For the purpose of showing the difference in the specific gravity in different specimens of pure milk, taken from the cows in the morning, and allowed to cool down to about 60°, I used the latter instrument with the following results: The first pint drawn from a native cow stood at 101°, the scale being graduated at 100° for pure milk. The last pint of the same milking, being the strippings of the same cow, stood at 86°. The mixture of the two pints stood at about 931⁄2°. The milk of a pure-bred Jersey stood at 95°, that of an Ayrshire at 100°, that of a Hereford at 106°, that of a Devon at 111°, while a thin cream stood at 66°. All these specimens of milk were pure, and milked at the same time in the morning, carefully labelled in separate vessels, and set upon the same shelf to cool off; and yet the variations of specific gravity amounted to 25°, or, taking the average quality of the native cows’ milk at 931⁄2°, the variations amounted to 171⁄2°.
But, knowing the specific gravity, at the outset, of any specimen of milk, the hydrometer would show the amount of water added. This cheap and simple instrument is therefore of frequent service.
The lactometer is a very different instrument, and measures the comparative richness of different specimens of milk. It is of very great service both in the butter and cheese dairy, for testing the comparative value of different cows for the purposes for which they are kept. This instrument is very simple and cheap and the practical dairyman can tell by it what cows he can best part with without detriment to his business. No cow should be admitted to a herd kept for butter-making without knowing her qualities in this respect.
Many would find, on examination, that some of their cows, though giving a good quantity, were comparatively worthless to them. Such was the experience of John Holbert, of Chemung, New York, who, in his statement to the state agricultural society, says: “I find, by churning the milk of each cow separately, that one of my best cows will make as much butter as three of my poorest, giving the same quantity of milk. I have kept a dairy for twenty years, but I never until the past season knew that there was so much difference in cows.”
Fig. 72. Lactometer.
The simplest form of the lactometer is a series of graduated glass tubes ([Fig. 72]), or vials, of equal diameter; generally a third of an inch inside, and about eleven inches long. The tubes are filled to an equal height, each one with the milk of a different cow, and allowed to stand for the cream to rise. The difference in thickness of the column of cream will be very perceptible, and it will be greater than most people imagine. The effect of different kinds of food for the production of butter may be studied in the same way. This form of the lactometer was invented by Sir Joseph Banks.
Various means are used for the preservation of milk. One of these is by concentrating it by boiling. Where this is followed, as it is by some dairymen, as a regular business, the milk is poured, as it comes from the dairy, into long, shallow, copper pans, and heated to a temperature of a hundred and ten degrees, Fahrenheit. A little sugar is then mixed in, and the whole body of milk is kept in motion by stirring for some three or four hours. The water is evaporated, leaving the milk about one fourth of its original bulk. It is now put into tin cans, the covers of which are soldered on, when the cans are lowered into boiling water. After remaining a while, they are taken out and hermetically sealed, in which condition the milk will keep for months. Concentrated milk may thus be taken to sea or elsewhere. Another form is that of solidified milk, in which state it is easily and perfectly soluble in water; and when so dissolved with a proper proportion of water, it assumes its original form of milk, and may be made into butter. A statement by Dr. Dorémus, in the New York Medical Journal, explains the process, as follows:
“To one hundred and twelve pounds of milk twenty eight pounds of Stuart’s white sugar were added, and a trivial portion of bicarbonate of soda,—a teaspoonful,—merely enough to insure the neutralizing of any acidity, which, in the summer season, is exhibited even a few minutes after milking, although inappreciable to the organs of taste. The sweet milk was poured into evaporating pans of enamelled iron, imbedded in warm water heated by steam. A thermometer was immersed in each of these water-baths, that, by frequent inspection, the temperature might not rise above the point which years of experience have shown advisable. To facilitate the evaporation, by means of blowers and other ingenious apparatus a current of air is established between the covers of the pans and the solidifying milk. Connected with the steam-engine is an arrangement of stirrers, for agitating the milk slightly, while evaporating, and so gently as not to churn it. In about three hours the milk and sugar assumed a pasty consistency, and delighted the palates of all present. By constant manipulation and warming, it was reduced to a rich, creamy-looking powder, then exposed to the air to cool, weighed into parcels of a pound each, and by a press, with the force of a ton or two, made to assume the compact form of a tablet (the size of a small brick), in which shape, covered with tin-foil, it is presented to the public.
“Some of the solidified milk which had been grated and dissolved in water the previous evening was found covered with a rich cream; this, skimmed off, was soon converted into excellent butter. Another solution was speedily converted into wine-whey by a treatment precisely similar to that employed in using ordinary milk. It fully equalled the expectations of all; so that solidified milk will hereafter rank among the necessary appendages to the sick room. In fine, this article makes paps, custards, puddings, and cakes, equal to the best milk; and one may be sure it is an unadulterated article, obtained from well-pastured cattle, and not the produce of distillery slops; neither can it be watered. For our steamships, our packets, for those travelling by land or by sea, for hotel purposes, or use in private families, for young or old, we recommend it cordially as a substitute for fresh milk.”