863 
CHAPTERS FOR STUDENTS. 
100 c.c. (= of 1000) will, therefore, contain 4*0 grams of soda, and will 
neutralize 6-0 'grams of acetic acid. Then, since 18‘2 grams of acid, acetic., 
33.P., are neutralized by the same quantity, they will contain 6 grams of real 
cicid 
Then 100 will contain 32'9, for 18-2 : 100 :: 6 : 32*9. And 32-9 is practi¬ 
cally the same as 33. 
Pure acetic acid should give no precipitate with sulphuretted hydrogen, show- 
ing the absence of lead and copper; with chloride of barium, showing the 
absence of sulphuric acid ; nor with nitrate of silver, showing the absence of 
hydrochloric acid. Sulphurous acid is tested for by the last test given in the 
B.P.; it operates thus,—the zinc and hydrochloric acid give hydrogen; whilst 
in the “ nascent state,” that is at the moment of being set free, this hydrogen 
attacks any sulphurous acid present, and converts it into water and sulphu¬ 
retted hydrogen :— 
H|SO s + 3H 2 = 3 H 2 0 + H 2 S. 
The latter, as it escapes, blackens the acetate-of-lead paper. 
Acetates, as a rule, are very soluble. They are easily recognized by giving a 
reddish-brown solution with a ferric salt (see tinct. ferri. perac.), by evolving an 
acetic odour when treated with sulphuric acid, and by giving, when boiled with 
alcohol and sulphuric acid, acetic ether, known by its agreeable odour. 
Acidum Aceticum Glaciale, Glacial Acetic Acid is probably prepared in 
several ways. It may be made by distilling dry acetate of soda with strong 
sulphuric acid, but the product so obtained is always contaminated with sulphu¬ 
rous acid. Another method consists iu decomposing dry acetate of lime with 
hydrochloric acid gas passed through it in a suitable apparatus: 
Ca (C 2 H 3 0 2 ) 2 + 2II Cl = Ca Cl 2 +2 H C 2 H 3 0 2 . 
And another, a very good process, consists in distilling the so-called binacetate 
of potash. This compound is easily made by dissolving acetate of potash iu 
strong acetic acid and distilling ; the receiver is changed as soon as the weak 
acid has distilled off and the crystallizable acid begins to condense. Binacetate 
of potash contains the elements of the ordinary acetate united with those of acetic 
acid, KC 2 H 3 0 2 , HC 2 H 3 0 2 ; on application of heat, the latter distils off and 
leaves the neutral acetate, which can, of course, be used over again foi the same 
purpose. . . 
The Pharmacopoeia describes it as concentrated acetic acid, corresponding to 
at least 84 per cent, of anhydrous acid, C 4 tl 6 0 3 . 
The necessary calculation is made somewhat as follows:—Two molecules of 
acetic acid, deprived of i^O, give the anhydride C 4 H e 0 3 . 
2 C 2 H 4 0 2 —H 2 0 = C 4 H 6 0 3 . 
Now C 2 = 12 x 2 — 24 
II 4 = 1x4= 4 
0„ = 16 X 2 = 32 
And C 4 = 12 X 4 = 48 
H 6 = 1x6=6 
th = 16 X 3 = 48 
60x2=120. 
102 
r So that 120 grams of acetic acid would give 102 grams of acetic anhydride. 
How much then would 100 give ? 
120 : 100 : : 102 : 85. 
The B.P. says 84, thus allowing 1 per cent, for accidental water. 
The tests by which its strength and purity are ascertained, are the same as 
for acidum aceticum. ., 
Note .—It must be understood throughout these papers that whenever an acid 
is spoken of, it is a compound of one or more atoms of hydrogen with a pecu- 
