io THE CHEMICAL CONSTITUTION OF THE PROTEINS 



(ii) Dilute Acid. 



Hydrolysis may be equally well affected by boiling the protein 

 with from 1020 parts of 20 per cent, hydrochloric acid for twenty- 

 four to forty-eight hours. [Van Slyke, 1911, 4.] 



Henriques and Gjaldbak [1910] have found that complete hydro- 

 lysis is produced by heating the protein with 3N hydrochloric acid 

 in an autoclave at 150 for one and a half hours. These observers 

 made no statement as to the quantity of acid they used. Their ex- 

 periments were confirmed by Van Slyke [1912, 2] who hydrolysed I '5 

 grams of protein with 50 c.c. of 3N acid, i.e., with thirty-three times 

 the quantity. Van Slyke showed further that complete hydrolysis was 

 effected either by heating at 100 for forty-eight hours with 20 per 

 cent, acid or at 150 with 3N acid. Henriques and Gjaldbak [1910] 

 found that the hydrolysis of egg albumin was not complete by 

 heating for twelve hours with concentrated acid, but was complete on 

 heating at 150 for 1-5 hours in an autoclave with 3N acid. There 

 was no advantage in heating at 1 50 for a longer period of time ; at 

 1 80 in an autoclave decomposition of the amino acids occurred with 

 the formation of ammonia. 



(iii) Alcoholic Hydrochloric Acid. 



Proteins are also hydrolysed by boiling with alcohol saturated with 

 hydrogen chloride. Pribram [1911] first drew attention to this fact, 

 showing that hydrolysis occurred with carefully dried protein and 

 carefully dried reagents ; the hydrolysis was more complete if the alco- 

 hol contained 3-5 per cent, of water. Similar results were previously 

 published by Pfannl [1910]. They are not in accordance with those 

 of Abderhalden and Hanslian [1912], who showed that no appreciable 

 hydrolysis took place if moisture was carefully excluded during all 

 operations. Weizmann and Agashe [1913] have isolated small quan- 

 tities of amino acids, but consider that the main result of hydrolysis 

 with alcoholic hydrochloric acid is the formation of complex products 

 intermediate between protein and amino acid. Herzig and Land- 

 steiner [1914] estimated the amount of esterification in the case of 

 serum proteins which were heated with various strengths of alcoholic 

 hydrochloric acid. Their results also show that hydrolysis of the 

 protein takes place, but only to a small extent. 



