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Full text of "Lessons in organic chemistry"

ff 






Edmund O'Wei, 





ORGANIC CHEMISTRY 



LESSONS 



IN 



ORGANIC CHEMISTRY 



PART I. ELEMENTARY 



G. S. TURPIN, M.A. (CAMB.), D.Sc. (LOND.) 

PRINCIPAL OF THE TECHNICAL SCHOOL, HUDDERSFIELD 



gorfe 
MACMILLAN AND CO. 

AND LONDON 
1894 

All rights reserved 



COPYRIGHT, 1894, 
BY MACMILLAN AND CO. 

INMEMQR1AW 



Xortoooti 
Berwick & Smith, Boston, U.S.A. 



CONTENTS 



ELEMENTARY 

CHAP. PAGE 

1. THE ANALYSIS OF ORGANIC BODIES . i 

2. EMPIRICAL AND MOLECULAR FORMULAE . . .12 

3. HYDROCARBONS OF THE METHANE SERIES . 19 

4. OLEFINES AND ACETYLENE. . . . .28 

5. HALOID DERIVATIVES . 37 

6. THE ALCOHOLS . . . . . -44 

7. ETHEREAL SALTS Ethers Mercaptan . . -55 

8. ALDEHYDES AND KETONES . . . . .61 

9. THE FATTY ACIDS . . . . . .68 

10. ACETYL CHLORIDE AND ACETIC ANHYDRIDE . . 79 

11. THE AMINES . . . . . .82 

12. THE AMIDES AND AMIDO- ACIDS . . . .88 

13. ALKYL COMPOUNDS OF PHOSPHORUS, ARSENIC, SILICON, 

AND THE METALS . . . . .92 

14. GLYCOL AND ITS DERIVATIVES. SUCCINIC, MALIC, AND 

TARTARIC ACIDS . .... 99 



889773 



ORGANIC CHEMISTRY 



CHAP. PAGE 

15. LACTIC AND CITRIC ACIDS. . . . 106 

16. THE ALLYL COMPOUNDS . no 

17. GLYCERINE AND ITS COMPOUNDS . . . . 115 

1 8. THE CARBOHYDRATES . . . . .119 

19. UREA AND URIC ACID ..... 128 

20. THE CYANOGEN COMPOUNDS . . . .131 



ELEMENTARY 

CHAPTER I 
THE ANALYSIS OF ORGANIC BODIES 

Province of Organic Chemistry. L/p> r the beginning 
of this century it was gcnei'aiiy supposed a j hat all chemical 
substances might be sharply divided' intQ tvrc'cksses, according 
as their formation was,' pr.'w&s ri.ojt,; pds,s:.il)l?; tyir'.htW.the aid of 
living organisms ; those compounds which had been obtained 
only from some animal or plant were called organic bodies, 
and the action of the mysterious "vital force" was believed 
to be necessary for their formation. In 1828, however, the 
German chemist Wohler prepared urea, a typical organic 
substance, from inorganic materials by a chemical reaction of 
very simple character, and thus broke down the separation 
which up to that time had been maintained between inorganic 
and organic substances ; but, as a matter of convenience, we 
still retain the name organic chemistry for a department of the 
science which is concerned with the chemistry of the com- 
pounds of two elements, carbon and hydrogen, and their 
numerous derivatives. Amongst these are included nearly all 
the substances formed by the complicated chemical processes 
lying at the base of life, whether animal or vegetable, as well 
as a still larger number which have been prepared artificially 
by the simple processes of the laboratory. Many compounds 
obtained, in the first place, from animals or plants have been 

IE B 



ORGANIC CHEMISTRY 



afterwards manufactured in the laboratory, and chemists have 
good reason to believe that in the future there will be no 
single substance known whose formation cannot be brought 
about by ordinary chemical reactions. 

The distinction betw r een organic and inorganic chemistry 
is, then, merely a convenient division of the vast material of 
the science, and organic chemistry may be defined as the 
chemistry of the hydrocarbons and their derivatives. 

Reasons for the separate Study of Organic Chem- 
istry. -- The reasons which make it convenient still to 
maintain an artificial separation between inorganic and organic 
chemistry are chiefly the immense number of organic com- 
pounds known a number which receives additions every- 
day and the different character of the problems presented to 
us by them as compared with the much less numerous and 
comparatively simple inorganic bodies. In organic chemistry 
the most important points claiming our attention are the 
grouping of the atoms present in .each compound, and the 
influence of th;is' grouping* on 'the 'properties of that compound. 
We shall find cases 'where the 'molecules of two different 
substances . c'oftta'in ' exactly ; sin>iU(r atoms, and in the same 
number, but -trie different arrangement - of the atoms in the two 
molecules produces bodies with markedly different properties. 

The name isomerism is given to this phenomenon. Cases 
of it are almost unknown in inorganic chemistry, but are 
extremely frequent in organic chemistry ; see p. 24 for a further 
account of it. 

On the other hand, we often find a series of organic com- 
pounds, all of different composition, but possessing very 
similar properties, owing to the presence in their molecules of 
the same group of atoms ; prominent instances of this are 
furnished by the homologous series, of which more is said 
on p. 21. 

Elements present in Organic Compounds. Every 
organic compound contains carbon, and in nearly every one 
hydrogen is also found ; the other elements may any of them 
occur, but those more frequently found are nitrogen, oxygen, the 
halogens, sulphur, and phosphorus. 

The carbon, hydrogen, and nitrogen are most satisfactorily 
detected by heating the substance with copper oxide in a 



ORGANIC ANALYSIS 



hard-glass tube ; the organic material is burned up by the 
oxygen of the copper oxide, some of which is reduced to 
metallic copper, and the products of the combustion are 
carbon dioxide, water, and nitrogen gas. If no water is 
produced by the combustion, then no hydrogen was present in 
the substance examined, and if no nitrogen be given off, that 
element was similarly absent from the material employed. 

EXPT. i. Take a piece of ordinary combustion tubing closed at one 
end ; introduce into it (a) enough dry cupric oxide (best granulated) to fill 
about three inches of the tube ; (b] then about one gram of sugar ; (c ) and 
lastly, fill the tube nearly to the open end with more granulated copper 
oxide. Close the open end of the tube with a well-fitting rubber stopper, 
through which passes a piece of glass tubing carrying a small bulb, and 
connect this with two small wash-cylinders, of which the first contains 
lime-water (better, baryta water), and the second strong solution of 
caustic soda. 




FIG. i. Apparatus for Experiments i and 2. 

Heat the tube carefully in a combustion furnace, or over a row of four 
Bunsen burners ; first applying heat at the two ends of the tube, and 
when these have become just red-hot, turning up gradually the two 
middle burners. Notice the production of water and CO 2 , and that no 
nitrogen escapes from the second wash-cylinder after the air has been all 
driven out. 

EXPT. 2. Repeat, using urea instead of sugar. Notice the large 
amount of gas evolved which is not absorbed by the caustic soda. Urea 
contains nearly fifty per cent of nitrogen. 



When proper precautions are applied this method of 
combustion with copper oxide enables us to determine with 
considerable accuracy the amounts of carbon, hydrogen, and 
nitrogen present in any organic substance. The carbon and 
hydrogen are usually determined by one experiment, the 
nitrogen by a second. 



ESTIMATION OF CHAP. 



Quantitative Determination of Carbon and Hydro- 
gen. There are several variations in the details of the 
experiment as adopted by different chemists ; we shall describe 
only one plan of work. 

A piece of hard-glass tubing, long enough to project about 
an inch from each end of the combustion furnace, is connected 

at the one end with a 
tube, through which 
or oxygen 
in each case dry and 

FIG. 2. Flask fitted with CaCl 2 tube, in which the f frrirn ~ ai .u rUr,v 
copper oxide is allowed to cool after being dried tree tr m Carbon Q1OX- 
by heating to redness. ide may be Supplied 

at will ; and at the 

other end, with a U tube containing lumps of porous CaCl 9 , 
to absorb and retain the water produced in the combustion, 
followed by a potash apparatus (Fig. 5), which similarly 
absorbs the carbon dioxide. 

About two-thirds of the combustion tube at the end nearer 
the absorbing tubes is filled with granulated copper oxide, 
kept in position by two plugs of copper gauze ; behind this is 
a " boat " of porcelain or platinum, into which about one-fifth 




FIG. 3. Tube arranged for combustion in a current of Oxygen ; the CaClo tube 
only is shown attached. 



of a gram of the substance to be analysed has been accurately 
weighed ; and then follows a longer plug of oxidised copper 
gauze, whose object is to prevent any backward diffusion of 
the products of the combustion. 

The copper oxide having been previously thoroughly dried, 
the portions of the tube on either side of the boat are first 
raised to a dull red heat, and the actual combustion is then 
begun by carefully and gradually applying heat to the 
substance in the boat, while a very slow current of pure air is 
passed through the apparatus. Towards the end oxygen is 
introduced in place of air, with the object of burning up any 
carbonaceous residue that may have been left in or about the 



CARBON AND HYDROGEN 



boat, and then air is again passed, in order to sweep along 
any CO 2 or oxygen that may be in the tube or absorbing 
apparatus. (Oxygen is heavier than air, hence the need of 
leaving the absorbing apparatus filled with air at the end, as 
at the beginning, of the combustion.) 

The CaCl 2 tube and the potash apparatus were, of course, 
weighed before the combustion was commenced ; they are 
weighed again after it is over, and the increase of weight 




FIG. 4. U-tube filled with CaClo for 
absorbing the water produced in the 
combustion. 




FIG. 5. Potash apparatus for 
absorbing the CO2- 



gives the amount of water and of carbon dioxide produced by 
burning a known weight of the substance. An example will 
best illustrate how the percentage of carbon and of hydrogen 
present in the substance may be calculated. 

Example. 0.2386 gram of a substance gave 0.4879 gram CO 2 and 
0.0870 gram H 2 O. 

The percentage of carbon = 100 x '- x = 55.76, 

.2300 n 



for .4879 gram COg contains .4879 x gram of carbon. 

The percentage of hydrogen = 100 x 7 x - = 4.05. 

.2386 9 

Quantitative Determination of Nitrogen. There 
are several methods in use, but the only one which is appli- 
cable to all organic bodies alike is that of Dumas, in which the 
substance is burned with copper oxide in an atmosphere of 
carbon dioxide, and the liberated nitrogen collected over a 
solution of caustic potash and measured. 



ESTIMATION OF 



CHAP. 



Fig. 6 represents the apparatus used. The combustion tube 
is filled with (a) a six-inch length of granulated oxide ; (b} a 
mixture of a known weight of the substance with powdered 
copper oxide ; (c) six or eight inches of granulated oxide ; 
(</) a spiral of copper gauze. It is connected at one end 



FIG. 6. 



with an apparatus for evolving carbon dioxide, from which, 
first of all, a steady stream of the gas is passed for at least 
half an hour, until the air is entirely driven out from the 
tube. During this time the granulated oxide on either side 
of the mixture (b) may be cautiously heated. When the air 
is expelled the collecting apparatus is filled to the tap with 




FIG. 7. Apparatus 
for evolving a 
steady stream of 
CO2 by the action 
of HC1 upon 
marble. 




FIG. 8. Apparatus in which the Nitrogen 
is collected over potash solution. 



potash solution by raising the bulb, the tap is closed, and 
the stream of CO 2 stopped ; the copper spiral is now heated 



NITROGEN 



to redness and the combustion proceeded with. At the end 
more CO 2 is passed, in order to sweep out any nitrogen from 
the tube and carry it into the measuring apparatus. 

It is necessary to mix the substance with powdered CuO, 
as otherwise the combustion would not be complete in the 
atmosphere of CO 2 . The object of the copper spiral is to 
reduce any oxides of nitrogen that might be evolved, and one 
must also be used in determining the carbon and hydrogen in 
a nitrogenous body. 

An example will illustrate the method of calculation. The 
work is much simplified by the use of tables which have been 
specially prepared for the purpose. 

Example. 0.2258 gram gave 28.3 c.c. moist nitrogen, measured at 
9.5 C. and 765.5 mm. 

The only difficulty is in calculating the exact weight of the nitrogen. 
It is measured over strong potash solution, whose vapour pressure at 
9. 5 C. is found in the tables as 7. i mm. ; the pressure of the nitrogen is 
therefore 765.5 7.1 = 758.4 mm. Its volume (measured dry) at o and 
760 mm. would therefore be 

758.4 273 

28. 3 x 1-2-IZ x /J = 27. 3 c.c. 
760 282.5 

and its weight 27. 3 x .0000896 x 14 = .03424 gram (i litre H weighs 
.0896 gram at normal temperature and pressure). The percentage of 

.03424 x 100 
nitrogen is therefore =15.16. 

Many organic bodies containing nitrogen evolve ammonia 
when heated with soda lime (some, however, give off only 
part, and others none, of their nitrogen in the shape of 
ammonia), and on this plan it is possible in many cases to 
detect the presence of nitrogen, and estimate its amount. In 
the quantitative process (known by the names of Will and 
Varrentrapp) the liberated ammonia is absorbed by means of 
dilute hydrochloric acid placed in a bulb tube of suitable 
construction. The amount of the ammonia is ascertained by 
estimating how much hydrochloric acid has been neutralised 
by it. 

This method has fallen into disuse, having been replaced 
by one due to Kjeldahl, which is applicable in all cases where 
Will and Varrentrapp's can be used, and is much more 



8 ESTIMATION OF CHAP. 

convenient. Kjeldahl decomposes the substance by heating it 
with concentrated sulphuric acid and addition of a little 
potassium permanganate. Under this treatment the nitrogen 
of the organic body is in many cases converted into ammonia, 
which is afterwards liberated by addition of caustic soda, 
distilled off and collected in a -measured volume of dilute acid 
of standard strength. The calculation is precisely similar, 
whether Will's or Kjeldahl's method be adopted. 




FIG. 9. One form of apparatus for the second part of Kjeldahl's process ; the 
ammonia is boiled off and absorbed by standard acid. 

Example. 1.2350 gram of a substance was treated by Kjeldahl's 
method, and the ammonia produced collected in 25 c. c. of dilute hydro- 
chloric acid of normal strength ; at the end of the distillation it was found 
that 15.3 c.c. of normal soda solution were needed to neutralise the excess 
of acid which still remained uncombined. 

The amount of ammonia produced was, therefore, sufficient to 
neutralise 9.7 c.c. ( = 25-15.3) of normal acid; that is to say, it was 
equal to the amount contained in 9.7 c.c. of a normal solution of 
ammonia. Such a solution contains 17 grams of NH 3 (molecular weight 
= 17) in a litre, and in 9.7 c.c. there would be 17 x 9. 7 milligrams NH 3 ; 
of this 14x9.7 mgms. are nitrogen, and therefore the percentage of 

14 x .0097 

nitrogen is xi 00=11.0. 

1.2350 

Detection and Quantitative Estimation of the 
Halogens. Organic substances containing chlorine, bromine, 
or iodine, do not, as a rule, react at all readily with silver 



THE HALOGENS 



nitrate ; it is necessary first to decompose the organic matter, 
for which purpose either of the two following methods may 
be used : 

() Carius's method employs nitric acid as the oxidising 
agent. About .2 gram of the substance is intro- 
duced along with I or 2 c.c. of fuming nitric acid 
and a crystal of silver nitrate into a tube of stout 
glass (" pressure " tubing of fairly soft glass with 
walls 2 to 3 mm. thick is the most convenient) 
about 40 cm. long and 2 cm. external diameter. 
The open end of the tube is next carefully heated 
in the blow-pipe flame until the walls have thick- 
ened considerably at the heated spot, and then 
cautiously drawn out into a thick-walled capillary 
tube, which is finally sealed. The tube so prepared 
is heated in a specially designed and very strong 
air bath (or " cannon ") to a temperature which 
varies, according to the character of the substance 
to be analysed, from I 50 to 300 C. for one or 
two hours. The tube must be allowed to cool 
inside the "cannon," and even when cold contains 
gases (carbon dioxide and oxides of nitrogen) 
under such considerable pressure that its opening 
can only be safely effected by heating the capillary 
tip of the tube in a flame until the softened glass .. 

. r FiG.io.-Sealed 

gives way before the internal pressure, and allows glass tube 
the compressed gases to escape. method^ 

The silver chloride (or bromide or iodide) analysis. 
formed is washed out from the tube with distilled 
water, collected on a filter, washed, dried with the needful 
precautions by heating to fusion in a porcelain crucible, and 
weighed. 

() The alternative or dry method consists in heating the 
substance with pure lime in a combustion tube heated in an 
ordinary combustion furnace. The calcium chloride (or bromide 
or iodide) produced is estimated in the usual way by precipita- 
tion with silver nitrate. 



Example. (The calculation is precisely similar in both cases.) .1638 
gram of the substance yielded .0953 gram AgCl. 



ESTIMATION OF 



CHAP. 



The percentage of Cl is therefore, since 145.4 P ai ~ts of AgCl contain 
37.4 of chlorine, 

x ioo 



The detection 
accomplished by 



.1638 145.4 
= 14.96. 

of the halogens 
applying roughly 




FIG. ii. Air-bath for Carius's method. 



can most certainly be 
one of the quantitative 
methods mentioned 
above ; but more 
conveniently by Beil- 
stein's plan, in which 
a little copper oxide, 
supported in a small 
loop at the end of a 
platinum wire, is 
heated in a Bunsen 
flame until this is no 
longer coloured,"and 
is then used to con- 
vey a small portion 
of the substance 
adhering to the 

copper oxide into the flame. If chlorine is present copper 
chloride will be produced, and its vapour will give the char- 
acteristic blue and green flame of copper. 

Sulphur and Phosphorus may be estimated by heating 
the substance with fuming nitric acid in a sealed tube (Carius's 
method ; see under Halogens). The sulphuric acid formed 
may be determined as barium sulphate, the phosphoric acid as 
magnesium pyrophosphate. 

In the case of the less volatile substances, a dry method 
may conveniently be used, in which fusion in a silver dish with 
solid potassium hydrate, and gradual addition of potassium 
nitrate, is employed to effect the oxidation of the sulphur to 
sulphuric acid. 

Example. .2178 gram of the substance gave .2586 gram of BaSO 4 . 
The percentage of sulphur is therefore, since 233 parts of BaS' > 4 
contain 32 parts of S, 

.2^86 32 

- x x ioo 

.2178 233 

= 16.3. 



SULPHUR AND PHOSPHORUS 



The qualitative recognition of sulphur or phosphorus in an 
organic body may be effected by heating the dry substance 
with a little metallic sodium. If sulphur is present, sodium 
sulphide will be formed, and may be detected by the evolution 
of H 9 S on addition of water and an acid, or by the use of 
sodium nitro-prusside, which gives an intense violet colouration 
with a trace of soluble sulphide. In the case of phosphorus, 
sodium phosphide (or if, as is advantageous, aluminium filings 
be employed, aluminium phosphide) is formed, from which 
the dampness of the breath is sufficient to evoke the character- 
istic smell of hydrogen phosphide. 

Oxygen. There is no convenient method known for the 
detection or estimation of oxygen in a compound. Its amount 
is determined by difference, i.e., by subtracting the percentages 
of all the other elements present from 100, and taking the 
remainder to represent the percentage of oxygen. 

QUESTIONS ON CHAPTER 'I 

1. Describe carefully the methods you would use for the quantitative 
estimation of the elements present in urea. 

2. Explain how the percentage of nitrogen in an artificial manure can 
be readily determined. 

3. Oil of mustard contains carbon, hydrogen, nitrogen, and sulphur. 
How would you prove that these elements and no others are present in it ? 

4. How is the percentage of chlorine in sodium chloride determined, 
and how must the method be modified in order to apply it to organic 
substances containing chlorine ? 



CHAPTER II 
EMPIRICAL AND MOLECULAR FORMUL/E 

THE Empirical Formula of a substance is the simplest 
formula which represents the results of analysis, and is 
calculated from these in the following way : Divide the per- 
centage of each clement by the corresponding atomic weight ; 
find the smallest whole numbers standing in the same ratio as 
the quotients thus obtained, and you will have the indices of 
the formula. This is best illustrated by examples : 

A substance contains the percentages given below; to find its empirical 
formula 

C = 40 per cent. 

11= 6.66 

= 53-33 

Then = ^=3.33 

6.66 
H = ==6.66 

i 

0=^=3.33 

and as these numbers are in the ratio 1:2:1, the empirical formula of the 
substance is CHvO. 

In the above example w r e have taken not the results of 
actual analysis, but the theoretical percentages. In calculating 
from the experimental numbers always more or less 
inaccurate we may sometimes have to choose between two 
or more formulae which agree about equally well with the 
analytical results. In such cases it should be remembered 



MOLECULAR FORMULAE 13 



that we usually find in a properly conducted analysis : (i.) 
about .1 or .2 per cent too little of carbon, unless halogens 
are present; (ii.) about .2 per cent in excess of hydrogen; 
and (iii.) about .2 or .3 per cent in excess of nitrogen (by 
Dumas's method). 

The chief causes of these slight errors are : (i. ) loss of CO 2 through 
incomplete absorption; (ii. ) trace of moisture in the copper oxide 
employed ; (iii.) presence of traces of air in the combustion tube and in 
the CO 2 used for expelling air from the tube. 

The Molecular Formula represents not merely the 
results of analysis, but is also in agreement with whatever 
information we are able to obtain - by application of 
Avogadro's hypothesis or otherwise as to the molecular 
weight of the compound. It is sometimes identical with the 
empirical formula, but is often a multiple of it, and the ratio 
is ascertained by a molecular weight determination. This 
may usually be effected by some one of the following methods. 

I. Chemical Methods are not of very general application, 
and give only a minimum value of the molecular weight. 
Their principle is that in substituting one element (or radical) 
for another, we cannot replace a fraction of an atom. If, then, 
in a particular compound it is found possible to replace, say, 
one quarter of the hydrogen in it by some other element, 
without affecting the other three - fourths, we conclude that 
there were four atoms (or a multiple of four) in the molecule 
of that compound. 

EXAMPLE I. The analysis of acetic acid leads to the 
empirical formula CH O ; but there are numerous derivatives 
of the acid whose analysis shows that one-fourth only of the 
hydrogen has been replaced, such as monochloracetic acid 
C 2 H 3 C1O 2 , silver acetate C 9 H. } AgO 2 , etc. Hence the molecu- 
lar formula must contain four atoms of hydrogen, and is 
written C 2 H 4 O 2 . 

EXAMPLE II. Another substance, also possessing the same 
empirical formula CH 2 O, is dextrose ; but this compound 
yields a derivative in which analysis shows that five-twelfths 
of the hydrogen have been replaced, while seven-twelfths are 
left ; there must then be not fewer than twelve atoms of 
hydrogen in the molecule, and its formula is put as C 6 H 12 O 6 . 



VAPOUR DENSITY 



CHAP. 



II. The Physical Methods much more convenient, 
and in some respects more decisive, than the chemical depend 
upon the " law of Avogadro," or upon its extension by Van't 
Hoff to the case of dilute solutions. 

As applied to gases the law states that at a given tempera- 
ture the pressure of a gas is proportional to the number of 
molecules in unit volume. If now we find the weights of equal 
volumes (at the same temperature and pressure) of two gases, 
we have the weights of equal numbers of molecules of the 
gases, and the ratio of these weights will give the ratio of the 
molecular weights. The vapour density of a substance is 
the ratio obtained by comparing the weight of a volume of 
that body (in the gaseous state) with the same volume of 
hydrogen at the same temperature and pressure. Admitting 
the weight of the hydrogen mole- 
cule to be 2, in accordance with 
the formula H 9 , it follows that, 
when hydrogen is taken as the 
standard, the molecular weight of 
any substance is twice its vapour 
de'isity. In determining this we 
do not need to measure both 
vnpour and hydrogen under iden- 
tical conditions, as by the help 
of Boyle's and Charles's laws we 
can easily reduce the results ob- 
tained to what they would be 
under the same pressure and tem- 
perature. The experimental pro- 
cesses which may be used for 
determining vapour densities are 
many, but the following are the 
most important : 

(a.) Victor Meyer's Method 
b> V ' Meyer ' s has almost entirely supplanted the 
older ones of Hofmann and Dumas ; 
the apparatus employed is shown in Fig. 12. A cylindrical bulb 
A, provided with a long and narrower neck, is heated to a steady 
temperature by some suitable means, usually by the vapour 
of a substance kept boiling in the jacketing tube. When 




FIG. 12. Apparatus for determining 



n VICTOR MEYER'S METHOD 15 

the temperature has become quite steady, the cork is removed, 
and a small glass tube or thin bulb, containing about half a 
decigram of the body to be examined, is allowed to fall into 
the bulb, the cork being quickly replaced. In order that the 
experiment may succeed, it is necessary that the temperature 
of the bulb should be at least 20 or 30 C. above the boiling 
point of the compound under investigation, when this latter 
rapidly evaporates, and in doing so fills the lower part of the 
bulb with vapour, driving out through the side tube a 
corresponding volume of air, which is collected in E and 
measured. 

It calculating the result it is unnecessary to know the 
temperature of A (it must, however, be steady). The vapour 
given off at the bottom of the bulb displaces its own volume 
of air, but this, before being measured, is cooled down to the 
temperature of the water over which it is collected. What we 
really obtain is, therefore, the volume which the vapour of the 
amount of substance used would occupy at the temperature 
and pressure in E. If, then, we divide the weight of sub- 
stance used by the weight of the volume V of hydrogen (at 
the temperature and pressure in E), we have at once the 
vapour density of the compound examined. 

The results, though not very accurate, are practically quite 
sufficient, as the question is usually not one of determining 
the exact molecular weight, but merely of the ratio of the 
molecular to the empirical formula. 

Example. .0623 gram of alcohol gave by Victor Meyer's method 
31.5 c.c. of air, measured at 15 C. and 750 mm. pressure. 

This volume would become 31. 5 x -~ x ~- c.c. at o C. and 760 mm. ; 

200 700 

2Q. ^ 

and this volume of hydrogen (29.5 c.c.) would weigh .0896 x ' gram. 
The vapour density is therefore 

.0623 1000 weight of substance 



.0896 29.5 weight of gas obtained reckoned as hydrogen 
or 23.6. 

(/?.) Hofmann's Method is still occasionally made use of 
for substances which cannot readily be vapourised without de- 
composition under the ordinary pressure, though modifications 



16 HOFMANN'S METHOD CHAP. 

of V. Meyer's method have also been made for this purpose. 
A long graduated tube, closed at one end, is filled with mercury, 
and inverted in a mercury trough, while round the upper 
portion of the tube a wider jacketing tube is placed, through 
which can be blown the vapour of some liquid of suitable 
boiling point. A small glass tube, containing about a fifth of 
a decigram of the substance, is introduced into the inner tube, 
and allowed to float up to the top of the mercury, where its 
contents are then vapourised on passing a current of steam or 
other vapour through the outside jacket. 

On this method we require to notice the volume occupied 
by the vapour, and the height of the mercury in the inner 
tube above its level in the trough, besides knowing the 
temperature of the jacketing vapour. Its advantage is that the 
substance evaporates under a pressure considerably less than 
that of the atmosphere, in consequence of its partial compensa- 
tion by the column of mercury in the inner tube. 

Example. .0243 gram of substance vapourised at the temperature of 
boiling aniline (183 C. ) gave 54.5 c.c. ; the height of the mercury 
column was 420 mm., that of the barometer 765 mm. 

Now 54.5 c.c. of hydrogen at 345 mm. pressure (765 - 420) and 183 C. 
would weigh 



54-5 xxx = .oo I33 gram 

hence the vapour density of the substance is 



.00133 

Molecular "Weight of Non-volatile Substances. 

There are many substances of which it is quite impossible to 
determine the vapour density, as they are not volatile without 
decomposition. In such cases we can obtain assistance by 
applying methods, first established experimentally by Raoult, 
depending upon certain properties of solutions. Van't Hoff 
has brought forward a theory by which these various facts are 
connected together, but for the purpose in view the experi- 
mental data of Raoult are sufficient. 

If we take 100 grams of water or any other solvent, and 
dissolve in it I gram of any substance, it is found that (a) the 
freezing point of the solution is lower, and (b] the boiling point 



RAOULTS METHOD 



is higher than that of the pure solvent. The amount of change 
is in each case dependent upon the molecular weight of the 
dissolved body. For the same solvent the change is proportional 
to the number of molecules dissolved in a given quantity of 
the solvent. 

The apparatus devised by Beckmann for applying the first 
method, depending on the de- 
pression of the freezing point, is 
shown in Fig. 13. About 20 
grams of the solvent are intro- 
duced into the central tube 
A of the apparatus, and the tem- 
perature being slowly brought 
down below the melting point, 
the exact temperature at which 
the solvent freezes is noticed 
on the thermometer. A small 
accurately weighed quantity 
of the substance to be exam- 
ined is now introduced into 
the tube A, and made to 
dissolve by vigorous stirring 
and gentle warmth ; then the 
temperature is again lowered, 
and when freezing occurs the 
freezing point of the solution 
is observed on the thermo- 
meter. 





FIG. 13. Beckmann 's apparatus 
determining molecular weights. 



for 



Let iv = weight of substance used ; 
W= ,, solvent 

/ = difference between freezing point of the solution 

and freezing point of solvent ; 
;;/ = molecular weight of the substance examined ; 

then the number of molecules of the substance dissolved in 

f tV 

W grams of the solvent is , and therefore in 100 grams of 
m 

the solvent there would be, for a solution of the same strength, 

C 



1 8 RAO LILTS METHOD 



I OO IV 

,, 7 molecules dissolved. According to Raoult's results the 

depression of the freezing point for the solution is proportional 
to this number, and we have 

i oo iv 



r^ 7/ 

or ;*=iooA , 

where A' is a constant depending on the nature of the solvent. 

The values of K for the most important solvents are as 

follows : 

Water . . . . .19 

Benzene ..... 49 

Naphthalene ..... 74 

Acetic Acid ..... 39 

For further particulars of this method, and of the similar one 
depending on the elevation of the boiling point, the student 
may advantageously consult Outlines of General Chemistry, 
by Ostwald, p. 137, or Quantitative Analysis, by Clowes and 
Coleman, p. 432. 

QUESTIONS ON CHAPTER II 

1. What reasons have we for writing the formula of acetic acid as 
C 2 H 4 O- 2 instead of the simpler one CH L >O ? 

2. Describe Victor Meyer's method of determining vapour density. 
Calculate the vapour density of a substance from the following data : 
.0582 gram of the substance was used, and 23.5 c.c. of air were expelled 
(measured at 18 C. and 755 mm. pressure). 

3. What methods can be used to determine the molecular weight of a 
substance such as sugar, which cannot be converted into vapour without 
decomposition? 

4. Butyric acid has the empirical formula CoH 4 O, and silver butyrate 
is found to contain 55.4 per cent of silver ; what do you conclude from 
these facts as to the molecular formula of the acid ? 

5. Calculate the molecular weight of a substance from the following 
results obtained by Raoult's method : 

Weight of acetic acid taken . . 20. 5 grams 

Freezing point of acetic acid . . 16.435 C. 

Weight of substance dissolved . . .1535 gram 

Freezing point of solution . . . 16.305 C. 



CHAPTER III 
HYDROCARBONS OF THE METHANE SERIES 

Methane or marsh gas is theoretically the simplest of all 
the compounds of carbon and hydrogen. Analysis shows that its 
empirical formula is CH 4 , and the fact that the gas is eight times 
heavier than hydrogen indicates the molecular weight sixteen, 
and shows that this simplest formula is also the molecular one. 

It occurs naturally in the gas which occasionally comes off 
in bubbles from the bottom of stagnant ponds ; in the " natural 
gas " escaping from fissures in the earth in certain oil-bearing 
districts, and constitutes the fire-damp of the coal miner ; 
while ordinary coal-gas contains about one-third of its volume 
of methane. 

Of methods used in the laboratory the three following are 
important, the first from the theoretical standpoint, and the 
two latter from that of practical work : 

1. Methane can be synthesised, i.e. built up from inorganic 
materials, by passing a mixture of H 2 S with vapour of CS 2 
over red-hot copper : 

2H 2 S + CS 2 + 8Cu - CH 4 + Cu,S. 

2. A convenient laboratory method, yielding, however, a 
somewhat impure methane, is to heat cautiously a mixture of 
sodium acetate with sodium hydrate (barium hydrate gives a 
less impure gas) : 



N,iC 2 H 3 2 + NaOH = Na 2 C0 3 + CH 4 
Sodium acetate. Methane. 



METHANE 



CHAP. 



If a glass vessel be used, it will soon be attacked by the melted 
caustic soda ; and though this action can be lessened by using 
an admixture of quicklime (soda-lime is best), it is more con- 
venient when possible to employ a copper retort. 




FIG. 14. Apparatus for the preparation of CH 4 from sodium acetate and 
soda-lime. 



EXPT. 3. Prepare marsh gas by heating some dry anhydrous (not 
crystallised) sodium acetate with about four parts of powdered soda-lime 
in a small glass flask fitted with cork and delivery tube. Collect two jars 
of the gas and examine its behaviour, (a) when a lighted taper is brought 
near, (^) when allowed to mix with bromine vapour contained in a second 
jar. 

3. Pure methane is best prepared by the action on methyl 
iodide, CH.^1, of the zinc-copper couple in presence of alcohol. 
The couple is merely zinc covered with a deposit of copper by 
treatment with a solution of copper sulphate, and acts in pres- 
ence of cither water or alcohol as an excellent reducing agent : 



CH. 



+ H = CH 



4 + 
Methane. 



HI. 



Methyl iodide. 
A more complete representation is given by the equation : 



CH 3 I + Zn + C 2 H 6 = Zn 5 + CH 4 . 



Methane is a colourless gas, without taste or smell, only 



in HOMOLOGY 



slightly soluble in water, and very difficult to condense to a 
liquid. It burns in the air with a nearly non-luminous flame, 
which becomes much brighter if both the air and the methane 
are strongly heated before combustion (regenerative burners), 
and the products of the burning are water and carbon dioxide : 

CH 4 + 2O 2 = CO 2 + 2 H 2 O. 

A mixture of i vol. CH 4 with 2 vols. O 2 explodes violently 
when ignited. When strongly heated alone, methane is 
decomposed with formation of carbon, hydrogen, and smaller 
quantities of other products. 

Methane is a very stable substance, and is not readily 
attacked even by the most active reagents. Nitric acid is 
almost without action upon it ; chlorine and bromine attack it 
slowly (more quickly in sunlight than in the dark) with forma- 
tion of " substitution products," in which one or more hydrogen 
atoms of the methane have been expelled (in combination with 
Cl or Br as HC1 or HBr) and their place taken by halogen 
atoms : 

CH 4 + Br 2 = CH 3 Br + HBr, 
Methyl bromide. 

or CH 4 + 2Br 2 = CH 2 Br 2 + 2 HBr, etc. 

Methylene bromide. 

Homology. Methane is the lowest member of a series of 
hydrocarbons, all of which can (in general) be prepared by 
similar reactions, and strongly resemble one another in their 
chemical behaviour. Each member differs from the one below 
it in the series by the replacement in its formula of an H atom 
by the group CH 3 , to which the name methyl is given ; the nett 
difference between any two successive members is therefore 
CH 2 . Such a series is called a homologous series, and the 
study of organic chemistry is much simplified by the possi- 
bility of classifying in this way the immense number of known 
compounds into groups of similar bodies. 

Starting from methane, CH 4 , we have as the formula of 
the next member of the series CH 4 + CH 9 or C 2 H 6 , for the 
third C a H 8 , and so on up to C 60 H 102 , the highest which has 
yet been prepared. The generic formula is C,,H OM + . 



ETHANE 



CHAP. 



Ethane, C 2 H 6 , stands next to methane, and can be prepared 
by similar reactions. In the first, we start not from sodium 
acetate (as for methane), but from the sodium salt of the acid 
next above acetic in the very important series of homologous 
acids, of which acetic forms the second and propionic the third 
member. Acetic acid is C 2 H 4 O 2 and propionic C 3 H G O<,. We 
proceed then as follows : 

i. Sodium propionate is heated with sodium hydrate, 

NaC.,H r O 9 + NaOH = Na CO Q + C H,, 

o 5 2 23 26 

Sodium propionate. Ethane. 

when ethane is evolved and sodium carbonate remains. 




FIG. 15. Apparatus for preparing C^H^ from ethyl iodide by the action of the 
zinc-copper couple. 

2. In the second method for preparing ethane, ethyl iodide, 
C.,H r( I (homologous with methyl iodide, CH^I), is reduced with 
the zinc-copper couple : 



HI PROPANE AND BUTANE 23 

C 3 H 5 I 4- H 2 = C 2 H 6 + HI. 
Ethyl iodide. Ethane. 

3. A third method is of a type applicable only to the pre- 
paration of those members of the series which contain an even 
number of carbon atoms in the molecule. In this case we 
start from methyl iodide, CH 3 I, and by treating it with metallic 
sodium, abstract the iodine and cause two methyl residues 
CH., to unite : 

o 

2CH 3 I + 2Na = 2NaI + C 2 H 6 . 
Methyl iodide. Ethane. 

In accordance with this method of preparation, the formula of 
ethane may be written CH 3 . CH ;r 

Ethane is a combustible gas, and burns with a more lumin- 
ous flame than methane. It resembles that gas very greatly 
in chemical behaviour, and reacts in the same way with the 
halogens, forming substitution products, such as 

C 2 H + C1 2 = C 2 H 5 C1 + HC1. 
Ethane. Ethyl chloride. 

Propane, C 3 H 8 ( = C 2 H 6 -f- CH 2 ), stands next above ethane. 
It may be prepared by methods corresponding to the first two 
of those given for ethane. The best is the following : 

i. Propyl iodide, C 3 H 7 I ( = C 2 H & I + CH 2 ), is reduced with 
the zinc-copper couple : 

C,H 7 I + H 9 = C.,H R + HI. 

pi 21 9 

Propyl iodide. Propane. 

Butane is the name given to the next hydrocarbon of this 
series with the formula C 4 H 1Q . We here encounter for the first 
time a fact of very great importance : that there may be, and 
often are, more substances than one corresponding to a parti- 
cular molecular formula. This experimental fact we interpret to 
mean that two molecules, each containing the same atoms in 
the same number, may yet be distinct both chemically and 
physically ; and this difference we explain as being clue to the 
different arrangement of the atoms in the molecule. The 
name isomerism is given to this phenomenon, and substances 



24 ISOMERISM CHAP. 

which possess identical molecular composition, and yet differ 
from one another in the way described, are said to be isomeric. 
In the majority of such cases it is found possible to give a 
reasonable representation of the different chemical behaviour 
of the isomeric bodies by structural formula, which are also 
considered to represent more or less exactly the actual grouping 
of the atoms inside the molecule. Let us now consider more 
fully this particular case of the butanes. 

In the first three members of this series no isomerism has 
been found to exist. Their formulae, CH 4 , C 2 H g , C 3 H 8 , may be 
expanded into CH 4 , CH 3 .CH 3 , CH 3 .CH 2 .CH 3 , which are in 
agreement with the valency hypothesis, and represent, more 
completely than the simple formulae do, the modes of formation 
and general chemical behaviour of the three substances. In 
each case the formula is obtained from that of the next lower 
compound by substituting methyl, CH 3 , for hydrogen. In 
methane there are four hydrogen atoms in the molecule, but 
these are all similarly circumstanced, and whichever of them 
be replaced we obtain the same ethane, CH 3 . CH ;r Similarly, 
when we proceed from this to propane ; the six hydrogen atoms 
in the ethane molecule are all of equal value, and we get 
always the same propane when any one of them is substituted by 
a methyl group. But at the next step this is no longer the case, 
for the eight hydrogen atoms in propane are not all similarly 
placed ; while six of them are alike, and the other two also 
like one another in position, there is a difference between the 
atoms attached to the two terminal carbon atoms and those 
which are connected to the carbon atom in the centre of the 
chain. Hence two formulae for butane may be deduced from 
that of propane by substituting CH 3 for H atoms of different 
value : 

CH 3 . CH 2 . CH 3 gives (i) CH . CH., . CH 2 . CH., 
and (2) CH 3 . CH". (CH 3 ) 2 . 

So far by paper work. Experimental investigation has proved 
that there are two butanes, each with the formula C 4 H JO , and 
each rightly placed, according to its general behaviour, in the 
methane series. 

Of these two butanes one is prepared from ethyl iodide by 
abstracting the iodine with sodium : 



PENTANE 



2CH 3 . CH 2 

Ethyl iodide. 



. OH.,. CH,,. CHo, 
Normal butane. 



and this mode of formation is well represented by the formula 
given in the above equation. This particular butane is called 
normal butane, or simply butane. For the other butane the 
formula CH 3 . CH . (CH 3 ) remains, and the name given to it is 
isobutane. 

Pentane, C & H 10 , is the generic name of the isomeric hydro- 
carbons corresponding to the formula given. If we attempt to 
work out the number of isomers which may in accordance with 
the valency theory be obtained, we find that three are possible ; 
and experimental work has enabled us actually to prepare 
isomeric pentanes, and to assign to each, one of the three 
formulae indicated by theory. 

The most important is normal pentane, CH 3 .CH .CH 2 .CH 2 . 
CH 3 , which is contained in crude petroleum, and can be isolated 
from it as a volatile inflammable liquid boiling at 37. This 
has been used as a means of obtaining a reliable standard of 
illumination for photometric purposes. 

The following table illustrates the isomerism of the butanes 
and pentanes : 



NAME. 


FORMULA. 


PREPARATION. 


Normal Butane 


CH 3 .CH 2 .CH;,.CH 3 


From ethyl iodide and zinc dust : 






2CH 3 . CH 2 I + Zn = C 4 H 10 + ZnI 2 


Isobutane 


CH 3 .CH 2 :(CH 3 ), 


From isobutyl iodide by reduction : 


Normal Pentane 


CH 3 .CHo.CH 2 .CH 2 .CH 3 


Separated from petroleum. 


Isopentane 


CH 3 .CH 2 .CH :(CH 3 ) 2 




(Dimethyl-ethyl- 






methane) 






Tetra-methyl- 


C(CH 3 ) 4 




methane 







Petroleum and Paraffin. In various parts of the world, 
more especially in Pennsylvania and in Baku, a province of 
Southern Russia, oil-bearing strata occur from which an in- 



26 PETROLEUM CHAP. 

flammable oil can be obtained. Wells are drilled through 
the overlying layers of earth until the oil is struck at a depth 
varying from 50 to 2000 feet and over. In many cases the 
newly-opened well " spouts " oil, frequently with uncontrollable 
violence, but as the original gas-pressure declines, it becomes 
necessary to have recourse to pumping. The crude oil requires 
to be refined, and both in America and in Russia this process is 
carried on, not at the wells themselves, but at large refineries 
conveniently situated for export. The oil is transported to the 
refineries by means of long lines of pipes, through which it is 
forced by powerful pumps. 

Investigation has shown that American and Russian petro- 
leums differ essentially in chemical composition. American 
petroleum is almost entirely a mixture of various hydrocarbons 
of the methane series from CH 4 itself up to solid hydrocarbons 
of very high molecular weight. The refining of the crude oil 
has for its chief purpose the separation of this complex mixture 
into a number of fractions, and is accomplished by distillation. 
The more volatile portions are the first to come over, and are 
followed by others of higher and higher boiling points. The 
most important fractions are : 

(1) Gasoline, B.P. 3o-ioo, used for making "oil-gas," 
which is simply air saturated with vapour of gasoline. 

(2) Petroleum proper, B.P. I 5o-3oo, used in lamps. 

(3) Higher boiling portions from which lubricating oils and 
vaseline are obtained. 

Russian petroleum contains only a very small percentage of 
hydrocarbons of the methane series, the chief bulk being 
" naphthenes " of the generic formula C n li 2u . These are dis- 
tinct from the olefines of the same formula, and will not be 
considered until the second part of this book in connection 
with the benzene hydrocarbons, from which they are derived. 
The products obtained by refining the Russian crude oil are 
very similar to those from American petroleum, but a larger 
yield of oils suitable for lubricating machinery is got, and the 
residue is not usually worked up for a vaseline-like product, but 
is generally employed as fuel. 

Another important source of hydrocarbons of the methane 



PARAFFIN 27 



series is the destructive distillation of bituminous shale or 
other material of similar composition. This process is largely 
carried on in the south-west of Scotland, and from the products 
various valuable mixtures of hydrocarbons are separated by 
refining. One of these is " paraffin oil " ; another is the white 
solid "paraffin wax," and both are made up almost exclusively 
of hydrocarbons of the methane series. 

Properties of the Hydrocarbons, C fl H 2n+iy . All the 
hydrocarbons of this homologous series, from marsh gas itself up 
to the highest member yet obtained, present an almost complete 
resemblance in chemical behaviour. They are all very inert 
substances, not attacked by nitric acid, and only gradually 
acted upon by chlorine or bromine. The products formed by 
the action of the halogens are substitution products, in which 
some of the hydrogen of the hydrocarbons has been replaced 
by chlorine or bromine. In no case are addition products 
formed by the members of this series. 

The physical properties of the members change gradually 
as we pass from one end of the series to the other. The lowest 
members are gases requiring great pressure or cold to convert 
them into liquids ; the pentanes are volatile liquids, and, 
ascending the series, we come to liquids of higher and higher 
boiling point ; while still farther up the series we meet with 
hydrocarbons which are solid at the ordinary temperature. 



QUESTIONS ON CHAPTER III 

1. Describe the preparation and properties of methane. 

2. Methane and ethane are members of a homologous series ; show 
the bearing of this statement upon the properties of the gas and the 
methods used for their preparation. 

3. What is meant by isomerism ? Deduce the formula of the two 
isomeric butanes from that of propane. 

4. What substances are contained in crude petroleum ? What com- 
mercial products are obtained from it, and by what processes ? 



CHAPTER IV 
OLEFINES AND ACETYLENE 

THE defines form a second series of hydrocarbons, of which 
the starting-point is ethylene, C 2 H 4 . The succeeding homologues 
differ always by CH 2 , and it thus follows that every member 
of the series has the same percentage composition. They differ, 
of course, in molecular weight, and therefore in vapour density. 
The generic formula is C n H. 2n , and while we again find the 
same similarity in general chemical behaviour between all the 
defines, as between all the hydrocarbons of the C w H 2M+2 
series, there are important differences between the two separate 
series. The chief of these are summed up in the contrast of 
the two terms saturated and unsatiirated, applied respectively 
to the methane and to the olefine series. 

Ethylene, C 2 H 4 , is the lowest known member of the series, 
and as in every reaction where we should expect a substance, 
CH 2 , to be produced we obtain instead C 2 H 4 , it seems estab- 
lished that no compound of the formula CH 2 can exist. The 
most convenient way of preparing ethylene is by the action of 
concentrated sulphuric acid upon ethyl alcohol, C 2 H 6 O, a 
reaction which may very concisely be represented thus : 

C 2 H 6 O - H 2 O == C 2 H 4 . 
Ethyl alcohol. Ethylene. 

What really happens is that ethyl-sulphuric acid, C 2 H. . HSO 4 , 
is first produced, and this, when heated, decomposes into 
ethylene and sulphuric acid : 



ETHYLENE 



29 



C 2 H 5 OH + 

Ethyl alcohol. 



H 2 S0 4 = 



C 2 H 5 



HS0 



H 2 



Ethyl-sulphuric acid. 



C 2 H 5 

EXPT. 4. Prepare ethylene by heating in a capacious flask (2 litres) a 
mixture of 40 c.c. methylated spirit with 200 c.c. concentrated H2SO4 
along with some sand, to prevent frothing. The gas can be purified 
from SO-j and other impurities by washing with solution of caustic soda, 
and can be collected over water. 




FIG. 16. Preparation of Ethylene from alcohol and sulphuric acid. 

Ethylene is a colourless gas with a faint sweetish smell, and 
burns in the air with a bright yellow flame. Like all the 
other members of the series, it is an unsaturated compound, 
being able to unite directly with several substances Cl, Br, I, 
H, HI, etc., nothing being driven out from the ethylene 
molecule to be replaced by the substituting atoms. This is 
explained on the valency hypothesis as due to those carbon 
valencies which are unsaturated in the molecule of ethylene. 

Ethylene combines readily with Cl, Br, and I (in alcoholic 
solution) at the ordinary temperature, with hydrogen when the 
two mixed gases are passed over platinum black ; ethane or 
a derivative of it is in each case the product. When passed 
into concentrated H 2 SO 4 , ethylene is absorbed and ethyl- 
sulphuric acid is formed : 



C 2 H 4 



H 2 SO 4 = C 2 H 5 . HSO 4 . 



3 o PROPYLENE CHAP. 

EXPT. 5. Fill two jars with ethylene and bromine vapour ; bring 
them together mouth to mouth. The colour of the bromine is rapidly dis- 
charged, and small oily drops of a liquid ethylene dibromide are formed: 



Try a similar experiment with methane and bromine. In this case the 
action takes place slowly, and the bromine makes its way into the methane 
molecule only by expelling some of the hydrogen : 

CH 4 + Br 2 = CH 3 Br+ HBr. 
Methane is termed a saturated compound, whereas ethylene is unsaturated. 

Propylene, C 3 H 6 , is obtained most conveniently by a 
reaction typical of a second general method of preparing the 
defines. Isopropyl iodide, C 3 H 7 I, a halogen derivative of the 
corresponding hydrocarbon of the methane series (in this case 
C 3 H g ), is treated with an alcoholic solution of potash, whereby 
one atom of hydrogen and one of the halogen are abstracted : 

C 3 H V I + KOH = C 3 H 6 + KI + H,0. 

Isopropyl iodide. Propylene. 

The formula of the isopropyl iodide is CH 3 . CHI . CH 3 . The 
C 3 H 6 obtained from this by abstraction of HI may be either 
CH 3 . C . CH 3 or CH 3 . CH : CH 2 , but the first formula is nega- 
tived by numerous facts, of which a very conclusive one is that 
propylene furnishes three isomeric chloro-propylenes, C 3 H 5 C1. 
This is readily explained by the second, but is quite inconsist- 
ent with the first. The two dots in the correct formula indicate 
that the two carbons, one on either side, are each capable of 
further uniting with an additional atom, and are connected 
together in a different manner from that prevailing between 
carbon atoms which are exerting their maximum valency. Two 
such carbon atoms as those we have been considering in the 
propylene molecule are said to be united by an ethylene 
linkage, or by a double bond; but it must not be imagined 
from the latter expression that such atoms are more firmly 
held together than those united in the ordinary way (single 
bond). As a matter of fact, an unsaturated molecule when it 
suffers decomposition usually breaks up most readily at the 
so-called double bond. Thermo-chemical investigation also 
shows that an ethylene linkage cannot be regarded as simply 



IV VAN'T HOFF'S TETRAHEDRAL THEORY 31 

the double of single linkage ; there is a real difference in kind 
between those two modes in which carbon atoms may be 
connected. 

Great assistance in correlating a very large number of ex- 
perimental facts is furnished by the tetrahedral theory of the 
carbon atom, which was proposed by Van't Hoff in 1877, and 
has since been extended by Wislicenus and other chemists. 
According to this valuable hypothesis, the carbon atom is re- 
garded as being similar in shape to a regular tetrahedron, a 
solid figure bounded by four equilateral triangles, and two 
carbon atoms may be connected together in the following 
three ways : 

a. Simple linkage : the two tetrahedra are in contact at a 
corner of each. 

b. Double linkage : the two tetrahedra are in contact along 
an edge of each. 

c. Triple linkage : the two tetrahedra have a whole face of 
each in contact. 

The first kind of linkage is exemplified in the case of ethane, 
the second in ethylene, and the third in acetylene. Substances 
which contain a double or triple linkage are unsaturated, and 
the theory affords a clear representation of the way in which 
an unsaturated body becomes saturated by addition of chlorine, 
bromine, etc. The following diagrams will illustrate these 
points better than any verbal explanations. 

To return to propylene : the theory which we have been 
considering embodies very conveniently a large number of ex- 
perimental generalisations, among them this, that such a 
formula as CH 3 .C.CH 3 , in which carbon acts as a divalent 
element, represents an arrangement of atoms incapable of 
permanent existence. We have already seen reason to reject it 
in favour of the alternative CH 3 . CH : CH 2 . 

There are a few exceptional cases in which carbon is divalent, and 
where it is therefore necessary to suppose that two of the four corners of 
the carbon tetrahedron are unemployed, e.g. CO. 

Butylene, C 4 H 8 , the next member of the series, furnishes 
an instance of isomerism. There are three isomeric butylenes, 
all of which may be looked upon as derived from ethylene by 



BUTYLENE 



CHAP, 



replacement of hydrogen by methyl or ethyl groups, and their 
names are best chosen to represent the manner of this 
derivation : 

a. Symmetrical dimethyl-ethylene, CH . CH : CH . CH 3 . 

b. Unsymmetrical dimethyl-ethylene, CH., : C(CH 3 ) 2 . 

c. Ethyl-ethylene, C,H 5 CH:CH 2 . 




FIG. 17. Representation of carbon atoms linked together as in 
(A) Ethane, (B) Ethylene, (C) Acetylene. 



The names are somewhat cumbrous, but have the advantage 
of telling as much about the substances as the formulas them- 
selves ; they are, in fact, merely the formulae in words instead 
of symbols. The methods by which these three isomers have 
been prepared are too complicated for us to enter into ; the 



ACETYLENE 



33 



important thing is that the theoretical number of isomers have 

been obtained. 

Acetylene, C 2 H 9 , is the lowest member of another series 

of unsaturated hydrocarbons. In this we have a triple linkage 

between the carbons, so that only two hydrogen atoms can be 

attached to them, one to each : HC ; CH. 

Acetylene can be made by several different reactions : 
(i) By heating ethylene dibromide, C 2 H 4 Br 2 , with an 

alcoholic solution of potash : 





FIG. 18. Preparation of Acetylene by the action of alcoholic potash on ethylene 
bromide ; both flasks contain potash, and the bromide is allowed to drop 
slowly from the tap-funnel into the heated potash in the first flask. 

CH Br . CH Q Br - 2HBr= HC ! CH. 
Ethylene bromide. Acetylene. 

(2) By direct combination of carbon and hydrogen, when 
the electric arc is passed between carbon poles in an atmo- 
sphere of hydrogen. 

(3) By the action of water upon barium carbide : 



BaC 2 + 
Barium carbide. 



2H.OH = C,H 2 

Acetylene. 
D 



Ba(OH) 2 . 



34 



ACETYLENE 



This is a very convenient method of preparing the gas 
when it is wanted in considerable quantity. 

(4) By the degraded combustion of coal-gas, such as 
occurs when the temperature of the flame is artificially 
lowered by contact with a metal surface (a Bunsen burner in 
which the gas is burning at the bottom of the brass tube) : 



Ethane. 



2 = C 2 H 2 + 2H 2 0. 

Acetylene. 



Acetylene is a colourless gas with an unpleasant smell. 
It is soluble in about its own volume of water, and burns in 
the air with a bright smoky flame. The most remarkable 
chemical characteristic of acetylene is its property of forming 
explosive compounds containing copper or silver. By means 
of these compounds acetylene can be readily detected and 
isolated from its mixture with other gases. 




FIG. 19. Preparation of Acetylene by the degraded combustion of coal-gas. 

EXPT. 6. Prepare some cuprous chloride, CuCl, by passing SO 2 gas 
into a solution of 90 grams NaCl and 200 grams crystallised CuSO 4 until 
the gas is no longer absorbed ; pour into about half a litre of water, and 
filter. The white precipitate of CuCl is collected, and dissolved in some 
strong ammonia solution. 

Open wide the air-holes of a large Bunsen burner, and light the gas at 
the bottom of the tube. Over the burner support a funnel, which is con- 
nected with a gas-washing bottle containing the ammoniacal solution of 
cuprous chloride. Join the other tube of the wash-bottle to an aspirator, 
and draw a steady current of air through the apparatus. 



IV 



ACETYLENE 



35 



A dark red precipitate will form in the solution of cuprous chloride. 
This has the composition C-jHCu, and when dry explodes on being 
heated, or if struck between two metal surfaces. Acetylene can be 
recovered from it by treatment with dilute hydrochloric acid. 



Acetylene unites readily with hydrogen, when the two gases 
are passed over platinum black, to form ethane : 



CH 

Acetylene. 






FIG. 20. Representation on the tetrahedral theory of the conversion of Acetylene 
into dichlor-ethylene and tetrachlor-ethane by the action of chlorine. 



Chlorine is without action upon the pure gas in the dark, 
but in sunlight dichlor-ethylene and tetrachlor-ethane are 
successively formed : 



36 ACETYLENE CHAP, iv 



(a) CH!CH + C1 2 = CHC1:CHC1, 

Acetylene. Dichlor-ethylene. 

(b) CHC1 : CHC1 + Cl., = CHQ 2 . CHC1. 2 . 

Dichlor-ethylene. Tetrachlor-ethane. 

These changes are represented on the tetrahedral theory by 
the diagrams in Fig. 20. 



QUESTIONS ON CHAPTER IV 

1. What is the chief difference in chemical behaviour between a satur- 
ated and an unsaturated compound ? 

2. Give the preparation of acetylene and the most important properties 
of the gas. 

3. Give an elementary account of the tetrahedral theory of Van't 
Hoff as applied to explain the structure of the three hydrocarbons 
C 2 H 6 , C 2 H 4 , C 2 H 2 . 

4. How is ethylene made ? What is formed when it is passed into 
concentrated sulphuric acid ? 

5. How could you prepare ethane from the elements carbon and 
hydrogen ? 



CHAPTER V 
HALOID DERIVATIVES 

IN any hydrocarbon it is generally possible to replace from 
one up to the full number of hydrogen atoms present in the 
molecule, by chlorine, bromine, or iodine. 

Methyl Chloride, CH 3 C1, is the first to be considered of 
all these haloid derivatives ; it may be prepared 

1. By the direct action of chlorine upon methane, according 
to the equation : 

CH 4 + C1 2 = CH 8 C1 + HC1, 

a process which is favoured by the influence of sunlight. 

2. From methyl alcohol, CH 4 O (a substance to be con- 
sidered in the next chapter, when we shall learn that the 
formula is conveniently written CH 3 . OH, in order to indicate 
the way in which the alcohol most readily reacts), by the 
action of various compounds containing chlorine. The equa- 
tion is simplest in the case when HC1 gas is used : 

CH 3 .OH + HC1 = CH 3 C1 + H a O, 
Methyl alcohol. Methyl chloride. 

a reaction which easily occurs when HC1 is passed into 
boiling methyl alcohol, to which some zinc chloride (a very 
hygroscopic substance) has been added. 

Methyl chloride is a gas with a pleasant smell, fairly 
soluble in water, and pretty easily condensed by cold or 
pressure to a liquid. It is used commercially in the manu- 
facture of certain aniline dyes, and for this purpose is prepared 



CHLOROFORM 



from a by-product of the beet-sugar industry, and sold com- 
pressed in strong steel cylinders. It burns with a green 
flame. 

Methene Chloride, CH 2 C1 2 , can be obtained by the 
further action of chlorine upon methyl chloride : 

CHoCl + Cl, - CH 9 CL + HC1. 

O A A A 

This is the second step in a series of successive substitutions 
of the hydrogen atoms by chloride ; the third step yields 

Chloroform, CHC1 3 , which is, however, more readily 



prepared by a complicated reaction where ordinary 
alcohol, C^H^O, is treated with bleaching powder. 



ethyl 




FIG. 21. Preparation of Chloroform from alcohol and bleaching powder. 



EXPT. 7. Mix 50 grams of bleaching powder with 250 c.c. of water, 
and put the mixture in a large retort, or large flask fitted to a Liebig's 
condenser (see figure) ; add 250 c.c. of methylated spirit, and heat the 
mixture until it begins to boil. Then remove the burner, and allow the 
reaction to proceed by itself. Chloroform and water are condensed in the 
flask B, the chloroform sinking to the bottom of the water. 

The mechanism of this reaction may be explained now, 
though it will scarcely be fully understood until further 
acquaintance with the subject has been made. The bleaching 
powder acts both as an oxidising and as a chlorinating agent. 
In the first capacity it removes two hydrogen atoms from the 
ethyl alcohol : 



METHYL IODIDE 39 



CH 3 . CH 2 . OH + CaQ a = CH 3 . CHO + H 2 O + CaQ 2 , 
Ethyl alcohol. Ethyl aldehyde. 

but the product CH g . CHO, ethyl aldehyde, is at the same 
time chlorinated and converted into trichlorethyl aldehyde 
or chloral : 

CH 3 . CHO + 3C1 2 = CC1 3 . CHO + 3HC1, 
Aldehyde. Chloral. 

while the chloral, under the influence of the lime of the 
bleaching powder, gives chloroform and calcium formate : 

2CC1 3 .CHO + Ca(OH) 2 - 2CHC1, + (HCO 2 ) 2 Ca. 
Chloral. Chloroform. Calcium formate. 

Chloroform is a heavy liquid of pleasant ethereal smell, and is 
much used in surgery on account of the property which its 
vapour possesses of producing insensibility when inhaled. 

Carbon Tetrachloride, CC1 4 , is the last product of the 
substituting action of chlorine upon methane : 

CHC1 3 + C1 2 =CC1 4 + HC1, 

and is obtained as a pleasant smelling liquid when boiling 
chloroform is subjected to the prolonged action of a stream of 
chlorine gas. 

Methyl Iodide, CH 3 I, is an important reagent often used 
in the synthesis of organic compounds. It cannot well be 
prepared by the direct action of iodine upon methane, but is 
readily obtained by the action of iodine and phosphorus upon 
methyl alcohol in the way described in detail for making 
ethyl iodide. It is a volatile liquid which turns brown when 
exposed to light ; it is much used in the organic laboratory. 

lodoform, CHI 3 , is used in surgery on account of its 
marked antiseptic properties. The method of preparation is 
analogous to that of chloroform, but instead of bleaching 
powder, we employ iodine together with some alkali, such as 
sodium hydrate or carbonate. 



40 ETHYL CHLORIDE 



EXPT. 8. Dissolve 10 grams of soda crystals in 50 c.c. of water, and 
add 8 c.c. of methylated spirit. Heat to about 70 C. , and then add 
gradually 5 grams of iodine. lodoform separates out as a yellow 
precipitate. 

lodoform is a yellow solid with a characteristic smell, and 
is slightly soluble in hot water, from which it crystallises in 
lustrous plates. 

Ethyl Chloride, C 2 H r) Cl, is a volatile liquid boiling at 
about 12 C., and can now be obtained sealed up in stout 
glass tubes, in which it is sold for use as a local anaesthetic 
in minor surgical operations. It acts in this way by virtue of 
the intense cold produced by its rapid evaporation when the 
liquid is allowed to spray from a fine opening upon the part 
where the operation is to be done. 

It is prepared by the action of HC1 gas upon ethyl alcohol 
in the presence of zinc chloride : 

C 2 H 5 . OH + HC1 = C 2 H 5 C1 + H 2 0, 

Ethyl alcohol. Ethyl chloride. 

and conversely when heated under pressure with water (better 
with solution of an alkali) ethyl chloride yields ethyl alcohol : 

C 2 H 5 C1 + H 2 O = C 2 H 5 . OH + HC1. 

Dichlor-ethane, C.,H 4 CL,, is the second in the series of 
substitution products obtained by the action of chlorine upon 
ethane : 

C 2 H 6 +C1 2 =C 2 H 5 C1 +HC1, 
C 2 H 5 C1 + C1 2 - C,H 4 C1 2 + HC1, etc., 

but we here meet with a further instance of isomerism, and 
there are two distinct substances possessing the formula 
C 2 H 4 C1 2 . In one of these, ethene dichloride, CH g . CHC1 2 , 
both chlorine atoms are connected with the same carbon atom, 
while in ethylene dichloride, CH 2 C1 . CH 9 C1, they are attached 
one to each of the two carbons. 

Ethene Dichloride, CH 3 . CHC1 2 , is obtained by the 
action of chlorine upon ethyl chloride, as a rather volatile 
liquid with a smell similar to that of chloroform. 

Ethylene Dichloride, CH 2 C1 . CH 2 C1, is prepared by the 



ETHYL BROMIDE 



direct combination of ethylene and chlorine, and is the oily 
liquid from whose formation the old name olefiant gas arose : 

C 2 H 4 + C1 2 = C 2 H 4 C1 2 . 
Ethylene Ethylene dichloride. 

Ethyl Bromide, C 9 H 5 Br, can be obtained by the action of 
bromine upon ethane : 

C 2 H 6 +Br 2 = C 2 H 5 Br + HBr, 

Ethane. Ethyl bromide. 

but more readily by the action of phosphorus tribromide (or 
phosphorus and bromine together) upon ethyl alcohol. 
Phosphorus tribromide reacts with water thus : 

PBr 3 + 3 H 2 O = P(OH) 3 + 3HBr, 

that is to say, the three bromine atoms are exchanged for the 
same number of hydroxyls. Ethyl (or any other) alcohol 
behaves similarly to water : 

PBr 3 + 3C 2 H 5 OH = P(OH) 3 + 3C 2 H 5 Br, 

yielding phosphorous acid and ethyl bromide. 

Ethyl bromide is a volatile liquid with a pleasant . ethereal 
smell. 

Just as with dichlor-ethane, C 2 H 4 C1 2 , there are also two 
isomeric substances of the formula C 2 H 4 Br 2 , and their modes 
of formation are precisely similar to those of the corresponding 
chloro-derivatives. 

Ethene Dibromide, CH 3 CHBr 2 , is obtained by the action 
of bromine upon ethyl bromide : 

C 2 H 5 Br + Br 2 = C 2 H 4 Br 2 + HBr. 
Ethene bromide. 

Ethylene Dibromide, CH 2 Br . CH 2 Br, by passing a 
stream of ethylene through bromine contained in a series of 
gas washing cylinders : 

C 2 H 4 + Br 2 = C 2 H 4 Br 2 

Ethylene bromide. 



42 ETHYL IODIDE 



Both ethene and ethylene bromides are heavy liquids with 
a smell similar to that of chloroform, but they differ markedly 
in many respects. 

Ethyl Iodide, C 2 H 5 I, is an important reagent prepared in 
a way precisely similar to that employed for ethyl bromide, 
except that iodine is used instead of bromine. 

EXPT. 9. 10 grams of red phosphorus and 60 c.c. of strong alcohol 
("absolute" alcohol must be used ; rectified spirits of wine is useless) 
are placed in a retort, and 100 grams of iodine added little by little. The 
mixture is allowed to stand for several hours, and is then distilled from the 
water-bath (see figure). If the alcohol employed has been weak, fumes of 




FIG. 22. Preparation of Ethyl Iodide. 

HI will be evolved in torrents, but from absolute alcohol only traces of 
HI will be given off. The methyl iodide is condensed in the Liebig's 
condenser, and collects in the flask. It is washed with caustic soda 
solution and water, then dried by being left to stand in a highly-corked 
flask over lumps of fused CaClo, and then re-distilled. 

The equation for the reaction is 

3C,H r pH + PI 3 = 3C a H, ( I + H s PO a . 

Ethyl alcohol. Ethyl iodide. 

Ethyl iodide is a colourless liquid with an ethereal smell. 
It boils at 72, and is heavier than water, sinking to the bottom 
like an oil. It gradually decomposes when exposed to light, 
and the liberated iodine colours the liquid brown. Both 
methyl and ethyl iodides are largely used in experimental 
organic chemistry, their use depending on the great mobility 



ETHYL IODIDE 43 



of the iodine contained in them. This iodine is readily 
exchanged for various atoms or radicles by appropriate 
reactions, and many new compounds have been obtained by 
this means. 



QUESTIONS ON CHAPTER V 

1. Describe the preparation of chloroform. In what way would you 
attempt to prove the correctness of the formula CHCIs, which is assigned 
to it? 

2. For what purposes are methyl and ethyl iodides employed, and 
how are they made ? 

3. Give an account of the two isomeric substances corresponding to 
the formula C 2 H 4 Br 2 . 



CHAPTER VI 
THE ALCOHOLS 

THE alcohols form a homologous series, of which the starting- 
point is methyl alcohol, CH 4 O. Of the four hydrogens in this 
molecule one is distinguished from the others by the greater 
readiness with which it is exchanged for other atoms or radicals, 
while the fact that methyl alcohol may easily be obtained from 
or converted into methyl chloride, CH g Cl, indicates to us that 
the formula CH 4 O may better be written CH 3 .OH. This 
leads us to consider water, H . OH, as the inorganic type of 
the alcohols, and it will be useful to remember that there exist 
many points of resemblance between water and the alcohols 
in their chemical behaviour. 

Methyl alcohol, CH g .OH, being the starting-point of the 
series, the next member is ethyl alcohol, C 9 H 6 . OH, and so 
on to the highest known member, myricyl alcohol, C % H 61 . OH ; 
the generic formula is C W H OW+1 . OH. Chemically, they are 
characterised by the presence of the group OH, the hydrogen 
of which may easily be replaced ( i ) by sodium or potassium : 

C 2 H 5 .OH + Na - C 2 H 5 .ONa + H, 

Sodium ethylate. 
with which compare 

H.OH + Na = H.ONa + H ; 
Sodium hydrate. 

or (2) by an acid residue to form an ethereal salt or "ester," 
in which the alkyl group, C w H 2w+1 , takes the place of a mono- 
valent metallic atom in an inorganic salt, as : 



CHAP, vi WOOD-SPIRIT 45 



(a) C 2 H 5 H + HO N0 2 = C 2 H 5 . ONO 2 + H 2 O, 
Ethyl nitrate. 

() CH 3 . OH + CH 3 . CO 2 H = CH 3 . CO 2 CH g + H 2 O, 

Methyl acetate, 
with which compare 

(a) NaOH + HO.N0 2 - NaNO 3 + H 2 O, 
Sodium nitrate. 

and (V) KOH + CH 3 .C0 2 H CH 3 . CO 2 K + H 2 O. 

Potassium acetate. 

On the other hand, the whole group, OH, in any alcohol is 
readily driven out by the action either of phosphorus penta- 
chloride or of HC1 (in the presence of some hygroscopic sub- 
stance such as ZnCl 2 ), and its place taken by a chlorine atom : 

CH 3 OH + HC1 = CH 3 C1 + H 2 O 
Methyl alcohol. Methyl chloride. 

C 2 H 5 OH + PC1 5 = C 2 H 5 C1 + HC1 + POC1 3 . 
Ethyl alcohol. Ethyl chloride. 

Methyl Alcohol, CH 3 . OH, is contained in wood-spirit, a 
product of the destructive distillation of wood. In this process, 
now largely carried on in scientifically -constructed retorts, 
there are obtained, besides the charcoal left in the retorts, the 
following : (a) non- condensable gases, chiefly CO, H 2 , and 
CH 4 , which, after admixture of hydrocarbon vapour, may be 
used for illuminating purposes ; (b) a watery liquid containing 
acetic acid, methyl alcohol, and many other substances ; and 
(c) tar. The watery distillate (b) is distilled anew after ad- 
dition of enough lime to retain the acetic acid, and the crude 
wood -spirit thus obtained, after some further treatment, is 
saturated with CaCl 2 and heated by steam to 100 C. The 
impurities are thus driven off, and a residue is left, consisting of 
a compound of CaCl 2 with methyl alcohol. This is mixed 
with water, when the methyl alcohol is liberated and can be 
recovered by distillation, but the distillate requires to be again 
rectified over quicklime in order to free it from water. 

Methyl alcohol is a light colourless mobile liquid with a 



46 METHYL ALCOHOL CHAP. 

spirituous odour. When ignited it burns with a pale blue 
flame. The pure alcohol is used in the manufacture of certain 
aniline dyes, and for this purpose it should be as free as pos- 
sible from acetone, a substance largely present in crude wood- 
spirit ; but for other purposes, such as for dissolving resins in 
the manufacture of varnish, a wood-spirit rich in acetone is 
desirable, on account of its greater solvent power. 

The presence of acetone can be detected and its amount estimated by 
means of its property of yielding iodoform when treated with iodine and 
potash. Pure methyl alcohol itself does not produce iodoform, whereas 
one molecule is obtained from each molecule of acetone present. 

Methyl alcohol boils at 66. It is considerably lighter than 
water, but mixes with it readily. 

Chemically, methyl alcohol is the type of a primary alcohol, 
that is, of one containing the group CH 2 . OH. Every primary 
alcohol when oxidised loses first two atoms of hydrogen, and 
gives an aldehyde characterised by the group CHO, which 
can be further oxidised to the group - COOH, so yielding an 
acid. In this particular case the alcohol, HCH 2 . OH, is first 
oxidised to formaldehyde, HCHO, and this to formic acid, 
HCOOH, by treatment with appropriate oxidising agents. 

As in all other alcohols, whether primary or other, the 
hydrogen of the OH group can be readily replaced by sodium 
or potassium : 



= 2CH 3 ONa + H 2 , 

Methyl alcohol. Sodium methylate. 

and the hydroxyl group, as a whole, is substituted by chlorine 
by the action of PC1 5 : 

CH 3 .OH + PC1 5 - CH ;j Cl + POC1 3 + HC1, 
Methyl alcohol. Methyl chloride. 

while, on the other hand, the synthesis of methyl alcohol can 
be effected by heating methyl chloride with water in sealed 
tubes to a temperature of 120 C. : 

CH,C1 + H . OH = CH 3 OH + HC1. 

Very important also is the ability of methyl alcohol to form 
ethereal salts, in which the methyl group of the alcohol plays 



VI 



ETHYL ALCOHOL 



47 



the same part as the metal in an inorganic salt. These are 
entirely similar to those derived from ethyl alcohol, which will 
presently be considered in more detail. 

Ethyl Alcohol, C 2 H 5 .OH, is prepared on a very large 
scale, though not in the pure state, by the fermentation of 
starch or sugar contained in various cereals and fruits. The 
term fermentation is applied to a process of chemical decom- 
position, depending for its continuance upon the influence of 
some " ferment," which yet seems to take no part in the 
chemical reaction, and 
is able to transform a 
disproportionately large 
amount of the ferment- 
ing substance. Fer- 
ments may be organised 
or unorganised. In the 
first case they are living 
micro-organisms whose 
activity as ferments is 
connected with their vital 
processes, and ceases 
with their death. The 
unorganised ferments 
are definite chemical 

Substances called en- FlG 23 ._p ure Yeast under the microscope. 

zymes, but no satis- 

factory explanation has been given of their action. 

In the case of the alcoholic fermentation of sugar we are 
concerned with an organised ferment, the yeast plant. This is 
a minute and structurally very simple plant, which, placed in a 
solution of sugar, is able to grow and multiply, provided the 
temperature be maintained between the limits of 5 and 40 
C. ; at the same time the sugar is gradually decomposed 
mainly according to the equation : 




Glucose. 



Alcohol. 



but there is always produced a certain amount of other sub- 
stances, of which the most important are higher alcohols and 
their ethereal salts ; these together constitute the fusel oil of 



ALCOHOLIC LIQUORS 



CHAP. 



the crude alcohol, and to its different nature are due both the 
pleasant flavour of good wine and the foul taste of cheap 
spirit. 

EXPT. 10. Dissolve 10 grams of sugar in 200 c.c. of warm water. 
Place in a 250 c.c. flask and add some yeast. Fit the flask with a cork 
and tube to pass any gas evolved through lime-water. 

Arrange a parallel experiment, using glucose or honey instead of cane- 
sugar. 

Notice that fermentation soon begins in the latter case, and that COo 
is evolved. The cane-sugar is much slower. 

The most important alcoholic beverages may be classified 

as follows : 

() Beer or ale, made by fermentation of the sugar in 

malted cereals (especially barley), and containing from 4 to 10 

per cent of alcohol. 

The malting is itself a fermentation process. The active 

principle is the diastase 
of the malt, an unor- 
ganised ferment which 
converts the starch of 
the cereal into sugar. 

(b) Wines, made by 
fermenting the sacchar- 
ine juice of ripe fruit. 
No ferment is artificially 
introduced, as in the 
case of brewing beer, 
but micro - organisms 
floating as dust in the 
air fall into the must 
and start fermentation. 
Wines contain from 10 

FIG. 24. Bloom of Grapes under the microscope, f , 

showing yeast cells at A. to 2O per CCllt Ol al- 

cohol. 

(<r) Spirits are much richer in alcohol (30 per cent and up- 
wards), and are made by distillation of the weaker spirituous 
beverages. A large quantity of cheap spirit is made by 
fermentation of malted potato- starch, and from the same 
source the bulk of the alcohol used in the arts and manu- 
factures is obtained. 




ALCOHOLOMETRY 



49 



Methylated Spirit. In order that the high price of 
alcohol due to the heavy duty upon it may not seriously inter- 
fere with its use for other purposes than as the basis of intoxi- 
cating beverages, the so-called methylated spirit is allowed to 
be sold duty free. This is a mixture of alcohol containing 20 
per cent of water with substances which make the spirit prac- 
tically undrinkable, but do not seriously interfere with its use 
for other purposes, and at the same time are difficult to 
remove. The present regulations order that certain small 
proportions of wood-spirit and of light petroleum shall be em- 
ployed as the methylating mixture. 

Alcoholometry. The method in general use for deter- 
mining the percentage of alcohol present in a given sample of 
liquid depends upon the gradual variation in the specific 
gravity of mixtures of alcohol and water as the proportion of 
alcohol is altered. The following short table illustrates the 
way in which the specific gravity changes : 



Parts by 




Parts by 




weight of 
alcohol in 100 


Specific gravity. 


weight of 
alcohol in 100 


Specific gravity. 


of mixture. 




of mixture. 







1. 000 


60 


.896 


IO 


.984 


70 


.872 


2O 


.972 


80 


.848 


30 


958 


90 


.823 


40 


.940 


IOO 


794 


50 


.918 







It would, of course, be quite incorrect to apply this table to 
such a liquid as beer or wine, in which other substances than 
water and alcohol are present, and influence the specific 
gravity. What is done in such cases is to take 100 c.c. of the 
liquid, distil over two-thirds of it, and make up the distillate 
to loo c.c. by adding water; we then have 100 c.c. of liquid 
containing all the alcohol which was originally present, but 
freed from the sugar and other non-volatile materials. By 
taking the specific gravity of this distillate we find at once 

E 



5 



PROOF-SPIRIT 



CHAP. 



from the table what percentage of alcohol there was in the 
beer or wine taken. 

The nomenclature employed in this country for stating the 
results, is very complicated. The standard taken is proof- 
spirit^ originally spirit of such strength that when poured 
over gunpowder and set fire to, it was just able to ignite the 
powder, while a more watery spirit failed to do so. The present 
legal definition of proof-spirit is that it should be of the specific 

I 2 

gravity , which corresponds to a proportion of 49.3 parts 

by weight of pure alcohol in 100 of the mixture. The strength 
of spirituous liquors is generally expressed as being so many 




FIG. 25. Distillation of small quantities. 

degrees over or under proof ; thirty degrees over proof implies 
that 100 parts of the spirit contain as much alcohol as 130 
parts of proof-spirit. 

Pure ethyl alcohol, absolute alcohol, is obtained from 
rectified spirit by treatment with quicklime and subsequent 
distillation. The spirit is allowed to stand over lumps of 
quicklime for several hours before distillation, and even then 
it is usually necessary to repeat the process before the alcohol 
is entirely freed from water. Whether this is the case can be 
made certain by shaking some anhydrous copper sulphate (a 
white powder obtained by heating the crystallised blue salt 
for several hours at 180 C.) with the alcohol, when the 
presence of even a trace of water will be detected by the white 
copper sulphate becoming tinged with blue. Anhydrous 



VI SYNTHESIS OF ALCOHOL 51 

alcohol is very hygroscopic, and must be preserved in well- 
stoppered bottles. 

Pure ethyl alcohol has a slight pleasant smell, and boils at 
a considerably lower temperature than water, viz. 78-3 C. 
Its specific gravity is .794 at I5C. It mixes readily with 
water, and can be used as a solvent for many substances (resins 
and other organic compounds) which are insoluble in water. 

Other methods besides that of fermentation of suga- may 
be used for the preparation of ethyl alcohol, but are of 
theoretical interest only ; the most important of them are : 

I. Ethylene, C 2 H 4 , is absorbed by concentrated sulphuric 
acid with formation of ethyl-sulphuric acid : 



and this, when treated with hot water, is decomposed into 
alcohol and sulphuric acid : 

C 2 H 5 . HS0 4 + H 2 = C 2 H 5 OH + H 2 SO 4 . 

As ethylene can be prepared by passing a mixture of acetylene and 
hydrogen over platinum sponge, and acetylene has been made by direct 
union of carbon and hydrogen, this gives a way by which it would Be 
possible to effect the synthesis of ethyl alcohol from its elements. 

II. Ethyl iodide, bromide, or chloride, when heated with 
water (or more readily, when heated with solution of an 
alkali) to a high temperature, yields ethyl alcohol, 

C 2 H 5 I + H,0 = C 2 H 5 OH + HI. 

This last method of preparation is strong evidence for the 
constitutional formula, CH 3 . CH 2 OH, which has been adopted; 
other evidence is forthcoming in the reactions of ethyl alcohol, 
all of which are well represented by this formula. Of these 
reactions the following only will be mentioned here : 

I. With metallic sodium or potassium, an alcoholate is 
formed and hydrogen is evolved : 

2C 2 H 5 . OH + 2Na = 2C 2 H 5 ONa 4- H,. 
Sodium ethylate. 

The alcoholates are readily oxidised, and are decomposed by water 
with formation of alcohol and a hydrate : 

C 2 H 6 ONa + H,O = Q,H 5 OH + NaOH. 



52 PROPYL ALCOHOL 



II. With PC1 5 , or HC1 in presence of a dehydrating agent, 
ethyl chloride is formed : 

C 2 H 5 OH + HC1 = C 2 H 6 C1 + H 2 O. 

Zinc chloride may be used as the dehydrating agent. Similar reactions 
occur with HBr . HI, also PBr 3 and PI 3 . 

III. With acids the alcohol combines to form ethereal salts 
(seep. 55): 

C 2 H 5 OH + H 2 S0 4 = C 2 H 5 . HS0 4 + H 2 O. 

Alcohol and sulphuric acid yield ethyl hydrogen sulphate and 
water. 

Propyl Alcohol, C 3 H 8 O, is the next higher homologue of 
ethyl alcohol, and is the lowest member of the series for which 
isomeric forms are possible. If we proceed from ethyl alcohol, 
CH 3 . CH 2 OH, by substituting a methyl group, CH 3 , for a 
hydrogen atom, we find that two isomeric alcohols are in- 
dicated for the formula C Q H C O : 

t> O 

CH 3 . CH 2 . OH CH 3 . CH 2 . OH 
gives gives 

* CH * 

CH 3 . CH 2 . CH 2 . OH CH> CH ' H 

3 
Normal propyl alcohol. Isopropyl alcohol. 

and both of these isomers are well-known substances. 

A third isomer, CH 3 . CH 2 . O . CH 3 , exists, but is not an alcohol ; it is 
methyl-ethyl ether. 

Normal propyl alcohol is found in fusel oil in considerable 
quantity, and can also be prepared synthetically by the action 
of water or potash solution upon the corresponding iodide : 

CH, . CH 2 . CH 2 I + H 2 = CH 3 . CH 2 . CH 2 OH + HI. 
Propyl iodide. Propyl alcohol. 

Isopropyl alcohol does not occur in fusel oil, but can only 



vi PRIMARY, SECONDARY, AND TERTIARY ALCOHOLS 53 

be obtained by synthetical methods, as by the action of water 
upon isopropyl iodide : 

CH 3 . CHI. CH 3 +H a O = (CH 3 ) 2 CHOH + HI. 

Both these alcohols are liquids of pleasant smell boiling at 
a somewhat lower temperature than water. Chemically, both 
exhibit the reactions characteristic of alcohols which are 
mentioned on p. 51, but they differ markedly from one another 
in their behaviour towards oxidising agents. Normal propyl 
alcohol, when oxidised, yields first an aldehyde and then an 
acid (propionic) : 

CH 3 . CH 2 . CH 2 OH ^CH 3 . CH 2 . CHO ^CH 3 . CH 2 . CO 2 H 

Primary alcohol. Aldehyde. Acid. 

a behaviour completely parallel to that of methyl and ethyl 
alcohols, and characteristic of all alcohols containing the group 
CH 2 . OH. Such alcohols are termed primary alcohols. 
Isopropyl alcohol, on the other hand, yields first a ketone, and 
this, on further oxidation, breaks up into several acids con- 
taining a smaller number of carbon atoms in the molecule. 
This behaviour is characteristic of secondary alcohols, 
which contain the group CHOH united to two alkyl groups : 

CH 3 C0 9 H 

(CH 3 ) 2 . CHOH ^(CH 3 ) 2 CO > and " 

H . CO 2 H 

Secondary alcohol. Ketone. Lower acids. 

The next alcohol we shall consider, butyl alcohol, will furnish 
us with a case of a tertiary alcohol. Such an alcohol 
contains the group C . OH combined with three alkyl groups, 
and on oxidation breaks up at once into bodies containing 
fewer carbon atoms in the molecule : 

(CH 3 ) 3 . COH >- bodies with fewer carbon 

atoms in the molecule. 
Tertiary alcohol. 

Butyl Alcohols, C 4 H 1Q O, occur in four isomeric forms. 
Their derivation from the two propyl alcohols by substitution 



54 BUTYL ALCOHOLS CHAP, vi 

of a methyl group for a hydrogen atom is shown in the 
following table : 

CH 3 . CH, . CH,OH yields (i.) CH 3 . CH 2 . CH 2 . CH,OH 

Normal butyl alcohol. 

(ii.) (CH 3 ) 2 CH . CH 2 OH 
Isobutyl alcohol. 

(iii.) CH 3 . CH 2 . CH(CH 3 ) . OH 
Secondary butyl alcohol. 

(CH 3 ) 2 CHOH yields (iv.) CH 3 . CH 2 . CH(CH 3 ) . OH 

(v.) (CH 3 ) 3 COH 
Tertiary butyl 
alcohol. 

but of these (iii.) and (iv.) are identical, so that the full 
number of isomers indicated by theory is four, and this is also 
the number actually known. Only one of them is sufficiently 
important to be further mentioned. Isobutyl alcohol, 
(CH 3 ) 9 CH . CH 9 OH, can be separated from fusel oil, in which 
it is present, by fractional distillation. It is a liquid boiling 
at 107 C., and possessing the characteristic smell of fusel oil. 
Amyl Alcohol, C 5 H 12 O. For this alcohol there are eight 
isomers indicated by theory, and of these all are now known. 
Two of these are largely present in fusel oil, and their mixture 
is the ordinary " amyl alcohol," a liquid of unpleasant smell, 
which boils at about 130 C. It is obtained from fusel oil by 
fractional distillation. 

QUESTIONS ON CHAPTER VI 

1. What tests would you apply to a substance given to you, in order 
to discover whether it is an alcohol or not? 

2. How is methyl alcohol obtained commercially? Mention important 
points in which it resembles, and others in which it differs from, ethyl 
alcohol. 

3. Give an account of the chief chemical changes which occur in 
brewing beer from barley. How would you determine the percentage of 
alcohol in a given sample of beer ? 

4. What are the characteristics of the three classes of alcohols, 
primary, secondary, and tertiary? 

5. Give an account of the two isomeric alcohols possessing the formula 
C 3 H 8 0. 



CHAPTER VII 
ETHEREAL SALTS 
ETHERS MERCAPTAN 

Ethereal Salts. As has been already mentioned, the 
alcohols are able to combine with acids somewhat in the same 
way as the inorganic metallic hydrates. The products in the 
case of the latter are termed salts, while those formed from 
the alcohols go by the name of " ethereal salts " or " esters " : 

CH 3 . OH-fHNO 3 = CH 3 NO 3 + H 2 O, 

Methyl nitrate, an ethereal salt. 
K.OH + HNO 3 = KNO 3 + H 2 O, 

Potassium nitrate, a salt. 

There are, however, several differences between the two 
classes of reactions, of which the most important is that the 
reaction does not occur so readily or completely with the 
alcohol as with the base ; often, especially when the acid is 
not one of the strongest, it is necessaiy to employ some 
dehydrating agent to favour the reaction. 

The reason is that the tendency to the reversed change, such as 
C 2 H 5 HS0 4 + H 2 = C 2 H 5 OH + H 2 SO 4 , 

becomes greater as the quantity of water present increases. By combining 
this water with some hygroscopic substance its effect is diminished. 

The most important ethereal salts of ethyl alcohol are 
perhaps the acetate and acid sulphate. 



ETHYL ACETATE 



Ethyl Acetate, CH 3 . CO 2 C 2 H 5 , can be prepared by 
heating a mixture of alcohol and acetic acid with strong 
sulphuric acid : 



C 2 H 5 OH 

Ethyl alcohol. 



CH 3 . CO 2 H 

Acetic acid. 



CH 3 C0 2 C 2 H 5 

Ethyl acetate. 



It is a volatile liquid with a strong fragrant smell. Its forma- 
tion in the way mentioned is employed as a test for acetic 
acid or an acetate. 




FIG. 26. Saponification of ethyl acetate by boiling with water and an alkali ; 
the reflux condenser prevents loss by volatilisation. 



EXPT. IT. In a test tube mix equal volumes of spirits of wine and 
strong sulphuric acid. Add some pieces of a solid acetate, and notice the 
fragrant smell of ethyl acetate which is evolved on gently heating the 
mixture. 

Like other ethereal salts, ethyl acetate is readily split up 
into the alcohol and acid from which it is formed. The change 
may be accomplished by heating with water in sealed tubes, 
or more readily by boiling with a dilute solution of an alkali : 



vii SAPONIFICATION 57 



CH 3 C0 2 C 2 H 5 + H 2 = CH 3 C0 2 H + C 2 H 5 OH. 
Ethyl acetate. Acetic acid. Ethyl alcohol. 

Changes of this kind, in which an ethereal salt is broken 
up by the action of water into the alcohol and acid from which 
it is formed, are often spoken of as cases of saponification. 
All such changes occur more readily when an alkali or an acid 
is present in the water. 

Ethyl acetate is used in the artificial preparation of per- 
fumes and flavouring essences. Several other ethereal salts, 
similar in composition, are also used for these purposes, as 

Ethyl butyrate, C 3 H 7 CO 9 C 2 H 5 , in pine-apple essence. 
Amyl acetate, CH 3 CO 2 C 5 H n , in pear essence. 

These and similar compounds also constitute the bulk of the 
natural essences extracted from the plants themselves. 

Ethyl Hydrogen Sulphate, C 2 H 5 HSO 4 , is formed when 
alcohol and strong sulphuric acid are mixed. It can be 
separated from unaltered sulphuric acid by means of its barium 
salt, which is soluble in water, whereas barium sulphate is 
insoluble. Ethyl hydrogen sulphate behaves as a monobasic 
acid, and when liberated from its barium salt, can only be 
obtained as a thick uncrystallisable syrup. 

Two of its reactions are important : 

(a) When heated alone it splits up into ethylene and sul- 
phuric acid : 

C 2 H 5 HS0 4 = C,H 4 + H 2 S0 4 . 

In this case a larger proportion of sulphuric acid is used, 
and the temperature of the reaction is higher. 

(b) When heated with alcohol it forms ether and sulphuric 
acid : 



C.jH 5 :HS0 4 ; + C 2 H 5 : H! = (C 2 H 5 ) 2 + H 2 S0 4 . 



In this case alcohol is present in larger quantity, and the 
decomposition proceeds at a lower temperature. 



58 ETHYL ETHER CHAP. 



ETHER 

Ether is now a term applied to a whole class of compounds, 
all of them oxides of organic radicles, such as methyl and 
ethyl. Methyl ether is (CH 3 ) 2 O, and ethyl ether (C 2 H 5 ) 2 O. 
This latter is the ordinary " sulphuric ether " of the chemists, 
the name being given from the fact that sulphuric acid is used 
in its manufacture, although the substance obtained has no 
sulphur whatever in its composition. 

Ethyl Ether, (C 2 H 5 ) 2 O, is ordinarily prepared by the action 
of ethyl-sulphuric acid upon alcohol : 

C 2 H 5 HS0 4 + C 2 H 5 OH ,= (C 2 H 5 ) 2 + H 2 SO 4 . 

EXPT. 12. In practice a mixture of alcohol and sulphuric acid (consist- 
ing, therefore, largely of ethyl-sulphuric acid) is heated in a flask to about 
140 C., and then a slow stream of alcohol is allowed to flow into the 
heated liquid. The vapours given off are condensed, and yield a mixture 
of water, alcohol, and ether. The layer of ether is separated, dried over 
quicklime, and redistilled. 




FIG. 27. Preparation of Ether. 

Ethyl ether is a colourless mobile liquid, boiling at 35 C. 
Its vapour is very heavy, and also readily inflammable, so that 
care must be exercised in working with ether in the neighbour- 
hood of a flame. The smell of ether is pleasant, but when 
inhaled in quantity the vapour produces insensibility, and is 



MERCAPTAN 59 



used as an anaesthetic in cases where chloroform is not per- 
missible on account of its depressing action upon the heart. 
When drunk in the liquid state ether produces a peculiar kind 
of short-lived intoxication, the after effects of which are very 
injurious to the health. 

The constitution of ether is not evident from the mode of 
formation given above, and its reactions are mostly not of a 
character to throw light upon this point. The preparation 
from ethyl iodide and sodium ethylate (see p. 51), 

C 2 H 5 I + C 2 H 5 ONa = C 2 H 5 . O . C 2 H 5 + Nal, 

is, however, strong evidence in support of the view that ordinary 
ether is oxide of ethyl. 



MERCAPTAN AND ETHYL SULPHIDE 

A large number of organic bodies are known in which it 
seems that an atom of sulphur plays the part of an atom of 
oxygen in closely related compounds. Such are the mercaptans 
(e.g. C 2 H 5 . SH), which correspond to the alcohols (C 2 H 5 . OH), 
and the alkyl sulphides^ e.g. (C 2 H & ) 9 S, which correspond to the 
ethers ( (C 2 H 5 ) 2 O). 

Ethyl Mercaptan, C 2 H 5 . SH, is formed by the action of 
potassium sulphydrate, KSH, upon ethyl bromide or iodide : 

C 2 H.Br+KSH = C 2 H 5 . SH + KBr 
c.f. C 2 H 5 Br + KOH = C 2 H 5 . OH + KBr. 

It is a volatile liquid of very strong and unpleasant odour. 
The hydrogen of the SH group is more readily replaced by 
metals than the corresponding H atom in alcohols. Not only 
does mercaptan react with sodium and potassium, but also 
with the oxides of heavy metals, such as mercury : 

HgO + 2C 2 H 5 . SH = (C 2 H 5 S) 2 Hg + H 2 O, 

(hence the origin of the name mercaptan, mercurium aptans), 
Ethyl Sulphide, (C 2 H 5 ) 9 S, can be prepared, 



60 ETHYL SULPHIDE 



(i) By acting on potassium sulphide, K 2 S, with ethyl 
bromide : 

K 2 S + 2C 2 H 5 Br = (C 2 H 5 ) 2 S + 2KBr. 

When a solution of caustic potash is saturated with H^S, the compound 
KHS is produced. If to this the same amount as was originally taken of 
caustic potash solution be added, K 2 S is formed : 



and KSH + KOH = K 2 S+H 2 O. 

(2) By treating the compound, C 2 H 5 SK (obtained from 
mercaptan by action of potassium), with ethyl bromide or iodide: 

C 2 H 5 . SK + C 2 H 5 Br = (C 2 H 5 ) 2 S + KBr, 
with which compare the method for preparing ether : 
C 2 H 5 . OK + C 2 H 5 Br = (C 2 H 5 ) 2 O + KBr. 

Ethyl sulphide, like nearly all volatile organic compounds 
which contain sulphur, has a most unpleasant smell. 

QUESTIONS ON CHAPTER VII 

1. What is meant by an " ethereal salt " ? How are such compounds 
prepared ? 

2. Mention some organic compounds of the class of ethereal salts 
which are used in artificial flavouring essences. 

3. What two substances can be prepared by heating ethyl alcohol with 
sulphuric acid ? How do the circumstances of the reaction need to be 
modified in the two cases. 

4. Why is ether regarded as ethyl oxide ? What sulphur-containing 
compound resembles it in composition, and how is it prepared ? 



CHAPTER VIII 
ALDEHYDES AND KETONES 

The Aldehydes are characterised by the presence of the 
monovalent group, CHO, whose structure is represented by the 

formula C^rJ that is to say, the general behaviour of the 



aldehydes is best represented by formulae in which this group 
is connected with an alkyl group, such as methyl or ethyl. 

The aldehydes occupy an intermediate position between the 
acids and the alcohols by whose oxidation they are produced ; 
thus, between ethyl alcohol, CH 3 . CH 2 OH, and acetic acid, 
CH 3 COOH, stands the aldehyde CH 3 . CHO, or in general : 

R . CH 2 OH - H 2 = RCHO ; and R . CHO + O = R . COOH ; 

Alcohol. - ^- Aldehyde. - ^- Acid. 

and the names of the aldehydes are best chosen so as to denote 
their connection with a particular acid, the one into which 
they are converted by addition of an atom of oxygen. Thus 
the first member of the aldehyde series, H . CHO, is termed 
formaldehyde, the second one, CH 3 . CHO, is acetaldehyde, 
and so on. 

Formaldehyde, H . CHO, is best obtained from the corre- 
sponding alcohol, methyl alcohol, H . CH 9 OH, by oxidation ; 
and this is most conveniently effected by passing warm air 
saturated with the vapour of methyl alcohol over a glowing 
copper spiral. 

EXPT. 13. In the centre of a piece of combustion tubing, about a foot 
in length, place a two-inch coil of copper gauze. Connect one end of the 



62 FORMALDEHYDE CHAP. 

tube through two gas-washing bottles (the first empty, the second half full 
of water) with an aspirator, and the other end with a gas-washing bottle 
containing methyl alcohol, kept at about 50 by being placed in a beaker of 
warm water. 

Now turn on the water tap of the aspirator until a vigorous current of 
vapour-laden air is passing over the copper gauze. Heat this gently with 
a Bunsen burner until it begins to glow, when it will continue to do so 
without any further use of the burner so long as the experiment is con- 
tinued. In order to minimise the danger of cracking the glass tube when 
the copper spiral suddenly begins to glow, it is well to support the spiral 
on a thin piece of mica or of asbestos paper. 

In this way are obtained only mixtures of formaldehyde 
with methyl alcohol and water. It has not been found possible 
to prepare pure formaldehyde, H . CHO, except in solution or 
in the state of vapour. When the solution is evaporated or the 
vapour cooled, a solid substance is obtained of the same com- 
position as formaldehyde, but not of the same molecular weight ; 
this is para-formaldehyde, and has the formula (CH 2 O)^ where 
x is possibly equal to 3, but is not known with certainty. Para- 
formaldehyde, (CH 9 O) 3 (?), is said to \>Q polymeric with form- 
aldehyde, CH 9 O, as the two substances have the same composi- 
tion, but different molecular weights. The opposite change is 
easily accomplished by vapourising the solid para-formaldehyde 
when a vapour whose density shows it to be made up of the 
simple molecules, CH O, is obtained ; but on cooling, these 
again gradually unite to the more complex molecules, (CH 2 O) 3 . 

Beyond its tendency to polymerisation, the chief charac- 
teristic of formaldehyde is the readiness with which it takes up 
oxygen from other substances to effect the change into formic 
acid : 

H . CHO + O-H. COOH; 
Formaldehyde. Formic acid. 

accordingly, formaldehyde is a strong reducing agent ; it 
reduces in the cold both Fehling's solution and solutions of 
silver salts. 

EXPT. 14. Prepare a quantity of Fehling's solution by dissolving 100 
grams of Rochelle salt (sodium potassium tartrate) in a little water, add- 
ing 30 grams of NaOH in 300 c.c. of water, and then 20 grams of crystal- 
lised CuSO 4 , dissolved in about 100 c.c. of water ; mix and keep in a 
stoppered bottle. 

Place some of the formaldehyde solution prepared in Expt. 13 in a 



ACETALDEHYDE 63 



beaker, and add Fehling's solution drop by drop. Notice that its dark 
blue colour is discharged and a light red precipitate produced. This is 
Cu a O, formed by reduction of the CuSO 4 : 

2CuSO 4 + 4KHO + H . CHO = HCO 2 H + Cu 2 O + 2K 2 SO 4 + 2H 2 O. 

EXPT. 15. Dissolve 3 grams AgNO 3 in a mixture of 20 c.c. strongest 
ammonia solution (sp. gr. .88) with its own volume of water, and add a 
solution of 3 grams NaOH in 25 c. c. of water. Keep in a small stoppered 
bottle in a dark place. 

Take some of this silver solution in a test tube, and add a few drops of 
the formaldehyde solution ; allow to stand in the cold. In a few minutes 
a brilliant mirror of metallic silver will be deposited on the sides of the 
test tube. 

O 3 + H.>O + HCHO: = HCOOH + 2HNO 3 + 2Ag. 



Acetaldehyde, CH 3 . CHO, is prepared by the oxidation 
of ethyl alcohol by distillation with a mixture of potassium 
bichromate and dilute sulphuric acid. 

EXPT. 16. Place in a flask 30 grams K 2 Cr.,O 7 (in small lumps) and 
120 c.c. water. Mix in a beaker 40 c.c. methylated spirit and 25 c.c. 
strong sulphuric acid, and allow to cool. Then add this mixture gradu- 
ally to the bichromate, taking care to keep cool by running water over the 
outside of the flask. 

Heat the mixture on the water-bath, and collect the distillate in a re- 
ceiver kept cold by ice. The impure acetaldehyde collected can be purified 
partly by fractional distillation, and finally by conversion into the solid 
compound which it forms with ammonia. 

Acetaldehyde is a colourless liquid, boiling at 21 C. and 
possessing a characteristic smell. Like formaldehyde, it is a 
strong reducing agent, as may be shown by experiments similar 
to Nos. 14 and 15. It further resembles the lower member 
of the aldehyde series in the readiness with which it poly- 
merises to paraldehyde (C 2 H 4 O) 3 . Acetaldehyde itself is a 
colourless very volatile liquid (B.P. 21 C.) with a pleasant 
smell, but on standing in contact with even a trace of various 
substances H 2 SO 4 , HC1, SO 2 , etc. it changes almost en- 
tirely to paraldehyde, which is a liquid at ordinary temper- 
atures, but solidifies in a freezing mixture, boils at 124, and 
gives a vapour whose density corresponds to the molecular 
formula. (C 2 H 4 O) 3 . Paraldehyde, though so directly obtained 



64 COMPOUNDS OF ACETALDEHYDE CHAP. 

from acetaldehyde, is not itself a real aldehyde at all. This 
is shown by its whole chemical behaviour, especially by the 
fact that it does not reduce metallic silver from an ammonia- 
cal silver solution, and leads us to conclude that in the 
formula of paraldehyde the group - CHO no longer occurs. 
Paraldehyde is easily reconverted into ordinary acetaldehyde 
by distillation with a little H^SO 4 . 

Metaldehyde is another substance of the formula (C 2 H 4 O) 3 obtained by 
polymerisation of acetaldehyde ; it is isomeric with paraldehyde. 

Compounds of Acetaldehyde. In some respects acet- 
aldehyde is more typical than its lower homologue of the group 
of aldehydes, and we have therefore delayed till now the con- 
sideration of certain reactions exhibited by aldehydes as a 
class, in which certain substances, such as NH 3 , HCN, etc., 
are added to the aldehyde molecule. 

(a) Acetaldehyde, like all the other aldehydes except 
H . CHO, unites directly with ammonia to form a compound 
of the type R . CH(OH)(NH 2 ) : 

OH 
CH 3 . CHO + NH 3 = CH 8 . CH<^ R 

This particular one is called simply aldehyde-ammonia, and is formed 
as a white crystalline solid when dry NH 3 is passed into an ethereal solu- 
tion of aldehyde. It is decomposed by dilute acids into aldehyde and 
ammonia. 

EXPT. 17. Pass NH 3 , dried by quicklime, into a solution of alde- 
hyde in ether ; collect on a filter the white precipitate produced, and 
show that some of it when warmed with dilute H 2 SO 4 regenerates alde- 
hyde. 

(V) Addition compounds with HCN are also formed by the 
aldehydes, thus 

/~\TT 

CH 3 . CHO + HCN = CH 3 . CH<^- 

(c) Sodium hydrogen sulphite, NaHSO y , also gives addition 
products, which are often used as a means of separating and 
purifying the aldehydes. The following equation represents 
what happens in the case of acetaldehyde : 

OH 
CH 8 . CHO + NaHS0 3 = CH 3 . CH<g QjNa - 



CHLORAL 65 



Compounds of this type are obtained when an aldehyde is shaken with 
a saturated solution of NaHSO 3 . They are white crystalline solids, soluble 
in water, and decomposed by dilute acids with regeneration of the alde- 
hyde. 

Chloral is a very important derivative of ordinary alde- 
hyde ; its formula is CC1 3 . CHO, and its systematic name 
trichlor-aldehyde. 

Chloral is prepared by passing chlorine into alcohol and 
decomposing the solid crystalline product (a compound of 
chloral and alcohol) with sulphuric acid. The reaction may 
be represented as occurring in two parts : 

(a) The alcohol is oxidised to aldehyde, 

CH 3 . CH 2 OH + C1 2 = CH 3 . CHO + 2HC1. 

Ethyl alcohol. Acetaldehyde. 

(b) The aldehyde is converted into trichlor-aldehyde or 
chloral, 

CH 3 . CHO + 3C1 2 = CC1 3 . CHO + sHCl. 
Acetaldehyde. Chloral. 

It is a liquid with a penetrating smell, and possesses most of 
the properties (reducing power, etc.) characteristic of the alde- 
hydes. It is decomposed by alkalies with production of chloro- 
form : 

CC1 3 . CHO + KOH = CHC1 3 + H . CO 2 K, 

Chloral. Chloroform. Potassium 

formate. 

hence perhaps the well-known narcotic power of chloral. 

Chloral Hydrate, CC1 3 . CHO + H 2 O, is a compound of 
chloral with water, produced by direct combination of the two 
liquids. It is a crystalline solid, and is the form in which 
chloral is usually administered. 



KETONES 

The ketones are a series of compounds resembling in many 
respects the aldehydes, but differing in others ; and we attempt 
to represent both resemblances and differences by giving to 
the ketones the formula R . CO . R, closely allied to the alde- 
hyde formula R. CO . H. 



66 KETONES CHAP. 

(i) Just as the aldehydes are obtained by carefully gradu- 
ated oxidation of primary alcohols, 

R . CH 2 OH + O = R . CO . H + H 2 O, 

Primary alcohol. Aldehyde. 

so the ketones are the first products formed by the oxidation 
of secondary alcohols, that is, alcohols in which the group 
CH(OH) is combined with two alkyl groups : 



. OH + O = >CO + H 2 0. 
Secondary alcohol. Ketone. 

(2) Another method of general application for the prepara- 
tion of ketones is the dry distillation of the calcium salts of 
fatty acids ; thus calcium acetate gives acetone or di-methyl 
ketone : 



CHgiCOO^ 

Calcium acetate. Acetone. 

(3) A third method of considerable importance is the treatment of 
acetyl chloride or similar compounds with zinc methyl, ethyl, etc. The 
reaction may be represented thus : 



Acetyl chloride. Zinc ethyl. Methyl-ethyl 
ketone. 

The ketones resemble the aldehydes in their power of form- 
ing addition products with HCN, and with NaHSO 3 . They do 
not possess the same energetic reducing power, nor do they 
combine with ammonia in the same way as the aldehydes. 

Acetone, (CH 3 ) 2 CO, or dimethyl ketone is the simplest 
ketone. It can be prepared by any of the general methods 
given above, the one generally adopted being the dry distilla- 
tion of calcium acetate : 

(CH 3 CO 2 ) 2 Ca = (CH 3 ) 2 CO + CaCO 3 . 

Acetone is also found amongst the products of the dry distilla- 
tion of wood (see p. 45), and is largely obtained from that 



viii ACETONE 67 

source. It is used as a solvent, and for the preparation of 
iodoform and other substances. It is a volatile inflammable 
liquid with a pleasant smell. 

Oximes and. Hydrazones. Special importance attaches to the com- 
pounds which aldehydes and ketones form with hydroxylamine, NH 2 (OH), 
and phenylhydrazine, C 6 H 5 NH . NH 2 . In these oximes and hydrazones 
the oxygen of the CO group in the aldehyde or ketone is replaced by a 
divalent residue, thus : 

(CH 3 ) 2 CO + H 2 N . OH = (CH 3 ) 2 C : N . OH + H 2 O 
Oxime. 

CH 3 COH + H 2 N . NHC 6 H 5 = (CH 3 )CH : N . NHC 6 H 5 + H 2 O. 

Hydrazone. 

The importance of these oximes and hydrazones lies in their great utility 
as a means of characterising the various aldehydes and ketones. The 
hydrazones especially are usually crystalline solids, only slightly soluble in 
the ordinary solvents, and are therefore much more easily identified than 
the aldehydes or ketones from which they are prepared. 



QUESTIONS ON CHAPTER VIII 

1. How is acetaldehyde prepared? Mention its chief properties. 

2. How are the aldehydes as a class characterised by their reactions, 
and how is their behaviour represented in the generic formula R . CHO ? 

3. What is the relation of chloral to acetaldehyde ? Give its pre- 
paration and properties. 

4. What bodies are formed by the oxidation of (a) ethyl alcohol, (3) 
aldehyde, (c) chloral? 

5. Illustrate the chief points of resemblance and difference in the 
chemical behaviour of aldehyde and acetone. 



CHAPTER IX 
THE FATTY ACIDS 

The Fatty Acids form an important homologous series, 
some higher members of which are contained in all natural 
fats. The lower members are liquids of strongly acid char- 
acter and sharp penetrating odour, but with increasing 
molecular weight the members of the series lose their solu- 
bility in water, and with it their acid taste and power of turn- 
ing blue litmus red. The power of forming salts is, however, 
unimpaired even in the highest member of the series yet 
obtained. 

The first acid of the series is formic acid, CH. 2 O 2 , the second 
acetic acid, C 2 H 4 O 2 . The general formula of the whole series 
is C^H 2M O 2 , but this is better written C M H 2M+1 . CO 2 H, to in- 
dicate that every acid of the series contains the "carboxyl" 
group, CO 2 H, combined with a hydrocarbon residue (or "alkyl " 
group), such as methyl, CH g , ethyl, C 2 H 5 , etc. Formic acid is 
then written H . CO 2 H, acetic acid CH 3 . CO 2 H, and so on. 

The reasons for writing the formulae in this way will be 
best understood if we consider in detail the case of acetic acid ; 
this has the molecular formula C 2 H 4 O 2 . Of the four hydrogens 
only one can be replaced by metals, i.e. the acid is monobasic, 
and therefore one of the four hydrogen atoms is differently 
related to the molecule from the other three. Again the action 
of phosphorus pentachloride on acetic acid or on sodium 
acetate yields a substance, acetyl chloride, of the formula 
C 2 H 3 OC1 ; that is, a Cl atom takes the place of an O atom and 
an H atom. This could not happen unless that O and that H 
were connected to form the monovalent hydroxyl group OH. 



CHAP. IX PREPARATION OF FATTY ACIDS 69 

We have now arrived at the formula, C 2 H 3 O . OH, for acetic 
acid. The next question is whether the three remaining hydro- 
gen atoms are all connected to the same carbon atom or not. 
Acetic acid treated with chlorine yields a derivative trichlor- 
acetic acid of the formula C C1 3 O . OH, in which the hydroxyl 
group is still present, and the other three hydrogens are re- 
placed by chlorine. Now trichloracetic acid readily yields 
chloroform when boiled with water : 

C 2 C1 3 O.OH = CHC1 3 + CO 2 , 

Trichloracetic acid. Chloroform. 

showing that all three Cl atoms, and therefore the three hydrogen 
atoms, whose places they occupy, are connected to the same 
carbon. Hence acetic acid contains the groups CH 3 and OH, 
and the only formula in agreement with these experimental 
results is CH 3 . COOH. 

General Methods of Preparation. (i) The first 
method is one which also furnishes valuable evidence in favour 
of the formula C, z H 2w+1 . CO 2 H for the series, inasmuch as we 
start in each case from a substance, C ; ,H 2 , Z+1 . CN, in order to 
prepare the corresponding acid. Such an alkyl cyanide is 
obtained by treating the iodide of the same radical with silver 
cyanide, e.g. : 

CH 3 I + AgCN = CH 3 .CN + Agl, 
Methyl iodide. Methyl cyanide. 

and when heated with water undergoes a reaction of the fol- 
lowing type : 

CH 3 .CN + 2H 2 O = CH 3 . CO 2 H + NH 3 . 
Methyl cyanide. Acetic acid. 

Such a reaction is spoken of as hydrolysis, and takes place 
much more readily when a dilute mineral acid is used instead 
of pure water ; or a solution of an alkali may be employed. 

(2) By the action of carbon monoxide on the sodium com- 
pound of an alcohol, e.g. from sodium methylate sodium acetate 
is obtained : 

CH 3 . ONa + CO = CH 3 . COONa. 



70 FORMIC ACID 



Similarly, sodium formate may be obtained from sodium hydrate: 
H . ONa + CO = H . COONa. 

This method is of theoretical interest only. 

3. An important practical method is the oxidation of a 
primary alcohol containing the same number of carbon atoms 
as the acid to be prepared : 

CH 3 . CH 2 OH + O 2 = CH 3 . COOH + H 2 O. 
Ethyl alcohol. Acetic acid. 

In the laboratory a mixture of potassium bichromate with 
dilute sulphuric acid is usually employed as the oxidising agent ; 
in the commercial manufacture of acetic acid (vinegar) the 
oxygen of the air is utilised. 

In this method the group CH 2 (OH) is oxidised to COOH. 
When a less complete oxidation is effected, the product is an 
aldehyde containing the group CHO : 

R . CH,(OH) > R . CHO > R . COOH. 

Primary alcohol. Aldehyde. Acid. 

Foimic Acid, H . CO 2 H, may be prepared by any of the 
three general methods, i.e. : 

(i) From HCN, hydrocyanic acid, by heating with a dilute 
mineral acid in sealed tubes : 

HCN + 2H 2 O = H . C0 2 H H- NH 3 . 
Formic acid. 

(2) From sodium or potassium hydrate, and carbon 
monoxide : 

NaOH + CO = H . COONa, 
Sodium formate. 

a reaction which occurs with great readiness when moist CO is 
passed over porous soda-lime heated to about 200 C. 

(3) By the oxidation of methyl alcohol : 

HCH., . OH + O, = HCOOH + H 2 O. 

Methyl alcohol. Formic acid. 



ix FORMIC ACID 71 



Another method of considerable interest in connection with the physio- 
logical chemistry of plants by which formates can be obtained is by the 
reduction of CO 2 in the presence of water. Thus, when thin slices of 
metallic potassium are exposed to a moist atmosphere of CO 2 they are 
gradually converted into potassium formate and carbonate : 

2K + 2CO 2 + H 2 O = H . CO 2 K + KHCO 3 . 

Possibly this reduction to formic acid is the first step in the transformation 
by plants of CO 2 into sugar and starch. 

The most practically useful method for preparing formic 
acid is by the decomposition of oxalic acid. This, when heated 
alone, or better with glycerine, breaks up as follows : 

C 2 H 24 = H ' CO 2 H + CO 2' 
Oxalic acid. Formic acid. 

A mixture of equal quantities of glycerine and crystallised oxalic acid is 
heated in a retort until no more CO 2 is evolved. The distillate collected 
during this period is a very weak formic acid. On adding more oxalic 
acid, and again heating, a stronger acid will be obtained, but the acid got 
in this way never contains less than about 40 per cent of water. 

Anhydrous formic acid is prepared from lead formate by 
the action of hydrogen sulphide. The lead salt is easily obtained 
from any (weak) formic acid. It is dried and then exposed to 
a stream of H 2 S gas in a tube kept warm by means of a 
steam jacket. The anhydrous acid distils over, and is a 
colourless liquid with an acrid odour and very caustic properties. 

Formic acid differs from the other members of the series in 
being a strong reducing agent. It reduces solutions of silver 
and mercury salts with separation of the metals. When heated 
with strong sulphuric acid it is decomposed into CO and water : 

H. CO 2 H = 

The Formates of the alkali metals are fairly stable sub- 
stances, which crystallise only with difficulty. Those of the 
heavy metals, such as silver, are very easily decomposed with 
separation of the metal. 

Acetic Acid, CH 3 . CO 2 H, can be obtained by any of the 
three general methods, i.e.: 



7 2 



ACETIC ACID 



(i) From CH.^ . CN, methyl cyanide, by heating with a 
dilute mineral acid or a dilute alkali : 



CH 3 .CN 

Methyl cyanide. 



H 3 . C0 2 H + NH 3 . 
Acetic acid. 



Methyl cyanide, CH 3 CN, can be made by acting with methyl iodide on 
silver cyanide : 

CH 3 I + AgCN = CH 3 CN + Agl. 

(2) From sodium or potassium methylate and carbon 
monoxide : 



CH 3 .ONa - 
Sodium methylate. 

For sodium methylate, see p. 46. 



= CH 3 . COONa. 

Sodium acetate. 



(3) By the oxidation of ethyl alcohol : 



CH 3 CH 2 OH 
Ethyl alcohol. 



H 3 . COOH 
Acetic acid. 



H 0. 



The only one of these methods employed on a large scale 
is the third. In the preparation of vinegar (which is a dilute 

acetic acid flavoured by 
minute quantities of 
other substances) the 
alcoholic liquid, whether 
wine, diluted brandy, or 
merely potato-spirit and 
water, is exposed to the 
simultaneous action of 
the air (which supplies 
the oxygen), and of the 
fermentative influence of 
a particular organism, 
the mycoderma aceti. 
The process is carried 
on most rapidly by al- 
lowing the alcoholic 
liquor to trickle through 
tubs filled with shavings, 
on which the mycoderma has developed. New shavings are 




FIG. 28. The mycodertna aceti or "mother of 
vinegar" seen under the microscope. 



ix THE ACETATES 73 

at first almost inactive, but they soon become coated with the 
organism, and the oxidation then takes place readily. 

Large quantities of acetic acid are also obtained as one of 
the products of the destructive distillation of wood. The acid is 
separated from the other products, chiefly methyl alcohol and 
acetone, by neutralising with lime and distilling the alcohol and 
acetone from the calcium acetate. This last is then decomposed 
by addition of sulphuric acid, and the acetic acid recovered by 
distillation. 

Acetic acid, when perfectly free from water, is a crystalline 
solid which melts at 17 C. The strongest acetic acid of 
commerce is termed " glacial acetic acid," from the fact that it 
is solid in moderately cold weather. It has a penetrating acid 
smell, and acts like a caustic on the skin. 

The salts of acetic acid, the acetates, are prepared by 
acting with the acid upon the oxide or carbonate of the metal 
whose acetate is required. They are all more or less readily 
soluble in water, and crystallise well. 

Sodium Acetate, NaC 2 H 3 O 2 , crystallises with three mole- 
cules of water. When heated above 1 00 C. the water of crys- 
tallisation is driven off, and the anhydrous sodium acetate is 
left as an amorphous mass. The anhydrous salt is used in 
organic synthesis as a dehydrating agent, and in the prepara- 
tion of methane : 

NaCHO + NaOH = CH + NaCO 3 . 



Ammonium Acetate, (NH 4 )C 2 H 3 O 2 , is a deliquescent 
solid. Its solution is made use of in qualitative analysis for 
dissolving lead sulphate, and so separating it from mercuric 
sulphide, with which it may be mixed in the course of working 
through the second group of metals. 

When strongly heated, ammonium acetate yields acetamide 
and water : 

CH 3 COONH 4 = CH 3 CONH 2 +H 2 O. 

Calcium Acetate, Ca(C 2 H 3 O 2 ) 2 , is used for preparing 
acetone : 



CHgCO.O' 



74 PROPIONIC ACID CHAP. 

Lead Acetate, Pb(C 2 H 3 O 2 ) 2 , is the " sugar of lead " of 
commerce, and is made by dissolving litharge in acetic acid. 
It is largely used in the manufacture of white-lead (basic lead 
carbonate) and chrome-yellow (PbCrO 4 ). 

Aluminium Acetate is obtained in solution when calcium 
acetate is mixed in the presence of water with aluminium 
sulphate. The solution decomposes on evaporation into acetic 
acid (which escapes as vapour) and alumina ; hence the ex- 
tensive use of aluminium acetate as a mordant, the alumina 
combining with the dye to form an insoluble lake, which adheres 
firmly to the fibre of the cloth. 

As tests for the presence of acetic acid may be utilised 
either the dark red colour of the solution of ferric acetate 
(destroyed on boiling, with separation of a basic acetate of iron) 
formed when ferric chloride is added to a solution of an acetate, 
or the formation of ethyl acetate with its characteristic pleasant 
smell when an acetate is heated with alcohol and concentrated 
sulphuric acid. 

It is, however, to be noted that these tests give almost identical results 
with any of the acids of this series. To distinguish acetic acid from its 
higher homologues, the surest plan is to prepare the silver salt and 
determine the percentage of silver which it contains. 

Propionic Acid, C 2 H 5 . CO 2 H, may be prepared by any of 
the three general methods, but most conveniently by the third, 
starting from normal propyl alcohol : 

C 2 H 5 . CH,OH + O 2 - C 2 H 5 . COOH + H 2 O. 
Propyl alcohol. Propionic acid. 

The constitution of propionic acid is shown by this method 
of preparation, as also by that from ethyl cyanide by hydrolysis : 

C 2 H 5 CN + 2H 2 O = C 2 H 5 CO,H + NH 3 . 
Ethyl cyanide. Propionic acid. 

Butyric Acid, C 3 H 7 . CO 2 H, is the lowest member of the 
series for which isomeric forms are theoretically possible or 
have been actually obtained. These are two in number, viz. : 

(i) Normal butyric acid, CH 3 CH 2 CH 2 CO 2 H. 
(ii) Isobutyric acid, 



xi BUTYRIC ACIDS 75 

Their constitution is made clear by their synthetical prepara- 
tion from normal propyl iodide and isopropyl iodide respect- 
ively through the intermediary of the cyanides : 

(i)CH 3 CH 2 CH 2 I - ^CH 3 CH. 2 CH 2 CN - ^CH 3 CH 2 CH 2 CO 2 H 

Normal propyl iodide. Normal propyl cyanide. Normal butyric acid. 

(ii) (CH 3 ) 2 CHI - > (CH 3 ) 2 CHCN - >- (CH 3 ) 2 CHCO 2 H 
Isopropyl iodide. Isopropyl cyanide. Isobutyric acid. 

Normal Butyric Acid, C 3 H 7 . CO 2 H, is present in butter 
in the form of glycerine butyrate, the ethereal salt of glycerine 
and butyric acid. There are, however, many other similar 
compounds of glycerine contained in butter, and the isolation 
of the butyric acid in a state of purity is a matter of difficulty, 
and the acid is more cheaply and easily obtained by the fer- 
mentation (under the influence of the bacillus subtilis} of sugar 
or starch. This process is carried out on a fairly large scale, 
the butyric acid being converted into its ethyl salt, which is 
used as a flavouring under the name of essence of pine-apples. 
The same fermentation of starch and sugar occurs in the 
human stomach in certain cases of deranged digestion. Start- 
ing from glucose (see Chapter XVIII), the change produced by 
the fermentation may be represented by the equation : 

C 6 H 12 6 = C 4 H 8 2 + 2C0 2 + 2H 2 . 
Glucose. Butyric acid. 

Butyric acid is an oily liquid with an unpleasant rancid smell. 
The change which butter undergoes in turning rancid may be 
represented (so far as the glycerine butyrate in it is concerned) 
as follows : 



,) 3 + 3 H 2 = C 3 H 5 (OH) S + 3 C 3 H r . CO 2 H, 
Glycerine butyrate. Glycerine. Butyric acid. 

and it is to the presence of free butyric acid in rancid butter 
that its characteristic taste and smell are due. 

Isobutyric Acid, C 3 H r CO 2 H, can be prepared from iso- 
propyl cyanide (see above), and resembles the normal acid in 
smell and taste, though differing considerably from it in some 
other physical and chemical properties. 



76 STEARIC ACID 



The fifth acid of the series is valerianic acid, C 4 H 9 . CO. 2 H, and theory 
indicates the possible existence of four isomers, all of which have been 
actually prepared. They may all four be regarded as derivatives of acetic 
acid, obtained from it by replacing one or more of the hydrogens of its 
methyl group by alkyl radicles. They are 

(i) Propyl-acetic acid, C 3 H 7 . CH 2 CO 2 H. 
(ii) Isopropyl-acetic acid, C 3 H 7 . CH 2 CO 2 H. 

~ 



(iii) Ethyl-methyl-acetic acid, ( T>CH . CO 2 H. 
(iv) Trimethyl-acetic acid (CH 3 ) 3 C . CO 2 H. 

Of these the second is present in valerian root, while all of them may be 
prepared synthetically by utilising some one or other of the general methods 
given on p. 69 as applicable to all the fatty acids. 

The higher acids are not of great importance until we come to those 
with sixteen and eighteen atoms of carbon in the molecule. 

Palmitic Acid, C 15 H 31 . CO< 2 H, and Stearic Acid, 
C 17 H 35 . CO H, occur in combination with glycerine as the 
chief constituents of animal fats. Glycerine palmitate is also 
largely present in most vegetable oils. These fats and oils 
serve as the starting-point of three important manufactures 
those of soap, glycerine, and stearic acid. In making soap 
the fats are heated with caustic potash or caustic soda solution, 
and in this way the compounds of glycerine with various fatty 
acids which are contained in the fat are " saponified," that 
is, are converted into glycerine and the potassium or sodium 
salts of the acids. If we consider only one of these com- 
pounds, the glycerine stearate, the change may be represented 
thus : 

rococ 17 H 35 

C 3 H J OCOC 17 H 35 + 3 NaOH = C 3 H 5 (OH) 3 + 3 C 17 H 35 COONa. 
|pCOC ir H M 

Glycerine stearate Glycerine. Sodium stearate 

or fat. or soap. 

The other compounds present undergo similar changes, so that 
there is obtained along with glycerine a mixture of the palmit- 
ates and stearates of sodium or potassium. This mixture con- 
stitutes soap, hard soap being the sodium salts and soft soap 
the potassium salts of the acids present in the fats employed. 
Formerly it was the practice for each household to make its 
own soap, but the tendency of modern life has led to the 
manufacture being carried on almost entirely in very large 



IX SOAP 77 

works. The process is of the simplest. The fat or oil is 
heated to boiling in large open vats along with the solution of 
soda or potash. When saponification is complete common 
salt is added, in order to make the soap separate from its 
solution in the mixture of water and glycerine, and a mass of 
genuine " curd soap " is obtained in the solid state above the 
liquid of dilute glycerine. In many soap-boiling establish- 
ments the practice is adopted of allowing the mixture of soap, 
glycerine, and water, which is the immediate result of the boil- 
ing with alkali, to solidify together. This kind of soap can 
obviously be sold at a much lower rate than the genuine pro- 
duct, but is also far less durable. 

In working up the fats for glycerine and stearic acid the 
process is again one of " saponification," that is, splitting up 
an ethereal salt of glycerine into glycerine and the acid com- 
bined with it : 

Fat + water = glycerine + stearic, etc., acid, 

and is now most largely carried on by subjecting the fat to the 
action of superheated steam in the presence of water and a 
small proportion of lime. The product is freed from lime by 
adding the proper amount of sulphuric acid ; and in this way 
the whole of the acids present in the fat are obtained in the 
form of a semi-solid mass, consisting chiefly of palmitic acid, 
C 15 H pl . CO 2 H, stearic acid, C^H^ . CO 2 H, and an unsaturated 
acid (see p. 28), oleic acid, C 17 H 33 . CO^H. Of these the first 
two are solid, while the last is liquid at ordinary temperatures, 
and can be removed by applying hydraulic pressure to the 
mixture of the three acids. The residue is the "stearic acid" 
of commerce, and is largely employed in the manufacture of 
candles. 

The isolation of pure palmitic or stearic acid from this 
mixture is a matter of some difficulty, and can only be accom- 
plished by a tedious process of fractional precipitation and 
crystallisation. The two acids are very similar in their pro- 
perties, but differ in their melting points. 

The process of fractional precipitation is carried out by adding to the 
solution of the two acids in alcohol a quantity of magnesia, only sufficient 
to combine with about a third of the amount of acid present. The pre- 



78 SOAP CHAP, ix 

cipitate is found to contain a much larger proportion of magnesium 
stearate than the original mixture did of stearic acid, while the palmitic 
acid is almost entirely left in solution. 

The salts of palmitic and stearic acids are all devoid of any 
tendency to crystallise. A mixture of the sodium salts con- 
stitutes the essential portion of hard soap, while soft soap 
contains the potassium salts. The lead salts are also im- 
portant ; they are obtained by treating fats or oils with latharge 
(lead oxide) and water, and form what is known as lead 
plaster. 



QUESTIONS ON CHAPTER IX 

1. The analysis of acetic acid leads to the empirical formula CHoO. 
Give reasons for adopting the molecular formula C 2 H 4 O 2 . 

2. Give arguments supporting the structural formula CHa . COgH for 
acetic acid. 

3. Write down the formulas and names of the first four of the series of 
fatty acids. Give three general methods which (with the necessary modi- 
fications) may be applied to the preparation of each of them. 

4. Mention the most convenient ways of obtaining formic and acetic 
acids in quantity. Point out any important difference between the two 
homologous acids. 

5. Give an account of the two isomeric butyric acids, their constitution, 
preparation, and properties. 

6. What is the chemical constitution of fats ? How is soap made from 
them? 



CHAPTER X 
ACETYL CHLORIDE AND ACETIC ANHYDRIDE 

ACETIC acid, CH^COOH, may be regarded as the hydrate of 
the radicle CH 3 CO to which the name "acetyl" is given. 
The chloride and oxide of acetyl are of great importance as 
reagents in the organic laboratory. 

Acetyl Chloride, CH 3 COC1, is prepared by treating acetic 
acid with phosphorus trichloride, and distilling the mixture : 

3CH 3 COOH + PC1 3 = 3CH 3 COC1 + P(OH) 3 . 

Acetic acid. Acetyl chloride. Phosphorous acid. 

It is thus obtained as a colourless volatile liquid, which fumes 
strongly in the air, and combines eagerly with water to form 
hydrochloric and acetic acids : 

CH 3 COiCl + H OH = HC1 + CH 3 COOH. 

Acetyl chloride. Acetic acid. 

Exactly parallel is the action of acetyl chloride upon organic 
alcohols and similar bodies which contain the group hydroxyl, 
OH. Thus with ethyl alcohol it gives ethyl acetate : 

CH 3 COC1 + HOC 2 H 5 = HC1 + CH 3 COOC 2 H 5 . 
Acetyl chloride. Ethyl alcohol. Ethyl acetate. 

Acetic Anhydride, (CH 8 CO) 2 O, acetyl oxide, is obtained 
by the action of acetyl chloride upon dry sodium acetate : 



8o ACETIC ANHYDRIDE CHAP. 

CHgCOONa + CH 3 COC1 == (CH 3 CO) 2 O + NaCl. 
Sodium acetate. Acetyl chloride. Acetic anhydride. 

It is a colourless liquid which boils at 136 C. It is heavier 
than water, sinking to the bottom as an oil, but reacts gradu- 
ally with it forming acetic acid : 

(CH 3 CO) 2 + H 2 = 2CH 3 COOH. 

Acetic anhydride. Acetic acid. 

This change takes place immediately with hot water. 

Acetic anhydride acts similarly to acetyl chloride, but less 
energetically, upon substances which contain the hydroxyl 
group. Both reagents replace the hydrogen of the hydroxyl 
by an acetyl group, CH 3 CO, and both are much used for the 
purpose of determining the number of hydroxyl groups, if any, 
present in the molecule of any compound. 

Both reagents act also upon the SH group of mercaptans, 
and upon the NH 2 or NH group of primary or secondary 
amines. They do not act at all readily upon the hydroxyl 
group in organic acids. 

The number of acetyl groups introduced in place of 
hydrogen atoms by the action of acetyl chloride or acetic 
anhydride can generally be discovered by analysis (combus- 
tion) of the body formed. In some cases it is better to 
proceed by expelling the acetyl groups from their combina- 
tion by boiling the substance with a measured volume of 
standard alkali solution, and determining the amount of 
alkali left in excess of what was needed to neutralise the 
liberated acetic acid. The method may be exemplified by 
a simpler case than any to which it would in practice be 
applied : 



CH 3 COOC 2 H 5 + NaOH = CH 3 COONa + C H r) OH. 

Ethyl acetate. Sodium acetate. Ethyl alcohol. 

Each molecule of alkali spent in neutralising liberated acetic 
acid represents one acetyl group in the body examined. 

EXPT. 17. In a small strong bottle place 25 c. c. of normal sodium 
hydrate solution (40 grams NaOH to the litre), and then run in i c. c. of 
ethyl acetate from a i c.c. pipette. Fit the bottle immediately with an 
indiarubber stopper, firmly tied down. Put the bottle in a beaker of 



AS A REAGENT 81 



water, and heat the water to boiling. Allow to cool. Then wash out 
the contents of the bottle, and determine how much normal sulphuric acid 
(49 grams H 2 SO 4 to the litre) is required to neutralise the sodium 
hydrate left uncombined. 



QUESTIONS ON CHAPTER X 

1. Describe how you would prepare acetic anhydride. 

2. Explain the use of acetyl chloride and acetic anhydride in investi- 
gating the constitution of an organic compound. 

3. Glycerine, C 3 H 5 (OH) 3 , forms a derivative, C 3 H 5 (OC 2 H 3 O) 3 , when 
treated with acetic anhydride. 1.026 gram of this glycerine acetate is 
heated with 25 c.c. of normal sodium hydrate until complete decomposition 
into glycerine and acetic acid is effected. How many c.c. of normal sul- 
phuric acid would be required to neutralise the sodium hydrate left in 
excess ? 



CHAPTER XI 
THE AMINES 

THE amines have for their inorganic type ammonia, NH 3 , 
and are derived from it by replacement of the hydrogen 
atoms with alkyl groups. If only one of the three hydrogens 
is replaced we have a primary amine, such as methylamine, 
NH 9 CHg. When two alkyl groups are introduced we have 
a secondary amine, such as dimethylamine, NH(CH.,) ; while 
in a tertiary amine all three hydrogens are replaced as in 
trimethylamine, N(CH ;3 ).,. 

The power possessed by ammonia of combining with acids 
to form neutral bodies the ammonium salts is retained by 
its alkyl derivatives. Indeed, the amines with which we are 
now concerned, and in which methyl and ethyl groups take the 
place of the hydrogen of the ammonia, are more strongly 
basic than ammonia itself, while resembling it very markedly 
in general chemical behaviour. The lower members of the 
series of amines are gases or volatile liquids smelling strongly 
of ammonia, but differing from it in being inflammable. They 
combine directly with acids to form salts, such as methylamine 
hydrochloride, NH 9 (CH 3 ) . HC1, which resemble the ammonium 
salts in many respects, but differ from them in being soluble 
in alcohol. 

Very important are the double salts which the hydrochlorides of the 
amines form with platinum tetrachloride. These correspond exactly to the 
ammonium compound, (NH^Cl^ . PtCl 4 , frequently used as a means of de- 
tecting and estimating ammonia. Like that body, they are decomposed on 
ignition, leaving a residue of metallic platinum, and in this way it is easy 



CHAP. XI PREPARATION OF AMINES 83 

to determine the percentage of that metal in any of these double salts. 
On examining the formulae of these compounds : 

(NH 3 . HCl) 2 PtCl 4 , (NH 2 CH 3 . HCl) 2 PtCl 4 , 

we see that each salt contains two molecules of ammonia, or an amine, for 
each atom of platinum, and we may write the formula as M 2 H 2 PtCl 6 , 
where M represents the amine. The atomic weight of platinum is 198, 
and if therefore we calculate from the percentage of platinum found by 
ignition how many parts by weight of the double salt contain 198 parts of 
that metal, we have the molecular weight of the salt. On subtracting 
from this 413 (2 + 198 + 213 : H 2 PtCl 6 ), the difference is twice the mole- 
cular weight of the amine. This is an easy and accurate method of deter- 
mining that constant, often the best way of identifying an unknown 
member of the amine series. 

Example. The platinum double salt of an amine gave the following 
results on ignition : .1935 gram yielded .077 gram platinum. Calculate 
the molecular weight of the amine. 

These numbers show that 198 parts of platinum are contained in 

198 x -483.3 parts of the double salt. Therefore 
M = ( 483.3 -4i3). 



and the amine is either dimethylamine, NH(CH 3 ) 2 , or ethylamine, 
NH. 2 C 2 H 5 , both of which have the molecular weight 35. To distinguish 
between these two isomers would require further experiment. See p. 84. 

General Method of Preparation of the Amines. 
The chief method was discovered by Hofmann, and consists 
in heating together ammonia (in alcoholic solution) and an 
alkyl iodide or bromide. By this reaction, which requires a 
temperature of about 100 C. and the use of sealed glass 
tubes such as are employed in Carius's method of analysis 
(see p. 9), a mixture of the iodides of primary, secondary, 
and tertiary amines is obtained, and the following equations 
represent the changes which occur : 



(1) NH 3 + CH 3 I = NH 2 CH 8 .HI. 

Methyl-ammonium iodide. 

(2) NH 8 + 2CH 3 I = NH(CH 3 ) 2 . HI + HI. 

Dimethyl-ammonium iodide. 



(3) NH 3 + 3CH 3 I "= N(CH 3 ) 3 . HI + 2HI. 
Trimethyl-ammonium iodide. 



84 PRIMARY AMINES CHAP. 

At the same time there is produced some amount of a com- 
pound, N(CH 3 ) 4 I, belonging to the class of quaternary am- 
monium salts : 



(4) NH 3 + 4 CH 3 I N(CH 3 ) 4 I + 3 HI. 

Tetra-methyl-ammonium iodide. 

The proportions in which these four substances are produced 
depend on the particular alkyl iodide employed. In any case 
their separation is a matter of considerable labour and diffi- 
culty. 

The quaternary ammonium salt (such as N(CH 3 ) 4 I) is not decomposed 
on boiling with soda or potash, and is thus easily separated from the three 
amines, of which a mixture is liberated on treating with alkali the pro- 
duct obtained by Hofmann's method. The tertiary amine, N(CH 3 ) 3 , is 
alone left unacted upon when this mixture is treated with nitrous acid, 
while the secondary amine is converted into a nitrosamine : 

NH(CH 3 ) 2 + HNO 2 = (CH 3 ). 2 N . NO + H 2 O, 
Dimethylamine. Dimethyl-nitrosamine. 

and the primary amine into an alcohol : 

NH 2 CH 3 +HN0 2 = CH 3 .OH + N 2 + H 2 O. 

Methylamine. Methyl alcohol. 

It is not very difficult thus to isolate the tertiary amine, and from the 
nitrosamine the secondary base can be recovered. The primary amine is, 
however, lost, but there are other much more convenient ways for the 
preparation of the primary amines, so that this disadvantage is not very 
serious. 

The Primary Amines of the type R.NH.,, where R 
represents an alkyl group (CH g , C 2 H 5 , etc.), are more strongly 
basic than ammonia itself. They are produced in Hofmann's 
general reaction, but are difficult to separate from the resulting 
mixture of ammonium salts. Several methods are known by 
which primary amines can be obtained in a state of purity, and 
the most important of these is also due to Hofmann. The 
amide (see p. 88) of an organic acid, on treatment with 
bromine and potash, undergoes a peculiar kind of partial 
oxidation : 

RCONH, + O = R. NH 2 + CO 2 , 
Amide. Amine. 



XI SECONDARY AND TERTIARY AMINES 85 

and the primary amine containing one carbon atom less in the 
molecule is obtained perfectly free from secondary or tertiary 
base. 

In reality an intermediate product R . CONHBr is first formed : 

R. CONH^j + Bn.+ KOH^RCONHBr+KBr+HiA 
and is then decomposed by more potash : 

R . CONHBr + sKOH = RNH 2 + K 2 CO 3 + KBr + H. 2 O. 

The primary amines react very readily with many reagents. 
We can only refer here to the formation of alcohols from them 
by the action of nitrous acid : 



RNH 2 + HNO 2 -R. O 
Primary amine. Alcohol. 

The Secondary Amines, R 2 NH, are best distinguished 
from primary and tertiary amines by the formation of nitros- 
amines, R 2 N . NO, on treatment with nitrous acid : 

R 2 NH + HNO 2 = R 2 N.NO + H 2 O. 

Secondary amine. Nitrosamine. 

These nitrosamines are mostly oils, insoluble in water, which 
regenerate the amine when boiled with concentrated hydro- 
chloric acid : 

R 2 N . NO + HC1 = R 2 NH + NOC1. 

The Tertiary Amines, R 3 N, are still more strongly 
basic than either primary or secondary amines containing the 
same alkyl groups. They are unacted upon by many reagents 
which readily affect the other two classes of amines, such as 
nitrous acid, acetic anhydride, etc., and can thus be easily dis- 
tinguished or separated from them. 

Methylamine, NH CH 3 , is a colourless gas, very soluble 
in water, and possessing a strong smell of ammonia. It is 
combustible. The most convenient method of preparing it in 
the laboratory is by the action of bromine and potash on 
acetamide, or a reaction represented by the following equa- 
tion : 

CH 3 CONH 2 + KOH + Br 2 = CH 3 NH 2 + 2KBr + K 2 CO 3 
Acetamide. Methylamine. 



86 METHYLAMINE 



A substance, CH a CONHBr, is formed as an intermediate product. For 
experimental details a book on Organic Preparations should be con- 
sulted. 

Methylamine is strongly alkaline, and combines readily with 
acids. Its hydrochloride, NH 2 CH 3 .HC1, is very soluble 
in water. The platinum double salt has the formula 
(NH 2 CH 3 . HCl) 2 PtCl 4 , and is only slightly soluble in water, 
from which it crystallises in minute hexagonal plates, whose 
appearance under the microscope is very characteristic. 

Dimethylamine, NH(CH 3 ) 2 , is a volatile liquid boiling 
at 7. Its odour is at once somewhat fishy and strongly 
ammoniacal. It is present in herring-brine, and in large 
quantity in a by-product of the manufacture of beet-sugar. 

Dimethylamine is most conveniently made on a small scale from a 
derivative of aniline. This substance, which is to be described more fully 
in Part II., is a primary amine of the formula C 6 H 5 .NH 2 , and can, by treat- 
ment with methyl chloride, be converted into C 6 H 5 . N(CH3)o, dimethyl- 
aniline. From this, by a peculiar reaction which we cannot here describe 
further, it is possible to prepare pure dimethylamine. 

Trimethylamine, N(CH 3 ) 3 , in the undiluted state smells 
of ammonia, but when largely mixed with air (possibly owing 
to some kind of oxidation) has a strong odour of rotten fish. 
It is present in herring-brine, as also in the by-product, already 
referred to, of the beet-sugar manufacture. This product is 
obtained by the dry distillation of beet-root molasses, and con- 
tains all three methylamines but dimethylamine in largest 
quantity. This mixture has been largely used in the manufac- 
ture of methyl chloride, as all the methylamines when heated 
with concentrated HC1 are converted into ammonia with 
separation of methyl chloride : 

N(CH 3 ) 3 . HC1 + 2HC1 - NH 3 + 3CH 3 C1, 
NH(CH 3 ) 2 . HC1 + HC1 = NH 3 + 2CH 3 C1, 
NH 2 CH 3 . HC1 = NH 3 + CH 3 C1. 

Tetramethyl- ammonium Iodide, N(CH 3 ) 4 I, is the 
chief product of the action of NH 3 on CH 3 I. The radicle 
N(CH 3 ) 4 is so strongly electro-positive that the compound 
N(CH 3 ) 4 I is not decomposed by potash or soda, but on treating 



XI ETHYLAMINE 87 

it with moist silver oxide, the ammonium hydrate N(CH 3 ) 4 OH 
is obtained : 

2N(CH 3 ) 4 I + Ag 2 O -f H 2 O - 2N(CH 3 ) 4 OH + 2AgI. 

The solution of this hydrate is as strongly alkaline as a 
solution of potash or soda, and it is interesting to notice the 
more and more marked alkaline character of the compounds 

NH 3 , NH 2 CH y , NH(CH 3 ) 2 , N(CH 3 ) 3 , N(CH,) 4 OH, 

as the number of alkyl groups attached to the nitrogen atom is 
increased. 

Ethylamine, NH 2 C 2 H 5 , is obtained along with di- and tri- 
ethylamines by heating together in sealed tubes ethyl iodide 
and alcoholic ammonia. Like other primary amines, it is 
decomposed by nitrous acid : 

NH 2 C 2 H 5 + HNO 2 = C 2 H 5 OH + N 2 + H 2 O, 

whereas Diethylamine, NH(C 2 H 5 ) 2 , forms a nitrosamine, 
(C 2 H 5 ) 2 N . NO, and Triethylamine is unaltered. 



QUESTIONS ON CHAPTER XI 

1. What substances are formed when ethyl iodide is heated in sealed 
tubes with an alcoholic solution of ammonia? 

2. How can you distinguish the three classes of amines, primary, 
secondary, and tertiary? 

3. How would you prepare mono-ethylamine ? What is the action 
upon it of hydrochloric and of nitrous acids. 

4. The platinum double salt of an amine gave the following result 
upon analysis : .2055 gram of the double salt left .0680 gram of platinum 
upon ignition. Calculate the molecular weight of the amine. 



CHAPTER XII 
THE AMIDES AND AMIDO-ACIDS 

The Amides, like the amines, are derived from ammonia ; 
but whereas in the amines the hydrogen of the NH 3 is re- 
placed by an alcohol radicle (or " alkyl " group), such as 
methyl, CH 3 , or ethyl, C 2 H 5 , in the amides the substituting 
group is an acid radicle. 

These acid radicles are those which yield acids when com- 
bined with the hydroxyl group OH (see p. 68), the radicle of 
acetic acid being CH 3 . CO, acetyl, that of propionic acid 
being C 2 H 5 . CO, propionyl. Ace/-a.m\de. is the name given 
to the amide CH S CONH 2 , in which one of the three hydrogens 
in the ammonia has been replaced by the acetyl group, whilst 
propion-a.m\&e is the name used for C 2 H 5 CONH 9 . 

Methods of Formation. (i) The first of these is by the 
action of ammonia upon the chloride of the acid radicle ; e.g. 
acetyl chloride yields acetamide : 



CH 3 COC1 + 2NH 3 = CH 3 CONH 2 + NH 4 C1. 

Acetyl chloride. Acetamide. 

This is analogous to the preparation of the amines from 
alkyl iodides (or chlorides) and ammonia ; but the reaction 
occurs far more readily with the acid chlorides, so that it is 
often necessary to employ means to moderate the violence of 
the action. 

(2) The second method only differs from the first in the 
use of an ethereal salt of the acid instead of the acid chloride. 



CHAP, xii ACETAMIDE 



Thus ethyl acetate when heated with ammonia gives acetamide 
and ethyl alcohol : 



CH 3 CO;OEt + H:NH 2 = CH 3 CONH 2 + EtOH. 

Ethyl acetate. Acetamide. 

This method in many cases requires the action of a high 
temperature (150 C.) for several hours, and involves therefore 
the use of closed vessels which can stand very considerable 
pressure. On the small scale, sealed glass tubes similar to 
those used in Carius's method of analysis (p. 9) are employed, 
but unless very well made, these cannot stand the pressure 
of the strong aqueous ammonia at 150 C. 

(3) The third method consists in heating strongly (230 C.) 
the ammonium salt of the acid, when it loses water and is 
converted into the amide : 

CH 3 COONH 4 = CH 3 CONH 2 +H 2 0. 
Ammonium acetate. Acetamide. 

Here again it is generally necessary to heat in closed vessels 
(sealed glass tubes), but the pressures produced are not great, 
and there is little risk of the tubes being burst. 

Acetamide, CH 3 CONH 2 , is best prepared by the third 
method. It is separated from unaltered ammonium acetate by 
distillation, and is obtained as a white solid, usually possessing 
a characteristic odour of mice, but apparently odourless when 
quite pure. It is not markedly acid or basic in behaviour, 
the basic character of the ammonia being removed by the 
introduction of the acid radicle. 

When boiled with much water acetamide is slowly converted 
into ammonium acetate : 

CH 3 CONH 2 + H,O = CH 3 COONH 4 , 
Acetamide. Ammonium acetate. 

and the same change takes place much more readily when an 
acid or alkali is present. 

With an alkali ammonia is evolved ; with an acid the ammonium salt 
of that acid is formed. 



90 GLYCOCOLL CHAP. 



AMIDO-ACIDS 

The amido-acids are derived from acids such as acetic, 
CH 3 . CO H, by introduction of an amido-group, NH 2 , in place 
of one of the hydrogens of the alkyl radicle (in this case 
methyl, CH 3 ) ; thus amido-acetic acid is NH 2 CH 2 . CO 2 H. 

The amido-acids are neutral to litmus, but chemically act 
both as acids and bases. They form salts with copper, silver, 
and other metals on the one hand, while on the other they com- 
bine with strong acids to form salts, such as HC1.NH 2 CH 2 CO 2 H, 
in which the amido-acid plays the part of a substituted 
ammonia. 

Many amido-acids occur in various animal tissues, and may 
be prepared from them. The most important and instructive 
artificial methods for their preparation are the following : 

( i ) By acting with ammonia on a halogen derivative of the 
acid, e.g. monochlor-acetic acid, CH 2 C1 . CO 2 H, yields amido- 
acetic acid, NH 2 CH 2 . CO 2 H : 

CH 2 C1.CO 2 H + 2. NH 3 = NH 2 CH 2 CO 2 H + NH 4 C1. 
Monochlor-acetic acid. Amido-acetic acid. 

In practice the ammonia is obtained from solid ammonium 
carbonate, which is heated with the monochlor-acetic acid. 

Monochlor-acetic acid is formed when chlorine acts upon 
acetic acid : 

CH 3 C0 2 H + Cl, = CH,C1 . CO 2 H + HC1. 

(2) The second method, somewhat more complicated, starts from the 
aldehydes. These are able to combine with ammonium cyanide to form 
compounds, such as CH 3 . CH(NH 2 )(CN) : 

XTtT 

CH 3 . CHO + NH 4 CN = CH 3 . CH< 2 +H 2 O. 

These when treated with dilute acids (see p. 69) yield amido-acids by con- 
version of the CN group into carbo.xyl, CO 2 H. 

Amido- Acetic Acid, NH 2 . CH 2 CO 2 H (Glycocoll), can 
be extracted from glue (therefore from bones) by treatment with 
sulphuric acid ; it is best prepared synthetically from mono- 
chlor-acetic acid by the action of ammonia. It forms a dark- 
blue copper salt (NH 2 CH 2 CO 2 ) 2 Cu, and also a chloride, 



LEUCIN 91 



HC1 . NH.,CH 2 CO 2 H. Glycocoll itself is a white crystalline 
solid, having a sweetish taste, and readily soluble in water. 

Of the more complicated amido-acids we may mention 
Leucin, C 4 H . CHNH 2 . CO 2 H, therefore amido-caproic 
acid, which is one of the most important products of the 
decomposition of albumen, either by putrefaction or by boiling 
with acids or alkalies ; it is also present ready-formed in 
various glands of the body as the pancreas, spleen, etc. 



QUESTIONS ON CHAPTER XII 

i. What substances are formed by the action of ammonia upon (a) 
monochlor-acetic acid, (/>) methyl chloride, (c) acetyl chloride? Give 
equations. 

2. What is the action of dilute hydrochloric acid upon (a) acetamide, 
(b) glycocoll? 

3. Describe the preparation of acetamide and of glycocoll from acetic 
acid. 



CHAPTER XIII 

ALKYL COMPOUNDS OF PHOSPHORUS, ARSENIC, 
SILICON, AND THE METALS 

COMPOUNDS OF PHOSPHORUS 

Phosphines. Phosphine, PH 3 , is much less basic in char- 
acter than ammonia, but is yet capable of combining with 
hydrogen iodide to form the compound phosphonium iodide, 
PH 4 L The organic phosphines, obtained by substituting the 
hydrogen in PH, { by alkyl groups, are stronger bases in pro- 
portion to the number of alkyl groups introduced. 

By the action of alkyl iodides on PH 3 only tertiary phos- 
phines, PR 3 , and phosphonium compounds, PR 4 I, are obtained. 
The primary and secondary bases can, however, be prepared 
by employing, instead of PH.,, a mixture of PH 4 I with oxide of 
zinc. The separation of these bodies is not then difficult, and 
depends on the gradual increase in their basic character 
from primary phosphine to phosphonium compounds : 

Tetra-methyl phosphonium iodide, P(CH 3 ) 4 I, is not decom- 
posed by KOH. 

Tri-methyl phosphonium iodide, P(CH 3 ) 3 .HI, is decom- 
posed by KOH. 

Dimethyl phosphonium iodide, HP(CH 3 )., . HI, is not decom- 
posed by water. 

Methyl phosphonium iodide, H 2 PCH g . HI, is decomposed 
by water. 

The phosphines are gases or volatile liquids, very inflam- 



CHAP, xin THE PHOSPHINES 93 

mable, and possessed of very strong unpleasant odours. Char- 
acteristic of the tertiary phosphines is the readiness with which 
they combine with O, S, C1 2 , etc., to form compounds such as 
P(C 2 H 5 ) 3 O, triethyl-phosphine oxide, in which the radicle 
P(C 2 H 5 ) 3 plays the part of a divalent metal. 

Methyl-phosphine, PH 2 (CH 3 ), is obtained along with 
diethyl-phosphine, PH(CH 3 ) 2 , by heating a mixture of 
phosphonium iodide with methyl iodide and zinc oxide in 
sealed tubes to a temperature of 150 C. : 

2PH 4 I + 2CH 3 I + ZnO = 2PH 2 (CH 3 ) . HI + ZnI 2 + H 2 O, 
Phosphonium Methyl-phosphonium 

iodide. iodide. 

PH 4 I + 2CH 3 I + ZnO = PH(CH 3 ) 2 . H I + ZnI 2 + H 2 O. 
Dimethyl-phosphonium iodide. 

On heating the resulting product with water, the methyl- 
phosphine, PH 2 CH 3 , is liberated, while the dimethyl-phosphine, 
PH(CH 3 ) 2 , remains combined with the hydriodic acid. On 
subsequently boiling with sodium hydrate, the secondary 
phosphine is in turn set free. 

Trimethyl-phosphine, P(CH 3 ) 3 , is prepared by heating 
phosphonium iodide with methyl iodide without the addition 
of zinc oxide : 

PH 4 I + 3CH 3 I = P(CH 3 ) 3 . HI + 3HI. 

Trimethyl-phosphonium iodide. 

The phosphine is obtained when the product is decomposed 
by boiling with potash or soda. 

All three of these methyl-phosphines are very inflammable, 
and exhibit intolerable odours ; they readily combine with 
chlorine, bromine, oxygen, or sulphur to form compounds 
such as P(CH 3 ) 3 or PH(CH 3 ) 2 C1 2 . 



COMPOUNDS OF ARSENIC 

The Arsines are connected with AsH 3 as the amines with 
NH 3 . No primary or secondary arsines (such as AsH 9 CH 3 ) 
are known, but tertiary compounds, As(CH 3 ) 3 , etc., have been 



94 CACODYL COMPOUNDS CHAP. 

prepared. These, like the parent substance AsH 3 , are incapable 
of forming salts. 

The most important organic compounds of arsenic form a 
series in which the radicle As(CH 3 ) 2 corresponds to an atom 
of a monovalent metal, and it has been found convenient to 
give a special name cacodyl to this radicle. 

Cacodyl Oxide, {As(CH 3 ) 2 } 2 O or Cdl 9 O, can be obtained 
by distilling As 2 O 3 with potassium acetate : 

4 CH 3 . C0 2 K + As 2 3 = *> + 2K 2 C * + 2CO 2> 



Potassium acetate. Cacodyl oxide. 

and from this oxide, by the action of acids, various salts can be 
made, amongst them cacodyl chloride, As(CH 3 ) 2 Cl, which 
when reduced with zinc furnishes free cacodyl, As (CH 3 ) 4 . 
All of these compounds are liquids of disgusting odour and 
intensely poisonous properties. They are also very inflammable, 
and their investigation, which was carried out by Bunsen, was 
a matter of great danger and difficulty, 

Of the organic compounds of arsenic, other than the cacodyl 
derivatives, we will mention only one. 

Arsenic Trimethyl, As(CH H ) s , which is obtained by the 
action of methyl iodide upon an alloy of arsenic and sodium. 
It is a colourless volatile liquid of unpleasant smell, readily 
combining with one atom of oxygen or two of chlorine to form 
compounds in which the arsenic is pentavalent, e.g. As(CH 3 ) 3 O, 
As(CH 3 ) 3 Cl 2 . It is not basic in character, and has no 
tendency to combine with acids to form salts in the same 
way as N(CH 3 ) 3 and P(CH 3 ) 3 . 

COMPOUNDS OF SILICON 

The organic derivatives of the tetravalent element silicon 
may be put side by side with other organic compounds in 
which the place of the silicon is taken by carbon, itself a 
tetravalent element ; thus 

Silicon Tetramethyl, Si(CH 3 ) 4 , may be compared with 
the pentane C(CH 3 ) 4 ; it is obtained by treating silicon 
tetrachloride with zinc methyl (see p. 95) : 

SiCl 4 + 2Zn(CH 3 ) 2 = Si(CH 3 ) 4 + 2 ZnCl 2 , 



ZINC METHYL 95 



and is a volatile liquid unaltered by water. The analogy with 
the pentane, C(CH 3 ) 4 , is not merely one of formulae, but is also 
seen to some extent in the chemical behaviour of the two com- 
pounds. This is not surprising in view of the fact that both 
are of similar type, and each contains four methyl groups ; but 
that there exists no complete analogy between the silicon 
derivatives and those of carbon is evident from the great 
differences between the simple corresponding derivatives of the 
two elements; thus silico-chloroform, SiHCl 3 , is a liquid fuming 
in the air and decomposed by water, therefore quite unlike 
chloroform itself, CHC1 3 . 

COMPOUNDS OF THE METALS WITH ALKYL RADICLES 

Many of the metals form alkyl compounds, usually volatile 
liquids which oxidise rapidly or even ignite spontaneously in 
the air ; they are obtained by the action of alkyl iodides upon 
the metals, or upon their alloys with zinc or sodium. 

A second method is to act with zinc methyl (or zinc ethyl, 
etc.) upon the chloride of the metal which is to be converted 
into an alkyl derivative. 

Zinc Methyl, Zn(CH 3 ) 2 , is obtained by the action of 
methyl iodide upon zinc and subsequent distillation. In the 
first place, direct combination of the zinc and methyl iodide 
occurs : 

Zn + CH 3 I = Zn< C j H 3- 

Methyl iodide. Zinc methyl-iodide. 
The compound thus formed is decomposed by further heating : 

/-TT 

2Zn< j 3 = Zn(CH 3 ) 2 + ZnI 2 . 
Zinc methyl-iodide. Zinc methyl. 

The first reaction takes place more readily when the zinc- 
copper couple of Gladstone and Tribe is used instead of zinc 
filings. This couple is merely an intimate mixture of finely 
divided copper and zinc, and can be most readily prepared by 
mixing zinc filings with one-ninth of their weight of copper-dust, 
obtained by reducing powdered copper oxide in a current of 



9 6 



ZINC ETHYL 



CHAP. 



hydrogen. The couple only requires to be heated for a few 
minutes in a flask to make it ready for use. 

EXPT. 18. Mix 90 grams zinc filings with 10 grams of reduced copper. 
Place the mixture in a flask fitted with cork and capillary tube, and heat 
for a few minutes over the bare flame of a Bunsen burner. When cool, 




FIG. 29. - Preparation of Zinc Ethyl. 

add 50 grams methyl iodide, and fit the flask with an inverted condenser 
and a tube for introducing coal-gas (see fig. 29). Heat on the water bath 
for ten hours ; then arrange the condenser for distillation and distil off 
the zinc methyl in a slow current of coal-gas. 

Zinc Ethyl, Zn(C H,).,, is similarly prepared. Both are 
important laboratory reagents for the purpose of introducing 
methyl or ethyl groups in the place of chlorine or other 



XIII LEAD TETRA-ETHYL 97 



element, e.g. a ketone can be made by the action of zinc ethyl 
on acetyl chloride : 

2CH 3 . CO . Cl + Zn(C 2 H 5 ) 2 = 2CH 3 . CO . C 2 H 5 + ZnCl 2 . 
Acetyl chloride. Methyl-ethyl ketone. 

Zinc methyl and ethyl fume in the air and very readily take 
fire, often spontaneously. They are decomposed by water : 



Zn(CH 3 ) 2 + 2H 2 = Zn(OH) 2 

Zinc methyl. Methane. 



and by the halogens : 



Zinc ethyl. Ethyl iodide. 

Mercury Methyl, Hg(CH 3 ) 2 , and Mercury Ethyl, 
Hg(C 2 H 5 ) 2 , are colourless liquids, whose vapours have only 
feeble odour, but are very poisonous ; they are prepared from 
sodium amalgam by the action of methyl or ethyl iodide : 

NaHg + 2CH 3 I 2NaI + Hg(CH 3 ) 2 . 

Methyl iodide. Mercury methyl. 

They are more stable than the zinc compounds, and neither 
take fire in the air nor are decomposed by water. Their 
general chemical behaviour is otherwise similar to that of their 
zinc analogues. 

Alkyl Compounds of other Metals. Many other 
metals also form similar compounds, the most important cases 
being perhaps those of lead and tin. 

By acting on lead chloride, PbCl 2 , with zinc ethyl the sub- 
stance lead tetra-ethyl, Pb(C 2 H 5 ) 4 , is obtained : 

2PbCL> + 2Zn(C,H 5 ) 2 = Pb(C 2 H 5 ) 4 + Pb + 2ZnQ 2 , 

a fact which proves that lead is really a tetravalent element, 
and is thus in complete agreement with the recent discovery 
of the existence of a lead tetrachloride, PbCl 4 . Lead tetra- 
ethyl is an oily liquid which takes fire when heated in contact 
with air. 

In the same way, by acting on stannous chloride, SnCl 2 , with 

H 



98 TIN ETHYL CHAP, xm 

zinc ethyl, we obtain tin tetra-ethyl, Sn(C 9 H 5 ) 4 , in which the 
maximum valency of the metal is exerted : 

2SnCl 2 +2Zn(C 2 H 5 ) 2 - Sn(C 2 H 5 ) 4 + Sn-f 2ZnQ 2 ; 
Zinc ethyl. Tin tetra-ethyl. 

but tin di-ethyl, Sn(C 2 H 5 ) 2 , can be got by treating an alloy 
of tin and sodium with ethyl iodide : 

SnNa + 2C 2 H 5 I = Sn(C 2 H 5 ) 2 + 2 NaI. 
Ethyl iodide. Tin di-ethyl. 

Sn(C 2 H 5 ) 4 is a liquid which can be distilled without decom- 
position, whereas Sn(C 2 H 5 ) 2 decomposes into the tetra-ethyl 
compound and metallic tin. 



QUESTIONS ON CHAPTER XIII 

i. Give the preparation of (a) phosphorium iodide, (b] tetra-methyl 
phosphonium iodide. What is the action of water and of potassium 
hydrate solution upon these two compounds ? 

2. How is free cacodyl obtained ? Give the formulae of cacodyl oxide 
and cacodyl chloride. 

3. Give the preparation of zinc ethyl. What is the action upon it of 
(a) water, (b] chlorine, (c] acetyl chloride ? 

4. What reasons have we for considering lead to be a tetra-valent 
metal ? 



CHAPTER XIV 

GLYCOL AND ITS DERIVATIVES. SUCCINIC, 
MALIC, AND TARTARIC ACIDS 

Glycol, C 2 H 4 (OH) 2 , is a substance containing two 
hydroxyls combined with the divalent radicle, C 2 H 4 , ethylene. 
Each of these hydroxyls behaves similarly to the hydroxyl in 
an alcohol, so that glycol may be termed a dihydric alcohol. 

It is obtained from ethylene bromide, C H 4 Br 2 , by replace- 
ment of the bromine : 



C,H 4 Br, + 2HOH = C 2 H 4 (OH) 2 

Ethylene bromide. Glycol. 

just as the ethyl alcohol can be got from ethyl bromide : 
C 2 H 5 Br + HOH = C 2 H 5 OH + HBr. 

It is necessary when preparing glycol from ethylene bromide 
in this way to heat with a large quantity of water to temper- 
atures of 150 C. or thereabouts; the reaction takes place 
more readily when sodium carbonate is added to the water. 
This method of preparation indicates the constitutional 

CH 2 OH 

formula | for glycol, according to which it may be re- 

CH 2 OH 

garded as a dihydric primary alcohol, and this view is strength- 
ened by consideration of the substance's general chemical 
behaviour. 



ioo GLYCOL A DIHYDRIC ALCOHOL CHAP. 

As a dihydric alcohol glycol reacts with sodium or potas- 
sium to form glycolates analogous to the alcoholates (p. 44) : 

O FT 
C 2 H 4 (OH) 2 + Na = C 2 H 4 <QNa + H ' 

and 

C 2 H 4 (OH) 2 + 2Na = C 2 H 4 (ONa) 2 + H 2 ; 

and ethereal salts of glycol can be obtained by the action on 
it of acids : 

C 2 H 4 (OH) 2 + 2CH 3 CO 2 H = C 2 H 4 (OC0 2 CH 3 ) 2 + 2H 2 O ; 
Glycol. Acetic acid. Ethylene acetate. 

just as ethyl acetate is got from ethyl alcohol and acetic acid, 
so here ethylene acetate is obtained. 

As a dihydric primary alcohol glycol furnishes, when treated 
with oxidising agents, bodies in which the groups CH 2 OH are 
successively oxidised to aldehyde groups CHO, and finally to 
carboxyl groups CO H. The substances thus obtained are 
presently to be considered. 

Glycol is a thick colourless liquid with a sweetish taste. 

The isomeric glycol, ethylidene glycol, CH 3 . CH(OH) 2 , does not seem 
able to exist unless in dilute solution ; instead of this we obtain aldehyde 
CH 3 . CHO when the ethylidene glycol might be expected, e.g. in action 
of water on CH 3 . CHC1 2 . 

Glyoxal, (CHO).,, is the di-aldehyde of glycol, and is 
formed along with other substances in the oxidation of glycol : 

CH 2 OH CHO 

I +0= i +H 2 0. 

CH 2 OH CHO 

Glycol. Glyoxal. 

Like other aldehydes, it readily reduces Fehling's solution or 
ammoniacal silver solution (see p. 62). 

Glycolic Acid, CH 2 (OH) . CO 2 H, is also formed in the 
oxidation of glycol : 

CH.,OH CH 2 OH 

I +0 2 =* I +H,0, 

CH 2 OH CO,H 

Glycol. Glycolic acid. 



xiv OXALIC ACID 



but is better prepared from mono-chloracetic acid by boiling 
with water, to which calcium carbonate in fine powder has 
been added (to combine with the HC1) : 

/~*TT /"*1 /"* /~\ TT T T /"\ J /^T-fr / f*\ tY \ / /" f~\ /T J t - i "^JT /^*1 

t/HgCl . CUgH + H 2 O -~c Lllfl-itry. ,CO 2 H,4-,HC1. 

Monochlor-acetic acid. v J - , o Glvcpjip acid., o ., , - 

Glycolic acid forms white crystals.' As an acid it yields well- 
defined salts, such as silver glycolate, CH 2 OH . CO 2 Ag, while 
as an alcohol it combines with acids to produce ethereal salts. 
Oxalic Acid, (CO 2 H) 2 , is a more completely oxidised pro- 
duct of glycol : 

CH 2 .OH CO.H 



20 9 = | +2H 2 0. 

Glycol. Oxalic acid. 



CH 2 . OH CO 2 H 



It is an important acid, the starting-point of a series of organic 
dibasic acids. Oxalic acid is found in many plants, especially 
the varieties of Oxalis, and can be prepared artificially in several 
ways, of which three further ones (in addition to the oxidation 
of glycol) may be mentioned : 

(1) Carbon dioxide when passed over heated metallic sodium 
combines with it to form sodium oxalate : 

2CO 2 + 2Na = C 2 4 Na 2 . 

Sodium oxalate. 

(2) Sodium formate when strongly heated evolves hydrogen 
and yields sodium oxalate : 

2H.C0 2 Na = H 2 + C 2 4 Na 2 
Sodium formate. Sodium oxalate. 

(3) An important practical method for the manufacture of 
oxalic acid is the action of caustic alkalies upon cellulose. 
Sawdust (the form of cellulose generally used) is mixed into a 
paste with a strong solution of potash, and then heated on iron 
plates. The product is extracted with water, and the oxalic 
acid separated by precipitation as calcium oxalate. 

Oxalic acid forms crystals which contain two molecules of 



SUCCINIC ACID 



water of crystallisation. When heated the crystals lose water, 
and then decompose into formic acid and carbon dioxide : 



? ,, = + . 2 . 

Oxalic* aei(5/ 1 Formic acid. 



Oxalic acid wlier. heated with strung sulphuric acid does not 
blacken^ but is 'decomposed' A>'tb evolution of the two oxides 
of carbon in equal volumes : 

C 2 O 4 H 2 =CO + C0 2 + H 2 0. 

Oxalic acid is a stronger acid than acetic, and being a dibasic 
acid forms two series of stable salts. 

Potassium Oxalate, C O 4 K 2 , is used in preparing the 
" ferrous oxalate developer," largely employed in photography. 

Potassium Hydrogen Oxalate, C 9 O 4 KH, along with 
free oxalic acid, composes the "salts of lemon" used for re- 
moving ink-stains from cloth. 

Ammonium Oxalate, C 2 O 4 (NH 4 ) , is used as a reagent 
in the laboratory. 

SUCCINIC, MALIC, AND TARTARIC ACIDS 

Succinic Acid, C 4 H 6 O 4 , was first obtained by distillation 
of amber, and this is still the way prescribed for its preparation 
in the British Pharmacopoeia. It is also present in some other 
resins and in lignite. The artificial methods for making the 
acid and its reactions are best represented by the constitutional 
formula given below ; the chief of these methods are : 

(1) Ethylene cyanide (from ethylene bromide and AgCN), 
when boiled with dilute acids or alkalies, yields succinic acid : 

CH 2 . CN CH 2 . CO 2 H 

I + 4 H 2 = I +2NH 3 . 

CH 2 .CN CH 2 .CO 2 H 

Ethylene cyanide. Succinic acid. 

(2) Succinic acid is also obtained by the reduction of malic 
acid, which can itself be similarly obtained from tartaric acid : 

C 4 H 6 6 O C 4 H 6 5 . 

Tartaric acid. Malic acid. 



xiv MALIC ACID 103 

C 4 H C 5 O C 4 H 6 4 . 

Malic acid. Succinic acid. 

The reduction can be effected by heating with hydriodic acid in sealed 
tubes. 

Succinic acid forms colourless crystals, soluble in water, 
and possessing an unpleasant taste. 

Malic Acid, C 4 H 6 O 5 , occurs in the juice of apples and of 
many other fruits. Its close relation to succinic acid is indi- 
cated by the reaction, above referred to, by which that acid is 
obtained by the reduction of malic acid, and the exact char- 
acter of the relation is made clear by the following method of 
preparation : 

(1) Malic acid is produced when monobrom-succinic acid 
is treated with silver oxide and water : 

CHBr . CO.,H CH(OH) . CO 2 H 

I + AgOH = | +AgBr. 

CH 2 . C0 2 H CH 2 . CO 2 H 

Monobrom-succinic Malic acid, 

acid. 

Malic acid is therefore monohydroxy-succinic acid. 

(2) Malic acid is formed by the partial reduction of tartaric 
acid : 

C e H 4 6 .. Q _ C(5 H 4 5 . 

Tartaric acid. Malic acid. 

Malic acid forms deliquescent needles. It is a somewhat 
stronger acid than succinic, and forms several well-crystallised 
salts. Very important is the existence of three isomeric forms 
of malic acid which differ chiefly in their action upon polarised 
light. One form, the ordinary one obtained from berries, 
rotates the plane of polarisation to the left ; a second form, 
prepared from dextro-tartaric acid, rotates the plane of polar- 
isation to the right ; while the third form, obtained synthetic- 
ally, is inactive. The fuller consideration of this case of 
isomerism is deferred until Part II. of this book. 

Tartaric Acid, C 4 H 6 O C , is present in the juice of many 
fruits, especially in that of grapes ; practically the only source 
of the acid is the . " argol," an impure potassium tartrate, de- 



io 4 TARTARIC ACID CHAP. 

posited during the fermentation of grape-juice. The constitu- 
tional formula of the acid is evident from its relation to malic 
and succinic acids (into which it is in turn converted by re- 
duction), and from the following synthetical methods of pre- 
paration : 

(i) Dibrom-succinic acid when boiled with water and silver 
oxide yields tartaric acid : 

CHBr . CO 2 H CH(OH)CO 2 H 

1 +2AgOH= | +2AgBr; 

CHBr . CO 2 H CH(OH)CO 2 H 

Dibrom-succinic Tartaric acid, 

acid. 

tartaric acid is accordingly dihydroxy-succinic acid. 

Tartaric acid furnishes another instance of the existence of 
isomers inexplicable by the theory hitherto alone employed for 
the explanation of cases of isomerism. The isomers again 
differ, just as was the case with the malic acids, chiefly in their 
action upon polarised light. Tartaric acid furnishes four such 
isomers, of which one is dextro-rotatory (rotates the plane of 
polarisation to the right), another is laevo-rotatory, while the 
other two are inactive. We shall here consider only the com- 
mon variety, dextro-tartaric acid, leaving the others to be dis- 
cussed in Part II. 

Dextro-tartaric acid is the tartaric acid of the shops. It is 
prepared from argol by conversion into calcium tartrate (treat- 
ment with milk of lime), and subsequent liberation of the free 
acid by addition of sulphuric acid. It is purified by recrystal- 
lisation, and forms large prismatic crystals which are readily 
soluble in water. The solution rotates the plane of polarisa- 
tion of light to the right. It is a dibasic acid, and the follow- 
ing salts formed by it are of importance : 

Potassium Hydrogen Tartrate, C 4 O 6 H 5 K, is the 
"cream of tartar" of the druggist, and is obtained by purify- 
ing the "argol" deposited in the fermentation of grape-juice. 
It is only slightly soluble in water, and hence sodium hydrogen 
tartrate will precipitate it from solutions of potassium salts, 
unless very dilute ; this reaction is sometimes used as a test 
for the presence of potassium in place of the more expensive 
method by means of platinic chloride. 



xiv THE TARTRATES 105 



Potassium Sodium Tartrate, C 4 O 6 H 4 KNa, is known 
as " Rochelle salt," and is prepared by mixing solutions of 
sodium hydrate and cream of tartar. 

Tartar Emetic is the name of a substance which is ob- 
tained by boiling cream of tartar and oxide of antimony with 
water. Its constitution is generally supposed to be repre- 
sented by the formula C 4 O 6 H 4 (SbO)K, according to which 
one hydrogen atom of the tartaric acid is replaced by the 
monovalent group (Sb'"O), antimonyl. Tartar emetic is then 
to be termed potassium antimonyl tartrate. 

The same group, SbO, exists in the compound which is obtained as a 
white precipitate when water is added to a solution of antimony chloride. 
This precipitate has the composition SbOCl, and is produced according to 
the equation 

SbCl 3 + H 2 = SbOCl + 2HC1. 



QUESTIONS ON CHAPTER XIV 

1. By what reactions would you proceed to prepare glycol from ethyl 
alcohol ? 

2. Show by its reactions that glycol behaves as a dihydric primary 
alcohol. 

3. Give two ways by which oxalic acid can be synthesised from its 
elements. Describe the commercial process for the manufacture ef the 
acid. 

4. What is the relation between succinic, malic, and tartaric acids? 
How can you pass from each of them to the others ? 

5. Write down the formulae of (a) salts of lemon, (b] tartar emetic, (c] 
cream of tartar, (d) succinic acid. 



CHAPTER XV 
LACTIC AND CITRIC ACIDS 

Lactic Acid is a substance present in sour milk which, when 
isolated and examined as to its chemical relationship, is found 
to be predominantly an acid, but also to possess some of the 
properties of alcohols. Its empirical formula is CH^O as 
determined by analysis, and as the acid cannot be vaporised 
without decomposition, we are unable to ascertain its mole- 
cular weight by a vapour density determination. It has 
recently become possible to employ other means for finding 
the molecular weight of the acid itself, but a little study of the 
compounds of lactic acid enables us to discover its molecular, 
and then its constitutional formula. 

Lactic acid forms only one sodium salt, sodium lactate, 
whose analysis indicates the formula C 3 H 5 NaO. ; , and therefore 
the molecular formula C 3 H 6 O 3 for the acid (this agrees with 
the vapour density of ethyl lactate C 3 H 5 O S . C 2 H 5 ). Lactic 
acid is therefore a monobasic-acid, and contains one carboxyl 
group, CO 2 H. But in this sodium salt there is yet left a 
hydrogen atom which can with some little difficulty be replaced 
by sodium, and behaves like the hydrogen atom of an alcoholic 
hydroxyl. Lactic acid is therefore seen to contain the group 
OH also. 

Lactic acid, CgH^O.j, may therefore be written C. 2 H 4 (OH) 
(CO 2 H), and the only question left to solve is whether the OH 
and the CO.,H are connected to the same or to different 
carbon atoms, whether it is 

CH 2 (OH) CH 3 

(a) | or (b) | 

CH 2 .C0 2 H CH <0 2 H 



LACTIC ACID 107 



Now lactic acid can be got from aldehyde, CH 3 . CHO, by 
adding to it HCN, and boiling the product with hydrochloric 
acid (see pp. 64 and 69) : 

CH 3 . CHO > CH 3 . CH< -> CH 3 . CH<^ R . 

Aldehyde. Lactic acid. 

and we are thus led to assign to lactic acid the formula ($) of 
the two given above. 

The lactic acid in sour milk is produced from the lactose or 
milk - sugar present in milk by the action of a particular 
ferment. Cane-sugar, starch, and other carbohydrates also 
yield lactic acid under the influence of the same ferment : 

C 12 H 2211 + H 2 = 4C 8 H 6 8 . 
Milk or cane sugar. Lactic acid. 

In preparing lactic acid the following is a good method of 
procedure : 

One kilogram of cane-sugar is dissolved along with about 5 grams of 
tartaric acid in 3^ litres of water ; after a few days some rotten cheese 
(30 grams) is rubbed into a paste with sour milk (i^ litres), and added 
to the solution with 400 grams of zinc oxide. The whole is left to 
ferment in a warm place for a week or ten days. Then the mixture is 
heated to boiling, filtered, and the filtrate evaporated. Crystals of zinc 
lactate separate out on cooling ; they are collected and dissolved in water, 
and the zinc removed by passing H^S. The zinc sulphide is removed by 
filtration, and the solution of lactic acid evaporated on the water bath. 

Lactic acid thus obtained is a thick syrupy liquid. The sodium 
salt has the formula C 3 H 5 NaO 3 , but when this is heated with 
metallic sodium, a second atom of the metal is introduced in 
place of the alcoholic hydrogen, and a substance of the 
formula C 3 H 4 Na ;i O 3 is obtained. 

Lactic acid can also be prepared by several synthetical methods : 

(1) From aldehyde CH :J . CHO (see above). 

(2) From the bromopropionic acid, CHs . CH 2 Br . CO-jH, and potash. 

Great interest attaches to the existence of an isomeric para- 
lactic acid which is present in the juice of meat. This 



io8 CITRIC ACID CHAP. 

behaves exactly like ordinary lactic acid in nearly every other 
respect, but differs from it in being able to rotate the plane of 
polarisation of light. This is connected by Van't Hoff, with 
the fact that one carbon atom in lactic acid is " asymmetric," 
that is, connected to four dissimilar radicles. For a fuller 
account of this theory, see the second part of this book. 

There is also known another acid, hydracrylic, which is isomeric 
with lactic acid. The formula (a) given above (p. 106) is indicated for it 
by its formation from ethylene as indicated below : 



CHoOH CH 2 OH CH 2 OH 

CH 2 CHoCl CH 2 . CN CH 2 . COoH. 

(+HC10). (Action of KCN). (Boiling with HC1). 

Citric Acid is found in lemons, currants, cranberries, and 
many other sour fruits. It is prepared commercially from lemon 
or lime-juice by means of the calcium salt. 

Its formula is found by analysis to be C 6 H 8 O 7> and it 
behaves as a tribasic acid. It contains, therefore, three 
carboxyl groups, and forms salts, such as C 6 H 6 (XK 3 , and 
ethereal salts, such as C 6 H 5 O 7 (C 2 H 5 ) 8 . In these the action of 
acetyl chloride proves the existence of an hydroxyl group (see 
p. 79). The acid therefore contains one OH and three CO 2 H 
group, and its formula may be written C 3 H 4 (OH)(CO 2 H) 3 . 

Citric acid crystallises in large prisms. As a tribasic acid 
it forms three series of salts, the three potassium salts being 
C 6 H 7 7 K, CgH 6 O 7 K 2 , and C 6 H 5 O 7 K 3 . 

Calcium citrate, (C 6 H 5 O 7 ) 2 Ca 3 , is remarkable as being less 
soluble in hot water than in cold, a property made use of in 
testing for citric acid. 

EXPT. 19. To some solution of citric acid in a test tube add lime 
water until the reaction is slightly alkaline. No precipitate is formed in 
the cold, but a white precipitate of calcium citrate appears on boiling. 



QUESTIONS ON CHAPTER XV 

i. How can lactic acid be obtained from sugar? Why is its formula 
written CsHgOg and not CH 2 O ? 



CITRIC ACID I09 



2. Mention some other substances which have the same percentage 
composition as lactic acid. How could you distinguish them ? 

3. What happens when (a) milk turns sour, (b] butter turns rancid, (c) 
wine goes sour ? 

4. Write down the formulae of (a) the three potassium citrates, (d] zinc 
lactate. 



CHAPTER XVI 



THE ALLYL COMPOUNDS 



THE allyl compounds may be regarded as being derived from 
the hydrocarbon propylene, C 3 H G , and their starting-point 
allyl alcohol stands to propylene in the same relation as 
ethyl alcohol does to ethane. 




FIG. 30. Preparation of Allyl Alcohol. 

Propylene has the formula CH 2 : CH . CH 3 , and from this 
three alcohols might be derived : 

1. CH(OH) : CH . CH 3 , a secondary alcohol, 

2. CH 2 : C(OH) . CH ;i , a tertiary 

3. CH 2 : CH . CH,(OH), a primary 



CHAP, xvi ALLYL ALCOHOL 



Of these, the third formula represents allyl alcohol, which 
in many respects behaves like any other primary alcohol, 
but differs from methyl alcohol and its homologues in being 
unsaturated (see p. 28). On the one hand, as a primary 
alcohol, it yields an aldehyde and then an acid when oxidised, 
while as an unsaturated compound it is able to combine 
directly with chlorine or bromine. 

Allyl Alcohol, C 3 H 5 .OH, is obtained by distilling a 
mixture of glycerine, C 3 H 5 (OH) 3 , with formic acid (oxalic acid 
may be substituted for this, but as it decomposes under these 
conditions into formic acid and CO 2 , the reaction is practically 
the same). The formic acid is oxidised to CO 2 and water : 

C 3 H 5 (OH) 3 + HCO 2 H = C 3 H 5 . OH + CO 2 +2H 2 O. 

Glycerine. Formic acid. Allyl alcohol. 

The following is the usual method for preparing allyl 
alcohol : 

Four parts of glycerine and one of crystallised oxalic acid are placed in 
a retort and gradually heated. At first much CO 2 is evolved, and dilute 
formic acid distils over. When the temperature of the mixture reaches 
190 the receiver is changed, and impure allyl alcohol is obtained as the 
distillate. This is purified by fractional distillation, and freed from water 
by treatment with anhydrous baryta. Pure allyl alcohol boils at 96. 

Allyl alcohol is a colourless liquid which, like all the allyl 
compounds, has an irritating, unpleasant smell. As an un- 
saturated body it combines directly with C1 or Br 9 to form 
derivatives of propyl alcohol : 

C 3 H 5 . OH + Br 2 = C 3 H 5 Br . OH. 

Allyl alcohol. Dibromo-propyl 

alcohol. 

As a primary alcohol allyl alcohol yields, when carefully 
oxidised, first an aldehyde allyl aldehyde or acrolein and 
then an acid acrylic acid : 

CH 2 : CH . CH 2 OH + O = CH 2 : CH . CHO + H 2 O 
Allyl alcohol. Acrolein. 

CH 2 : CH . CHO + O = CH 2 : CH . CO 2 H. 

Acrolein. Acrylic acid. 



ALLYL IODIDE 



Acrolein, C 2 H 3 . CHO, is also produced when glycerine or 
fats (which are compounds of glycerine) are heated to decom- 
position. It is best obtained by distilling glycerine to which 
twice its weight of KHSO 4 has been added : 

C 3 H & (OH) 3 = C 2 H 3 . CHO + 2H 2 O. 
Glycerine. Acrolein. 

Acrolein is a volatile liquid with an extremely irritating 
odour. Its chemical behaviour is fairly summed up in the 
statement that it is an unsaturated aldehyde. 

Acrylic Acid, C 9 H . CO 9 H, is best obtained from acrolein 
by boiling it with water and oxide of silver : 

C 2 H 3 . CHO + Ag,0 = C 2 H 3 , C0 2 H + 2 Ag. 
Acrolein. Acrylic acid. 

Acrylic is a well-marked acid. It is of course an un- 
saturated body and, as such, combines readily with chlorine, 
bromine, etc., to form derivatives of propionic acid : 

C 2 H 3 . CO 2 H + Br 2 = C 2 H 3 Br 2 . CO 2 H. 

Acrylic acid. Dibrom-propionic acid. 

It is a liquid similar to acetic acid in appearance and smell. 

Allyl alcohol forms ethereal salts with acids, but of these 
the following are alone of sufficient importance to be mentioned 
here : 

Allyl Iodide, C 3 H 5 I, is a colourless liquid, which can be 
obtained from the alcohol by the action of H I : 



C 3 H 5 .OH + HI - C 3 H 5 I + H 2 0, 

Allyl alcohol. Allyl iodide. 

or more conveniently from glycerine by the action of phos- 
phorus and iodine, a reaction which may be supposed to occur 
in the two following stages : 

C 3 H 5 (OH), + PI 3 = C 3 H 5 I 3 + H 3 P0 3 

Glycerine. Glyceryl iodide. 

C 3 H 5 I 3 C 3 H 5 I + I 2 

Glyceryl iodide. Allyl iodide. 



XVI 



OIL OF GARLIC 



The experimental details of the second method of prepara- 
tion are as follows : 

A quantity of glycerine is freed from water by heating in an open dish 
for at least half an hour to such a temperature that the liquid is near its 
boiling point and evolves abundant fumes. The anhydrous glycerine must 
be placed in a well -stoppered bottle while still warm. 

A tubulated retort is fitted with a cork and connected with an 
apparatus for generating CO 2 , so that a slow current of that gas can be 
passed through the retort during the whole experiment ; 150 grams of the 
anhydrous glycerine is then placed in the retort, along with 100 grams of 
powdered iodine ; 60 grams of yellow phosphorus is weighed out and cut 
into small pieces, which are taken up one by one at the end of a knife, 
dried between filter-paper, and introduced through the tubulus into the 
retort. A violent reaction occurs as each piece of phosphorus is added, 
and impure allyl iodide distils over ; it is washed with a solution of soda, 
separated by means of a tap-funnel from the soda, dried by contact with 
a few pieces of fused calcium chloride, .and re-distilled. Pure allyl iodide 
boils at 101 C. 




FIG. 31. Preparation of Allyl Iodide. 



Allyl Sulphide, (C 3 H 5 ).,S, is the chief constituent of oil of 
garlic, which is obtained by distilling garlic with steam, and 
gives that plant its characteristic smell and taste. It can be 
prepared artificially by the action of allyl iodide upon 
potassium sulphide : 

K 2 S + 2C 3 H 5 I _ 2KI + (C 3 H 6 ) 2 S. 
Allyl iodide. Allyl sulphide. 

Allyl Iso-thiocyanate, C 3 H 5 . NCS, is present in oil of 
i 



ii4 OIL OF MUSTARD CHAP, xvi 

mustard, obtained by distillation of mustard seeds. It can be 
prepared artificially by the action of allyl iodide upon potassium 
thiocyanate KCNS : 

KCNS + C 3 H 5 I = KI + C 3 H 5 . NCS. 
Oil of mustard. 

It is a liquid with the strong penetrating odour and taste of 
the natural "oil of mustard." 



QUESTIONS ON CHAPTER XVI 

1. How can allyl alcohol he obtained from glycerine? What reactions 
stamp allyl alcohol as an unsaturated compound ? 

2. By what reactions is it possible to prepare acrylic acid from 
glycerine ? 

3. What reasons have we for regarding allyl alcohol as an unsaturated 
primary alcohol ? 

4. Give the formulae and systematic names cf (a) oil of mustard, (l>] 
oil of garlic. How can each be prepared artificially ? 



CHAPTER XVII 
GLYCERINE AND ITS COMPOUNDS 

Glycerine is contained in fats and fatty oils combined 
with organic acids in the form of ethereal salts. When these 
compounds are heated with alkalies in the preparation of soap 
the glycerine is set free, and when the soap is separated by 
addition of salt from the liquor in which the glycerine is 
contained, this latter can be easily recovered. In many soaps 
now manufactured the water and glycerine are not separated 
from the true soap, but the whole is allowed to cool, when it 
solidifies to a mass naturally less firm than a pure soap and 
less durable, but pleasanter to use and far more profitable to 
manufacture. Soap manufacture is accordingly not a very 
important source of glycerine ; far more is obtained in the 
preparation of stearic acid for candles. The best process 
conducts the saponification of the fat by means of superheated 
steam with the use of a small proportion of lime. Stearic 
acid (mixed with other fatty acids) and glycerine are 
produced : 

Fat + Water = Stearic Acid + Glycerine. 

Glycerine is found by analysis to have the formula C 3 H g O 3 . 
It behaves as a trihydric alcohol, and yields ethereal salts 
with various acids, in which three acid groups are introduced 
into the glycerine molecule ; this leads us to write the formula 
as C 3 H 5 (OH) 3 . 

Glycerine when perfectly pure forms colourless crystals 
which melt at 17 G, about the ordinary temperature of a 
room. It is, however, very hygroscopic, and a trace of water 



n6 GLYCERINE CHAP. 

is sufficient to convert it into a syrupy liquid ; this has a 
sweet taste, and is sometimes added to wine to give it body 
and sweetness. It is also used as a cosmetic and for keeping 
leather articles soft and pliable ; it is the starting-point in the 
manufacture of nitro-glycerine and dynamite. 

When distilled under the ordinary pressure, glycerine is 
largely decomposed, acrolein being one of the principal 
products : 

C 3 H 5 (OH) 3 = C,H 4 + 2H 2 0, 
Glycerine. Acrolein. 

but under diminished pressure or in a current of superheated 
steam it can be distilled without decomposition. 

Glycerine can be prepared synthetically from allyl tribromide 
CH 2 Br. CHBr.CH 2 Br, just as glycol from CH 2 Br . CH 2 Br and ethyl 
alcohol from C 2 H 5 Br ; its' constitutional formula is CH 2 (OH) . CH(OH) . 
CH 2 (OH), and when oxidised it yields first glyceric and then tartronic 
acids : 

CH 2 . OH CO 2 H CO 2 H 

I I 

CH . OH > CH . OH 

I I 

CH 2 . OH CH 2 . OH 

Glyceric acid. 

The most important compound of glycerine is the nitrate, 
generally known as nitro-glycerine; this is obtained by the 
action upon glycerine of a mixture of concentrated sulphuric 
and nitric acids ; the product is added to water when the 
nitro-glycerine separates as an oil, which has to be thoroughly 
washed before being stored or worked up into dynamite, as 
otherwise the traces of acid left in the oil render it liable to 
explode on very slight provocation. 

Nitro-glycerine has the constitution C 8 H & (NO 3 ) H ; it is the 
nitrate of the tri-valent radicle C 3 H 5 (glyceryl), and its 
formation is represented by the equation : 

C 3 H 5 (OH) 3 + 3 HN0 3 = C 3 H 5 (N0 8 ) 3 + 3 H 2 O. 
Glycerine. Glyceryl nitrate 

or nitro-glycerine. 

The sulphuric acid used in its manufacture merely aids the 




xvii NITROGLYCERINE 117 

action of the nitric acid by combining with the water 
produced. 

By boiling with water and an alkali, nitro-glycerine (like 
other ethereal salts) is converted into the alcohol and acid 
from which it was formed : 

C 3 H 5 (N0 3 ) 3 + 3KOH = C 3 H 5 (OH) 3 + 3KNO 3 . 

Nitro-glycerine. Glycerine. 

Nitro-glycerine, like most other similar compounds (see gun- 
cotton, p. 126), decomposes very readily when heated or 
exposed to sudden shock. The substance contains more 
oxygen than is required to burn up the carbon and hydrogen 
contained in it : 

2C 3 H 5 (N0 3 ) 3 = 6C0 2 + 5H 2 + 3 N 2 + O ; 

hence no oxygen from outside is required, and nitro-glycerine 
can burn or explode when cut off from contact with air. 
Moreover, the oxygen with which the carbon and hydrogen 
combine is present in the same molecule with them, and in 
consequence the change represented in the above equation 
takes place with extreme rapidity and suddenness when once 
started. The heat produced in the reaction is therefore also 
very suddenly developed, and the destructive power of nitro- 
glycerine is far in excess of that of a quantity of gunpowder, 
which in burning would give out the same total amount of 
heat. 

Nitro-glycerine is a very dangerous substance to handle, as 
even when very carefully prepared it requires only a slight 
shock to make it explode. This disadvantage is largely 
removed in dynamite, which is a mixture of nitro-glycerine 
with very fine siliceous earth. More recently this has been 
almost superseded by blasting- gelatine, a jelly-like solid 
obtained by dissolving gun-cotton in nitro-glycerine, which is 
even safer to handle, and can, by varying the proportions, be 
made in different grades of violence according to the purpose 
intended. By addition of camphor, or other appropriate 
substance to this mixture, a material is obtained of sufficiently 
moderate explosive power to be used in ordinary firearms 
the modern smokeless powder. 



n8 THE CHLORHYDRINS CHAP, xvn 

Of some theoretical interest are the chlorhydrins, 
compounds obtained from glycerine by the action of HC1 or 
of PC1 5 ; in these the hydroxyl groups of the C.,H 5 (OH) 3 are 
more or less completely replaced by chlorine ; they are 
ethereal salts of the trihydric alcohol glycerine and hydro- 
chloric acid. 

There are two mono-chlorhydrins, (a) CH 2 (OH) . CH(OH) . CH 2 C1 
and (/3) CH 2 (OH). CHC1 . CH 2 (OH), of which the first is obtained by 
the action of HC1 on glycerine. 

Of the two di-chlorhydrins one has the formula CH 2 C1 . CH(OH) . 
CH.,C1, and is obtained by the action of HC1 on glycerine ; the other one 
is CH 2 C1 . CHC1 . CH 2 (OH), and is the addition product of allyl alcohol 
(see p. in) and Clo. 

Trichlorhydrin, C 3 H 5 C1 3 (CH 2 C1 . CHC1 . CH 2 C1), is the 
final result of the action of HC1 (or better, PC1 5 ) upon 
glycerine ; it is one of the five possible isomeric trichloro- 
propanes, and is a liquid with a smell like chloroform. 

QUESTIONS ON CHAPTER XVII 

1. What is the chemical constitution of fat? How are the fats worked 
up in the manufacture of glycerine ? 

2. What happens to glycerine (a) when heated in the air, (l>) when 
treated with a mixture of nitric and sulphuric acids? 

3. What chemical changes occur when nitro-glycerine (a) explodes, 
(b) is heated gently with dilute caustic soda? 

4. How is the dangerous violence of nitro-glycerine modified in several 
modern explosives ? 



CHAPTER XVIII 
THE CARBOHYDRATES 

The Carbohydrates are a class of bodies of extreme 
importance, especially in plant life ; not only are they the 
chief constituents of all plants, but they are also present in 
many animal tissues. 

All the carbohydrates are composed of the three elements, 
carbon, hydrogen, and oxygen, and of these elements the two 
latter are present in the proportion in which they combine to 
form water ; their number is very large, and their accurate 
investigation is surrounded with such difficulties that only 
in recent years has much real knowledge of their chemistry 
been gained. 

The chief difficulty was that no reagent was known with which the 
carbohydrates would yield well-characterised products ; the compounds 
which they, as aldehyde and ketone-alcohols, form with phenyl-hydrazine 
can, however, for the most part be distinctly and easily recognised, and it 
is by their help that much of our recent knowledge in this field has been 
won. 

THE GLUCOSES 

The first family of the carbohydrates to be considered is 
the Glucoses ; these have the empirical formula CH 2 O, and 
most of them have the molecular formula C 6 H 12 O 6 , as has 
been proved by the application of Raoult's method for the 
determination of molecular weights (see p. 16). 

There are, however, bodies known of the molecular formulae C 5 HioO 5 
(arabinose) and C 7 H 14 O 7 (heptose), which are best included in this group. 



THE GLUCOSES 



The glucoses have a sweet taste, though less sweet than 
cane-sugar ; they are easily soluble in water, and at once 
reduce Fehling's solution (p. 62) ; they also readily ferment 
under the influence of yeast. The various glucoses differ 
from one another in crystalline form, in their solubility in 
various reagents, and in other properties ; their isomerism 
cannot be satisfactorily accounted for by the ordinary theories 
of the structure of carbon compounds, and its fuller explana- 
tion is undoubtedly to be found in the application of Van't 
Hoff's theory of the tetrahedral carbon atom (see p. 108). 
In view of this, special importance is attached to the varying 
power of the different glucoses to rotate the plane of polarisa- 
tion of light. 

Chemically the glucoses are, in the first place, alcohols ; 
they (at least those of the formula C 6 H 12 O 6 ) contain five OH 
groups (each of which can be replaced by acetyl upon treat- 
ment with acetic anhydride, see p. 79). In the second place, 
the reducing power of the glucoses leads to the conclusion that 
they are aldehydes or ketones as well as alcohols ; they contain 
therefore five OH groups and one CHO or CO group. 

This CHO or CO group can be converted by reduction into 
a sixth alcohol group CH 2 OH or CHOH. We thus obtain 
by reduction of a glucose a hexhydric alcohol, which may be 
regarded as the parent of that particular glucose. The alcohol 
obtained has in each case the formula C ( .H 8 (OH) 6 , but while 
two of the glucoses (dextrose and levulose) yield mannitol, a 
third (galactose) yields an isomer of that substance, viz. dulcitol. 

Mannitol is also contained in manna, and is present in many plants, 
as is also the isomeric dulcitol. Both are derivatives of normal hexane, 
C 6 H ]4 , and their isomerism is to be explained by Van't Hoff's theory of 
the tetrahedral carbon atom. 

Dextrose, C H 12 O 6 , is present in many fruits, and also in 
honey. It rotates the plane of polarisation to the right. 

Dextrose is formed in the hydrolysis (splitting up of com- 
pounds by addition of water) of many other carbohydrates. The 
hydrolysis is effected by heating with water under pressure, or 
more easily by boiling with a dilute mineral acid. Thus we 
have the following reactions : 

Cane-sugar + H 2 O = Dextrose + Levulose 
Starch + HJ3 = Dextrose 



DEXTROSE AND LEVULOSE 



The dextrose of commerce is prepared by treating starch with boiling 
dilute sulphuric acid under pressure. The solution is freed from sulphuric 
acid by adding calcium carbonate and filtering from the calcium sulphate ; 
it is then evaporated, and leaves a tough non-crystalline mass. 

Levulose, C 6 H 12 O 6 , occurs along with dextrose in fruits 
and honey, and the "invert-sugar" obtained by the action of 
dilute acids on cane-sugar is a mixture of equal parts of dex- 
trose and levulose. 

Levulose rotates the plane of polarisation more strongly 
than dextrose, but to the left. 

The dextrose and levulose which are present together in honey and in 
invert-sugar can be partially separated by washing the mixture with cold 
alcohol. The more soluble levulose is thus removed dissolved in the 
alcohol, and the less soluble dextrose remains for the most part un- 
dissolved. 



Galactose, C 6 H 12 O , 



is formed along with dextrose in the 
hydrolysis of milk-sugar : 

Milk-sugar -f H 2 O = Dextrose + Galactose. 

Unlike dextrose and levulose, galactose does not ferment with 
yeast. When reduced it yields dulcitol : 





Rotation of 
polarised light. 


Action of yeast. 


Reduction 
product. 


Dextrose 


To right 


Ferments 


Mannitol 


Levulose 


To left 


Ferments less 
rapidly than 
glucose 


Mannitol 


Galactose 


To right 


Does not fer- 
ment 


Dulcitol 



CANE-SUGAR GROUP OR BIOSES 

The members of this group are made up of two molecules 
of glucose united together with elimination of a molecule of 



HYDROLYSIS OF SUGAR 



CHAP. 



water. When hydrolysed (see above) they take up water to 
form two molecules of glucose. The formula is Cj^H^Ojj, 
and the following table indicates the relation of the most im- 
portant members of the group to the glucoses : 

Cane-sugar -f H 9 O = Dextrose + Levulose 
Milk-sugar + H 2 O = Dextrose + Galactose 
Maltose + H 2 O = Dextrose + Dextrose 

The Bioses are not so strong reducing agents as the Glucoses. 
None of them is able to reduce Fehling's solution in the cold, 





FIG. 32. Sugar-cane. 

Yield of canes per acre, 30-40 tons, 

containing about 5 tons of sugar. 



FIG. 33. Sugar-beet. 
Yield of beet per acre, 15-20 tons, 
containing about 2 tons of sugar. 



but maltose does so readily when heat is applied, 
reduce it only very slowly even when boiled. 



The others 



CANE-SUGAR 123 



Cane-sugar, C 12 H. 22 O U , is present in the sap of many 
plants, especially the sugar-cane and the beet-root. In order 
to obtain the sugar the sap is extracted either by crushing 
and pressure, or by cutting into thin slices and soaking in 
water. The juice is purified by filtration and other processes, 
and is then evaporated in vacuum-pans until sugar separates 
out from the juice on cooling. 

A portion only of the sugar is thus obtained in the crystal- 
line state, the remainder is left in the form of a thick syrup 
after the crystals have been removed, and the sugar in it is 
prevented by impurities from crystallising. These " molasses " 
may either be fermented and converted into spirit (rum), or 
by certain modern processes the impurities may be separated 
and the sugar obtained in the solid form. 

In one of these, the diffusion process, the syrup is put into 
what are practically huge bags made of parchment paper, and 
these bags are placed in pure water. The sugar of the molasses 
diffuses through the pores of the parchment paper faster than 
the impurities which are mixed with it, and there is thus ob- 
tained in the liquor surrounding the bags a solution of sugar 
sufficiently pure to yield a crystalline product on evaporation. 

The other process depends on the formation of a nearly 
insoluble compound with lime, having the composition 
C 12 H.,. 2 O n 3CaO. This is precipitated from the molasses 
by addition of powdered quick-lime, and after being purified 
by washing, is decomposed by passing a stream of CO 2 through 
water with which the " lime saccharate " is mixed. The lime 
is separated as calcium carbonate, and a weak syrup of pure 
sugar is obtained, which can readily be concentrated by evapora- 
tion. 

Cane-sugar crystallises in large monoclinic prisms (sugar- 
candy). It is very soluble in water, but is easily crystallised 
from its solutions by evaporation unless the presence of im- 
purities interferes. Solutions rotate the plane of polarisation 
of light to the right. On boiling with a dilute acid cane-sugar 
is converted into a mixture of dextrose and levulose : 

C 12 H 2211 + H 2 = C 6 H 126 + C 6 H 120 '> 
Cane-sugar. Dextrose. Levulose. 

and as levulose has a higher rotatory power than dextrose, the 



124 MILK-SUGAR 



mixture of the two thus obtained rotates to the left ; this in- 
version is the origin of the name invert-sugar, which is applied 
to the product thus obtained. 

When heated, cane-sugar melts at 160 C., and if then 
allowed to cool solidifies to a semi-transparent mass (" barley- 
sugar"), which is devoid of crystalline structure. On long 
standing this gradually becomes crystalline again. If heated 
to about 200 C., cane-sugar is changed into a brown sub- 
stance known as "caramel," or "burnt-sugar," which is used 
as colouring matter by cooks. 

Cane-sugar when subjected to the influence of the growing 
yeast-plant is first changed into a mixture of dextrose and 
levulose. As soon as any considerable quantity of these 
glucoses has been formed alcoholic fermentation sets in, fol- 
lowing chiefly the equation 

C 6 H 12 6 2C 2 H 6 + 2C0 2 . 

Glucose. Ethyl alcohol. 

Milk-sugar, C 12 H 22 O n , is present in milk, and remains 
dissolved in the whey after the casein has been separated in 
the manufacture of cheese. It is less soluble in water than 
cane-sugar, and much less sweet. Its solutions rotate the 
plane of polarisation to the right. 

Milk-sugar does not easily ferment with yeast, but by the 
action of certain bacteria it readily ferments with production 
of lactic acid : 

C 12 H 22 11 + H 2 = 4 C 3 H 6 3 . 
Milk-sugar. Lactic acid. 

This is the change which occurs when milk turns sour. 

As has been already mentioned, the hydrolysis of milk- 
sugar yields dextrose and galactose : 

C 12 H 22 U + H 2 = C 6 H 12 6 + C 6 H 12 6 . 

Milk-sugar. Dextrose. Galactose. 

Maltose, C 12 H 92 O 11 , is contained in malt, having been 
produced by the action of a certain ferment diastase upon 
the starch present in the barley or other grain which has been 
malted. 



xvin STARCH 125 

Upon hydrolysis boiling with a dilute acid maltose yields 
dextrose only : 

Maltose. Dextrose. 

It resembles the glucoses much more closely than do cane- 
and milk-sugar ; thus it ferments quickly (i.e. without previous 
conversion into glucoses) with yeast, and reduces Fehling's 
solution readily when warmed with it. 

THE CELLULOSE GROUP 

In this group we include a number of carbohydrates whose 
constitution is less understood even than that of the glucoses 
and bioses. It is very probable that their molecular weights 
are very high, but it has not yet been found possible to deter- 
mine their real values, and we can only give the empirical 
formulae. The most important members of the group are 
starch, dextrin, and cellulose all C 6 H 10 O 5 and the gums, 
whose probable formula is C 5 H 10 O 5 . 

Starch, C 6 H 10 O 5 , is the form in which very many plants 
store up their reserves of food. It is largely present in many 
roots and seeds, as the following table will show : 

Per cent 
of starch. 

Potatoes . .' . 20 
Wheat, maize . . 60 
Rice . . . . 70 

Starch is also a very important food for animals ; and arrow- 
root, sago, and tapioca are nearly pure starch extracted from 
certain plants. The separation of starch from the other con- 
stituents of the plants is effected by beating them with water 
into a thin pulp, which is then filtered through fine sieves. 
The fibrous matter is kept back, and the milky liquid which 
runs through deposits the starch on standing. This is then 
collected and dried. 

Starch is really insoluble in water, but when boiled with it 
yields a liquid which can be filtered without separating the 
starch. This is, however, merely present in a very fine state 



i26 CELLULOSE 



of subdivision, forming what is called a " colloidal " solution. 
The starch in it is unable to pass through a membrane of 
parchment paper, whereas substances in real solution are able 
slowly to diffuse through such a membrane. Neither has the 
starch any effect on the freezing-point of the water containing 
it (see p. 1 6). 

When heated to about 200 C., starch is changed into dex- 
trin. 

Very characteristic of starch is the intensely blue compound 
which it forms with iodine. This furnishes a very sensitive 
test either for starch or for free iodine. The blue colour dis- 
appears when sufficient heat is applied, but reappears on cool- 
ing. 

Dextrin, C 6 H 1Q O 5 , is obtained by simply heating starch to 
about 200 C., or by boiling it with dilute acids. Dextrin is 
used as a substitute for gum. It is not coloured blue by 
iodine. 

Cellulose, C 6 H 1Q O 5 , is the chief constituent of the cell- 
walls of plants ; wood is chiefly cellulose, while cotton-wool 
and filter-paper are nearly pure cellulose. This is insoluble 
in all ordinary solvents, but concentrated sulphuric acid 
dissolves it, and the solution when diluted and boiled yields 
first dextrin and then dextrose. 

The exact chemical constitution of cellulose is matter for 
future investigation. It appears, however, to contain three- 
fifths of its oxygen in the form of hydroxyl groups OH, as \ve 
find that by the action of acids ethereal salts of cellulose may 
be prepared in which three acid groups are introduced into 
the formula C 6 H 10 O 5 ; the real molecular formula of cellulose 
is unknown, but it is more convenient to regard these ethereal 
salts as derived from the doubled formula C 12 H 2Q O 10 , in which, 
of course, there are six hydroxyls. 

The most important of these salts are the nitrates ; these 
are prepared by treating cellulose (cotton-wool) with strong 
nitric acid, the action being aided by the addition of concen- 
trated sulphuric acid. When the strongest acids are employed 
the product obtained is gun-cotton, which is found to be 
cellulose hexa-nitrate : 



= C 12 H 144( N 3)(i + 6H 2' 
Cellulose. Gun-cotton. 



xvin GUN-COTTON 127 

This material is a violent explosive, and is prepared by 
steeping cotton-wool for a few minutes in a cold mixture of the 
strongest nitric acid with two or three times its weight of 
concentrated sulphuric acid. When thoroughly freed from 
acid by washing, gun-cotton is comparatively quite safe to 
handle, and may even be set fire to without anything more 
violent than a rather quick combustion taking place ; but 
when subjected to the shock set up by exploding a small 
charge of fulminate embedded in the gun-cotton, the molecules 
of the latter break down suddenly, and a powerful explosion 
results ; the rearrangement of atoms which then occurs may 
be roughly represented by the following equation : 

C i2 H u4( N 3)c = 3N 2 + 7H.O + 9 CO + 3 C0 2 . 

Gun-cotton. 

Pyroxylin is a less highly nitrated cellulose, chiefly the 
tetra-nitrate ; it is prepared with a somewhat weaker nitric 
acid. Its solution in a mixture of alcohol and ether is the 
collodion which is largely used in photography (wet -plate 
process), and in surgery for covering wounds with a thin 
flexible film which prevents access of air. 



QUESTIONS ON CHAPTER XVIII 

1. What are the chief members of the group of "glucoses" ; what is 
their formula, and what explanation of their isomerism may be advanced ? 

2. What is the action upon dextrose of (a) Fehling's solution, (l>) 
yeast, (c) acetic anhydride? 

3. What two substances are present in largest quantity in honey? 
How do they differ from one another ? 

4. What products are obtained by the action of boiling dilute acids 
upon (a) cane-sugar, (b] milk-sugar, (c) maltose? 

5. Describe the preparation of gun-cotton, and give its chemical 
constitution. 



CHAPTER XIX 
UREA AND URIC ACID 

Urea, CO(NH ) t> , is one of the most important waste- 
products of the animal economy ; the food which animals 
consume is converted during its passage through the blood 
and tissues of the body chiefly into urea, carbon dioxide, and 
water. The urea is secreted along with a considerable 
proportion of the water by the kidneys, and it was from urine 
that this substance was first obtained in 1773. 

Urea thus obtained and afterwards carefully purified was 
found by analysis to have the composition CON 2 H 4 . This is 
also the composition of ammonium cyanate, (NH 4 )NCO, and 
though that body is itself quite distinct from, and isomeric 
with', urea, in 1828 Wohler made the very important discovery 
that a solution of ammonium cyanate in water yields urea on 
evaporation. The great readiness with which this change 
occurs while indicating that urea is the more stable of the two 
isomers also seems to show that they are not very different in 
constitution. Several synthetical methods which have since 
been discovered for the preparation of urea show that it may 

be regarded as the amide of carbonic acid, CO-^,^, ' 2 . Thus 

just as the amide of acetic acid (acetamide) can be got by the 
action of ammonia on acetyl chloride : 

CH.,.COC1 + NH, = CH.,. CONH., + HC1, 

O O o 

Acetyl chloride. Acetamide. 

so urea can be obtained by the action of ammonia on carbonyl 
chloride COCL, : 



CHAP, xix PREPARATION OF UREA 129 

COC1 2 + 2NH 3 = CO(NH 2 ) 2 + 2HC1. 
Carbonyl Carbamide 

chloride. or urea. 

The most convenient way of preparing urea is by 
evaporating a solution in water of potassium cyanate and 
ammonium sulphate mixed in equivalent proportions ; the 
potassium cyanate is easily obtained by heating potassium 
ferrocyanide with manganese dioxide. 

EXPT. 19. Heat four parts potassium ferrocyanide with two parts of 
MnOa in a clay crucible, extract the cooled melt with water, add three parts 
of ammonium sulphate, and evaporate to dryness. Potassium sulphate 
and urea are left, and may be separated by extraction with alcohol, in 
which the urea only is soluble. 

Urea crystallises in rhombic prisms which are easily 
soluble in water. It is a mon-acid base, and forms salts of 
which the nitrate CON 9 H 4 . HNO 3 is very sparingly soluble 
in water containing nitric acid, and may therefore be used as 
a means of detecting urea in solutions not too dilute. 

Like other amides urea is decomposed on boiling with 
dilute alkalies, and ammonia is given off: 

CO(NH 2 ) 2 + H 2 O = CO, + 2NH 3 . 
Urea. 

Another important reaction of urea is its behaviour when 
treated with bromine and caustic soda (sodium hypobromite) ; 
it is then oxidised to CO and water while the nitrogen is 
given off as such : 

CON 2 H 4 + 3NaOBr = CO 2 + 2H 2 O + N 2 + aNaBr. 

EXPT. 20. Put some solution of urea in a boiling tube, add caustic 
soda and bromine water ; notice that a gas is given off in bubbles, and by 
testing with a match show that it puts out the flame. (The gas cannot 
be CO , because the solution contains excess of alkali. ) The experiment 
can be so arranged that the nitrogen may be collected and measured ; 
from its amount that of the urea can be calculated, and on this a method 
for estimating urea is based. It must, however, be remembered that 
many other nitrogen compounds also give off their nitrogen when treated 
with a hypobromite. 

Uric Acid, C 5 H 4 N 4 O 3 (5443), may be regarded as a less 
completely oxidised result of the digestive and absorptive 



130 URIC ACID CHAP, xix 

processes than urea. Uric acid is present only in small 
quantity in the urine of man, but in certain abnormal con- 
ditions of the body it is more largely produced, usually with 
very unpleasant consequences. Both uric acid and its salts are 
soluble only with difficulty in water, hence they are difficult to 
remove when produced in the body in any considerable 
quantity, and either gout, in which accumulations of urates 
occur in various parts of the body, or other disturbances of 
the healthy procedure occur. 

In some animals, on the other hand, especially birds and 
reptiles, uric acid is largely secreted, and both guano (which 
is produced by sea-birds) and the excreta of serpents contain 
considerable quantities, and from either of these sources the 
acid may readily be prepared. 

If guano is used it is best boiled with a solution of borax (i to 100 of 
water), in which uric acid is fairly soluble. Addition of hydrochloric acid 
to the filtered solution precipitates the bulk of the uric acid present. 

Uric acid is a white powder, soluble only very slightly in 
pure water, but more readily in water containing certain salts 
in solution. It is a weak di-basic acid, but the best 
characterised salts are these with only one equivalent of metal, 
such as C 5 H 3 KN 4 O 3 , potassium urate ; they are all very 
slightly soluble in water. 

To test a substance for the presence 01 uric acid a few 
drops of dilute nitric acid are added to it, and then evaporated 
on the water bath ; if a yellow residue is left which is coloured 
purple by addition of ammonia, we may conclude that uric 
acid was contained in the substance examined. 



QUESTIONS ON CHAPTER XIX 

1. How can urea be prepared from potassium ferrocyanide ? 

2. What is the action upon urea of (a) sodium hypobromite, (l>) 
boiling caustic soda solution ? 

3. What products are formed by the action of ammonia upon (a) 
carbonyl chloride, (b) acetyl chloride ? 

4. From what sources can uric acid be obtained ? Write down the 
formulae of uric acid and of potassium urate. 



CHAPTER XX 
THE CYANOGEN COMPOUNDS 

THE cyanogen compounds include a large number of sub- 
stances which are alike in containing the monovalent radicle 
cyanogen - CN, made up, as its formula shows, of one atom 
each of tetravalent carbon and trivalent nitrogen: -C = N. 
Sometimes the special symbol Cy is used to denote the 
cyanogen radicle. 

The starting-point in the preparation of the various cyanogen 
compounds is potassium ferrocyanide, or " yellow prussiate of 
potash," but as the composition of this substance is somewhat 
complex it is better to begin with other and simpler bodies. 

Cyanogen, C 2 N 2 , a compound whose molecule is formed 
of two cyanogen radicles united together (just as free chlorine 
or hydrogen is C1 2 or H 2 ), is made by heating mercuric 
cyanide to a red heat, when it decomposes into mercury and 
cyanogen : 

Hg(CN) 2 =Hg + C 2 N 2 . 

It is a poisonous gas with a characteristic smell, and burns in 
air with a peculiar ("peach-blossom colour") flame; its mix- 
ture with oxygen explodes violently on application of a flame : 



Cyanogen is readily soluble in water, and must therefore be 
collected over mercury. 

Chemically cyanogen behaves as the "nitrile" of oxalic acid. It can 
be obtained from the amide of oxalic acid oxamide (CONHaJa by with- 
drawing water (action of 



132 HYDROCYANIC ACID CHAP. 

CONH 2 
CONH 3 

and the inverse reaction can be brought about by allowing a solution of 
cyanogen in water or dilute acid to stand for several days : 

C 2 N 2 + 2H 2 O = C 2 O 2 (NH 2 ) 2 . 

Compare the relation of methyl cyanide (acetonitrile) CH 3 CN to aceta- 
mide, pp. 89 and 134. 

Hydrocyanic Acid, HCN, or " Prussic Acid," is now 
most largely prepared by the action of boiling dilute sulphuric 
acid upon potassium ferrocyanide : 

2K 4 FeCy ( . + 3H 2 SO 4 = 3K 2 SO 4 + K 2 Fe 2 Cy 6 + 6HCN. 

By this method a solution of hydrocyanic acid in water is 
obtained, from which the anhydrous acid can be prepared by 
passing the vapours through tubes containing calcium chloride 
or other suitable dehydrating agent. 

An older method of preparing the dilute acid is from 
amygdalin, a compound present in bitter almonds, laurel 
leaves, and parts of various other plants. The amygdalin, 
when the leaves, etc., steeped in water, are exposed to the air, 
usually undergoes a fermentation which results in the forma- 
tion of hydrocyanic acid, oil of bitter almonds (benzaldehyde, 
see Part II.), and sugar. The hydrocyanic acid is then easily 
obtained by distillation. 

The salts of hydrocyanic acid the cyanides are formed 
whenever carbon and nitrogen come in contact with a strong 
base at a high temperature. The nitrogen may be supplied 
in the free state, or may be present in combination with other 
elements. Thus potassium cyanide is formed when nitrogen 
is passed over a heated mixture of potash and powdered coal, 
and cyanides are always formed in distilling coal for the manu- 
facture of coal-gas from the joint interaction of ammonia with 
the nitrogen and carbon present in the coal. The two chief 
sources of the cyanides (which are largely manufactured for 
use in electro-plating, for making Prussian blue, and other pur- 
poses) are to be associated with this method of formation. 
They are 



xx SOURCES OF THE CYANIDES 133 

i . Potassium ferrocyanide, yellow prussiate of potash, which 
is made by carbonising nitrogenous animal refuse (horn, leather 
scraps, etc.) and heating the residue, which, though chiefly 
carbon, still contains a considerable proportion of nitrogen, 
with caustic potash and iron filings. 

2. An important source of cyanides is now found in the 
by-products of the manufacture of coal-gas. The cyanides 
formed during the destructive distillation of the coal are re- 
tained chiefly in the lime-purifiers, and are extracted from the 
spent lime by treatment with quicklime at steam heat. This 
decomposes the insoluble cyanogen compounds present in the 
spent lime, and converts them into soluble calcium ferro- 
cyanide. 

Cyanides are now also recovered from the by-products of 
other manufactures blast-furnaces, coke-ovens, etc. 

Other reactions, of theoretical interest only, by which hydrocyanic acid 
or its salts can be obtained, are 

i. The action of the electric discharge upon a mixture of acetylene and 
nitrogen : 



2. The action of ammonia upon chloroform (in the presence of caustic 
potash) : 

NH 3 + CHC1, = 3HC1 + HCN. 

Pure hydrocyanic acid, free from water, is a colourless volatile 
liquid, with a strong smell and intensely poisonous properties. 
It is a well-marked acid, but its salts with the alkaline metals 
are easily decomposed, even carbon dioxide being sufficiently 
powerful to liberate the acid from potassium or ammonium 
cyanides ; hence it is that these substances always smell of 
hydrocyanic acid when exposed to the air. The cyanides of 
the heavy metals are, on the other hand, much more stable, 
silver cyanide being unattacked even by the strong acids. 

The solution of hydrocyanic acid in water readily decom- 
poses with formation of ammonium formate and other sub- 
stances. A similar change occurs more readily by the action 
of dilute mineral acids, showing that hydrocyanic acid may be 
regarded as the nitrile of formic acid : 

HCN + 2H 2 O = HC0 2 H + NH 3 , 

Hydrogen cyanide. Formic acid. 

with which compare 



134 THE CYANIDES 



CH 3 CN + 2H 2 O - CH 3 . CO 2 H + NH 3 . 
Methyl cyanide Acetic acid, 

or " acetonitrile." 

Potassium Cyanide, KCN, is manufactured by heating 
potassium ferrocyanide in iron vessels until decomposition 
occurs according to the equation : 

K 4 FeC N 6 = 4 KCN + FeC 2 + N 2 . 

The potassium cyanide is separated from the iron-carbide by 
extracting the mass with water ; the solution is evaporated, 
and the residue, after being fused, is brought into market in 
lumps or sticks. 

Perfectly pure potassium cyanide is best obtained by passing vapours 
of HCN into a solution of KOH in alcohol. 

Potassium cyanide is very soluble in water, and is extremely 
poisonous. It is largely used in electro-plating for preparing 
the solutions of gold or silver, and in the gold-fields for dis- 
solving the gold from the quartz containing it. It is used in 
the laboratory as a reducing agent in blow-pipe work. 

Mercuric Cyanide, Hg(CN) 2 , is prepared by boiling 
Prussian blue with water and mercuric oxide, or by dissolving 
mercuric oxide in hydrocyanic acid. It is fairly soluble in 
water, is very poisonous, and forms good crystals. It does 
not evolve any perceptible amount of hydrocyanic acid when 
treated with cold dilute sulphuric acid, but gives it off slowly 
on boiling. 

Silver Cyanide, AgCN, is obtained as a white precipitate 
when a solution of potassium cyanide is added to one of silver 
nitrate. It is insoluble in acids, but dissolves readily in excess 
of the solution of KCN owing to the formation of a soluble 
double salt AgCN . KCN. 

On this is based a method for the quantitative estimation of soluble 
cyanides ; standard solution of silver nitrate is added to the solution of the 
cyanide until a permanent white precipitate just begins to form. When 
this occurs, one molecule of AgNO 3 has been added for every two mole- 
cules of the cyanide present : 

. KCN + KNO 3 . 



XX THE FERROCYANIDES 135 

Double Cyanides. In the double salt just referred to 
AgCN . KCN we have an example of the marked tendency 
shown by various cyanides of different metals to combine to 
form double cyanides. In some of these double salts the com- 
bination is only loose and is readily broken, while their pro- 
perties are not fundamentally different from those of simple 
cyanides. But in another important class of double cyanides 
the combination is so complete that the essential properties of 
the constituent salts entirely disappear in the double cyanide 
formed by their union. 

Potassium Ferrocyanide, K 4 FeCy 6 , is such a double 
cyanide. Its formula may be regarded as showing it to be 
made up of 4KCy-fFeCy 9 , four molecules of potassium 
cyanide with one of ferrous cyanide, but in reality neither the 
cyanogen group, nor the iron contained in the ferrocyanide 
can be detected by their ordinary reactions. The ferrocyanide 
is almost non- poisonous in comparison with the intensely 
poisonous nature of the soluble simple cyanides, and the iron 
in it is not precipitated by ammonium sulphide. 

Potassium ferrocyanide is largely manufactured to serve as 
a starting-point for the preparation of Prussian blue and other 
cyanogen compounds. It is known commercially as yellow 
prussiate of potash, and is made by heating in shallow iron 
pans a mixture of charred nitrogenous refuse (horn, skin, etc.) 
with potash and iron filings. The ferrocyanide is extracted 
with water from the fused residue and purified by recrystallisa- 
tion. It forms large tabular crystals of an amber colour. It 
dissolves easily in water, and the solution gives characteristic 
precipitates with solutions of several metallic salts, e.g. with 
copper sulphate solution a brown precipitate of copper ferro- 
cyanide is obtained : 



K 4 FeCy 6 + 2CuSO 4 = 2K 2 SO 4 + Cu 2 FeCy 6 . 
Potassium Copper 

ferrocyanide. ferrocyanide. 

When a strong acid, (HC1), is added to the concentrated 
solution of potassium ferrocyanide, a white precipitate of 
ferrocyanic acid, H 4 FeCy (5 , is produced : 

K 4 FeCy 6 + 4 HC1 = 4 KC1 + H 4 FeCy 6 . 



136 



PRUSSIAN BLUE 



CHAP. 



The complex radicle, Fe(GN) ( . or FeCy 6 , which is present 
in ferrocyanic acid and the ferrocyanides, carries the name 
" ferrocyanogen." 

Potassium Ferricyanide, K.^FeCy,., is formed by oxidis- 
ing a solution of the ferrocyanide by means of chlorine : 



2K 4 FeCy + C1 2 = 2KC1 



2K a FeCy 6 . 



It may be regarded as built up from three molecules of KCN 
with one of ferric cyanide FeCy,,, but just as is the case with 
the ferrocyanide the properties of the compound are essentially 
different from those of the simple cyanides. 

Potassium ferricyanides is the commercial " red prussiate 
of potash," and forms deep-red crystals. 

Iron Salts and the Ferro- and Ferricyanides. 
The reactions between solutions of iron salts and ferro- or ferri- 
cyanides are of importance in analytical chemistry, and for the 
thorough understanding of the composition of Prussian blue. 
They are best shown in a tabulated form : 



Solution used. 


Potassium Ferrocyanide. 
K 4 FeCy 6 . 


Potassium Ferricyanide. 
K 3 FeCytj. 


Ferrous salt 


Light-blue pp. of ferrous 
ferrocyanide, which 
gradually darkens in 
the air 


Dark blue pp. of ferrous 
ferricyanide ; Turn- 
bull's blue 


Ferric salt 


Dark blue pp. of ferric 
ferrocyanide ; Prus- 
sian blue 


No pp., but the solution 
becomes very dark 
green in colour 



Prussian Blue, as indicated above, is chemically to be 
regarded as ferric ferrocyanide, Fe 4 (FeCy 6 ) 3 or Fe 7 Cy lg , and 
is formed when potassium ferrocyanide is added to a solution 
of a ferric salt. In actual practice it is made by adding the 
ferrocyanide to a somewhat oxidised solution of ferrous sul- 
phate, and then completing the oxidation by means of air. 

Cyanic Acid, HCNO. It has been mentioned that 



THE CYANATES 137 



potassium cyanide is a powerful reducing agent, and is used 
as such in analytical chemistry for the purpose of reducing the 
metals from their salts by fusion with sodium carbonate and 
the cyanide. In such reactions the potassium cyanide is con- 
verted by addition of oxygen into potassium cyanate : 

KCN + O = KCNO. 



The cyanate is more cheaply prepared by heating potassium 
ferrocyanide with an oxidising agent, such as MnO 2 or 
K 2 Cr 2 O r 

Potassium Cyanate, KCNO, is a white solid, easily 
soluble in water. The solution gradually decomposes when 
kept. On addition of an acid free cyanic acid is not obtained, 
but only its products of decomposition with water ammonia 
and carbon dioxide : 

HCNO + H 9 O = NH, + CO 9 . 

A o L 

Ammonium Cyanate, NH 4 CNO, is of special importance 
on account of its ready transformation into urea, CO(NH 2 ) 2 , 
see p. 128. It is most easily obtained in solution by mixing 
strong solutions of potassium cyanate (prepared as above) and 
ammonium sulphate. The difficultly soluble potassium sul- 
phate will separate out in part : 

2KCNO + (NH 4 ) 2 SO 4 - K 2 SO 4 + 2NH 4 CNO, 

and the solution on evaporation yields urea along with some 
potassium sulphate. 

Free Cyanic Acid, HCNO, has to be prepared indirectly. 
When solid urea is heated ammonia is at first evolved, but 
after a time ceases ; if the residue is dissolved in potash 
solution, addition of an acid precipitates Cyanuric Acid, 
H y C 3 N 3 Oy, which is produced according to the equation : 

3CON 2 H 4 *=H 8 C 8 N 8 O 8 + 3NH r 

Urea. Cyanuric 

acid. 

If this cyanuric acid is collected and dried, and then heated 
in a retort, vapours of cyanic arid, HCNO, are evolved : 

H 3 C 3 N 3 O 3 = 3HCNO, 
Cyanuric acid. Cyanic acid. 



138 CYANIC ACID CHAP, xx 

and can be condensed in a tube surrounded by a freezing 
mixture to a very volatile liquid, with a marked and acrid 
odour. Cyanic acid very readily undergoes polymerisation, 
forming either cyanuric acid or another polymer cyamelide 
whose molecular formula is uncertain. 



QUESTIONS ON CHAPTER XX 

1. Give three methods by which hydrocyanic acid can be prepared. 

2. How would you proceed in order to obtain mercuric cyanide from 
potassium ferrocyanide ? 

3 What happens when you heat the following substances, (a) mercuric 
cyanide, (b) urea, (c) potassium ferrocyanide? 

4. What is the composition of Prussian blue? Describe its manu- 
facture. 



I NDEX 



ACETALDEHYDE, 63 


Alcoholates, 51 


Acetamide, 89 


Alcoholometry, 49 


Acetic anhydride, 79 


Alcohols, general characteristics of, 


Acetone, 66 


44 


Acetyl chloride, 79 


Allyl compounds, in 


Acetylene, 33 


Amides, 88 


Acid, acetic, 68, 71 


Amido-acetic acid, 90 


,, acrylic, 112 


Amines, 82 


,, amido-acetic, 90 


,, primary, secondary, and 


,, butyric, 74, 75 


tertiary, 82, 84, 85 


,, citric, 1 08 


Argol, 103, 104 


,, cyanic, 137 


Arsines, 93 


,, formic, 70 


Asymmetric carbon atom, 108 


,, glycolic, 100 
hydrocyanic, 132 
,, lactic, 1 06 


BUTANE, 23 
Butylene, 31 


malic, 103 


CACODYL compounds, 94 


,, oxalic, 101 


Cane-sugar, 123 


,, palmitic, 76 


Carbon, estimation of, 4 


, , para-lactic, 107 


,, tetrachloride, 39 


,, propionic, 74 


Carius's method of analysis, 9 


,, prussic, 132 


Cellulose, 126 


,, stearic, 76 


Chloral, 39, 65 


,, succinic, 102 


Chlorhydrins, nS 


tartaric, 103 


Chloroform, 38 


,, uric, 129 
Acrolein, 112, 116 
Alcohol, allyl, in 


Couple, zinc-copper, 20, 95 
Cyanides, 133 
Cyanogen, 131 


amyl, 54 




butyl, 53 


DEXTRIN, 126 


dihydric, 99 


Dextrose, 120 


ethyl, 47, 51 


Dihydric alcohol, 99 


methyl, 45 


Dulcitol, 120 


,, primary, secondary, and 


Dynamite, 117 


tertiary, 53 




propyl, 52 


ETHANE, 22 


,, trihydric, 115 


Ether, 58 



140 



ORGANIC CHEMISTRY 



Ethereal salts, 55 
Ethyl acetate, 56 

,, alcohol, 47, 51 

, , bromide, 4 1 

,, chloride, 40 

,, ether, 58 

, , iodide, 42 

,, niercaptan, 59 

,, sulphide, 59 
Ethylamines, 87 
Ethylene, 28 

bromide, 41 

FEHLING'S solution, 62, 120, 122 
Fermentation, 47 
Formaldehyde, 61 
Formulae, empirical, 12 
,, molecular, 13 
Fusel oil, 47 

GALACTOSE, 121 
Garlic, oil of, 113 
Glucose, 119 
Glycerine, 115 
Glycocoll, 90 
Glycol, 99 
Glyoxal, 100 
Gun-cotton, 126 

HALOGENS, estimation of, 9 
Hofmann's method, 15 
Homology, 2, 21 
Hydrogen, estimation of, 4 
Hydroxyl groups, determination of, 
80 

INVERT-SUGAR, 124 
lodoform, 39 
Isomerism, 2, 23 

KETONES, 65 

LEAD ETHYL, 97 
Levulose, 121 

MALTOSE, 124 
Mannitol, 120 
Mercury methyl, 97 
Methane, 19 
Methyl alcohol, 45 
,, chloride, 37 



Methyl iodide, 39 
Methylamine, 85 
Methylated spirit, 49 
Milk-sugar, 124 
Mustard, oil of, 113 

NITROGEN, 'estimation of, 6 
Nitro-glycerine, 116 

PARAFFIN, 27 

Paraldehyde, 63 

Pentane, 25 

Petroleum, 26 

Phosphines, 92 

Phosphorus, estimation of, 10 

Potassium ferrocyanide, 135 

Proof spirit, 50 

Propane, 23 

Propylene, 30 

Prussian blue, 136 

Pyroxylin, 127 

RAOULT'S method, 17, 119 

SAPONIFICATION, 57 

Saturated compounds, 28 

Silicon, compounds of, 94 

Soap, 76 

Starch, 125 

Sulphur, estimation of, 125 

TARTAR, cream of, 104 

,, emetic, 105 
Tetrahedral carbon atom, theory 

of, 31, 35, 120 
Tin ethyl, 98 

UNSATURATED compounds, 28 
Urea, i, 128 

VAN'T HOFF'S theory, 31, 120 
Vapour density, 14 
Victor Meyer's method, 14 

WOOD, distillation of, 45 
YEAST, 47 

ZINC ETHYL, 96 
,, methyl, 95 



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