54 



PROTEINS. 



CaO, results substantially confirmed by Van Slyke and Hart ; 

 3CaO to the molecule is equal to 1-40 per cent., and 5CaO (the 

 neutral salt) to 2-34 per cent. 



Van Slyke and Bosworth have prepared what they term 

 monobasic compounds with the alkalies and alkaline earths 

 which contain 



NH 4 



Na, 

 K, 



0-20 - 1-40 



Atom to molecule 

 containing 134 



atoms of 



nitrogen. 



0-26 = -36 



0-44 = -35 



0-13 = -28 



0-22 - -32 



Sr, 0-48 = -32 



Ba, 0-76 = -33 



these compounds do not agree with any simple ratio, but 

 show a marvellous concordance, and have led Van Slyke and 

 Bosworth to conclude the casein has a molecular weight of 

 8,888 and to be 8 basic. It is by no means established that 

 these are molecular compounds, and the evidence from the salts 

 of casein, except the neutral salt, is of comparatively minor value. 



The composition of the casein complex as it exists in milk is 

 elucidated by the observations given below. 



By filtering through a porous cell, by boiling with the minimum 

 amount of acid required to precipitate the curd at 100, or by 

 curdling w T ith rennet, the casein carries down with it in each case 

 the same amounts of phosphoric acid (including that of the casein) 

 and lime. The figures are for 0-477 per cent, nitrogen in each case: 



CaO. 

 0-116 



Porous cell, 



Acid, 



Rennet, 



P 2 5 . 

 0-123 



Mean, 



0-120 

 0-119 

 0-118 



0-120 

 0-117 

 0-120 



The amount of ash in the last two cases was 0-23, which is prac- 

 tically the sum of the CaO -f P 2 5 , while in the former it was 0-27, 

 the difference being alkali approximately equal to the acidity. 



The P 2 5 calculated for 3 P to 134 N = 0-054 per cent., and 

 the remainder of the P 2 5 0-066 per cent. = 11-0 equivalents 

 or 3-67 mols. of P 2 5 as phosphate ; the CaO is 16-7 equi- 

 valents, leaving 5-7 = 2-85 molecules CaO combined with the 

 casein. The acidity = 3-34 molecular, and this replaces alkali 

 when the curd is removed. It appears then that casein in milk 



o ,G<~r 



is Ca 2 . 85 Na s . 3 (casein) H x- (Ca 3 P 2 8 ), or, rounding off the figures, 

 z 



is Ca 3 Na 3 H (casein) . 2Ca 3 (P0 4 ) 2 , a slightly acid salt, and in 

 equilibrium with the slightly acid serum. 



On boiling with a quantity of acid just sufficient to combine 



/ pQctpin \ 

 with the sodium, this is removed, and a salt Ca 3 H 4 I A ) 



