determined by Lavoisier. He found that it 
contained 39.4 of phosphorus to 60.6 of oxygen, 
which gives 7.36 for phosphorus when = 5.66, 

90 New View of Daltons Atomic Theory chap. 

and 7.15 when = 5.5; phosphoric acid being 
supposed, on the model of sulphuric acid, to be 
made up of 2 atoms of oxygen combined with i of 
phosphorus. At the same time it is possible that 
the number 7.2 (columns (2) and (4), Table A) was 
derived from some early determination of the density 
of phosphuretted hydrogen, since the composition of 
phosphoric acid does not enter into the early tables. 
The number 9.3 (columns (6) and (7) ) corresponds, 
when the atomic weight of = 7, with the ap- 
proximate composition, 40 per cent of phosphorus 
to 60 of oxygen, which is quoted in the New 
System^ ii. p. 41 3. The final number 9 (columns (8) 
and (9) ) results from the " facts " that phos- 
phuretted hydrogen contains its own volume of 
hydrogen, and is ten times as heavy as hydrogen, 
the atom of the gas being regarded as made up of 
one atom of each of its constituents. 

VI. The Alkalis and Alkaline Earths 

The atomic weights of these bodies do not 
appear in the tables until August 1806, some three 
years after the first table had been drawn up. The 
following table contains the various numbers, which, 
as will be seen, do not vary much : — 


Baltoris Atomic Weight Numbers 

Table B 





Potash . 


Barytes . 
Alumine . 






22 + 
26, 28 
22-10 ? 

20 ± 











(i) Notebook, ii. 284, 14th August 1806. 

(2) Notebook, ii. 282, 23rd August 1806. 

(3) Notebook, ii. 247, i6th September 1806, and ii. 256, 
22nd October 1806, and New System^ part i. p. 219. 

(4) New System^ part ii. p. 547. 

Although Dalton did not endeavour until 1806 
systematically to apply the atomic theory to explain 
the composition of salts, he nevertheless made 
occasional attempts in this direction at earlier dates, 
and these are of some interest as showing that his 
ideas were at all events uninfluenced by Richter's 
results, of which in 1 803-1 804 he seems to have 
been ignorant. 

The very first reference to the atomic weight 
of the alkalis occurs in the Notebook, i. 287-288, 
at the end of one of the sectional notebooks, the 
remainder of which is occupied with experiments 
on gases, etc., dated August 1804. It is, however, 
quite possible that the entries in question, which 

92 New View of D alt on' s Atomic Theory chap. 

are reproduced below, are of a different date from 
this, since the matter contained in them is quite 
disconnected from that on the preceding pages : — 

[i. 287] 

Barytes - carbonat - 


54 (Four.) 





Mur. acid mur. am. - 


mur. soda 


mur. li 



Strontian - sulphat 


[i. 288] 

Lime from carb. lime = 


from sulph. lime = 

= 21 

from oxalat lime = 


from phosph. lime = 

= 15 

Magnesia - oxalat 



Potash - sulph. pot. 

30 + 

nitrat pot. 
carb. pot. 


14 nearly true ? 

mur. pot. 
Alumine sulph. 


The numbers have evidently been obtained from 
the analytical results by calculating to the nearest 
whole number how much of the base would com- 
bine with the amount of acid represented by the 
atomic weight of the latter. 

In most of these cases it has been possible to 
trace back the numbers to their source, and to find 
the actual analysis from which the calculation was 

Daltons Atomic Weight Numbers 


table : 

This will be seen from the following 

Table C 


Percentage composition. 

Author of 


Theory, cal- 
culated from 
the Atomic 








Barium carbonate 
Calcium carbonate 
Magnesium carbonate . 
Potassium carbonate . 
Barium sulphate . 
Calcium sulphate 
Magnesium sulphate . 
Calcium oxalate . 
Calcium phosphate 
Barium muriate . 
Potassium muriate 








































It will be noticed that the results are incom- 
patible with Richter's '^ touchstone of analysis," for 
the combining proportions of lime and baryta vary 
with each salt from which they are calculated, and 
do not even stand in the same ratio to one another, 
as they should do were the analyses correct. 

Dalton's next attempts to obtain atomic numbers 
for the earths were made in 1806. In August of 
that year the two columns (i) and (2) (Table B) 
are found, and these are followed in September by 
a careful comparison of the composition of a large 
number of salts, the results of which are embodied 

94 iW-K; View of Dalton s Atomic Theory chap. 

in column (3), which was published in the New 
System^ part i. 

A table of the amount of base combining with 
one part of acid in the salts of the seven chief bases 
with the five chief acids was first drawn up from 
the analyses of Kirwan, Chenevix, and others ; the 
atomic weights were then calculated from these 
numbers assuming the atomic weight of the acids, 
a selection made of the most suitable number, and 
finally a table of composition drawn up, from which 
the following (Table D) is an extract, more than 
40 salts being included in the original. 

Table D 

[ii. 248] — September 1806. 




Per cent. 

Acid. Base. 


Sulphate of soda 

I to I 



55 45 

56 44 

„ of potash 

I to I 



45 55 + 

45 55 

„ of lime 

I to I 



60 40 + 

59 41 

Nitrate of soda 

2 to I 



Sl\ 42i 

57i 42i 

„ of lime 

2 to I 



62.3 Zl'l 

64J 35i 

Muriate of soda 

I to I 



45 55 

42 58 

Carbonate of soda 

I to I 



41 59 

40 60 

etc. etc. 

The atomic weights of the acids here employed 
are those of column (7), Table A. 

It will be observed that the agreement with the 
analytical results is by no means perfect. Kirwan's 
results were, as a matter of fact, inconsistent with 
one another, as was pointed out by Richter and 


V^ 'TH ','\'.«^ 

III Dalton's Atomic Weight Numbers 95 

afterwards by Wollaston, and there seems reason to 
suspect that the trouble involved in the examina- 
tion and arrangement of these faulty results may 
have been the cause of Dalton's celebrated declara- 
tion of independence. " Having been in my pro- 
gress so often misled by taking for granted the 
results of others, I have determined to write as 
little as possible but what I can attest by my own 

The experiments which Dalton instituted in 
accordance with this plan are fully detailed in the 
New System^ and require no further discussion 

VII. The Metals 

In dealing with the constitution of the metallic 
salts and oxides, and with the atomic weights 
of the metals, Dalton followed the same lines 
as he had done in the case of the alkalis and 
their salts. He first of all made use of the existing 
analytical material, and selected the atomic weights, 
which disagreed least with the often inconsistent 
analyses of the metallic oxides. When new results 
appeared in the chemical literature of the day they 
were embodied in these lists, and finally the whole 
subject was experimentally treated in the manner 
described in full in the various sections of the New 
System^ vol. ii. The numbers adopted for the 
most important metals at different times are con- 
tained in the following table : — 

96 New View of Daltons Atomic Theory 







11 ' r<-) 
" t^ ON 





>^ «-rv 



xi-. ON N VO '^h 

N N 



|>.o., /v. 






i>^vo 00 





lr^ ON VJ-^V0 tJ- 

Th ^ 

- ~ - 




II H-o 









On >-'"> 

^ ^ ^ 





V § 



LTvVO N ^ 

M r<^ 



VO On Lr^VO ^* 

^ VO 


"m^ +' 










On »-^ 
















II 1 1 +1 

^ ON 

+1 1 

i^VO l>. N 

t^ ON tJ^ I-* t<^ 

1 ^^ 




II ^ 

, i^ 




ro N VO 00 OnVO fn 


'^ ^ 

ro 1^ 


m t-i 

cTiVO li-^vo 

N VO uo 






II ^^ 




00 N VO r^iVO 

1-1 00 




N \j^ i-nVO "^ 

N N 


UTi li-l l-O 




C4 1^ N N 



II 2 2 



N N N 



. . . 




. . . . 

• <L) 








1— ( 

Tin . 











N . 

N b^ 

y 180 


d.^ d. 

•s »v 

• tt .I-H J J2 


4-> -M , 

N Tj- 

rt rt 

•I-H .1-1 

^ _ _ 

.rl -f-l 

^ ^ ^ 

J^ J^ 

^ ^ ^ 




(U <u 

§ g § 

2 Z fe; fe; fe; 

VO t^ 00 ON O 










c^^ s 



^ 00 ^ 



^ " i 

>-( 1- w 







X -^ -C 


T3 Dh T3 
Tf- <u VO 





^ VO t^ 



CO ^ ^ 
N N N 


.^ .J .^ 








^ J^ ^ 





^ ^ JQ 




<L) <L> <U 














Ill Daltons Atomic Weight Numbers 97 

The theory which guided Dalton in his selec- 
tion of the atomic weight of a metal was that the 
oxide was most probably composed of one atom 
of metal to one atom of oxygen, whilst when two 
oxides existed, the second and higher of the two 
was composed of one atom of metal to two of 
oxygen. The very earliest list of numbers (i) is 
dated March 1804, the numbers being calculated 
for = 5.5, ^^^ taken, as a rule, from very inac- 
curate analyses. 

The numbers in column (2) (Table E) have 
been calculated from a table found in the Notebook, 
i. 318. This table contains the composition of 
twenty-three metallic oxides as found by experi- 
ment by various chemists, expressed in the manner 
shown by the following extract : — 

[i. 318]. Theory of oxides of metals : — 

1st oxide is i metal and i oxygen. 
2nd oxide is i metal and 2 oxygen. 







5. Copper . 88J to 11^ 

80 to 20 

88.9 to I I.I 

80 to 20 

6. Iron . 73 to 27 

52 to 48 

68.5 to 31.5 

52 to 48 

13. Manganese 80 to 20 

74 to 26 

80 to 20 

66.7 to 33.3 

and 60 to 40 

and 57 

to 43 

It will be seen that Dalton has been testing the 
theory placed at the head of the page, by assuming 
that the experimental composition of one of the 
oxides of each metal was correct, and calculating 
that of the other according to his theory. 

All the analyses quoted in this table are to be 


98 JSlew View of Daltoris Atomic Theory chap, m 

found in Thomson's System of Chemistry^ 2nd 
edition, 1804. 

The numbers in columns (3) and (6), Table E, are 
taken from short accounts of the metals in question 
jotted down in the Notebook. Those of earlier 
date are almost unaccompanied by analytical data, 
whilst the later ones contain an elaborate list of the 
analyses which had at that time been published ; 
those of Wenzel, Bergman, Klaproth, Morveau, 
Berthollet, Pelletier, Kirwan, Lavoisier, Proust, 
and others, being quoted. It was only after 1807 
that Dalton's own analytical researches on the com- 
position of the metallic salts were instituted, and in 
this difficult branch of practical work, begun at so 
late a period in his life, he never attained any great 
skill. The revolution in chemical analysis which 
was inaugurated by the work of Klaproth, Berzelius, 
Rose, and Proust, soon raised the standard of 
accuracy far above that to which Dalton had 
attained, and his work in this respect must be 
classed with that of the old school rather than the 

Vf-'' '*■ 


dalton's lecture notes 

Notes of Lectures delivered at Royal Jnstitut ion in 
London December and January 1 8 1 o 

Lecture 15. — On Heat 

T.'T^rd January 18 10. — The very general import- 
ance of facts and experiments relating to heat will 
be admitted by all who are acquainted with the 
mechanical arts and with physical science. Facts 
and experiments, however, relating to any subject, 
are never duly appreciated till, in the hand of 
some skilful observer, they are made the foundation 
of a theory by which we are able to predict the 
results and foresee the consequences of certain 
other operations which were never before under- 
taken. Thus a plodding experimentalist of the 
present time, in pursuit of the law of gravitation, 
might have been digging half-way to the centre of 
the earth in order to find the variation of gravity 
there, were it not that the sublime speculations of 
Newton have already anticipated the result, and 

lOO New View of Daltons Atomic Theory chap. 

spared him the undertaking of a fruitless and 
endless labour. 

In reference to the subject before us, it has been 
found that if a quantity of any elastic fluid be com- 
pressed by mechanical force, its temperature is 
raised, or it parts with a quantity of its heat — 
and it recovers the same quantity of heat again 
upon being liberated, and the same volume as it 
previously possessed. This is a particular fact. 
Again, it has been found that a piece of iron may 
be hammered till it is red-hot ; that it is con- 
densed in volume by the operation ; and that it 
does not, like the air, recover its former heat and 
former volume of its own accord, but requires to 
be heated red-hot again and cooled slowly before 
it resumes its original temperament and volume. 
This is another fact. But of how much more 
importance would it be to ascertain from these and 
such like facts that it is an universal law in nature 
that whenever a body is compressed^ whether by 
mechanical or chemical agency, it loses a portion of 
its heat ; and whenever a body is dilated it gains 
a portion of heat from other bodies ? 

Now, whether this is in reality a law of nature 
is not yet, perhaps, clearly ascertained ; but this is 
certain that a person apprehending such a law is 
more likely to have a proper bent given to his 
investigations than one who makes a number of 
experiments without any fixed object in view. 

I have made these observations to shew that. 


Daltons Lecture Notes loi 

however guarded we should be, not to let a theory 
or hypothesis, contradicted by experiment, mislead 
us ; yet it is highly expedient to form some pre- 
vious notion of the objects we are about, in order 
to direct us into some train of enquiry. 

The doctrine of heat is justly considered as 
constituting a fundamental part of chemical 
science. It constitutes the basis of mechanical 
power in that most useful instrument, the steam- 
engine. The cause of animal heat forms one of 
the most important enquiries in physiology. Even 
in the mechanical arts the knowledge of heat is 
necessary. The clock and watchmakers are not 
competent to their arts if they do not understand 
the laws of expansion by heat. We have known 
instances of very large castings of iron having been 
pulled to pieces by their own reaction, before ever 
they were cooled, by the careless or injudicious 
manner of cooling them. And every one knows 
the nice attention to temperature that is requisite 
in manufacturing and working with glass. 

It would be endless to enumerate the arts, 
Sciences, and manufactures in which a knowledge 
of the nature and laws of heat is advantageous and 
even expedient. If the economy of fuel was the 
only object in pursuit in these speculations it 
would be well deserving our attention. 

Thtjirst question that naturally arises for our 
discussion is — 

I02 New View of Dal tori s Atomic Theory chap. 

What is Heat'? 

Were we to proceed as the experimental philo- 
sopher must do — that is, in the analytical mode of 
investigation, this question would most properly be 
the last. But as we profess to teach or instruct 
from the knowledge we have previously acquired, 
or in the synthetical way, this question may 
properly be considered at the outset. 

1. Theory — Heat a distinct and peculiar elastic 

fluid sui generis ; its leading features are 
to be repulsive of its own particles ; and 
attractive of those of other matter . . . 
quantity incapable of change. 

2. Theory — Heat is a quality of bodies — con- 

sists in some kind of vibration of the 
particles — is, like mechanical forces, 
communicated from one body to an- 
other ; is incapable of change in quan- 
tity, like the force of elastic bodies. 

3. Theory — Heat is a quality of bodies — con- 

sists in some kind of vibration of the 
particles — and is capable of being gener- 
ated or destroyed^ consequently is capable 
of change in quantity in different bodies 
without reciprocal communication. 
Animadversions on these theories : — 

Refer to diagram. 

Refer to a candle burning. 

IV Daltons Lecture Notes 103 

Refer to ordinary combustion. 
Refer to the heat of the human body. 
Refer to freezing water. 

This leads to capacity for heat : refer to two 
equal electric jars, one thick, the other 
thin ; 
And to capacity as applied to the human intel- 
lect — thick skull and thin. 
^antity of heat and intensity of heat con- 
sidered : refer to water and mercury. See diagram 
of capacity. 

Whatever theory of heat we adopt we must 
allow of quantity and intensity of heat. 

Measure of intensity or temperature by the 
thermometer : — 

Investigations of De Luc, Crawford, etc., con- 
cerning the thermometer. 

De Luc finds mean 119° 

Crawford o . instead of 122' 

121 J 

Principle wrong that equal weights (or equal 
bulks) of water mixed at any different temperature 
should give the mean. Reason assigned. Error, 
8° above the mean. 

These considerations induced me to try some 
other method : — 

I. Discovery that water and mercury expand 
by the same law — namely, the expansion 
as the square of the temperature from 
the point of greatest density or con- 
gelation. See diagrams. 

104 New View of Daltons Atomic Theory chap. 

2. That the force of steam is in geometrical 

progression to equal increases of tempera- 
ture or intensity of heat. Instances in 
steam of water and ether. 

3. That the expansion of air is in geometrical 

progression to equal increments of tem- 
Animadversions on former experiments on 
the expansion of gases, General Roi, 
Morveau, etc. See diagram. 

4. Refrigeration of bodies in geometrical pro- 

gression to equal increments of tempera- 
This law, suspected by Newton, but found 
not to answer by the common thermo- 

Experiment — If a thermometer be heated to 
400° above the temperature of the air and suffered 
to cool, it will be found : — 


200° in 2 


of time. 

100 „ 2 



50 „ 2 



25 ,, 2 



I2i „ 2 


„ etc. etc. 

Here the quantity of heat thrown oif in any 
given time is as the intensity or excess of tempera- 
ture, as it ought to be. Hence the thermometer 
so graduated must be concluded to be an accurate 

IV Daltons Lecture Notes 105 

measure of intensity of heat, or, as it is more fre- 
quently called, temperature. 

The agreement of these four important pheno- 
mena in establishing a great fundamental law of 
heat is such as must carry conviction to every one 
who will take the trouble duly to consider them — 
the only doubt that can exist is as to the accuracy 
of the facts. This at present may be said to rest 
entirely on my authority, though it need not in 
fact do so. I might appeal to Betancourt in 
regard to steam, to General Roi in regard to 
expansion of air, to Blagden in regard to expan- 
sion of water. The experiments on the refrigera- 
tion of bodies are more peculiarly mine. They are, 
however, the most easily made, etc. 

It is now one and a half year since these results 
were before the public. No animadversions on 
them in this country, notwithstanding their evi- 
dent importance. Perhaps the repetition of the 
experiments, and the confirmation of them, may 
be soon expected from France, etc. If this should 
be the case we may well exclaim — Where are the 
descendants of Newton^ of Bacon^ of Hooke^ and of 
Boyle^ that the merits or demerits of the produc- 
tions of Englishmen cannot be ascertained in their 
own country ? I trust and hope, for the honour of 
my country, that this inattention to new and im- 
portant views on a subject of so much consequence 
as that of heat, is somehow or other accidental or 
apparent only^ and is not to be ascribed to the want 

io6 New View of D alt on s Atomic Theory chap. 

of ardour in the pursuit of science, or to the 
incompetency of those whom the public look up 
to as judges and authorities. 

Lecture i6. — On Heat 

24M January 18 10. — From the observations 
made by several gentlemen at the conclusion of last 
lecture, I apprehend I may have expressed my 
ideas somewhat incorrectly in some points relative 
to the quantity of heat which a mercurial or other 
thermometer receives or parts with in its progres- 
sive expansion or contraction, as determined by the 
new graduation. 

Now I would have it understood that I con- 
ceive the new graduation of the thermometer to be 
significant only of the intensity of heat in the ther- 
mometer, and not of the quantity ; this last, namely, 
the quantity of heat, I conceive increases with the 
number of degrees or volume of the mercury, so 
that a small portion of the heat added goes to 
increase the capacity of the body for heat, and the 
rest goes to increase the intensity. In the ordinary 
range of the mercurial thermometer — from freezing 
to boiling water — however, the expansion is so 
small, and the increase of capacity so trifling, that 
in a practical point of view we may reckon the 
increase of quantity of heat to hold the same ratio 
as the increase of the intensity^ and the quantity of 


Baltons Lecture Notes 107 

heat to be expended solely in producing that 

Refer to air thermometer. 

In a water thermometer, however, this conclu- 
sion cannot be admitted. For it is evident, grant- 
ing the accuracy of the new graduation, that the 
excess of temperature of 8°, observed upon mixing 
equal quantities of water of 32° and 212°, can only 
be accounted for on the supposition that these 8° 
arise from the superior capacity of water of 212° 
to water of 32°. I stated the fact in the former 
lecture that equal quantities of water of the two 
temperatures just mentioned, on being mixed, give 
a temperature of 130° on the new scale, instead of 
122°, the arithmetical mean. This excess of 8° 
must then be ascribed to the greater capacity of 
water in the higher part of the scale. 

Refer to the gradual expansion of air — effect 
proportional to cause. Something like this in the 
expansion of solids. 

But it has been observed that the law of ex- 
pansion of liquids exhibits something strange. 

Water expands i for 1° in one part, and 340 
for 1° in another part ; and even expands by cold 
the same as by heat ! ! 

I have attempted a solution of this under the 
head oi congelation. Refer to diagrams. 

Specific heat of bodies is the numerical relation 
of the real quantity of heat in equal weights or in 
equal bulks of two different bodies. 

io8 New View of Daltoris Atomic Theory chap. 

Thus if the specific heat of a given bulk of 
water be expressed by i, that of the same bulk of 
mercury will be nearly \, If weights be used 
instead of bulk : then the relation will be i to -^^ 

Method of ascertaining specific heats : — 
Liquids, the glass, globular, suspended with a 
thermometer. Time marked in cooling — 
Solids — by putting them heated into a given 

volume of water, etc. 
Gases — difficult. 

Notion of equilibrium of heat : — Dr. Craw- 
ford's, Prevost's, on combined^ fr^^> latent^ 
etc., heat. 

Theoretical or speculative views on the heat of 

gases : — 

The principle will perhaps extend to all other 

Heat produced by combustion and chemical 

I St mixture of sulphuric acid and water : — 

Mix 1.6 sulphuric acid. 

I — W. gives temperature 260''. 

Diminution of capacity about -^, 
Refer to diagram, and explain numerically ; 

also to air bottle by the bye. Ignited wire 

in hydrogen. 
Hence may be inferred that in combustion the 

like effect is produced. 

IV Daltons Lecture Notes 109 

Difficulty of proof in gases : — 

2. Mixture of snow and salt produces cold, 

attended with some increase of capacity. 

3. Nitric acid and lime produces heat. Lavoi- 

sier and Laplace found cap. of mixture 
increased, I found it diminished^ but less 
in proportion than other bodies. 

Combustion of oil, tallow: — 

10 grs. heated 2 quarts water 5°. 

Hydrogen raises equal vol. W. 4°. 5. 

Coal gas lo'', etc. See New System (p. jj). 

Hence infer the large quantity of heat in 
oxygen gas. Objection refuted. 

Ignition in galvanic and electric circuits ex- 

Natural zero of temperature or absolute cold. 
See diagram. 

Suppose a mixture produced 200° of heat, and 
was found to have lost gV^h of its capacity. 
Then the zero would be at 4000° below 
the temperature. 

Radiation of heat : — 

Common explanation from diagram. 

Heat of common fire radiant. 

Leslie's discovery of effect of surfaces. . . . 

Glass and paper to metal as 8 to i. 
One of his positions controverted. See 


no New View ofDaltons Atomic Theory ckap. 

Comparison of Heat and Electricity and Light 

In proportion as we advance in our knowledge 
relating to light, heat, and electricity, in the same 
proportion we find resemblances amongst them. 
Solar light and heat are subject to reflection and 
refraction : ordinary heat is subject to reflection, and 
can be brought to a focus, like light. Heat and 
electricity are alike found in all bodies, and in 
different quantities and intensities. Whenever we 
rob any body of its electricity, we must give the 
same quantity to another ; the case is the same 
with heat. Electricity can be conveyed with a 
celerity which is perhaps only equalled by the 
celerity of radiant heat or of light. The principal 
visible effect of electricity in igniting wires is the 
exhibition oi heat. 

May we not then look forward to the time 
when these three important agents shall be shown 
to arise from one and the same principle ? And, 
in the meantime, is it not most consistent to 
conclude that these agents are of the same nature ? 
If any one of these three, heaty lights and electricity 
be deemed a fluid, then the other two must also 
be dittvncdi fluids. If any one of these be deemed 
powers or properties, then all three must be deemed 
powers or properties of matter. Now with regard 
to light, our knowledge concerning it remains 
nearly the same as it was in the time of Newton, 
His decided opinion concerning light was that 



Daltons Lecture Notes 1 1 1 

of its being a body^ not a property of other bodies. 
Experience has added much to our knowledge 
of heat and electricity since the time of Newton — 
and from the preceding remarks it should seem 
that there are many striking features of resemblance 
amongst the three. May it not then be argued that 
the notion of heat and electricity being also bodies^ 
is more conformable to the Newtonian philosophy 
than the opposite doctrine, which considers them as 
mere qualities or properties of bodies ? 

Lecture 17, see ante^ P- I3- 

Lecture 18. — Chemical Elements 

30//^ January 18 10. — ;In the last lecture we 
endeavoured to show that matter, though divisible 
in an extreme degree^ is nevertheless not infinitely 
divisible. That there must be some point beyond 
which we cannot go in the division of matter. 
The existence of these ultimate particles of matter 
can scarcely be doubted, though they are probably 
much too small ever to be exhibited by microscopic 

I have chosen the word atom to signify these 
ultimate particles, in preference to particle^ molecule^ 
or any other diminutive term, because I conceive 
it is much more expressive ; it includes in itself 
the notion of indivisible^ which the other terms 
do not. It may perhaps be said that I extend 

.' '^tr^'J^ 

1 1 2 New View of Dalton's Atomic Theory chap. 

the application of it too far, when I speak of 
compound atoms; for instance, I call an ultimate 
particle of carbonic acid a compound atom. Now, 
though this atom may be divided, yet it ceases 
to be carbonic acid, being resolved by such 
division into charcoal and oxygen. Hence I 
conceive there is no inconsistency in speaking of 
compound atoms, and that my meaning cannot 
be misunderstood. 

It has been imagined by some philosophers 
that all matter, however unlike, is probably the 
same thing ; and that the great variety of its 
appearances arises from certain powers communi- 
cated to it, and from the variety of combinations 
and arrangements of which it is susceptible. 
From the notes I borrowed from Newton in the 
last lecture, this does not appear to have been 
his idea. Neither is it mine. I should apprehend 
there are a considerable number of what may be 
properly called elementary principles, which never 
can be metamorphosed, one into another, by any 
power we can control. We ought, however, to 
avail ourselves of every means to reduce the 
number of bodies or principles of this appearance 
as much as possible ; and after all we may not 
know what elements are absolutely indecomposable, 
and what are refractory, because we do not apply 
the proper means for their reduction. 

We have already observed that all atoms of 
the same kind^ whether simple or compound, must 

r^;«^4H?f:»» ^v^ 

IV Daltons Lecture Notes 113 

necessarily be conceived to be alike in shape, 
weight, and every other particular. 

Figure of simple atoms : — May be globular, 
or of the 5 regular bodies. Tetrahedron, 
Whatever may be the figure they must be 
virtually globular or nearly so, from the 
great quantity of heat surrounding them. 

1. Combination of simple atoms constituting 

compound atoms. 
Combinations generally one to one. 

2. Manner of finding the relative weights of 

Instance earths and metals — carbonates, sul- 
phates, etc. 

3. Arrangement of 3 or more atoms constitut- 

ing one compound atom. 

See water, etc., and nitrat ammonia. 

Hexagon — hence perhaps origin of hexa- 
gonal crystals. 

4. Of water — 

Ox. Hyd. 

Lav. 85 - 15 -5.6 : I 
corrected 87 J - I2| - 7:1 

Why I to I ? because neither syn. nor analysis shows any other. 

5. Ammonia — 

26 azote + 74 hyd = 4.2 to i 
ought to be 30 „ +70 „ =5.1 „ I 

Henry with ours, "J Hence with nit. gas, always 
never so low as 26 ?• too much azote, or else 
„ so high as 29 J right. 



114 New View of Daltons Atomic Theory chap. 

6. Compounds of azote and oxygen are 4 or 
5 at least. 

Wt. Diamr. 

1. Nitrous gas 12 .947 

Davy — 42 to 47 azote 
Sp. gr. I.I — Theory 42 58 oxy. 

48 measures azote — of which 24 remain 
by electrification. 


2. Nitrous oxide 17.2 from Nitrat. am. 

Davy — 61 to 63 azote 
Sp. gr. 1.6 — Theory 59 J 40 J oxy. 

Nit. ox. Hyd. 

Decomp. by hyd. i measure + i gives i azote. 

3. Nitric Acid — 

Cavendish — from 25 to 30 azote 
Davy — 29.5 azote 

Az. Oxy. 

Sp. gr. 2.4 — Theory 27 - 73 
Exhibition of it in elastic form (see Table) : — 

Oxy. Nitrous. 

I took from 1.4 to 2.3. 

4. Oxynitric acid — 26.1. 

4 oxy. to 1.3 nit. gives I oxy. + 1.3 nitrous. 

5. Nitrous acid — 31.2. 

I meas. oxy. takes 3.6 nitrous in water. 
I meas. oxy. to 3.6 nitrous gas in a tumbler glass 
form nitrous acid. 

This acid gives out nitrous gas when combining. 

Remarks on nitric acid : — 

See Table on Board. 
2 to I strongest acid exhibited. 
I „ I — very strong. 
I „ 2 — boiling point 248° Max. 
I „ 3 — nothing remarkable. 
I „ 4 — ^acid of easiest freezing (Cavendish). 

Baltoris Lecture Notes 1 1 5 

Lecture 19. — Chemical Elements 

3 1 J-/ January 18 10. — In the preceding investi- 
gations on the number and weights of the ele- 
mentary principles constituting water ^ ammonia^ and 
the various compounds of azote and oxygen, you 
will have remarked that the conclusions were 
derived principally from the facts and experience 
of others, without any additional facts of my own 
discovery that merit particular notice. 

The composition and decomposition of water 
had been ascertained by British and Foreign 
chemists ; that of ammonia by Berthollet and 
several others ; the compounds of azote and 
oxygen had been successively developed by Caven- 
dish, Priestley, Davy, and others. I may, how- 
ever, observe that the nitrous compounds have 
occupied a great portion of my time and attention 
at different seasons. The elegant and instructive 
experiments on the effect of electricity on nitrous 
gas deserve notice. By electrifying nitrous gas over 
water, in a short time 100 measures are reduced to 
24, which, upon examination, are pure azote. 

I. Theory of it explained. 2. Theory of the forma- 
tion of nitric acid in Mr. C.'s experiments. 

The simple and easy method of combining the 
least portion of oxygen with the greatest of nitrous 
gas, which I pointed out in the last lecture, was 
the result of my own investigation, and affords a 

1 1 6 New View of Daltons Atomic Theory chap. 

convincing proof of the real nature of what is 
called nitrous acid^ which is constituted of i atom 
of oxygen united to 2 of nitrous gas. (See figure.) 

From the preceding remarks it will be per- 
ceived that I advanced thus far in my theoretic 
progress without meeting with much obstruction. 
The way had been paved by others. But when I 
directed my views to the compounds of charcoal 
and oxygen, and charcoal and hydrogen, I found 
that all the then commonly received doctrines 
were adverse to my proceeding, and irreconcilable 
with my views. 

Mr. Tennant's experiments in the Philosophical 

Transactions^ ^7975 had shown the identity of 

diamond and charcoal in a chemical point of view, 

but the succeeding experiments of Guyton Mor- 

veau on the combustion of diamond supplanted 

the former in the judgment of great part of our 

chemists. Diamond was concluded to be a simple 

body, and charcoal the oxide of diamond. Mr. 

Cruikshank soon after discovered the gas called 

carbonic oxide. The doctrine of the compounds 

of charcoal, or rather diamond and oxygen, then 

stood thus : — 

Diamond . 18 parts. , 

Oxy. . . 10 5) 

28 charcoal. 
Oxy. . . 41 

69 carbonic oxide. 
Oxy. . . ^ 

100 carbonic acid. 

IV Daltons Lecture Notes 117 

A very little reflection convinced me that the 
doctrine of charcoal being an oxide of diamond 
was highly improbable — and experience confirmed 
the truth of Lavoisier's conclusion that 28 parts 
charcoal + 72 oxygen constituted carbonic acid ; 
also that carbonic oxide contained just half the 
oxygen that carbonic acid does, which indeed had 
been determined by Clement and Desormes, two 
French chemists, who had not, however, taken 
notice of this remarkable result. Carbonic oxide, 
being lighter, is the more simple. 

Hence 28 + 36 = carb. ox. ^ ^^^^^ (^.^ + 7 = 1 2.4 
+ 36 = carb. acid / \ +7 = 19.4 

Hence carb. acid = 19 as supposed in last lecture. 

c. ox. ox. acid. 

2. Charcoal and hydrogen : — 

Generally mixtures, etc. 
Berthollet's late paper ; remarks. 
Species — ( i ) defiant gas. 

100 — take 300 oxy. — gives 200 acid. 

Exp. by electr., 200. 

By 200 forms carb. oxide, 200. 

(2) Carburetted hydrogen — coal gas. 

100 — take 200 oxy. — gives 100 acid. 

Exp. by electr., 200. 

By 100 oxy. gives 200. 

All these prove charcoal to be 5. 

Hyd. flame red pale. 

Carb. oxide blue. 

Carb. hyd. white, like a candle. 

Olefiant g. very brilliant white. 

1 1 8 New View of Daltons Atomic Theory chap. 

3. Sulphur. Wt. 13 1 found from the acids : — 

1. Sulphurous oxide. 

2. Sulphurous acid. 

3. Sulphuric acid. 

Boiling point of strongest 620% contains 81 per cent. 
Common acid contains 79, boils 590°. 
Remark on Kirwan's table. 
Freezing'acid - 1.78 - i + 2 water - 435°. 
Theory — Clement and Desormes, Nicholson, 17. 
Sulphuretted hyd., i + i. 

My book wrong.^ Burned gives sulphurous acid and 

4. Phosphorus : — 

Phosphorous acid. 
Phosphoric acid. 
Phosphuretted hyd. 

5. Alkalies and earths : — 

Hydrate of lime. 

6. Metals. 

7. Metallic oxides. 

8. Metallic sulphurets : — 

Mr. Hatchett*s paper on mag. pyrites gives the 
2nd, 3rd, and 5th of iron. 

Lecture 20. — Chemical Elements 

yd February 18 10. — When we consider the 
very important part which the two elements of 
hydrogen and oxygen seem to perform in the arrange- 
ments of chemical compounds, we are inclined to 

^ The several numbers for sulphur adopted by Dalton are found 
in Table A, p. 83. 

2 Sulphuretted hydrogen is given in part i. of New System as i of 
sulphur to 3 of hydrogen. 


Baltofis Lecture Notes 119 

wonder that no more than one compound of these 
two elements themselves should be found. 

Water^ that most beneficial and essential of all 
liquids, is formed of hydrogen and oxygen. 
Besides this one, there is not a compound of 
these two elements generally known and recog- 
nised as such. It is singular if we have not some- 
where a principle consisting of two atoms of 
oxygen and one of hydrogen ; or two of hydrogen 
and one of oxygen. The former of these ought to 
be an acid^ conformably to what we observe in 
other similar cases. The latter ought to be a com- 
bustible gas. All the other common elements, 
azote^ charcoal^ sulphur^ and phosphorus^ combine, 
each one with two atoms of oxygen, to form acids. 
Why should not hydrogen do the same ? This 
question has been frequently put, but no satis- 
factory answer has been given. Upon comparing 
the results of experience, and applying the theo- 
retic views which I have been endeavouring to 
develop, it appears to me very probable at least that 
the acids denominated fluoric and muriatic^ with 
their derivatives, are constituted of the elements of 
hydrogen and oxygen, and are in reality the very 
compounds of which we have just been hinting. 

I would not, however, be understood to mean 
that these views are the necessary results of the 
atomic theory ; and that its truth or falsehood 
depends upon the determination of the question. 
From the want and imperfection of facts relating to 

1 20 New View of Daltons Atomic Theory chap. 

these subjects, nothing perhaps decisive can be yet 
advanced. I intend to point out such reasons and 
such facts as have induced me to adopt the opinion, 
and must leave it to others to judge how far they 
support the probabiUties above mentioned. 

1. Fluoric -acid: — 

1. Fluoric acid gas from fluate of lime 

— a gas combined with flint — super- 
jiuate of silica. Very heavy gas. 

2. No steam in this or muriatic acid 

gas ; proved from no condensation 
by cold, etc. 

3. 50 grains fluate of lime gave 75 

sulphate, mean between Richter 
and Scheele. Hence 15 acid +23 
lime = fluate of lime. 

4. Mr. Davy finds potassium burn in 

this gas ; some hyd. is given out 
and fluate of potash formed. 

5. Hence 15 being the weight — 2 oxy» 

+ I hyd., etc. 

2. Muriatic acid : — 

1. Does not contain steam. 

2. Mr. Davy finds potassium to burn in 

this gas, give hydrogen, and form 
muriate of potash. 

3. Its weight is 22 = I hydro. + 3 oxygen. 

4. Liquid muriatic acid. i and 20 

water boils at 232°. See diagram. 

IV Daltons Lecture Notes 121 

3. Oxymuriatic acid : — 

1. Gas has sp. gr., 2.34. 

2. Mr. Davy and the French chemists 

seem to think this is the simple and 
mur. acid the compound. Burns 
with carbonic oxide, etc. 

3. The effect of light on a mixt. of 

this and hydrogen. 

4. Hyperoxymuriatic acid: — 

I. Consists of I oxy. mur. acid +5 
oxygen, i hyd. + 9 oxygen. 

5. Acetic acid. 

Neutral salts : — 

1. Carbonates. 

2. Sulphates. 

3. Nitrates. 

4. Muriates. 

5. Acetates. 

6. Metallic salts : — 

Corrosive sublimate. See diagram. 
Action of common electricity on compound 
gases and gaseous mixtures : — 

1. No effect on the simple gases hyd., 

azote, oxy. 

2. Ammonia. Decomposed rapidly. 

3. Carbonic acid. Decomp. into car- 

bonic oxide and oxygen. Recom- 
posed again. 

122 New View of Daltons Atomic Theory chap. 

4. Ether and alcoholic vapour decom- 


5. Nitrous gas and nitrous oxide. De- 


6. Compounds of charcoal and hydrogen. 


7. Compounds of sulphur and phos- 

phorus with hydrogen. Decom- 

8. Mixt. of any combustible gas and 

oxygen, new combinations, quick or 
slow. Generally more rapid than 
the former. 
Difficulty of forming any theory. 

Conclusion of the course. 

I cannot conclude this course of lectures with- 
out expressing my high satisfaction with the 
general attention that has been given to the sub- 
jects under discussion and with the indulgence 
which has been given me when adverse circum- 
stances occurred. I shall always associate these 
grateful impressions with the recollection of the 
event. To those who feel highly interested them- 
selves in the promotion and extension of science, it 
is a peculiar satisfaction to meet with others of the 
same description. I shall now return to com- 
parative retirement, in order to prosecute the train 
of enquiry and investigation which I have briefly 
developed in the late lectures ; the results, I am 

IV Baltons Lecture Notes 123 

confident, will be found of importance ; and will 
contribute to establish that beautiful and simple 
theory of chemical synthesis and analysis which I 
have adopted from a conviction of its application 
to the general phenomena of chemistry, and which 
will in due time, I am persuaded, be made the 
basis of all chemical reasoning respecting the abso- 
lute quantities and the proportions of all elementary 
principles, whether simple or compound. 

R. I. yd February 18 10. 

Then follow in Dalton's handwriting the fol- 
lowing extracts from Newton's Principia. 

[i]. Newton. Query 31. 

" The parts of all homogeneal hard bodies 
which fully touch one another, stick together very 
strongly. And for explaining how this may be, 
some have invented hooked atoms, which is beg- 
ging the question ; and others tell us that bodies 
are glued together by rest — that is, by an occult 
quality, or rather by nothing ; and others that 
they stick together by conspiring motions — that 
is, by relative rest among themselves. I had rather 
infer from their cohesion that their particles attract 
one another by some force, which in immediate 
contact is exceeding strong, at small distances per- 
forms the chemical operations, above mentioned, 
and reaches not far from the particles with any 
sensible effort." 

" All bodies seem to be composed of hard 

124 New View of Daltons Atomic Theory chap. 

particles." " Even the rays of light seem to be 
hard bodies/' " and how such very hard particles 
which are only laid together and touch only in a 
few points, can stick together, and that so firmly 
as they do, without the assistance of something 
which causes^ them to be attracted or pressed 
towards one another, is very difficult to conceive." 
" It seems probable to me that God in the 
beginning formed matter in solidy massy ^ hardy im- 
penetrable^ movable particles, of such sizes and 
figures^ and with such other properties^ and in 
such proportion to space as most conduced to 
the end for which he formed them ; and that 
these primitive particles being solids, are incom- 
parably harder than any porous bodies compounded 
of them ; even so very hard as never to wear or 
break in pieces ; no ordinary power being able to 
divide what God Himself made One^ in the first 
creation. While the particles continue entire they 
may compose bodies of one and the same nature 
and texture in all ages ; but should they wear 
away or break in pieces, the nature of things 
depending on them would be changed. Water 
and earth, composed of old worn particles and 
fragments of particles, would not be of the same 
nature and texture now, with water and earth 
composed of entire particles in the beginning. 
And therefore that nature may be lasting, the 
changes of corporeal things are to be placed only 
in the various separations and new associations^ and 

^\-,''?^^y''- rM^ ' 

IV Daltoris Lecture Notes 125 

motions of these permanent particles ; compound 
bodies being apt to break, not in the midst of 
solid particles, but where those particles are laid 
together, and only touch in a few points. . . ." ^ 

[2]. Again, ". . . God is able to create particles 
of matter of several sizes ^xid, figures^ and in several 
proportions to the space they occupy, and perhaps 
of different densities and forces. ... At least I 
see nothing of contradiction in all this. . . ." 

Again, " Now by the help of these principles, 
all material things seem to have been composed 
of the hard and solid particles above mentioned, 
variously associated, in the first creation, by the 
counsel of an intelligent agent. ..." 

Newton, Prop. 23, B. 2. 

" If the density of a fluid, composed of particles 
mutually repulsive, be as the compression, the 
repulsive powers of the particles are reciprocally 
proportional to the distances of their centres. 
And, vice versa^ particles endued with such forces 
will compose an elastic fluid, the density of which 
is as the compression.'' 

Lectures on Natural Philosophy, etc 


20th April 1 8 14. — It is scarcely necessary, I 
should think, to insist at large upon the importance 
and general utility of the sciences usually compre- 

^ Horsley's Newton^ vol. iv. p. 260. 

126 New View of Daltons Atomic Theory chap. 

hended in a Course of Natural Philosophy and 

In this country, where the arts and sciences are 
more generally cultivated than in any other, and to 
which circumstance, it is allowed, we owe in some 
degree our present pre-eminence, there cannot be 
wanting any powerful stimulus to excite the atten- 
tion to subjects of this nature. 

The sciences of Mechanics and Chemistry, taken 
in their largest acceptation, are certainly the most 
generally interesting to us in the present state of 
civilised society. In the large sense of the word 
mechanics must be considered as comprehending 
hydrostatics, hydrodynamics, and pneumatics. The 
many important inventions and improvements in 
modern machinery are derived from principles 
which it is the object of these sciences to explain. 

Several of the arts depend upon chemistry ; and 
as the knowledge of chemistry is daily improving, 
so must that of the arts. 

The truly noble and sublime science of astro- 
nomy is more than any other adapted to enlarge 
and expand the mind ; but besides this, an acquaint- 
ance with it is essential to the practice of naviga- 
tion, an art of primary consideration to a com- 
mercial and insular people. 

Optics, that most curious and highly useful 
science, the favourite one of our immortal Newton, 
has lately received considerable improvements from 
the investigations of various philosophers. 



Daltons Lecture Notes 127 

Lectures on Mechanics, etc. 

20th April 1 8 1 8. — It will be universally allowed 
that the cultivation of mechanical science, in the 
present state of society more especially, is an object 
of primary importance. Agriculture, the arts and 
manufactures, are all interested in the science. It 
would seem to follow that it is the duty of every 
one to make himself acquainted with the first 
principles of the science ; and it certainly is the 
duty and interest of those who are actively em- 
ployed in mechanical occupations, or in the super- 
intendence of such concerns, to acquire a knowledge 
of the principles more in detail, according to the 
branch of science which may be more immediately 
the object of their attention. 

The Ancients knew little of mechanics as a 
science. Galileo, who lived about two centuries 
ago, may be considered as the father of the modern 
science of mechanics. Since his time many cele- 
brated mathematicians in different countries have 
distinguished themselves on this subject ; the names 
of Newton, Leibnitz, the Bernoullis, are well 
known as originals in this department of science : 
but it would be unfair to mention a few names 
only, where so many are entitled to honourable 
distinction. In the progress of the science a con- 
troversy arose, which was carried on with great 

128 New View of Daltons Atomic Theory chap. 

warmth and even animosity ; and though it has 
now been discussed for more than a century, 
modern writers on mechanics are far from being 
unanimous on the subject. It related chiefly to 
the measure of force in moving bodies. One party 
maintained that the force of a body in motion is in 
direct proportion to its velocity ; the other party 
contended that the force is in proportion to the 
square of the velocity. According to the former, a 
body moving with twice the velocity has twice the 
force ; according to the other it h^isfour times the 
force. The dispute is evidently one of great im- 
portance to the science, as our estimate of the 
quantity of moving force in bodies must be materi- 
ally influenced as we adopt the one or the other of 
these conclusions. 

We shall have occasion to advert to this subject 
more particularly in the second part of mechanics, 
or that branch called dynamics ; in the meantime 
I may observe that those who wish to obtain infor- 
mation on this head will find an excellent disquisi- 
tion on moving force in the second volume (new series) 
of the Manchester Memoirs^ which I consider as the 
best essay that has appeared on the subject, and 
which in my opinion is completely decisive of the 
controversy. Though in the above-mentioned 
essay the force of moving bodies is determined to 
be as the square of the velocity, yet the author has 
shown that the advocates of both sides have taken 
partial views of the phenomena, and hence he in 

mp^^TWSf^T^fJP^ • '^* • 

IV Daltons Lecture Notes 129 

some measure accounts for the continuance of the 
dispute. In the collision of bodies two things 
always happen, a change of motion and a change 
of figure ; the circumstances attending the former 
have always been minutely observed, but those 
attending the latter have frequently been overlooked, 
and sometimes the fact itself discarded under the 
idea of the bodies being perfectly hard^ as it is 
termed. But no such idea can be admitted as 
deducible from observation. 

Another unfortunate circumstance has been the 
consideration that moving force is generated by 
pressure acting for a certain time^ whereas it ought 
rather to be considered as arising from pressure 
acting through a certain space. 

But we shall not pursue the subject farther at 

From the preceding observations it may be in- 
ferred that our systems of mechanics are as yet in 
an imperfect state. Many authors in our own 
language, as well as in others, have compiled 
systems which contain important principles and 
judicious illustrations; but they are all more or 
less defective in regard to one principal object — 
namely, the application of moving force to the 
various exigencies of practical mechanics, and 
particularly so in the estimation of its quantity or 

A good treatise on the elements of mechanics 
is therefore still a desideratum in science. 




JDr. T. C. Hope to Dalton 

Dear Sir — Since I had the pleasure of conversing 
with you in Manchester, I have thought a good 
deal upon the subject of your speculations. I can- 
not say that I am more disposed to agree with you 
in them, though indeed some things that seemed 
to be strong objections now appear less decisive, 
and the whole pleases me with its ingenuity. 

I made the following experiment, and I beg 
you will tell me how far you think it accords with 
your theory : — 

I took two bottles nearly of the capacity of 
§xii, I filled one with carbonic acid gas and the 
other with hydrogen gas, and holding the latter 
inverted and perpendicular over the former, I con- 
nected them by a tube filled with hydrogen gas 4 
inches long and between \ and \ of an inch in 

In this situation I left them for an hour, 

Ff?t>»,r^iY.f^'. ' 

CHAP. V Letters Written and Received by Balton 1 3 1 

presuming that, as each gas had an elasticity = 30 
inches of $, in that period, and probably in a 
much shorter, a mutual exchange of half of the 
contents of each would take place, provided the 
theory were true. The result was that a quantity 
of carbonic acid gas=i^ oz. m. had entered the 
bottle containing hydrogen, ascertained by observing 
the amount of the absorption occasioned by lime- 
water, and an equal bulk of hydrogen had descended 
into the carbonic acid determined by the amount 
of unabsorbed residuum after washing with lime- 

Suppose a bottle were filled with sand and the 
atmospheric air were extracted from the intersticial 
spaces by an air-pump, and a communication then 
established between the interior of this bottle and 
a bottle either of hydrogen or carbonic acid gas. 
Don't you imagine that in much less than an hour, 
that in a few seconds, the gas would make its way 
between the particles of the sand, though the in- 
terstices between them must be incomparably smaller 
than those between the particles of another gas ? 

In our last conversation you mentioned that 
you had ascertained that water does not expand as 
its temperature sinks from 40° to 32°. Would you 
be so obliging as state to me the data on which you 
form your opinion ? 

Would you also communicate to me the other 
very interesting positions respecting heat which you 
read to me ? 

132 New View of Daltons Atomic Theory chap. 

I see from Mr. Henry's paper that he is dis- 
posed to adopt your opinion that elastic fluids are 
absorbed by, or rather enter into liquids, upon the 
same principles elastic fluids mix together. Will 
this apply to those cases in which water absorbs 
many times its own bulk ? 

As in the course of my lectures which I have 
just begun I shall have very soon occasion to speak 
on these subjects, I should be glad how soon you 
favoured me with a letter in reply. — I am, dear 
sir, your very obedient servant, 

Thos. Chas. Hope. 
Edinburgh, \th November 1803. 


The argument advanced by Hope against 
Dalton's theory of mixed gases is combated by 
the latter in the New System^ vol. i. pp. 175-6. 
The idea that the interstices between the particles 
of sand must be incomparably smaller than those 
between the particles of a gas is interesting in 
view of the estimate arrived at from the molecular 
theory of gases that i cb. c. of air contains about 
2 1 trillions of molecules. 

In the New System^ p. 426, Dalton shows that 
the absorption of ammonia depends on the pressure 
of ammonia above the liquid, in just the same way 
as the absorption of any gas depends on the pressure 
of that gas on the liquid. 

TiUp-JP •;.' ", 

Letters Written and Received by Bait on 133 

Dr. T. C. Hope to Balton 

Dear Sir — I have availed myself of all the 
time you allowed me before you should expect 
a reply to your very acceptable letter of 8th 
November. In this period I have had occasion to 
peruse your various papers in Manchester Memoirs^ 
and to consider them with mature attention. I 
have been greatly pleased with their ingenuity, 
and delighted with some of the general principles 
which you have established. 

I cannot say, however, that yet I agree with 
you in some of them, and the constitution of 
mixed gases is one of the hypotheses to which I 
cannot subscribe. With regard to the experiments 
of which you mention you had lately presented 
an account to the Society similar to the one I 
detailed, I must express my concurrence in the 
sentiment that " The effects being alike in the 
different cases, are to be ascribed to the same 
cause." Now, you mention that the appearances 
exhibited by oxygen and nitrous gas did not differ 
from those arising from other gases. Between the 
former the action is unquestionably chemical, and 
countenances the opinion that that of the others 
may be of a similar nature. I confess, however, 
that I have difficulty in applying this to the case 
of oxygen and hydrogen, which I presume you 
likewise tried. For if chemical attraction were 

134 New View of Daltons Atomic Theory chap. 

here exerted, there should be condensation and 
production of water. 

The reason you assign for the slow inter- 
mixture of the two gases affords what I conceive 
the strongest objection to the theory in general. 
You impute it to the operation of the atmospheres 
of caloric surrounding the particles of the different 
gases. This atmosphere I deem the essential cause 
of the elasticity and repulsion among the particles 
of the gas, and I cannot conceive that this atmo- 
sphere as it surrounds a particle of oxygen should 
repel the atmosphere that surrounds another particle 
of oxygen and should not repel the atmosphere 
that envelopes a particle of azote, hydrogen, or any 
other gas. 

I shall, with much impatience, expect the 
establishment of the general law of expansion of 
fluids which you announce to me. I imagine, 
however, you must make an exception in the 
case of water, on account of its peculiarity of 
constitution. From the interesting experiments 
you hinted, when I had the pleasure of conversing 
with you, and from the differences you notice 
as occurring apparently in the volumes of this fluid 
according to the nature of the material of the 
apparatus, you may perhaps imagine I am claim- 
ing an exemption in favour of water to which 
it is not entitled. Mr. Hutchinson indeed 
yesterday gave me a short account of your 
late communication, which from his account 

V Letters Written and Received by Dalton 135 

appears to bear the same stamp of ingenuity 
which so strongly characterises your former 
papers. When I was preparing to lecture on the 
motions produced among the particles of fluids, 
I foresaw that your refutation of the supposed 
peculiarity would throw a great many fine pieces 
of reasoning respecting its importance in the 
economy of nature, etc., into the greatest con- 
fusion. I was determined, therefore, to satisfy 
myself by actual experiment, but in a manner 
which I should conceive to be free from every 
objection at least arising from the influence of 
the vessel. I made the experiment and convinced 
myself that the supposed law is a real and true 
one. I hope you will excuse me for having 
announced in my lectures the grounds on which 
you denied its existence, having mentioned them 
in those terms of respect, in which I speak of 
all your speculations. That notice I deemed an 
essential preamble to the statement of my own 

The outline of my experiments is : — Take a tall 
jar full of ice-cold water, have a thermometer near 
bottom and near surface, place in a warm room. 
Bottom gains temperature soonest, and rises quickest 
to 39i°, then top equals and afterwards gains tem- 
perature fastest. Take same jar full of water at 
50°, surrounded with water of 32° or ice and 
water. Bottom cools quickest till it comes to 
40° — then equality prevails, and below 40° top 

136 New View of Dal ton s Atomic Theory chap. 

cools quickest. Take a tall jar full of water at 
50°, surround a few inches of top (by due con- 
trivance) with freezing mixture. Bottom cools 
quickest to 40° or 39V, then is stationary for any 
time, while top cools quickly to 32° and freezes. 

Take tall jar with water 40° and place a few 
inches of bottom in freezing mixture. Top cools 
at first fastest, then nearly at same rate with 
bottom till 32°, when congelation around sides 
of glass takes place. Mr. Hutchinson witnessed 
one of the experiments. I know not whether 
they will seem as decisive to you as they do 
to me. 

I have hunted the different public and private 
libraries for Gren but in vain. Lord Glenlee has 
a copy of it, but unluckily it is sixty miles off. 
If you can't get the information you desire else . . . 

Dr. T. C, Hope to Dalton 

Dear Sir — Above a month has elapsed since I 
wrote you, but my letter from foolish negligence 
was never sent to the post office. 

While in London I had no thoughts of inter- 
rupting those occupations in which you must 
have been incessantly engaged, by renewing any 
controversial discussion. 

Since I heard from you I multiplied and 
varied my experiments, and had so uniform results 
that, in spite of your friendly caution, I ventured 

V Letters Written and Received by D alt on 137 

to read the detail of them to the Royal Society of 
this place. My object was to prove that there 
really does exist the supposed peculiarity in the 
constitution of water in regard to the effects of 
heat upon its volume. It seems, therefore, to me 
very strange that that fluid, that has suggested 
your general law of expansion, should be an 
exception to it. 

As I am persuaded that you have not hastily 
concluded that the common notion is erroneous, 
and that you have proceeded on the support of 
ingenious experiments, I am very anxious to 
learn the particulars of those which have decided 
your opinion. Mr. Hutchinson communicated to 
me a general outline of them. 

Shall they soon be published, or could I by 
any means have a perusal of them ? 

A principal reason for my eagerness on this 
point is, that I shall be determined in all pro- 
bability as to the printing of my paper by what 
you shall do. If you publish, from the great 
weight which your well-merited reputation gives 
you with the scientific world, I shall feel myself 
called upon to defend a truth which I conceive 
I have established. If you do not mean to com- 
municate your experiments to the world, mine 
may also remain unknown, seeing that they only 
go to determine a matter of fact, of which at 
present no doubt is in general entertained. 

Want of time prevents me from saying any- 

138 New View of Daltoris Atomic Theory chap. 

thing at present respecting the other points on 
which we differ. Those which are purely specu- 
lative will long afford room for discussion. Re- 
specting a matter of fact, which can easily come 
under the test of experiment, we cannot be long 
at variance. 

Wishing you every success in your investiga- 
tions. — I am, dear sir, your most obedient servant, 

Tho. Chas. Hope. 
Edinburgh, 29M March 1804. 

Br, T. C. Hope to Dalton 

gth August 1804. 
Dear Sir — Undismayed by the caution you 
gave me, I have ventured to put to the press my 
sentiments on the contraction of water by heat. 
After the permission you gave me to state your 
sentiments and the curious experiments upon 
which you grounded your opposition to the 
general opinion as the circumstances which called 
forth my attention to the subject, I hope I have 
not exceeded the bounds of that leave in intro- 
ducing the enclosed paragraph into my paper. 
I expect in a few days to have the pleasure of 
transmitting the paper itself, and shall then be 
impatient to learn whether my experiments make 
any impression on you. I beg you will let the 
note addressed to our friend reach him. — I am, 
dear sir, your obedient servant, 

Tho. Chas. Hope. 

V Letters Written and Received hy Dalton 139 


Dalton's views as to the temperature of greatest 
density of water are fully explained in the New 
System^ pp. 22-35. The experiments to which 
Hope refers (Royal Society, Edinburgh (1805), 5, 
379) were carried out in the early part of 1803. 

Dalton perceived that when a liquid is heated 
in a vessel there may be an apparent point of 
greatest density, due to the fact that whilst the 
vessel expands almost equally for equal intervals of 
temperature, the liquid expands more as the tem- 
perature rises (according to his own view in pro- 
portion to the square of the temperature above that 
of the greatest density). Hence if the absolute 
expansion of the liquid at any temperature is less 
than that of the vessel, an apparent contraction 
will occur, whilst as the temperature rises the 
expansion of the liquid will increase and finally 
become greater than that of the vessel. 

By observing the apparent temperature of 
greatest density in vessels made of different materials, 
and allowing for the expansion of these materials, 
the actual temperature of greatest density can of 
course be calculated, and Dalton seems to have 
concluded from his early experiments that this 
actual temperature was that of the freezing point, 
the calculated and observed apparent temperatures 
agreeing very well, as shown below, especially in 
the case of lead. 

1 40 New View of 'Daltori s Atomic Theory chap. 

[Notebook, vol. i. p. 177]. ^oth May 1803. — "iV. 5. Water 
may be stated to expand -^ from F. to B., allowing for glass. 
Glass should by this be y^ = 42°. 

Lead by Smeaton is y^. This gives 50° for the stationary 

[P. 186]. "29M June 1803. — Large lead vessel. (A cooling 

45° =160 
46 = 150 
48 + = 130 
49I =127 
50I =126 
51I =127 

53 =130 

sz\ =135 

It appears that 50°J is the lowest point of lead." 

Hope's celebrated experiment was independent 
of the expansion of the vessel, and we find Dalton 
in the New System admitting the existence of a 
maximum density above the freezing point. His 
own observations, however, as there recorded, led 
him to place it at 36°, instead of 39.5°, as deter- 
mined by Hope. The mean of the most accurate 
modern determinations is 39°.27 F . {/^ -o\ C.) 

JDr. T'. C Hope to Dalton 

Dear Sir — I shall have much pleasure in 
seeing you in Edinburgh and forwarding, so far 
as lies in my power, your scheme of a short course 
of lectures. 

I cannot, however, form any reasonable con- 

V Letters Written and Received by Dalton 141 

jecture respecting the probability of a numerous 
audience. The number of students that enter 
into the more difficult discussions upon the subject 
of your speculations is by no means large, and 
there are not many gentlemen unconnected with 
the university who are sufficiently conversant with 
these subjects to take a deep interest in them. I 
do not state these circumstances by any means to 
start any obstacle to your plan, but to prepare 
you for being satisfied with a moderate number of 

In case you put your intentions in execution, 
the sooner you come to Edinburgh the better, as 
after the beginning of April the students begin 
to desert. — I am, sir, your most obedient servant, 

Tho. Chas. Hope. 

Edinburgh, 6th March 1807. 

T*. Thomson to Dalton 

Dear Sir — I have just received your letter, and 
think that the course of lectures which you pro- 
pose to give here will be highly grateful to all 
the true lovers of philosophical chemistry. It is 
impossible to foretell the degree of success which 
you will meet with here. Indeed that will depend 
in some measure upon the exertions of your friends. 
I shall do everything in my power to promote 
your success, both by mentioning your plan in my 
class and by recommending it privately to my 

142 New View of Daltons Atomic Theory chap. 

friends, and if there be anything of which you 
may stand in need and which I can supply, you 
may freely command it. I do not know what 
place you may pitch upon for giving your lectures, 
but if you are unprovided and if my class-room 
will answer your purpose, I shall give you the 
use of it with much pleasure. I have given a 
pretty detailed account of your theory of atoms 
in my new edition not yet published ; but it is 
very possible that it differs from your conclusions 
in many particulars. 

It may perhaps be worth your while to con- 
sider with yourself and to consult your friends 
whether it would not be better to extend your 
lectures to twelve or so and to charge a guinea, 
instead of half a guinea. You would be thus 
enabled to do justice to your subject, and the 
profit would be the same. — I am, dear sir, yours 
sincerely, Thomas Thomson. 

Edinburgh, 8M March 1807. 

I hope Mr. William Henry, whom we had the 
pleasure of seeing here some time ago, has not 
been the worse for his winter journey. I can give 
you very little chemical news from Edinburgh. 
But when you come you will see what we are 
doing. I have to thank Mr. Henry for the use 
of his paper on Urinary Calculi, which I have 
not yet returned, because in a few weeks I shall 

V Letters Written and Received by Balton 143 

be at that part of my new edition and wish to 
have it by me, I have also received from him 
a piece of zinc wire sent by I do not know what 
gentleman. Might I beg the favour of you to 
present him my respects, and to let him know 
that I have got these things, and that I am much 
obliged to him for his attention. 

W, Allen, RR.S., to Dalton 

London, 'jth of 2nd month 1809. 
Respected Friend — I received thy interesting 
letter, and to begin with the first subject in it the 
present price of quicksilver is 5s. 4d. With respect 
to thy experiment in which only from 4 to 5 per 
cent of carbonic acid was found in the expired, 
thou wilt find by reference to the paper that we 
obtained about 5 per cent in that which was pushed 
off from the mouth into a eudiometer, but it is to 
be remarked that in this case the air proceeding 
from the vesicles in the lungs gets mixed with the 
air in the fauces and mouth which has never entered 
that organ, hence there is great difference between 
a short and a long expiration. The subject of 
aqueous vapour is reserved for our next communica- 
tion ; we did not intentionally omit the name of 
Crawford, but shall probably have occasion to 
notice him in our subsequent reports on this subject. 
We have made no further experiments on the 
absorption by charcoal than those detailed in the 


144 New View of Daltons Atomic Theory chap. 

transactions, which appear fully to warrant the 
inference drawn from them. 

We can only say with respect to our eudiometer 
that its results are beautifully uniform, and that it 
is managed with less difficulty than any other. We 
conceive there is a strong objection to the use of 
nitrous gas on divers accounts ; in the first place, it 
is very liable to contain a mixture of azote or 
nitrous oxide ; and in the next place, it would be 
very troublesome to be obliged to examine your 
nitrous gas for this, whereas in our method we 
know that the green sulphate will not take up any 
azote, and consequently this source of error is 
avoided, and any nitrous gas which might have 
mixed with the air under examination is readily 
taken out by a simple solution of green sulphate. 

I intend to keep a look out for Attwood upon 
motion, but it is now very scarce, and only to be 
picked up by chance. 

Davy thinks he has proved azote to be a com- 
pound of oxygen and hydrogen ; for having caused 
potassium to absorb a considerable quantity of 
ammonical gas he procured scarcely anything but 
hydrogen from it, and a considerable portion of 
potash was found. Some of his late experiments 
have led him to query whether oxygen and hydrogen 
are not water combined with the electric fluid in 
a peculiar way. If this should be established, the 
foundation of the Lavoiserian theory is removed. 
Present me kindly to Henry, and tell him that I 


V Letters Written and Received by D alt on 145 

fully purpose to attend at his election and put in 
my ball for him, though it will be no otherwise 
necessary than as a testimony of friendship. 

Requesting to hear from thee when convenient. 
— I remain, thine sincerely, W. Allen. 


The papers to which reference is made are (i) 
" On the Changes produced in Atmospheric Air and 
Oxygen Gas by Respiration," by Allen and Pepys 
[Philosophical Transactions^ 1808, p. 249), and (2) 
" On Respiration," Allen and Pepys [Philosophical 
Transactions^ 1809, p. 404). 

The oxygen in the expired air was determined 
by treating it first with a solution of nitrous gas in 
green vitriol and then with a solution of green 
vitriol, a process proposed by Davy. Since the 
nitrous gas prepared from copper by nitric acid 
always contains nitrogen and nitrous oxide, this 
process was an undoubted improvement upon the 
old one. 

Davy's experiments on ammonia are to be 
found in the Bakerian lecture for 1808, and an 
appendix to it, read 2nd February 1809 [Philo- 
sophical Transactions^ 1809). 

The experiments on charcoal are to be found 
in a paper " On the Quantity of Carbon in Carbonic 
Acid," etc., by Allen and Pepys [Philosophical Trans- 
actions^ 1807, p. 267). 

146 New View of Dal ton s Atomic Theory chap. 

T, Thomson to Dalton 

Edinburgh, i-^th November 1809. 

Dear Sir — I have been looking for some time 
for the second volume of your chemical work, the 
period at which you had promised to publish it 
having long elapsed. I hope nothing has come 
in the way to prevent you from prosecuting your 
important plan. From the nature of your subject 
you must not look for a very rapid sale, you will 
not therefore, I trust, be disappointed if the book 
should go slowly off. Those only who have made 
some progress in the science will be interested in 
your speculations. 

I write you at present to give you some in- 
formation respecting your atomic theory, which I 
hope will not come too late for your second volume. 
Berthollet has written a long attack upon it in the 
introduction to the French translation of my 
System of Chemistry^ a book which I have not 
seen and cannot therefore give you any account of 
his argument. But in the second volume of the 
Mem, D'Arcueil which Mr. Chenevix brought 
over, and of which I have got a copy, there are 
several dissertations which I wish you saw. Ber- 
thollet has repeated your experiments respecting 
the spontaneous mixture of different gases. The 
apparatus nearly resembled yours, but was more 
elaborate. The gases were always uniformly mixed 

V Letters Written and Received by Dal ton 147 

in twenty-four hours if one of them was hydrogen 
(as hydrogen and carbonic acid, hydrogen and 
oxygen, hydrogen and azote) ; but other gases did 
not mix uniformly in that time (as air and carbonic 
acid, azote and oxygen, azote and carbonic acid, 
oxygen and carbonic acid). Air and carbonic acid 
did not mix uniformly in seventeen days. In the 
highest globe there were forty-two of carbonic acid, 
in the lowest fifty. These experiments are rather ad- 
verse to your peculiar opinion respecting the gases. 
Berthollet in one other dissertation denies that there is 
any such gas as carbonated hydrogen, I have never 
examined the gas from marshes, which I take to be 
the only carbonated hydrogen gas known ; but I cer- 
tainly shall next summer. You have, and upon your 
authority I went. I trust I shall find you correct. 
Every gas from animal and vegetable substance, and 
from salt, which I have tried, and I have tried a 
great many, contains oxygen, so that I cannot 
from my own experience contradict Berthollet. 
Dr. Henry's experiments are similar to mine, except 
that his opinion about the presence of pure hydrogen 
gas in some of his gases appears improbable. Ber- 
thollet admits the accuracy of the experiments 
adduced by Dr. Wollaston and me in support of 
your theory. But he says it does not apply to the 
sulphates. He quotes my analyses of the sulphates 
of potash, and gives several of his own of a similar 
nature. My experiments were made with care ; 
but the results give negative conviction, as I went 

148 New View of Daltons Atomic Theory chap. 

on wrong data respecting the composition of 
sulphate of barytes. The most important paper 
respecting your atomic theory is by Gay-Lussac. 
It is entirely favourable to it, and it is easy to see 
that Gay-Lussac admits it, though respect for 
Berthollet induces him to speak cautiously. His 
paper is on the combination of gases. He finds 
they all unite equal bulks, or two bulks of one to 
one of another, and three bulks of one to one of 
another. The following are his facts : — 




is composed 

of 100 azote and 

300 hydrogen. 

Sulphuric acid . 



100 sulphurous acid 

50 oxygen. 

Muriate of ammonia 



100 ammoniacal and 

100 muriatic acid gas 

Carbonate of ammonia 



100 do. 

100 carbonic acid. 

Subcarbonate of ammonia 



100 do. 

50 do. 

Fluoborate of ammonia 



100 ammoniacal gas 

100 fluoboric acid gas 

Subfluoborate of do. 



100 do. 

50 do. 




100 hydrogen 

50 oxygen. 

Oxide of azote . 



100 azote 

50 oxygen. 

Nitrous gas 



100 do. 

100 do. 

Nitric acid . 



100 do. 

200 do. 

Nitrous acid gas . 



300 nitrous gas 

100 do. 

Nitric acid . 



200 nitrous gas 

100 do. 

Oxymuriatic acid 



300 muriatic acid gas 

100 do. 

Carbonic acid 



100 carbonic oxide 

50 do. 

100 carbonic oxide 




. 50 do. 

In some of these results I had anticipated him, 
as may be seen in my System^ third edition. He says 
your experiments on the nitrous gas eudiometer are 
inaccurate. Oxygen either combines with 2*^^ its 
bulk of nitrous gas or with 3^^ its bulk. His 
method is to add a sufficient quantity of nitrous gas 
in a wide vessel, and not to agitate : ^ of the 

V Letters Written and Received by Balton 149 

diminution is oxygen. These are the most im- 
portant facts respecting gases contained in the 
volume above alluded to. I thought it right to let 
you know them, that you might repeat the experi- 
ments, and either constate or refute them in your 
next volume. I shall repeat them when I have as 
much leisure, which is not at present. There is 
a dissertation on the respiration of fishes by Hum- 
boldt. He finds that not only the oxygen gas 
but part of the azote also in the water disappears. 
The water of the river Seine was found to contain 
0.075 of gas. This gas contained about 31 per 
cent oxygen, the remaining 69 were azote. These 
proportions also differ from yours. Gay-Lussac 
has shown in a dissertation that the quantity of 
acid which combines with a metallic oxide is 
always proportional to the quantity of oxygen which 
it contains. Thus if two oxides a and b contain 
the first one, and the second two of oxygen, b will 
combine with twice as much acid as a. If this 
rule hold it furnishes a very easy method of ascer- 
taining the composition of metallic salts. The 
fluoboric acid mentioned in the preceding table is 
obtained by heating fluate of lime and boracic acid. 
It is a compound of boracic and fluoric acids. It 
has been demonstrated by Davy and by Gay-Lussac 
and Thenard, that muriatic acid gas contains at 
least ^th of water essential to its gaseous state. 
Pray make my best respects to Dr. Henry. I have 
been looking for his dissertation on common salt in 

150 New View of Dal tons Atomic Theory chap. 

the journals, but it has not yet made its appearance. 
I send you two copies of a paper of mine, printed 
some months ago. But the copies were somehow 
mislaid till the other day. — I am, dear sir, yours 
faithfully, Thomas Thomson. 

H, Davy to Dalton 

My dear Sir — I should be glad if you would 
inform me by what process you procure phos- 
phoretted hydrogene, weighing 25 grains the 100 
cubical inches, as I should like to examine this 

I am surprised that you should not have read 
in my paper the examination of the quantity of 
water in potash. I rate it at 16 per cent ; but this 
water does not exist in the potash formed by com- 
bustion from potassium. See the end of the first 

I have no objection to the theory that the me- 
tallic oxides and earths are compounds of water and 
unknown bases ; but then fused potash must con- 
tain two of water. With respect to whether the 
metals of the alkalies are compound or simple, I 
do not think that of any importance as to the dis- 
covery, but of great importance as to theory, and 
in all my papers I have taken the two views. But 
the French view is absurd ; they assume that 
potash is a compound of water, and something which 
cannot be procured free from water, and yet they 


V Letters Written and Received by Dalton 151 

call potassium a compound of potash (assumed to 
be a compound of water) and hydrogene. It 
certainly may be a compound of an unknown alka- 
line basis and hydrogene. 

You ask what becomes of the water in the 
galvanic processes. It is decompounded, and 
hydrogene is always disengaged at the negative 
surface when the battery is in high action. 

When fused potash is passed over iron turnings 
the water of the potash is decomposed with the 
alkali, and torrents of hydrogene come over, hold- 
ing potassium in solution. 

I shall be sorry if you introduce into your 
rising system an hypothesis which cannot last con- 
cerning the alkaline metals. 

I will let you know when the managers can 
settle your account. 

I am now opposing a result which I cannot get 
over of the conversion of ammonia into oxygene 
and hydrogene. — I am, my dear sir, with much 
esteem and regard, faithfully yours, 

H. Davy. 

Friday, 25M May 18 10. 


The paper here mentioned is the Bakerian 
lecture for 1809, read i6th November 1809 and 
published in the Philosophical Transactions^ 18 10. 

Dalton in the New System^ part ii., published in 
November 18 10, gives two accounts of potassium 

152 New View of Daltons Atomic Theory chap. 

and sodium, one (pp. 260 and 262) in the earlier 
portion of the book, in which they are looked upon 
as metals, and the second under the headings of 
" Potassium, or Hydruret of Potash," and " Sodium, 
or Hydruret of Soda," in the concluding portion 
(pp. 484 and 502). In this last account Dalton 
takes up the view which he ascribes to Gay-Lussac 
and Thenard, that potash is undecompounded, and 
potassium is a compound of this with hydrogen. 
Dalton describes the product of combustion of 
potassium in oxygen as " potash as dry as pos- 
sible to be procured, according to Mr. Davy ; 
that is, the first hydrate," containing 16 per cent 
of water ; whereas in the letter before us Davy 
expressly says that the 1 6 per cent of water present 
in fused potash " does not exist in the potash formed 
by combustion from potassium." 

Davy's account of the French view appears to 
differ from Dalton's, as according to the former 
Gay-Lussac considered potash to be a compound of 
water, and something which cannot be procured 
free from water. The difference is, however, only 
apparent, as it is this " something " to which Dalton 
assigns the name potash and the weight 42 [New 
System^ p. 486). 

T". C. Hope to Dalton 

2nd yanuary 1 8 1 1 . 

Dear Sir — Accept of my best thanks for the 
copy of your second volume, which Mr. Holland 

V Letters Written and Received by Dal ton 153 

conveyed to me. I should have returned my thanks 
sooner, but I was unwilling to acknowledge its 
arrival till I could say I had carefully perused the 
work. I have done so both with much interest 
and advantage. You have increased our stock of 
chemical knowledge by many valuable facts. 

I need not conceal from you that I am by 
no means a convert to your doctrine, and do not 
approve of putting the result of speculative reasoning 
as experiment. 

Still, however, I admire the ingenuity of your 
speculations, and the happy adjustment of its sub- 
ordinate parts. 

It must be gratifying to you to see your doctrines 
adopted by the first names in the chemical world. 
With sentiments of respect. — I am, dear sir, your 
very obedient servant, Thos. Chas. Hope. 

7". T/iomson to Dalton 

30 GiLMORE Place, loth August 18 12. 

Dear Sir — When I left London in March I 
intended to have returned immediately, but several 
unforeseen circumstances have detained me here all 
summer. Owing to this your letter lay long in 
London. I did not receive it till lately, and could 
not therefore write you an answer sooner. 

I have been obliged to put off the commence- 
ment of my journal till the ist of January, but 
have not by any means laid aside the plan. I am 

154 N^'^ View of Daltons Atomic Theory chap. 

much obliged to you for your paper on the oxy- 
muriates which you offer, and shall accept of it most 
thankfully. I doubt not from your great acuteness 
that you will throw considerable light on that 
difficult subject. I have a few papers on various 
chemical subjects of no great value I fear ; but such 
as they are tKey will increase our information, and 
I mean to insert them in my journal when it 

When I came home to-day I found your paper 
on " Animal Heat " on my table. I return you thanks 
for it, and shall read it immediately with attention. 
I presume that I am already acquainted with the 
theory which you adopt, viz. Dr. Crawford's. 
It appeared to me till lately a complete explanation 
of the subject. But I confess I have now altered 
my opinion. There is a paper by Dr. Currie in 
the Philosophical 'Transactions for 1792, giving an 
account of a set of experiments which he made 
in consequence of a shipwreck that happened at 
Liverpool. These experiments have not been 
attended to. They struck me forcibly last winter 
when I was engaged in writing the History of the 
Royal Society^ and appear to me to be utterly incon- 
sistent with Crawford's theory and to overturn it. 
Mr. Brodie's experiments you have seen. They 
are also rather hostile to Crawford's theory, though 
of themselves I do not consider them as sufficient 
to overturn it. They are equally inconsistent with 
Dr. Currie's experiments. Dr. Crawford's ex- 

V Letters Written and Received by Dalton 155 

periment respecting the specific heat of venous and 
arterial blood must be repeated, and I mean to 
repeat it the first opportunity. 

I set off in a few days for Norway on a minera- 
logical expedition. I mean to cross that kingdom 
and go to Stockholm, visiting the principal Nor- 
wegian and Swedish mines. I expect a great fund 
of entertainment and information. I propose to be 
in London in October. If you send up your paper, 
which I should like to get by the end of October, 
address it to Mr. Baldwin, bookseller, 47 Paternoster 
Row. Compliments to Dr. Henry. — I am, dear 
sir, yours faithfully, Thomas Thomson. 


"On Respiration and Animal Heat" (read 21st 
March 1806), published in Manchester Memoirs^ 
ii. S.S., p. 15 (1813). 

Crawford's theory was that in the lungs the 
blood gave out carbonaceous matter which com- 
bined with oxygen to form carbonic acid, and 
the heat thus liberated was taken up by the blood 
which had by the process become arterial and of 
greater specific heat. During the circulation this 
heat was given out in order to supply the waste 
from the body and the process repeated. 

Currie's experiments (Philosophical T'ransactions^ 
i7()'2.^ p. 199) were on the effect of immersion in 
cold water on the human body, and he found that this 

156 New View of Daltons Atomic Theory chap. 

treatment occasioned a sudden fall of temperature 
followed by a gradual rise. This rise was not ac- 
companied by any acceleration of the circulation, as 
would be required by Crawford's theory. 

' Berzelius to Dalton 

LoNDRES, ce I Aout 1812, 

Leicester Square 27. 

Monsieur ! — Vous m'avez beaucoup oblige par 
le present de votre ouvrage sur le nouveau Systeme 
de la Philosophie Chimique ; lequel me fit d'autant 
plus de plaisir, que j'avois longtemps souhaite de 
connoitre vos idees sur un point chimique qui 
m'avoit longtemps occupe. 

Malheureusement je ne Tai re9u que peu de 
jours avant mon depart de Stockholm, ainsi je n'ai 
pas encore eu tems que de le parcourir ; et je 
trouve qu'il merite d'etre etudie. II y a plusieurs 
points ou nos resultats ne sont point parfaitement 
d'accord, j'aurois souhaite que le temps que je puis 
depenser sur mon voyage m'auroit permis d'aller 
vous voir a Manchester, afin que nous aurions pu 
discuter cette matiere de vive voix ; mais mal- 
heureusement pour moi je suis oblige a renoncer 
a cette esperance. Je resterai a Londres jusqu'au 
commencement du mois d'octobre ; je le con- 
sidererais comme un grand bonheur pour moi si 
vos affaires vous y ameneront pendant ce tems-la ! 

Agreez, Monsieur, les sentiments de la plus 


V Letters Written and Received by D alt on 157 

parfaite consideration pour vos talents distingues 
avec lesquels j'ai Thonneur d'etre, Monsieur, votre 
tres humble et tres obeissant serviteur, 

J AC. Berzelius. 

P,S, — Je prends la liberte de vous envoyer ci 
inclus une dissertation de M. Gilbert sur les pro- 
portions determinees. Cette dissertation est le 
commencement d'un ouvrage plus detaille qu'il 
s'est propose de publier. 

Dalton to Berzelius 

Manchester, 20th September 181 2. 

Respected Friend — I see your letter of the ist 
ult., and the acceptable present which you were so 
good as to transmit along with it. I have been 
gratified with perusing it ; but much more with 
the perusal of your own papers in the Annales de 
Chimie^ a regular series of which I have lately 
received up to March 18 12 inclusive. 

I have been induced to compare your results 
with my own, and am glad to find that in general 
there is as near an approximation as we have a right 
to expect in the present state of the science. We 
are agreed that an ultimate portion of sulphur, for 
instance, is nearly twice the weight of one of 
oxygen, as exhibited in sulphuric acid and oxide of 
lead. My numbers for the atoms of sulphur and 
oxygen are 1 3 and 7 respectively ; but on further 


New View of Daltons Atomic Theory chap. 

consideration I am inclined to adopt 14 as the 
nearest integer for sulphur ; and I am disposed to 
modify certain other numbers which I have enclosed 
in parentheses below. Your numbers and mine 
will then be compared as under : — 




• 7 



. 14 



. 90 

95 (90) 

Carbonic acid 

. 19 + 



. 67 or 




. 55 or 




. 88.6 

100 (90 or 92) 

Muriatic acid 


22 (23) 

Iron . 

. 48 



• 41 


Soda . 



Ammonia . 





24 (25) 

Zinc . . . . 



Phosphoric acid . 

25 or 


23 (24), etc. etc. 

You adopt the ratio of oxygen to hydrogen in 
water as well as Davy, ']\ to i upon the single 
authority of Biot ; I am inclined to prefer the ratio 
of 7 to I , which has so many authorities in its favour. 

There are at least 5 sulphurets of iron. 


1. 50 + 

2. 50 + 


78 + 22. 
64 +36. 

3. 50+ 42 = 54l + 45i 

4. 50+ 56 = 47 +53. 

5. 50 + 168 = 23 + 77. 

Vauquelin, An. de Chimie^ lately. 
Hatchett, Philosophical Transactions 

on magnetical pyrites. 
Hatchett and Proust. 
Got by sulphate of iron and sulphure 

of Hme. 

7*, 'irCV^.'tv:^' 

V Letters Written and Received by Dal ton 159 

The red oxide of lead, I apprehend with Proust, 
is the yellow and brown oxide combined. The 
black oxide of iron is the second, and the red the 
third, the first not being yet ascertained. 

Your analysis of tht yellow powder from sulphate 
of iron I imagine is not quite correct. The powder 
is I atom of oxide + i of acid ; the oxide is 64 or 
rather perhaps 71+35 sulph. acid: by heat the 
acid is driven off and leaves about from 60 to 71 
red oxide. 

My ideas accord with yours on oxymuriatic 
acid and muriatic acid. Potassium and sodium I 
now consider as metals ; calcium, barium, etc., as 
somewhat doubtful. 

I cannot at all enter into your disquisitions and 
Davy's on what you call ammonium. I consider 
azote and hydrogen as simple substances, as far as 
is yet known. 

The French doctrine of equal measures of gases 
combining, etc., is what I do not admit, under- 
standing it in a mathematical sense. At the same 
time I acknowledge there is something wonderful 
in the frequency of the approximation. 

The doctrine of definite proportions appears to 
me mysterious unless we adopt the atomic hypothesis. 
It appears like the mystical ratios of Kepler, which 
Newton so happily elucidated. The prosecution 
of the investigation can terminate, I conceive, in 
nothing but in the system which I adopt of particle 
applied to particle, as exhibited in my diagrams. 

1 60 New View of Daltons Atomic Theory chap. 

I have no expectation of visiting London 
shortly, and should have been glad if your views 
had led you to visit this place, and to time an oppor- 
tunity of chemical discussions on those points w^here 
we may differ. I should have wrote sooner, but I 
wished to read your papers first that I might throw 
out a few observations. — I remain with great esteem, 
yours truly, John Dalton. 

No. 10 George Street. 

P.aS. — If you do not favour us with a visit here, 
I shall be glad to hear from you again before you 
leave this country. 

Berzelius to Dalton 

London, ce i6th October 18 12. 

Monsieur ! — Bien de remerciments pour votre 
obligeante lettre, a qui j'aurois du avoir repondu il 
y a longtemps, si non des petits voyages aux envi- 
rons de Londres m'auroient empresse de rien entre- 
prendre. Je suis a present au point de m'en aller, 
et j'ai cru devoir vous prier de m'honorer de vos 
communications meme quand je serai de retour 
dans ma patrie, je ne manquerai point a vous faire 
part de tout ce que (je) puis avoir d'interessant a 
vous mander. 

L'observation que vous venez de faire sur le 
sous-sulphate d'oxide de fer est parfaitement fondee, 
aussi je m'appercevois de I'inexactitude de cette 

'»»-»T V 

V Letters Written and'^Received by Dalton i6i 

analyse lorsque je trouvai la loi d'apres laquelle 
Tacide sulphurique se combine aux bases salines. 
Vous trouverez une discussion detaillee sur cette 
matiere dans les Annales de Chimie^ dans la partie 
de mon dernier traite ou j'ai parle des sels a eaux 
de base. Dans le vrai sous-sulphate Tacide est 
combine avec 6 fois autant d'oxide de fer que dans 
le sulphate neutre. Vous verrez aussi a cet endroit 
quelle substance singuliere que fut la poudre jaune, 
que j'ai pris pour sous-sulphate pur dans mon 
premier traite. Vous appelez le sulphate d'oxide 
de fer ordinaire un supersulphate ; je ne puis pas 
en voir la cause, parceque Tacide y neutralise une 
quantite de base dont Toxigene est \ de celui de 
Tacide, tout comme dans le sulphate neutre de 

Votre opinion que le minium est une combi- 
naison de I'oxide noir avec I'oxide jaune, est peut-etre 
fondee sur la difficulte de concevoir un demi-atome ; 
je crois qu'il faut laisser les experiences maturer la 
theorie. Si celle-ci commence a s'occuper de 
presser la nature dans les formes, elle cessera 
d'etre utile et de se perfectionner. Vous avez 
raison en ce que la theorie des proportions 
multiples est une mystere sans I'hypothese atomi- 
stique, et autant que j'ai pu m'apercevoir tous les 
resultats gagnes jusqu'ici contribuent a justifier 
cette hypothese. Je crois cependant qu'il y a 
des parties dans cette theorie, telle que la science 
vous la doit a present, qui demandent a etre un 


1 62 New View of Daltons Atomic Theory chap. 

peu alterees. Cette partie p. ex. qui vous necessite 
de declarer les experiences de Gay-Lussac sur les 
volumes des gases qui se combinent, pour ine- 
xactes. J'aurois cru plutot que ces experiences 
etoient la plus belle preuve de la probabilite de la 
theorie atomistique, et je vous avoue d'ailleurs que 
je ne croirai pas si aisement Gay-Lussac en defaut, 
surtout dans une matiere ou il ne s'agit que de 
mesurer bien ou mal. 

Mais le papier m'ordonne a finir. Si vous 
vouliez m'honorer de vos lettres, mon adresse sera 
ci-apres Stockholm^ sans autre addresse plus par- 
ticulier ; je pars demain au soir pour me rendre 
par Marverg a Gottembourg. — Que Dieu vous 
benisse. J. Berzelius. 


In the very interesting comparison of results 
contained in Dalton's letter to Berzelius, Dalton's 
numbers are (for the most part) those published 
in the New System^ part ii. (1810). The num- 
bers ascribed to Berzelius have been calculated 
from those actually given by the Swedish chemist, 
which were all referred to 0=ioo. In many 
cases it has been necessary to divide by 2 to obtain 
comparable numbers. 

A translation of the second of the letters from 
Berzelius has been published in Henry's Life of 
Dalton, It is added here in the original for the 
sake of completeness. A number of accents have 

wf.: ^>r :- 

V Letters Written and Received by Dal ton 163 

been added, but the construction has not been 

Berzehus' first analysis of the " yellow powder " 
(Gilb. Ann, 37, 308), gave the result — 

Sulphuric acid . . . 27.33 100 

Ferric oxide . . . 72.67 266 

100.00 366 

According to which the acid neutralises 4 
times as much base as in the neutral sulphate — 

Sulphuric Acid . . 39.56 
Ferric Oxide . . . 60.44 



According to Dalton, on the other hand, the 
powder contained one atom of oxide to one of acid, 
and therefore had the composition — 

Acid . *. . 35 33 100 
Oxide . . .71 67 203 

106 100 303 

As explained by Berzelius in the following 
letter, referring to the paper published in Gilbert, 
40 (18 1 2), 294, the true subsulphate of iron was 
found to contain — 

Acid . . . 20.2 
Oxide . . . 79.8 


The specimen analysed was prepared by saturating 
sulphuric acid with ferric oxide, partially precipi- 
tating with ammonia, and digesting the brownish- 
red precipitate with the liquid. The "yellow 

164 New View of Daltons Atomic Theory chap. 

powder," originally obtained as a deposit from a 
solution of ferrous sulphate, and of the composition 
stated above, was then again examined. A sample 
procured from a vitriol works had the composi- 
tion — 

Acid . . . 15.9 100 

Oxide . . . 62.4 392.52 
Water . . . 21.7 

and therefore contained acid and oxide in the same 
ratio as the brownish-red precipitate just described. 
Another sample was prepared in the same way as 
the first one, viz. by dissolving iron in dilute 
sulphuric acid, to which a little nitric acid had 
been added, and then exposing the solution to the 
air for some days at 25-30° in contact with slips of 
metallic iron. 

The yellow precipitate was found to contain — 

18.5 of water strongly charged with ammonia. 
32 „ acid. 
49 „ oxide. 

And was therefore an ammoniacal compound. 

The " disquisitions on ammonium " (Gilbert, 
40 (18 1 2), 176 et seq,)^ consist of an elaborate ex- 
position of the result of assuming that ammonia 
contains oxygen. 

The analogy of ammonia with the alkalis, its 
basic properties, and the production of ammonium 
amalgam, led many, and among them Berzelius, to 
think it possible that ammonia really contained 
oxygen, the discovery of which in potash and soda 

V Letters Written and Received by Dalton 165 

was the recent and brilliant achievement of Davy. 
Now ammonia is decomposed by electricity into 
nitrogen and hydrogen, in which, therefore, the 
oxygen must be contained. According to the 
dualistic theory the nitrogen and hydrogen would 
then both be oxides, the combination of which to 
form ammonia would be quite analogous with 
that of oxide of sulphur and oxide of potassium 
to form sulphate of potash. 

According to Berzelius nitrogen and hydrogen 
would, under these circumstances, have to be con- 
sidered as oxides of an unknown substance — am- 
monium — their composition being — 






Oxygen . 



When the elementary nature of nitrogen and 
hydrogen had been finally established, the term 
ammonium was transferred to the group of ^ttoms 
contained in the salts formed by the union of 
ammonia with acids, in which sense we still em- 
ploy it. 

Dalton's views on the combination of gases by 
volume have already been discussed (p. 47). 

J. Otley to Dalton 

Mr. Dalton — Sir — I received yours of the 8th, 
and am much obliged to you for the analysis of 

1 66 New View of D alt on s Atomic Theory chap. 

the gas. The books for Mr. Knight shall be care- 
fully forwarded. 

Derwent Lake varied very little in height for a 
month after you saw it, which was unusually low 
for such a length of time. About the 6th of 
August the floating island began to appear above 
water ; I was' upon it on the 21st, at which time 
the lake had risen about 8 inches, and the island 
was only in its highest parts about 4 inches above 
water ; its length was 88 yards, its greatest breadth 
25 ; but some parts of it was less than half that 
breadth. The gas on coming up (by boring under 
water near the edge of the island) had then a very 
perceptible smell, which I compare to that of a 
foul gun. Whether this smell is strongest when 
the island first emerges, or whether at other times 
it is taken away or lessened by the greater depth of 
water through which the gas ascends I am not 
able to determine. 

I endeavoured to ascertain whether the island 
consisted of the same kind of peat earth through- 
out, which I find to be nearly the case ; and also 
to examine more particularly the earth underneath 
it, which I have been inclined to call a vegetable 
oxide. On taking up some of this at the depth of 
1 3 feet below the surface, I found it intermixed 
with specks of a bluish-green colour, which from 
its turning black with infusion of galls I take to be 
a sulphate of iron. This makes me suspect that in 
my hypothesis of the generation of the gas I may 


V Letters Written and Received by Dalton 167 

have laid too much stress upon the decomposition 
of the vegetable matter of the island ; or could 
the iron be originally contained therein ? 

The gentleman who brought your letter having 
kindly proffered to take anything I might w^ish to 
send, I embrace the opportunity of sending you a 
small specimen of the earth of the island, taken at 
I foot below the surface ; a smaller one from the 
under surface of the island, and another, that with 
the clayey appearance, from beneath the island at 
the depth of 13 feet below the surface, that is 
4 feet below the water under the island. This 
you will find when dry to be uncommonly light. 
From knowing the qualities of these substances 
you will be able to form an opinion where it is 
most likely for the gas to be generated. 

The island never appeared so high above water 
this season as it did in 1808, and on the ist of 
September, the lake having risen about 2 feet, it 
was entirely covered, and so it remains. At 
present, though, the lake is now considerably 

A writer in the Cumberland Pacquet has 
advanced an opinion of the island being raised 
by the air contained in the leaves of the plants 
growing upon it, viz. the Lobelia Dortmanni and 
Isoetes Lacustris. This, I think, requires very 
little consideration to refute it. — I remain, sir, 
your very humble servant, Jona. Otley. 

Keswick, 14//1 September 181 5. 

1 68 New View of D alt on s Atomic Theory chap. 

P.aS. — The earth taken from beneath the island 
I find useful in cleaning the cases of watches. — 


L, Howard to Dalton 

Tottenham, 12th mo. 13, 18 16. 
Esteemed Friend — I shall willingly give thee 
some account of our process for making sulphuret 
of potash. Our method is to mix dry subcarbonate 
of potash with sublimed sulphur and throw them 
into a crucible heated to redness, effecting the 
fusion as quickly as possible : there is an effer- 
vescence at the moment of the union, indicating 
that the sulphur expels the carbonic acid. As the 
sulphur burns freely the whole time, some of it 
must be lost, but our last account of the propor- 
tions stands thus : — 

135 lbs. kali prop. 
27 lbs. flor. sulph. 

Pro. 108 lbs. kali sulph. 

So that the loss in carbonic acid, water, some por- 
tion burned and volatilised, and a little waste, is 
54 lbs. 

The colour of the product varies in different 
parts from straw to liver colour. Is this from a 
different proportion of sulphur retained, or its dif- 
ferent degree of oxidation ? The Pharmacopoeia, 
I think, orders half the weight of the alkali in sul- 
phur. We use one-fifth, all above which I should 

V Letters Written and Received by Dalton 169 

consider as wasted, but I have never examined the 
proportions in which potash and sulphur really 
exist in our compound, which in appearance is like 
that of other chemists. 

If a set of my meteorological observations as 
published in Nicholson and Thomson will be 
acceptable, I will send them on thy indicating by 
what conveyance. I know not whether the pre- 
sent will be in time for Thomas Hoyle. I should 
be glad to receive from thee any striking facts in 
this line, as I have some thoughts of endeavouring 
to bring the mass of materials, which I have been 
now for ten years collecting, to bear upon the sub- 
ject in the form of a few familiar lectures. I think 
thou once gave me an account of a remarkable 
electrical appearance on the cross of your parish 
place of worship, which, if it was not during an 
actual thunderstorm, would be valuable to me, if 
stated with the time, place, and circumstances. I 
have rummaged the Philosophical Transactions and 
divers other works for the most appropriate in- 
stances of various metereological phenomena, and 
shall be in some respects much indebted to thy 
own and other papers in the Manchester Memoirs, 
Pray what is the most recent publication of these ; 
or is there anything since vol. v. p. 2 ? My 
barometer has lately indicated the highest and 
lowest points for the last twelve months, viz. 
30.63 inches on the 30th ult., being the middle of 
a week's elevation, and 28.60 inches last night, the 

lyo New View of Daltons Atomic Theory chap. 

1 2th being the crisis of a very short depression, 
preceded by quick oscillations for a week past. 
We had a storm of wind the forepart of the night, 
and thunder and hail to-day at noon. Our rain 
for the year is on the point of exceeding 30 inches, 
a very large amount for this part of the island, and 
we may yet 'have an inch or two more. I met 
with little weather but thunderstorms and wet in 
our late tour on the Continent, which, however, 
did not deprive me of a most sublime and incon- 
ceivably extensive view of the chain of the Alps as 
we approached from the south of Germany, being 
at the time on some very high calcareous ground 
near Duttlingen, and not far from the sources of 
the Danube, but at full 150 miles from the back- 
ground of our prospect, which, being seen wholly 
through the upper and clear atmosphere, we could 
distinguish the light and shade of every mountain, 
and determine what was rock, what turf, what 
snow, and what glacier, with as much ease as I 
have usually been able to distinguish here at one 
tenth of the distance. I noticed on my first getting 
back the difference between the Continental atmo- 
sphere and our own in point of transparency, even 
in so wet a summer, was quite striking ; as was 
likewise the smallness of the features of the land- 
scape in our little island compared with the bolder 
sweeps of the Continent. 

I shall be glad to hear from thee at thy leisure, 
and remain thy sincere friend, Luke Howard. 

V Letters Written and Received by Dalton 171 

T, Thomson to Dalton 

Glasgow, I'^th August 1818. 

My dear Sir — I regretted very much not having 
the pleasure of meeting you when I was in Man- 
chester about a month ago. But my time was so 
Hmited that I could not spare three days which a 
journey to Keswick would have taken up. I have 
been under the necessity of resuming the sole 
editorship of the Annals of Philosophy^ very much 
against my inclination. Several very awkward 
things took place in consequence of my having 
my name standing as editor to a journal over 
which I had no control. I wished of course to 
have my name struck off the title-page. To this 
the bookseller objected with so much obstinacy 
that I was obliged to resume the sole editorship 
as the only alternative. Unluckily I was totally 
unprepared for this step, and am quite destitute of 
materials. I must therefore solicit the assistance of 
my friends to help me out for a number or two 
by their contributions. Upon you in particular I 
reckon with some confidence, and will take it as a 
particular favour if you would favour me with a 
paper by the ist of October, for I shall have the 
November number to edit. The subject, of course, 
I leave to yourself No subject of experiment 
from you can come wrong. I was happy to learn 
from Dr. Henry that you had begun to print. 

172 New View of Daltoris Atomic Theory chap. 

You will find the investigation of the metallic 
oxides particularly difficult. Our present methods 
are bad, because we cannot distinguish between 
mixtures and chemical combinations. Many of 
Berzelius' determinations are certainly wrong, par- 
ticularly the oxides of antimony. I suspect that 
some of the' vegetable acids unite not to the oxides 
but to the metals themselves, at least in some cases. 
Thus I think that oxalate of zinc is a compound of 
oxalic acid and zinc. But these observations are 
entre nous^ to be ascertained hereafter. The gases 
constitute the department of chemistry capable of 
the most accurate investigation. You will find the 
doctrine of volumes (as soon as you are satisfied of 
its accuracy) peculiarly valuable as a method of 
investigation. I am just beginning to fit up my 
laboratory. — I am, dear sir, yours faithfully, 

Thomas Thomson. 

P. Harris to Dalton 

Eaglesfield, 12th mo. 19M, 1821. 

My much esteemed friend John Dalton — I sat 
down at my desk yesterday afternoon at half-past 
one to reply to thy last favour a few weeks ago, but 
before I got pen to paper it came on so particu- 
larly dark I could not see to write (and thou knows 
my desk is not above five feet from the window). 
I soon found the cause with a clear witness. 
Almost immediately commenced nearly one of the 

V Letters Written and Received by Dalton 173 

most awful thunderstorms I ever remember. I 
am now this day fifty years and eleven days old, 
and I or none in this past that I have yet con- 
versed with ever remember such a one this time a 
year, and it is a matter of doubt whether there has 
been any like it even in summer. Distant thunder 
was heard all the morning and forenoon, but 
nothing particular to make any remark of, but 
this sheet whereon I am now writing, a little after 
half-past one, was covered with a reddish part 
tinged with blue flash of lightning for a moment, 
and immediately after, I think I almost may say 
safely, one of the loudest peals of thunder I ever 
heard ; it made my house to shake, doors and 
windows, etc., and continued in this way for nearly 
half an hour — thunder and lightning succeeding 
each other alternately, with torrents of rain and 
hail. At same time I sat pensive and quiet con- 
sidering the awfulness of the scene. On looking 
towards the fire I perceived the irons with pretty 
sharp tops towards the chimney, and knowing 
sharp points of iron attract the lightning from 
Benjamin Franklin's experience, I thought I would 
lay them horizontal on the fender. Before I had 
done that, on taking my hand off them, it and the 
irons were totally covered with lightning for a 
moment, but no injury to me. 

I do not as yet hear of any lives being lost, but 
at Dean Scales, about a mile oiF us, the lightning 
entered a chimney or roof and nearly destroyed 

174 New View ofDaltons Atomic Theory chap. 

two beds, tore up the floor, etc., and at Blind Crake 
something similar. A person just left me says he 
sheltered under a tree near it which the lightning 
struck, but he escaped without much injury. It 
came in a southern direction, I am informed, from 
the mountains — the Pillar, Knockmurton, etc. etc. 
I feel greatly obliged to thee for thy attention 
respecting the dial. On considering thy remarks 
respecting it I think it may be the best for me to 
get a round stone properly done a little below the 
plate, towards the ground, with O. G., etc., agree- 
able to some of the orders of architecture, and 
about \i\ or 12 inches over at top, not quite 
finished, but so as the mason can do it when 
put up or before. (We have a very good one 
here.) I should feel much gratifyd if thou 
could make it convenient to do it when down 
in 7th month next, when we hope to have the 
pleasure of seeing thee here. I think if three 
pieces of brass about |^ or f of an inch long could 
be soldered or screwed on the underside of it about 
an inch from the margin, a little thicker at the 
bottom, and about \ an inch diameter, they might 
be let into the stone by pouring melted lead 
into the hole, and immediately putting the dial 
plate on before the lead stiffened, or make a 
small cutting in • your stone under your plate to 
your lower side to pour your lead in after and make 
it fast. I had no intention when I mentioned 
your dial to thee but to put it up at Pardshaw 

V Letters Written and Received by Dalton 175 

Hall, but on considering I propose to have it in 
my own garden here. I may get one after for 
there, but, however, as the initials Dr. D. is 
put on let them remain. They may be seen at 
Eaglesfield many years after thee and I've gone. 

With respect to sending it, William and Jona- 
than Harris has occasionally cotton twist coming 
from Tatlock and Love, Manchester. Perhaps it 
might be enclosed safe in one of these parcels in a 
wood box. If thou thinks that mode of convey- 
ance safe I will direct W. and J. to inform 
their friends to call on thee, or perhaps thou 
could on them, and if thou has time thou can 
see if that mode will not hurt the gnomon when 
packed, it being the most particular part to attend 
to. I have been rather unwell for two or three 
weeks in something like a rheumatick complaint, 
pain in my back, etc. I am a little better at pre- 
sent, though not able to stir much out of doors, 
yet the weather has been remarkably stormy here 
for a few weeks. Strong winds, and of course much 
damage in shipping, as also at Liverpool, etc. etc. 
It might be expected after such a dry summer. 
Thou would hear of the rather sudden and unex- 
pected removal of our worthy friend Wilkinson. 

My brother Wm. Harris is a little confined 
in a cold at present. My dear S. H. is pretty 
well, and desires to be kindly remembered to thee. 
— I am respectfully thy friend, 

PoNsoNBY Harris. 

176 New View of Baltons Atomic Theory chap. 

N,B, — Could ye year 1822 be engraven on any 
part without hurting the line or figure, etc. If it 
could I should like it to be done. 

Z/. Howard to Dalton 

London, 5M mo. 31, 1822. 
Dear friend John Dalton — I have to request 
thy acceptance of the copy marked for thee of the 
within paper, and likewise the favour of getting 
delivered for me the two other copies to their 
respective addresses. The Royal Society has nomi- 
nated a committee for examining into the state of 
the meteorological institute belonging to it, which, 
having existed several months, has, I believe, done 
nothing as yet. The only time I have attended it 
we were chiefly occupied about the best mode in 
theory of ascertaining the exact height of the 
column in the barometer, and could by no means 
agree upon it. Dr. Young seemed exceedingly 
difficult to satisfy on this point. For my own part 
I think it of much more consequence to meteor- 
ology that observations be constantly and faith- 
fully, than that they be very minutely, made. We 
must creep before we fly in this infant science. 
The astronomers have got the start of us by some 
thousand years, and they may boast of their sub- 
divisions of seconds, and be as rigorous as they 
please, and predict with just confidence, while we 
can with difficulty make out a theory for any train 

V Letters Written and Received by D alt on 177 

of phenomena, and are forced to grope on in con- 
jectures. Howsoever, if the science continue to 
obtain the attentions of really capable men, we 
shall see something perhaps before we die that is 
worth notice in it. Wouldst thou have supposed that 
we have yet a bishop among our labourers. Such 
is the fact. The good old Bishop of Durham sent 
for me some time back to put into my hands about 
fifty years' observations on the barometer and ther- 
mometer, with remarks on weather, etc., kept by 
himself (when at home, and in his absence by his 
gardener) at his seat in Oxfordshire. I made up 
the year 1821 and sent him results, which agreed 
very well with ours near London, and I think the 
set, continued so long and with but little interrup- 
tion, likely to be valuable to future investigators. 
My kind regards to Dr. Henry when thou seest 
him. A letter from thee is always acceptable to 
thy affectionate friend, Luke Howard. 

T*. T'homson to Dalton 

Glasgow, i^th April 1823. 

Dear Sir — I take the opportunity of Mr. 
Davies's passing through Glasgow to acknowledge 
the receipt of your letter of October last, which 
Mr. Davies did me the favour to bring. It would 
have given me great pleasure to have forwarded 
Mr. Davies's view by every means in my power, 


178 New View ofDaltons Atomic Theory chap. 

but his stay here was too short to enable him to 
attempt any chemical investigations. 

My atomic labours are now drawing to a close. 
I have now determined all the simple bodies except 
about five or six, which are so scarce that I am 
afraid I can hardly investigate their atoms success- 
fully. I have made out gold, platinum, rhodium, 
iridium, and am at present occupied with palla- 
dium. I have also made out a great many of the 
crystallised salts, and mean to prosecute the ex- 
amination somewhat further. The triple salts are 
very numerous, and in general they crystallise 
admirably. I think I could almost double the list 
of salts. 

I am at present endeavouring to deduce by 
simple and decisive experiments the ratio between 
the weights of oxygen and hydrogen gases, and 
oxygen and azotic gases. What I have done leads 
me to think that I shall be successful. My winter 
course is now drawing towards a conclusion, when 
I shall have more leisure for experimenting. Be 
so good as make my best respects to Dr. Henry. 
I meant to have written him, but am unluckily 
interrupted. — I am, dear sir, yours truly, 

Thomas Thomson. 

Glasgow, 19M April 1825. 
Dear Sir — I do not know whether you have 
lost sight of the atomic theory, but the work 
which accompanies this letter, and which I have 


V Letters Written and Received by Dalton 179 

just published/ will show you that it has occupied 
a great deal of my attention ever since I came to 
reside in Glasgow. This work contains the sum 
total of my experimental investigations during my 
residence in Glasgow. If you take the trouble to 
look it over you will be convinced that I have not 
been idle. My experiments have amounted to 
many thousands, and they have been all made with 
as much accuracy as the present state of our means 
enabled me to attain. The results I think beauti- 
ful. You will see that chemistry is now raised 
to the rank of a mathematical science, and that, 
assisted by the tables which I have given at the 
end of the second volume, analyses may henceforth 
be made with much greater accuracy than hereto- 

I hope to have the pleasure of meeting you in 
Manchester about the beginning of June, as I mean 
to go to London about that time, and shall take 
Manchester in my way. I shall then perhaps hear 
how you are occupied, and whether you have any- 
thing at present on the anvil. — I am, dear sir, 
yours truly, Thomas Thomson. 

T>avy to Dalton 
Somerset House, loth January 1826. 
My dear Sir — I have been absent in Wales 
during three weeks, but I never received the 

^ The work mentioned is entitled An Attempt to Establish the First 
Principles of Chemistry by Experiment (1825). 

1 8o New View of Daltons Atomic Theory chap. 

note to which you allude in your last letter, 
though I may have mistaken you and confounded 
it with one that came into my hands before my 

I am very happy to find that you have done 
the Royal Society the honour to communicate 
with them. . I shall present your paper with great 
pleasure, and I hope it will not be the last that 
you will favour us with. 

I shall feel infinite pleasure in knowing that 
the services you have rendered science were fully 
appreciated and properly rewarded ; but I am 
afraid that in these times philosophical merit has 
little chance of receiving its proper meed either 
from the State or the public, and must trust too 
much to posterity. 

You have, however, a sure reward in the 
conviction that you have not only raised an 
imperishable reputation for yourself, but exalted 
the glory of your country by your development 
of the theory of definite proportions. — I am, my 
dear sir, your sincere friend, H. Davy. 


Dalton's first communication to the Royal 
Society was entitled " On the Constitution of the 
Atmosphere" (1826), and was followed by two 
others which appeared in the Philosophical Trans- 
actions — " On the Height of the Aurora Borealis " 

V Letters Written and Received by Balton 1 8 1 

(1828), and " Sequel to an Essay on the Constitu- 
tion of the Atmosphere; with some account of 
the Sulphurets of Lime " (1837). 

D, Gilbert to Dalton 

Eastbourne, Sussex, 6th August 1826. " 

Dear Sir — I flatter myself that you will have 
the goodness to excuse me for troubling you on 
a subject intimately connected with some of your 
most successful pursuits, and in which I have 
continued for many years to take a most lively 

Bred amidst the mines of Cornwall, surrounded 
by steam-engines, and having some on my own 
land, my attention has been directed from my 
earliest years (when Mr. Watt's improvement was 
first introduced) to the theory of their construc- 
tion and of the principles on which they act. 

On my going to Oxford in 1785, I first 
acquired a knowledge of Dr. Black's most import- 
ant discovery of latent heat, when it immediately 
occurred to me that if several hundred degrees of 
heat were rendered latent in the conversion of water 
into steam, and if about 40° doubled its power, 
that an immense advantage must be derived from 
the use of steam carried to a power so high as 
the strength of materials would allow. 

But in this supposition I entirely overlooked 
a most important element in the calculation. I 

1 82 New View of Daltons Atomic Theory chap. 

tacitly assumed that steam raised to 212° was 
subsequently carried up to 252°, etc., etc., without 
receiving fresh supplies from the generating water. 
But this cannot (probably) be effected on account 
of the non-conducting nature of steam ; and con- 
sequently, as the water increases in temperature, 
fresh quantifies, carrying with them latent heat, 
are sent to the former steam. 

Consequently, the intensity of steam, arising 
from heated water at different temperatures in 
close vessels, becomes an element almost of equal 
importance with the corresponding elasticity. 

For instance, if the heat rendered latent by 
passing from water into steam is represented by 
960°, and if the capacity of steam for heat is to 
that of water (weight for weight) as 1.55 to i, 
and if 40° double the elasticity, then taking unity 
for the density of the steam at 212° and d for 
its density at 252°, the latent heat in the latter 
case will be ^x 960. The heat absorbed to raise 
the temperature is^x40xi.55=:/^x 62. Suppose 
them = 2X96o, in which case there will neither 
be gain nor loss, then ^x 1022=1920, or d= 


I presume that the density is not so great as 
the above, but that it is very considerable appears 
from the small advantage gained by the use of 
strong steam in relation to the fire consumed. 

Now if you have any direct experiments or 
deductions, which coming from you I should 

V Letters Written and Received by Dalton 183 

esteem almost as authentic as experiments them- 
selves, you would confer a great obligation on me 
by communicating them. 

I have so many occupations in London, during 
the sitting of Parliament, that it is scarcely in my 
power to consult public libraries, and having last 
year ordered the whole of those most valuable 
works, by which you have instructed the scientific 
world, I was extremely disappointed by an answer 
informing me that they were out of print. 

I can rely on your well-known zeal in every- 
thing connected with the progress of investigation 
and discovery for excusing my freedom in thus 
addressing you, and I remain, dear sir, your very 
faithful and humble servant, 

Davies Gilbert, F.R.S. 

T, Thomson to Dalton 

Glasgow, 8//; December 1826. 

Dear Sir — This letter will be delivered by 
Dr. Colquhoun, an old assistant of mine, who 
has gone up to Manchester on business, and is 
anxious to be introduced to you. He is a very 
well-informed man and an excellent chemist, and 
would be very likely, unless he be absorbed (as 
has hitherto been the case with all my promising 
pupils here) in the vortex of manufacture and 
business, which is here all powerful. He has 

184 New View of D alt on s Atomic Theory chap. 

already written several good papers, which have 
appeared in the Annals of Philosophy, 

I am at present occupied chiefly with minera- 
logy, I mean to analyse every mineral not hitherto 
accurately analysed as far as I can get specimens 
of them. 

A very curious paper has been just published 
by Berzelius. There are four bodies, oxygen, 
sulphur, selenium, and tellurium capable of form- 
ing salts by combining with acid and alkaline bases. 
Oxygen in this way forms all the salts hitherto 
known. Thus 

Azote + Oxygen ") ^ 

^ ^ ' form Nitre. 

Potassium + Oxygen 


Sulphur may be substituted for oxygen and con- 
stitute a new set of salts as numerous as those 
hitherto known. Thus 

Arsenic + Sulphur ) o i i. • r r» 

T^ . o 1 L r rorm bulpnarseniet or rotassium. 

rotassium + Sulphur j ^ 

Selenium may be substituted in the same way 
for oxygen and sulphur, and so may tellurium. — I 
am, dear sir, yours truly, Thomas Thomson. 

Pray make my best respects to Dr. Henry 
when you see him. I saw his son some time 
ago on his way to Edinburgh. 


V Letters Written and Received by D alt on 185 

D, Gilbert to Dalton 

Eastbourne, Sussex, 15M January 1828. 

Dear Sir — I have this morning been favoured 
with your letter of the nth; and I answer it 
at once, to say that I am sure the Royal Society 
will be most happy to receive any communication 
with which you may have the goodness to favour 
them. And certainly the aurora borealis is one of 
those curious phenomena that demands the atten- 
tion of every one, connected as it is with the 
height of the atmosphere and with electricity, 
which is itself intimately related to magnetism. 

The monthly statements of work done by the 
steam-engines of Cornwall are certainly deduced 
from calculations founded on the dimensions of the 
boxes, plungers, and working pieces, the length of 
the stroke, and the length of the lift. And when 
boxes or plungers move in brass working pieces 
from 12 to 18 inches in diameter, making strokes 
of 8 or 10 feet, perhaps eight or ten times in a 
minute, I do not believe that the water escaping 
bears any material proportion to what is actually 
raised : at all events their monthly statements give 
an exceptionally uniform result, and in that way 
it appears that about two-thirds of all the loss 
has been saved by the recent improvements, and 
this is confirmed by the Custom-house returns. 

I am much gratified by your approval of my 
last paper in the Philosophical Transactions, In 

1 86 New View of Daltons Atomic Theory chap. 

respect to the particular point I must confess 
myself to be fully convinced of the perfect accuracy 
of the abstract assumption, whatever may be the 
result of experiments. In the same way as a 
resistance proportionate to the squares of velocity 
is absolutely true, although it can only be approxi- 
mated to in'any physical fluid. 

In the return for last November one of the 
engines performs 67 millions, and a trial has since 
been made in the presence of several captains of 
mines deputed for the purpose of witnessing it, 
when the figures exceeded 64 millions. 

According to another mode of estimating, 67 
millions performed by a bushel of coal weighing 
8 1 pounds equals that weight (lifted) through an 
ascent of rather more than 1 5 1 miles. 

I shall go to London to-morrow. 

If your communication be addressed to me 
under cover weighing less than an ounce and 
not more than this, by the same post, I shall be 
most happy to receive them. — Believe me, dear 
sir, your much obliged and very humble servant, 

Davies Gilbert. 

D. Brewster to Dalton 

Allerly by Melrose, ibth March 1831. 
Dear Sir — Being at present engaged in some 
experiments on the structure of the spectrum, and 
on the absorption of light, I am exceedingly 

V Letters Written and Received by Dalton 187 

anxious to learn if any change has taken place in 
your eyes in their insensibility to red light. You 
would oblige me greatly if you could give me an 
account of the appearance to your eye of a spectrum 
formed by the light of the sky by looking through 
a prism at a narrow longitudinal aperture formed 
by the edges of window-shutters nearly closed. 
You will understand the object I have in view 
when I mention that I have found the spectrum 
to consist of three spectra of the same length, viz. a 
red^ 2i yellow^ and a blue spectrum, so that all these 
three colours exist at every part of the common 
spectrum. Now as your eye is insensible to red 
light, but sensible to yellow or blue^ the red space 
should not vanish, but should appear yellowish with 
a slight tinge of blue, the yellow being very faint. 

I should like also to know if white objects 
appear to you yellowish with a tinge of ^ blue, or 
rather green, as they should do if the eye is 
insensible to red light. Of course you cannot 
recognise the red light which exists in violet. 

I intend to reprint in the next number of my 
journal your paper on this subject in the Manchester 

It is proposed to have a great meeting of 
scientific individuals in Great Britain, to be held 
at York on the i8th-25th July. It would be very 
gratifying if you and Dr. Henry could attend. — I 
am, dear sir, ever most faithfully yours, 

D. Brewster. 

1 88 New View of D alt on s Atomic Theory chap. 

W, Whewell to Dalton 

Cambridge, loth September 1831. 

My dear Sir — I send you the copies of our 
transactions excepting the first part, which you 
mentioned that you have already, and I beg you to 
present them to the Philosophical and Literary 
Society of Manchester from the Philosophical 
Society of Cambridge. 

I take the liberty of enclosing a pacquet for Dr. 
Traill, which I hope it will not be inconvenient to 
you to send to Liverpool by some of the usual con- 

I have made some enquiry concerning Miss 
Hague, whom I mentioned to you as having a 
similar affection of vision to your own. I have 
not yet heard the particulars of her case. But 
Professor Gumming tells me that Dr. Wollaston 
described to him the case of a lady who could not 
distinguish a ruby from an emerald except by the 
figure, and who thought a fawn colour very like a 
light green. 

I beg my regards to Dr. Henry and the other 
kind friends whom I had the pleasure of becoming 
acquainted with in Manchester, and am, dear sir, 
yours very faithfully, W. Whewell. 

V Letters Written and Received by Dalton 189 

T". Thomson to Dalton 

Primrose, loth May 1834. 

Dear Sir — I hope you will excuse the liberty I 
take in forwarding to you my observations on Mr. 
Graham's Law of the Diffusion of Gases. I was 
much gratified to learn from Dr. Henry that you 
consider the view I have taken of the subject as 
sound and free from objection. My object in 
publishing these observations was entirely a desire 
that Mr. Graham's facts, which afford so striking a 
confirmation of your admirable theory of the con- 
stitution of mixed gases, should not be generally so 
misconstrued as they have been by Mr. Graham, 
who considers them as involving some newly dis- 
covered property of gases, and inexplicable by any 
existing theory. — I remain, dear sir, with much 
respect, yours truly, Thomas Thomson. 


This letter is from T. Thomson of Primrose, 
the calico-printer, and not from T. Thomson, the 
professor of chemistry at Glasgow. 

y. Dalton to H, Dalton 

Kendal, 14M December 1834. 
Respected friend Henry Dalton — It falls to 
my lot to have the melancholy task of informing 

190 New View of Daltons Atomic Theory chap. 

thee of the decease of my brother Jonathan Dalton ; 
he died on the morning of the nth inst. after an 
increased severity of his affliction for a few days ; I 
believe all the alleviations that could be availing 
were afforded : I received the account on the 
evening of the nth, and arrived here on the 12th. 
The funeral is fixed for to-morrow morning. 

I find by his will he has left all his real and 
personal estate to me, and made me the sole 
executor ; the real estate thou art acquainted with ; 
the personal is very small, and the debts are con- 
siderable, amounting to nearly ^^9^0 ; but about 
one half of this was owing to me. 

I find thy letter of the 9th July 1834 with a 
note that it was answered by him on the 12th. I 
understand that my brother wrote thee (or rather 
got an amanuensis to write) about three or four 
weeks since, and no answer having come to hand 
yet, I judged it expedient to inform thee of the 
present circumstances without delay. 

As I have no doubt thy agency has been satis- 
factory to my brother, I hope it will be continued 
to me : when the late half year's rent is received 
and disbursements paid I think it will be best to 
remit to W. D. Crewdson and Son, bankers here, 
to be placed to my account with them, and to 
request from them an acknowledgement of the 
receipt, and they may inform me as may be con- 

Should anything occur to require my attention. 


V Letters Written and Received by Dalton 191 

my address will be at 40 George Street or 27 
Falkner Street, but " Dr. Dalton, Manchester," will 
generally find me. 

At my distance from Eaglesfield I cannot often 
visit it ; but no one knows what may happen. 

During my stay of two or three weeks in 
London last spring, I had occasion to call once or 
twice on my namesake in Regent Street. 

I do not pay postage in order to secure a more 
careful delivery. 

With my respects to thyself and family, and to 
my few remaining friends at Eaglesfield, I remain, 
thine sincerely, John Dalton. 

P.S, — I shall remain two or three days here. 


Printed by R. & R. Clark, Limited, Edinburgh. 


Date Due 

Novi , 





Library Bureau Cat. No. 1137 



3 5002 00067 4726 

Roscoe, Henry E. . . _ ,.„„,, „„ 

A new view of the origin of Dalton s ato 



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