62 THE GENERAL CHARACTERS OF THE PROTEINS 



solution, and precipitation from the latter by dilute acetic acid. 

 From egg-albumin (not crystalline) a product containing 3*62 per 

 cent, of chlorine was obtained. By a modification of the method, pro- 

 ducts containing other quantities of chlorine could be obtained. Thus 

 by chlorinating in the presence of potassium chlorate, dissolving the 

 precipitate thus formed in alcohol, and adding ether to the alcoholic 

 solution, a derivative was obtained which contained 6*41 per cent, of 

 chlorine. As will be noticed later, a definite series of bromine 

 derivatives could be obtained from proteins, each with a constant 

 amount of bromine, by varying the method of preparation. It was 

 not found possible to obtain such a definite series either with chlorine 

 or iodine preparations. 



Blum and Vaubel prepared chlorine preparations from proteins 

 in the presence of sodium hydroxide; they state that it is impossible 

 to obtain products containing the maximum amount of combined 

 chlorine in the presence of free acid, which is formed by the action of 

 halogen on the protein ; consequently they carried out the reactions 

 in the presence of sodium hydroxide, which was added from time to 

 time to neutralise the acid as it was formed in the reaction. They 

 obtained from egg-albumin and caseinogen preparations containing 

 2 per cent of chlorine. 



Habermann and Ehrenfeld prepared a chlorine derivative from 

 caseinogen. They dissolved 100 grams of the protein in 700 

 c.c. of 5 per cent, potassium hydroxide solution, to which was added 

 50 grams of potassium chlorate; through this solution hydrogen 

 chloride gas was passed. After completion of the reaction the 

 liquid was filtered off from the potassium chloride formed during 

 the reaction, and diluted with water, whereupon the chloro derivative 

 separated, which contained between 13 and 14 per cent, of halogen. 



Panzer also prepared a chlorine derivative of caseinogen. He made 

 a paste of i kilogram of the protein with 4 litres of 20 per cent, 

 hydrochloric acid ; to this 450 grams of potassium chlorate were 

 added in small quantities at a time, and considerable evolution of heat 

 took place. After cooling water was added, and the undissolved sub- 

 stance filtered off. This was a chlorine derivative containing about 

 8*3 per cent, of chlorine considerably less than that in the prepara- 

 tion which Habermann and Ehrenfeld obtained by a similar method. 



Bromine Derivatives of Proteins. 



Some preliminary investigations on the action of bromine on 

 proteins were published by Loew, but most of our knowledge on this 

 subject is due to the investigations of Hopkins and Pinkus. As 

 already mentioned, they obtained different products with definite 

 bromine content by varying the methods of preparation. They 

 obtained three distinct bromine derivatives from egg-albumin. 

 Derivative I. was obtained by treating the protein solution in the 

 cold with bromine until the solution was distinctly coloured ; a 

 precipitate (crude bromination product) formed suddenly ; this was 

 dissolved in I per cent, sodium hydroxide, from which it was 

 precipitated by the addition of acetic acid. The precipitate was 

 dialysed against water, and then washed with alcohol, in which it 

 is only slightly soluble. It contained 3*92 per cent, of bromine. 

 Derivative II. was prepared by dissolving the crude bromination 



