80 
Proceedings of Royal Society of Edinburgh. 
SESS. 
The Alkaline Earths as Precipitants of Casein. 
Of these, calcic salts seem to be the readiest precipitants, only 
the soluble salts of calcium having any effect, which shows that 
this precipitation of pro-casein is not a mechanical process occurring 
round the particles of an insoluble salt as round foci, for the calcic 
phosphate, carbonate, and hydrate (the two former being added 
solid) have no precipitating power at all. Ringer, indeed, holds 
that CaH 2 0 2 dissolves casein. The soluble salts of barium and 
strontium also precipitate pro-casein, the following of which were 
tested — baric chloride, nitrate, carbonate, strontic nitrate, and 
lactate. (The rather insoluble baric carbonate has not much preci- 
pitating power). Thus one cannot say it is the metal calcium 
which is effective in this precipitation, because both Ba and Sr can 
act vicariously ; nor is it the Cl in association with it, seeing that 
CaS0 4 , CaS, and Ba2(R0 3 ), that is to say sulphuric acid, sulphur, 
and nitric acid act equally well. The salts of magnesium have little 
or no precipitating power ; this is interesting in that magnesium is 
the lightest atomically of the group, so that the three alkaline earths, 
Ca, Ba, and Sr, which have so many properties in common, have this 
additional one — the power of precipitating pro-casein. Of course, 
MgS0 4 in saturation precipitates it just as it does caseinogen. 
The union of some calcic salt with pro-casein in the normal clotting 
of milk is alluded to later. Chlorides of the heavy metals preci- 
pitate it ; RaCl does not. Chlorine w 7 ater and pure iodine each 
precipitates pro-casein. 
It is interesting that calcic orthophosphate, being the chief 
calcic salt native in milk, should be so inert when added pure to 
milk or “ decalcified ” milk. Since it appears in the various wheys, 
it must be soluble in milk-plasma ; but may, of course, be in some 
kind of combination with the caseinogen too. I have failed to 
imitate any such solution of Ca 3 2(P0 4 ) in egg-albumin. 
III. The Chemistry of Casein. 
The product of rennet action, the curd, if allowed to dry, will of 
itself become a horny dull yellow mass of brittle character, and 
breaking with a vitreous fracture. Without any such pressure as is 
