THE CHEMISTRY: OF “THE -PROTEINS 103 
processes of hydrolysis and esterification, its rotation is gener- 
ally found too low, and the melting-point of its benzoyl 
derivative is not quite sharp. 
The presence of valine, or a-aminoisovalerianic acid, is not 
mentioned in this paper. Its separation from leucine, with 
which it is generally present, is carried out with difficulty, and 
depends on the fractional crystallisation of the free acids and 
their copper salts. 
Leucine, again, as it results on hydrolysis, is _ partially 
racemised. Its characterisation is therefore more difficult, but 
this is carried out by completing the racemisation by heating it 
with baryta at 170-175° C. for twenty-four hours, and then con- 
verting it into its hydantoin derivative. Isoleucine is probably 
mixed with leucine, but no special separation of this isomer was 
performed by Fischer. 
Proline is the only amino acid which is easily soluble in 
absolute alcohol. By evaporating the mixture in which it is 
contained to dryness and extracting with absolute alcohol, 
it can be easily isolated. This compound, when obtained by 
hydrolysis, also exists in the racemic and optically active 
forms; by conversion into the copper salt the two varieties 
can be separated by alcohol in which the copper salt of the 
active form is soluble. The racemic acid is characterised by 
a determination of the amount of water and the content in 
copper of its copper salt, the active acid by its hydantoin 
derivative. 
Phenylalanine is so easily isolated as ester that an analysis 
of its hydrochloride, obtained by evaporating the ester to dry- 
ness with hydrochloric acid, is sufficient for its identification. 
Small quantities can be identified by oxidation to phenylacet- 
aldehyde, which has a very distinctive smell. 
Serine, on account of the insolubility of its ester in petroleum 
ether, generally requires no great amount of work to charac- 
terise it. After hydrolysis by baryta, the solution is concen- 
trated when it crystallises out, and elementary analysis 
determines its nature. The #-naphthalene sulpho-compound 
may be used, if further characterisation be necessary. 
Aspartic and glutamic acids are separated partially after the 
hydrolysis of their esters by baryta, when the barium salt of 
dl-aspartic acid crystallises out on cooling. A further quantity 
may be isolated by crystallisation of the free acid, but the 
