Page:Popular Science Monthly Volume 7.djvu/122

112 entitled to have what he pays for, and he can find out very satisfactorily what it is that he pays for, by the employment of the lactometer.

Good milk consists of about 88 per cent, water, combined with about 12 per cent, of solid matter dissolved or diffused in it, which makes it heavier than water. This increased relative weight is known as its specific gravity, and water being taken as 1000, the specific gravity of milk varies from 1023 to 1034. Without inquiring into the proportions of its several solid constituents, the lactometer determines their amount by indicating the specific gravity of the sample tested. The instrument is simply a glass tube closed at the lower end, and properly weighted, with a scale affixed, which shows the result when it is floated in a sample of milk. Milks from different cows and at different times vary in richness and poorness, so that it becomes important to fix such a standard that all samples which fall below it shall be classed as adulterated, or condemned as unmarketable. The New York Board of Health has been engaged for a considerable time, under the intelligent direction of Prof. Chandler, in investigating this subject, and, as a result of very extensive observations, they have fixed upon a specific gravity of 1029 as a fair minimum standard for pure milk, so that, "whenever the gravity falls below this number, the milk may be considered as containing ah excess of water and consequently as poor in quality, or adulterated."

The standard adopted is, beyond doubt, sufficiently low. A German chemist tested the milk of 124 cows, and found the maximum specific gravity to be 1034.3, the minimum specific gravity to be 1029.5, and the mean 1031.7. Hence the standard of merchantable milk adopted by the New York Board of Health is lower than the poorest milk from these 124 cows. It may be remarked that milk of 1034 will bear an addition of 16.67 per cent, of water to reduce it to 1029.

This standard has been made legal in New York—that is, a dealer selling milk below 1029 is liable to a fine. Whatever may be the result of this policy, a most important step has been taken in fixing a minimum standard, and thus making it possible for milk-buyers, quickly and certainly, by the use of the instrument, to ascertain whether the character of the article they are purchasing is above or below it. We say, then, to every householder interested, get a lactometer. Taglibue, of 69 Fulton Street, New York, makes and sells them for $1.25 apiece, with the scale adopted by the New York Board of Health. The instrument is perfectly simple, and will last a hundred years, with care, but it is not a good thing for children to play with. On a card accompanying it, we read: "Fill the jar with the milk to be tested; allow it to cool to the temperature of 60° Fahr., then immerse the lactometer and notice the mark on the scale that is level with the surface of the milk, which will show the quality." The standard of pure milk adopted is marked P, and is taken as 100 on the scale. If the lactometer stands at that point, the milk is legal. If it sinks below it the milk is too thin, and the point in the scale at which it stands indicates its excess of water. If the mark P stands above the surface, the milk is richer than the standard, and the scale shows its superior quality. Of course, the instrument cannot give an analysis of the milk, and if a milkman reduces a high grade of milk to a somewhat lower standard, by admixture of water, the lactometer cannot show it; but it will tell exactly the quality of the milk every time, so that the buyer may know how he is being served. The general use of the lactometer could not fail to exert a beneficial influence upon the morals of the milk-trade.