ioo 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 



