CHEMISTRY. 



alcohol yields water and a volatile substance called 

 hydrochloric ether, or chloride of ethyl ; just as 

 caustic soda, with hydrochloric acid, yields water 

 and chloride of sodium, C 2 H 6 O -f HC1 = H 2 O + ': 

 C 2 H 5 C1, corresponding to NaHO + HC1 = H 2 O + 

 NaCl; and as caustic soda is regarded as the oxide 

 of hydrogen and sodium, and represented by the 

 graphic formula, Na O H, so we may call alcohol 

 the oxide of hydrogen and ethyl, C 2 H 5 O H. The 

 substances produced by the action of acids upon 

 alcohol (which may be looked upon as the salts of 

 ethyl) are called ' compound ethers ' or ' esters,' 

 and are named after the acid employed in pro- 

 ducing them : thus, nitrous acid acts on alcohol 

 to produce nitrous ether ; acetic acid, to produce 

 acetic ether ; and so on. The analogy between 

 the compounds of ethyl and those of such a metal 

 as sodium can be carried farther ; and just as 

 we have anhydrous oxide of sodium, Na 2 O or 

 Na O Na, so we have anhydrous oxide of 

 ethyl, (C 2 H 5 ) 2 O or C 2 H 5 O C 2 H 5 . This sub- 

 stance is common ether, often, but improperly, 

 called sulphuric ether, because sulphuric acid is 

 used in making it. When alcohol is mixed with 

 sulphuric acid, the first change which takes place 

 is the formation of water and ' sulphovinic acid,' 

 which is the acid sulphate of ethyl, C 2 H 5 OH + 

 H 2 SO 4 = HOH + C 2 H 5 HSO 4 . This sulphovinic 

 acid is obviously the analogue of bisulphate of 

 soda, NaHSO 4 . When sulphovinic acid is heated 

 along with alcohol, ether and sulphuric acid 

 are formed thus, C 2 H 5 OH + C 2 H 6 HSO 4 = 

 C 2 H 6 O C 2 H5 + H 2 SO 4 . In the ordinary 

 process for making ether, these two actions go on 

 together, so that the sulphovinic acid is decom- 

 posed as fast as it is formed, and ether and water 

 distil over together, leaving sulphuric acid behind. 

 A comparatively small quantity of sulphuric acid 

 is thus able to convert a large quantity of alcohol 

 into ether and water. 



Common ether is a colourless liquid, of specific 

 gravity 0-723, boiling at 96 F. It is therefore a 

 very volatile substance ; and as it evaporates 

 rapidly below its boiling-point, it can be used to 

 produce intense cold. It is also used as a solvent 

 for fats and oils, and as an anaesthetic in surgery. 



Acetous Fermentation, Acetic Acid. If fermented 

 liquors that is, solutions containing alcohol and 

 nitrogenous substances are exposed to the air, 

 they gradually become sour, and what is called 

 'vinegar' is produced. This change is known as 

 the ' acetous fermentation,' and, like other fermen- 

 tations, depends on the growth of a fungus, Myco- 

 denna aceti, the vinegar-plant, or 'mother of 

 vinegar.' The acetous fermentation not only 

 requires the presence and growth of a ferment, but 

 also the presence of air or oxygen, and in this 

 differs essentially from the other two kinds of 

 fermentation which we have been considering. It 

 is, in fact, a process of oxidation taking place under 

 the influence of the ferment. In the ' quick pro- 

 cess ' for making vinegar, weak alcohol is made to 

 trickle through casks containing wood-shavings, 

 and pierced with holes for the admission of air. 

 The shavings become coated with mycoderma, 

 and the oxidation of the alcohol proceeds very 

 rapidly. Alcohol can also be oxidised by various 

 oxidising agents, and we can thus trace the pro- 

 cess more minutely than is possible in the case of 

 the acetous fermentation. When alcohol is heated 

 with a mixture of sulphuric acid and solution of 



bichromate of potash (or what comes to the same 

 thing, sulphuric acid and chromic acid), the alco- 

 hol loses hydrogen, and the chromic acid loses 

 oxygen ; these combine to form water, and the 

 chromic acid is reduced to chromic oxide, which, 

 with the sulphuric acid, forms chromic sulphate. 

 The alcohol, by the loss of hydrogen, is converted 

 into a very volatile liquid, called aldehyd (rt/cohol 

 ^AyaTrogenatum that is, alcohol from which hy- 

 drogen has been removed), having the composi- 

 tion indicated by the formula C 2 H 4 O that is, 

 C 2 HgO H 2 . Aldehyd is very easily oxidised, 

 readily taking up another atom of oxygen, and form- 

 ing acetic acid, C 2 H 4 O 2 . Besides the oxidation of 

 alcohol, there are various ways in which acetic acid 

 can be produced ; of these, the most practically 

 important is the distillation of wood. As has beea 

 already stated (p. 332), wood consists principally 

 of cellulose. When it is heated to redness in a 

 retort, closed so as to exclude air, and provided 

 with a tube, by which the gaseous and volatile 

 products can be led to a cooling and condensing- 

 apparatus, a great many different substances are 

 formed. They may be grouped thus : i. The 

 charcoal which remains in the retort ; 2. Uncon- 

 densable gases which pass through the condenser ; 

 and 3. Volatile substances, which flow as liquids 

 from the condenser. Of these we may again distin- 

 guish the tar, which contains the substances in- 

 soluble, or sparingly soluble in water, and a watery 

 liquid floating upon the tar, and consisting chiefly 

 of water, acetic acid, and a light inflammable 

 liquid called pyroxylic spirit These may be 

 separated from one another by converting the 

 acetic acid into an acetate by the addition of a 

 base (soda, lime, or oxide of lead) distilling off the 

 pyroxylic spirit ; and, if the acetic acid is required 

 as such, decomposing the acetate by means of 

 sulphuric acid, and distilling. Pure acetic acid is 

 a colourless liquid, with a pure sour taste and 

 pungent odour ; at 32 F. it freezes, and forms a 

 colourless crystalline mass, which does not fuse till 

 the temperature is raised to about 60 F. The spe- 

 cific gravity of the liquid is 1-063. ^ boils at 246 

 F. Its composition is represented by the formula 

 C 2 H 4 O 2 . The strongest vinegar of commerce con- 

 tains about 5 per cent of pure acetic acid. The 

 most important acetates are : Acetate of soda, 

 acetate of lead (sugar of lead), basic acetate of 

 lead (Goulard's solution), acetate of copper, basic 

 acetate of copper (verdigris), acetate of alumina, 

 and ferric acetate ; the last two are used as 

 mordants in dyeing and calico-printing. 



ALCOHOLS AND THEIR DERIVATIVES. 



Many substances have a chemical character 

 similar to that of common alcohol that is to say,, 

 they form compound ethers when treated with 

 acids, lose two atoms of hydrogen to form bodies 

 analogous to aldehyd, which, again, easily take up 

 oxygen, and are converted into acids correspond- 

 ing to acetic acid. Thus, there is a substance con- 

 tained in pyroxylic spirit called ' methylic alcohol,' 

 which has the formula CH 4 O (or CH 3 O H). 

 With hydrochloric acid, it forms water and 

 CH 3 C1, chloride of methyl ; when oxidised, it 

 is converted into CH 2 O, its aldehyd ; and this, 

 again, into CH 2 O 2 , formic acid. Formic acid is 

 interesting as the acid contained in the bodies 

 of red ants, and in the stinging fluid of the common 



