Open main menu

Page:Popular Science Monthly Volume 24.djvu/516

This page has been validated.
500
THE POPULAR SCIENCE MONTHLY.

We may therefore conclude that, regarding these from the point of view of nitrogenous or flesh-forming, and carbonaceous or heat-giving constituents, these chief materials of flesh and of cheese are about equal.

The same is the case as regards the fat. The quantity in the carcass of oxen, calves, sheep, lambs, and pigs varies, according to Dr. Edward Smith, from 16 per cent to 31·3 per cent in moderately-fatted animals, while in whole-milk cheeses it varies from 21·68 per cent to 32·31 per cent, coming down in skim-milk cheeses as low as 6·3. Dr. Smith includes Neufchâtel cheese, containing 18·74 per cent among the whole-milk cheeses. He does not seem to be aware that the cheese made up between straws and sold under that name is a ricotta, or crude curd of skim-milk cheese. Its just value is about threepence per pound. In Italy, where it forms the basis of some delicious dishes (such as budino di ricotta, of which anon), it is sold for about twopence per pound or less.

There is a discrepancy in the published analyses of casein which demands explanation here, as it is of great practical importance. They generally correspond to the above of Mulder within small fractions, as shown below in those of Scherer and Dumas:

Scherer. Dumas.
Carbon 54·665 53·7
Hydrogen 7·465 7·2
Nitrogen 15·724 16·6
Oxygen, sulphur 22·146 22·5

In these the one hundred parts are made up without any phosphate of lime, while, according to Lehmann ("Physiological Chemistry," vol. i, p. 379, Cavendish edition), "casein that has not been treated with acids contains about six per cent of phosphate of lime; more, consequently, than is contained in any of the protein compounds we have hitherto considered."

From this it appears that we may have casein with, and casein without, this necessary constituent of food. In precipitating casein for laboratory analysis, acids are commonly used, and thus the phosphate of lime is dissolved out; but I am unable at present to tell my readers the precise extent to which this actually occurs in practical cheese-making where rennet is used. What I have at present learned only indicates generally that this constituent of cheese is very variable; and I hereby suggest to those chemists who are professionally concerned in the analysis of food, that they may supply a valuable contribution to our knowledge of this subject by simply determining the phosphate of lime contained in the ash of different kinds of cheese. I would do this myself, but, having during some ten years past forsaken the laboratory for the writing-table, I have neither the tools nor the leisure for such work; and, worse still, I have not that prime essential to practical re-