MILK owes its whiteness and opacity to an emulsion composed of the caseons matter and butter, with sugar of milk, extractive matters, salts, and free lactic acid ; the latter of which causes fresh milk to redden litmus paper. Milk, in general, contains from 10 to 12 per cent. of solid matter, on being evaporated to dryness by a steam heat. The mean spe cific gravity of cows' milk is 1.030, but it is less if the milk be rich in cream. The specific gravity of the skimmed milk is 1.085; and of the cream is 1.0244. 100 parts of creamed milk contain— Osseous matter, containing some butter 2'600 Sugar of milk 3'500 Alchoholie extract, lactic acid, and lactates 0'600 Salts ; muriate and phosphate of pot ash, and phosphate of lime 0'425 Water 92'875 Cream consists of—butter separated by churning Osseous matter precipitated by the coagulation of the milk of the but ter Butter-milk 92•0 100'0 When milk, contained in wire-corked bottles, is heated to the boiling point in a water bath, the oxygen of the included small portion of air under the cork seems to be carbonated, and the milk will after wards keep fresh, it is said, for a year or two • as green gooseberries and peas do by the same treatment.
Milk is sometimes adulterated with po tato starch, which gives it a creamy con sistence. This fraud may be detected by pouring a few drops of solution of iodine into it, which immediately gives it a blue or purple tint. Emulsion of almonds, also occasionally used, may be detected by the taste.
The substances most commonly used for. the purpose of adulteration appear to be water, flour, starch, and finely pow dered chalk.
On examining a little of the milk under the microscope, the peculiar granules of starch and flour may be readily seen, larger and more oval than the milk glob ules, if either of these substances are pre sent. Should any doubt exist as to their real nature, the addition of a drop or two of the solution of iodine will impart to the farina granules a dark purple color. The presence of chalk may be still more easily discovered, since, owing to specific gravity, it soon subsides to the bottom of the liquid, where it may at once be recognized by its effervescing on the addition of a little muriatic acid.
We have no chemical means of ascer taining whether water has been fraudu lently added to milk, the only effect being to dilute it and render it poor in quality. A knowledge of the specific quantity can not here be made available, since the ab straction of cream, which has a lower specific gravity than milk, may be made to neutralize the effect produced by the addition of water ; the tendency of the removal of the cream being to raise the specific gravity of the fluid, and that of the addition to lower it.. A specimen of milk, therefore, which has been impover ished by the abstraction of its cream, and still further weakened by the addition of water, may be made to possess the same specific gravity it had when taken pure from the cow.
A new method of increasing the quan tity of cream produced from milk, and preserving milk, has been discovered by Francis Bernard Bekaert, a citizen of Bel gium, and we find it thus described in Newton's London Journal for January, 1848, in an account of a patent for the purpose, taken out in England :—" The invention consists, firstly, in a method of increasing the quantity of cream pro duced from milk, by the addition of one table-spoonful of the liquid, hereafter de scribed, to every quart of new milk ; the milk is then stirred once or twice round, and left in the pan or vessel the and the skimming may take place at the expira tion of the usual time, but the patentee prefers to delay it a little. He states that, by the application of the liquid, is much larger quantity is forced to the surface of the milk than can be obtained in the or dinary way. The liquid is prepared by adding to one quart of water, one ounce of the carbonate of soda, one tea-spoon ful of a solution of turmeric or cureinna, and three drops of marigold water. When nicking large quantities of the li quid, it is not requisite to weigh the soda, as the same purpose is answered by putting such a quantity of soda into water as will, when dissolved, on appli cation of a salometer known in Belgium, by the denomination of apereset,' show a density equal to ten degrees. The soda is first mixed with the water, and then the solution of turmeric and the marigold water are added.