48 THE PROTEINS. [CH. II. 



(b) To another add one drop of strong acetic acid. A white 



precipitate of serum-albumin i? formed. 



(c) Grind the remainder in a mortar with solid ammonium 



sulphate, till the fluid is saturated. A white precipitate 

 of serum-albumin is formed. Filter off the precipitate 

 and test the nitrate for proteins either by boiling or by 

 the glyoxylic or xanthoproteic reactions. Proteins are 

 absent, showing that all the proteins of serum are precipi- 

 tated by complete saturation with ammonium sulphate. 



NOTE. A certain test for albumin in a solution is to half-saturate it with 

 ammonium sulphate, filter off any precipitate that may be present and boil the 

 filtrate. A heat-coagulum indicates albumin. 



38. Serum has been dialysed in collodion sacs (see p. 2) for 

 24 hours against distilled water in a tall cylinder. Note the heavy 

 precipitate of serum-globulin that has fallen to the bottom of the 

 sac. Pipette off some of the clear fluid and add an equal volume of 

 saturated ammonium sulphate. A precipitate of "pseudo-globulin " 

 (see note on p. 46) is obtained. Now pipette off some of the deposit, 

 add about two volumes of distilled water, and divide into three 

 portions, A, B, and C. To A add a couple of drops of saturated 

 ammonium sulphate. To B add a drop of dilute soda. To C add a 

 drop or two of dilute HC1. The globulin dissolves in each case. 



39. Dilute 3 cc. of serum with about five times its volume of 

 tap water, add a drop of 2 per cent, calcium chloride, and boil the 

 mixture in a boiling tube. Add one drop of I per cent, acetic 

 acid and boil again. Continue this procedure until a definite 

 coagulum has formed, and the fluid between the flocks appears to be 

 clear when examined in a thin layer. Filter. The filtrate should 

 run through the paper rapidly and be crystal clear. If it filters 

 slowly or comes through opalescent, repeat the experiment until 

 the desired result is obtained. Test the filtrate for proteins by 

 Millon's and the xanthoproteic tests. Only insignificant traces 

 should be found. 



NOTE. This is the method usually adopted for removing albumins and 

 globulins from solution, but it must be noted that it is almost impossible to 

 remove the last traces by this procedure. If it is necessary to do so, colloidal 

 iron (see Ex. 310), metaphosphoric acid (see Ex. 17), or some other reagent must 

 be employed. The objection to the use of such reagents is that they are apt 

 to precipitate the proteoses, peptones, etc. 



