100 SCIENCE PROGRESS 
caustic soda solution until the free hydrochloric acid is neutral- 
ised, then an excess of finally granulated potassium carbonate. 
For convenience, the residue from a kilogram of protein is 
divided into four or six portions, which is of great importance 
in ensuring thorough cooling of the mixture. The esters of 
aspartic acid and glutamic acid, which are very sensitive to 
alkali, are thus first separated and dissolved by the ether which 
is poured off and renewed by adding a fresh quantity. The 
other esters are then liberated by adding 33 per cent. caustic 
soda, the whole mass being well shaken with the ether, which 
is from time to time renewed and replenished by another supply. 
Finally, sufficient alkali to combine with the whole of the 
hydrochloric acid and solid potassium carbonate is added, so 
that a pasty mass is formed, whereby the esters, which are very 
easily soluble in water, are salted out and extracted by the ether. 
Throughout the whole process thorough cooling is absolutely 
essential, and a large amount of ether is required. 
The combined ethereal extracts are dried by shaking first 
with potassium carbonate for ten to fifteen minutes, from which 
they are poured off, and then for twelve hours with anhydrous 
sodium sulphate. The ether is distilled off, preferably at 
the ordinary temperature in vacuo, and a brown oil remains, 
consisting of the esters of the amino acids. 
In the process of extraction a certain quantity of the esters 
is destroyed by the alkali and therefore not taken up by 
the ether. The amino acids can be recovered from this by 
neutralising with hydrochloric acid, filtering off the potassium 
chloride as it separates on concentration, extracting the residue 
with alcohol, and repeating the above process of esterification. 
This may be repeated again, but a certain loss still occurs. To 
avoid this as far as possible it is preferable to liberate the esters 
from their hydrochlorides by means of sodium ethylate. This 
is the second and newer method. The hydrochloric acid is 
therefore removed as completely as possible by evaporation in 
vacuo, the residue dissolved in five or six times its quantity of 
alcohol, and in a small portion of this the amount of chlorine 
is determined. The calculated amount of sodium dissolved in 
alcohol to combine with the whole of the chlorine is then added 
to the thoroughly cooled solution, the sodium chloride formed 
filtered off, and the alcoholic solution evaporated under greatly 
diminished pressure. A certain quantity of the lower-boiling 
