98 SCIENCE PROGRESS 



separation and identification of the monoamino acids, on the 

 other hand, by the older methods was extremely crude, and 

 only where a large amount of one or two of the monoamino 

 acids was present, was their isolation and characterisation 

 carried out. Fischer, by introducing the ester method of sepa- 

 rating the monoamino acids from one another, has advanced our 

 knowledge of these acids considerably. His method, though 

 not yet quantitative, gives us the means of obtaining about 

 70 per cent, of the total products. 



In the majority of his experiments Fischer used concentrated 

 hydrochloric acid as the hydrolysing agent, in some cases dilute 

 sulphuric acid. This is particularly useful when tyrosine and 

 diaminotrioxydodecanic acid only require isolation, the best 

 results being obtained by boiling the protein for twelve to 

 fifteen hours with five to six times its quantity of 25 per cent, 

 sulphuric acid. This solution, after filtration and dilution with 

 twice its volume of water, is neutralised with baryta, the excess 

 of which is removed with sulphuric acid. The solution, after 

 thoroughly washing out the precipitate of barium sulphate, is 

 concentrated till these acids crystallise out. This method is 

 extremely simple, but requires many days to carry out, as the 

 filtration and washing out of the barium sulphate is very 

 laborious. An improvement has recently been introduced 

 by Abderhalden and Teruuchi, who use hydrochloric acid to 

 hydrolyse the protein ; after removal of the greater quantity 

 of hydrochloric acid by evaporation in vacuo, the solution is 

 treated with caustic soda in sufficient amount to exactly combine 

 with the remainder of the hydrochloric acid, when the tyrosine 

 crystallises out. 



In all cases where the separation of tyrosine was not required, 

 hydrochloric acid was used as the hydrolysing agent on account 

 of its far greater convenience. The protein is covered with three 

 times its quantity of concentrated hydrochloric acid in a flask ; 

 in a short time the majority of the proteins go into solution if 

 the vessel be occasionally shaken, and the hydrolysis is com- 

 pleted by boiling the solution under a reflux condenser for five 

 or six hours. The solution first becomes dark violet in colour 

 and then dark brown ; a large proportion of the hydrochloric 

 acid escapes as gas, and a solution remains consisting of the 

 hydrochlorides of the amino acids in 25 per cent, hydrochloric 

 acid. Humin substances and fat-like masses, which separate 



