160 
The Phosphates of Milk. 
a small quantity of soluble phosphate of soda or potash mechanically 
retained by the layer of suspended casein which coats the surface of 
the filter. Even if it were all supposed to represent phosphorus 
chemically combined with the casein, it would amount to only one- 
tenth of the phosphorus present in casein, as given by Hammersten in 
his Traite de Chimie Physiologique. There is, therefore, every 
reason to believe that the phosphorus found by all analysts in the 
purest preparations of precipitated casein really belongs to phos- 
phate of lime entangled in the precipitate, and forms no part of the 
chemical molecule of casein. 
Passing to the minerals in solution, it will be seen that these 
include sensible quantities of both phosphoric acid and lime ; hence 
some phosphate of lime must exist in true solution in milk. The 
quantity of phosphoric acid is nearly double that required to form 
the tribasic phosphate of lime ; but as the ash of the filtered milk 
is alkaline, instead of acid, it cannot be admitted that a mixture of 
monocalcic and bicalcic phosphates is present in the solution. In 
all probability, the alkalinity of the ash is due to trisodium phos- 
phate, and, adopting this view, three-fourths of the saline ingredients 
of the filtered milk are thus accounted for : — 
Grammes 
Phosphate of lime (tribasic) 0107 
„ soda „ OTO-1 
Common salt 0 - 140 
0-351 
According to this view, milk would contain in solution over one 
part in a thousand of the alkaline phosphate of soda, a quantity suffi- 
cient to render its reaction perceptibly alkaline to litmus, whereas, in 
fact, it is slightly acid ; moreover, the tribasic phosphate of lime is an 
insoluble salt in the proportion represented. These objections are 
met by the discovery of Soxhlet, that milk contains citric acid in 
quantity reaching nearly one part per thousand. It is evidently 
this citric acid which is combined with the excess of soda in the 
fresh milk to form sodium citrate, and this, in common with the other 
alkaline citrates, has the property of dissolving tribasic phosphate 
of lime. The phosphate of soda in the fresh milk will then be the 
ordinary neutral bibasic phosphate, and on calcination this will 
combine with the soda set free by the burning off of the citric acid 
to form the alkaline trisodium phosphate found in the ash. 
The analyses of other milks cited by M. Duclaux give similar 
results. It appears that phosphatised milk, or milk supposed to be 
enriched beyond the normal proportion in phosphates, is advertised 
on the Continent at a high price ; this is claimed to be natural milk, 
the enrichment being supposed to be brought about by an addition 
of phosphates to the food given to the cows. The author’s analyses 
show that in three cases examined these milks were no richer in 
phosphates than ordinary milk, so that it is, to say the least, 
extremely doubtful whether any augmentation in the proportion of 
phosphates can be produced by this means. On the other hand 
