444 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



(r) Serum is half-saturated with ammonium sulphate. The pre- 

 cipitate is treated with saturated sodium chloride solution. The 

 globulin is insoluble. It can be purified by dissolving in dilute salt 

 solution and precipitating with sodium chloride. 



The globulin is obtained in a coagulated state by treating the 

 precipitate with alcohol and ether, or it may be obtained by dissolving 

 in dilute salt solution, acidifying and boiling. The coagulum is 

 washed with boiling water and dried with alcohol and ether. 



Properties. 



The uncoagulated protein is a white amorphous substance, insoluble 

 in water, but soluble in dilute salt solutions. It is precipitated by 

 saturating its solution with sodium chloride or magnesium sulphate or 

 by half-saturation with ammonium sulphate. 



It gives the general reactions of the proteins and is a typical 

 globulin. The coagulated protein is insoluble, but dissolves on warm- 

 ing in dilute acids and alkalies, undergoing conversion into derivatives. 



Pseudoglobulin. 



Preparation. 



Serum is half- saturated with ammonium sulphate solution. The pre- 

 cipitate is treated with saturated sodium chloride solution. The pseudo- 

 globulin dissolves and is thrown out again by half-saturation with ammonium 

 sulphate. It is dissolved in sodium chloride solution and the solution 

 dialysed. 



In a coagulated state it is obtained by precipitating with alcohol and 

 drying with alcohol and ether, or by acidifying the solution and boiling, drying 

 the coagulum after washing with alcohol and ether. 



Properties. 



The uncoagulated protein, if its solution in water be evaporated in vacuo, 

 will form an amorphous glassy mass of a yellow to brown colour. The coagu- 

 lated protein is an amorphous white or nearly white powder. 



Pseudoglobulin is not a typical globulin as it is soluble in water and in 

 saturated sodium chloride solution. 



Its solution gives the general reactions for proteins. 



Serum Albumin. 



Preparation. 



Serum albumin remains in solution after the globulins have been 

 precipitated by half-saturation with ammonium sulphate. It is pre- 

 cipitated by complete saturation of the filtrate with ammonium sulphate. 



It is purified by dissolving in water, half- saturating with ammonium sul- 

 phate, filtering and completely saturating with ammonium sulphate and re- 

 peating the process several times. The final solution is dialysed to remove 

 ammonium sulphate and the coagulated protein obtained either by acidifying 

 and boiling, or by precipitation with alcohol, or it may be evaporated in vacua. 



