52 



PROTEINS. 



Lehmann found that in " genuine " casein 1*4:5 to 1-75 parts 

 of lime were combined with 100 parts of casein ; and Soldner 

 has also shown that two lime compounds exist containing 1*55 

 and 2-39 per cent. CaO respectively. 



N 

 The author has found that -^-r sodium and potassium carbonate 



JLwv/ 



solutions treated with an excess of casein dissolve 1-86 and 1-83 

 parts per 100 c.c. respectively. 



Levites has also shown that casein contains 0*93 per cent, of 

 nitrogen removed by the action of nitrous acid i.e., as free 

 NH 2 group this compound, however, yielded as much nitrogen 

 as ammonia (1-67 per cent.) as the original casein. 



When dissolved in dilute alkali it has a Isevo -rotatory action 

 on polarised light. J. H. Long gives the specific rotation of 

 casein when 5 grammes are dissolved in 100 c.c. of water with 



N 

 the number of c.c. of -alkali given as follows : 



NaOH, 



KOH, 

 LiOH, 



NH"OH, 



22-5 



45-0 



67-5 



90 



45 



22-5 



45 



45 



- 95-2 : 



- 103-5 C 



- 107-6 C 

 111-8 C 



- 104-4 C 



- 94 -8 C 



- 100 -8 C 



- 97-8 c 



It is precipitated completely from milk by copper sulphate ; 

 if the solution be neutral, a definite compound containing about 

 1 per cent, of copper is obtained ; basic compounds are probably 

 obtained if the solution be alkaline. Mercury salts precipitate 

 casein completely, even in acid solution ; it is also precipitated 

 by meta-phosphoric acid. 



The composition of casein is as yet unknown, though there 

 are certain considerations which throw some light on the probable 

 formula ; it is highly probable that the sulphur and phosphorus 

 exist in molecular proportions, though the mean percentage of 

 phosphorus is practically always found to be higher than that 

 of the sulphur, but Van Slyke and Bosworth have shown that 

 if the whole of the calcium be removed during the purification 

 of the casein by precipitation with ammonium oxalate, the per- 

 centage of phosphorus is lower than that found previously, 

 going down to about 0-70 per cent., and Van Slyke and Baker 

 find 0-80 ; the sulphur, on the other hand, is partially removed 

 by alkaline treatment, and as casein is purified by continued 

 dissolution in alkalies, the sulphur will tend to be low. The sum 

 of the two will, however, tend to be more nearly correct, and the 

 ratio between the sum divided by the sum of the atomic weights 



