THE PHYSICAL PROPERTIES OF THE PROTEINS 23 



diluted to 10 c.c. ; the numbers in the first horizontal line indicate 

 the number of cubic centimetres of normal solutions of various salts 

 contained in the 10 c.c. 



INFLUENCE OF VARIOUS CHLORIDES ON COAGULATION POINT. 



It will be seen from the above table that the increase in the 

 quantity of salt raises the coagulation temperature up to a certain 

 point, after which, in some cases, further additions of salts cause no 

 increase, and in other cases even a diminution. 



It is not necessary here to discuss the physical meaning of such 

 numbers as these ; enough has been said to indicate that the coagula- 

 tion temperature is a constant which is markedly influenced by a 

 variety of factors. The chief ones are, as Starke pointed out : (i) the 

 reaction of the solution, (ii) the amount of neutral salts present, in a 

 minor degree (iii) the concentration of the protein, and (iv) the rate at 

 which the solution is heated. Far less reliance can be placed on co- 

 agulation temperatures as a constant for identification of proteins than 

 on such a constant as the melting point of a crystalline substance, 

 especially when it is remembered that it is often difficult to exactly 

 regulate the amount of salt, acid or alkali present in any given 

 solution. 1 



Method (according to Pauli). 



The liquid to be tested is placed in a test-tube, provided with a 

 stirrer, and in it is immersed a thermometer graduated in -^ or T 2 o de- 

 grees. The test-tube is immersed in water in a beaker of I litre 

 capacity, which is likewise provided with a thermometer and stirrer. 

 The whole is slowly heated with a small burner, the liquid in both 

 test-tube and beaker being carefully stirred, so that both vessels attain 

 the same temperature. When there is a black background and the 

 apparatus receives light from two sides the smallest turbidity is readily 

 recognised. The time a solution takes to coagulate should also be 

 noticed ; this factor bears no relation to the coagulation tempera- 

 ture. 



1 Wolfgang Ostwald has recently represented the relation between the amount of 

 salt present and the coagulation temperature by the following equation -^ = kc m where 



t = temperature, c salt concentration, and k and m are constants. He draws attention to 

 the similarity between this and an adsorption equation. Pauli, in some very recent 

 work, comes to the conclusion that the coagulation point is influenced by the condensa- 

 tion of ions on the surface of the colloidal particles. 



3 



