DECOMPOSITION OP GELATINE BY CHROMIC ACID. 29 
ART. VIII. — ON THE PRODUCTS OF DECOMPOSITION OF 
GELATINE BY CHROMIC ACID. 
.By A. Schlieper. 
The best proportions for oxidizing gelatine by chromic acid 
are those pointed out by Prof. Marchand, viz. 2 parts ordi- 
nary glue, 8. of bichromate of potash; 15 of sulphuric acid, 
and 50 parts of water. The amount of sulphuric acid may be 
somewhat diminished, but not increased, otherwise the opera- 
tion would not succeed, and nothing but formic acid would be 
obtained. The glue is first allowed to swell in the water, and 
the sulphuric acid then added ; when the mixture has cooled, 
it is poured into the retort containing the bichromate in the 
state of a fine powder ; distillation is now commenced, taking 
care to cool well, and the operation discontinued when the 
mass begins to swell. The distilled product is turbid, has an 
acid reaction, and a strong odour of prussic acid, of which it 
contains a large quantity. It is redistilled over oxide of mer- 
cury, collecting only the first portions ; as soon as the liquid 
which passes has lost its aromatic odour and is decidedly acid, 
it is tolerably certain that all the oily constituents have passed 
over. The product amounts to from one-fifteenth to one- 
twentieth of the whole. After having separated the oily por- 
tions, the recipient is changed and the distillation continued ; 
a turbid liquid now passes, which contains the volatile acids in 
solution; it is neutralized with bary tic water, and after eva- 
poration the barytic salts decomposed by sulphate of soda, and 
the soda salts submitted to distillation with dilute sulphuric 
acid. The product thus obtained is a concentrated aqueous 
solution of the volatile acids ; it has a strong smell of vinegar 
and cheese. To effect the separation of the acids, the liquid 
is saturated with carbonate of soda and evaporated to dryness, 
the dried soda salt reduced to powder and agitated with dilute 
sulphuric acid (1 part of acid to 3 of water) in a narrow cylin- 
3* 
