Milk is a complete food, and, therefore, naturally it is not a simple chemical compound, but a mechanical mixture of a number of substances. The present state of chemical knowledge on the subject does not permit of its composition being given in detail, but for practical purposes, such as those of measuring its purity and food value, this is not necessary.
A proximate analysis, in which, at least, some of the ingredients are lumped together, is sufficient, and has been adopted everywhere by analysts. On this basis the average composition of cows' milk may be stated as follows:
| Per cent. | |
| Water | 87.50 |
| Fat | 3.50 |
| Casein and albumen | 3.65 |
| Milk sugar | 4.60 |
| Ash | 0.75 |
| ——— | |
| 100.00 | |
| ——— |
The constituents other than water added together form the "total solids," and they amount to 12.5 per cent.
| Per cent. | |
| Water | 87.50 |
| Total solids | 12.5 |
| —— | |
| 100.0 | |
| —— |
The Constituents of Milk
In the illustration, a pint of milk is shown in a glass jar, and the various percentages of water, casein, sugar, ash, albumen, and fat, which make up its constituent parts, are shown in separate bottles, the percentage of each being stated beneath.