212° F., in order to remove all traces of the fluid. The loss of weight experienced as the result of this treatment equals the amount of fat.
The amount of mineral salts is determined by igniting the residue until it is perfectly white. The heat must be very gradually increased in order to avoid loss from sputtering. The ash is then directly weighed, and its percentage value obtained as in the case of the total solids, that is, by the ratio of its weight to the amount of milk originally taken. The water is readily found by subtracting the per cent of total solids from 100.
The operations described above are all very easily made, and require comparatively but a short time. They presuppose, of course, the employment of a certain amount of apparatus, but if one can depend upon the courtesy of some chemical or pharmaceutical friend for the use of an analytical balance, all of the other requirements can be met at no very great expense. An analysis such as has been outlined, will show conclusively the quality of any suspected sample of milk, for the milk will deviate from the normal condition just in proportion as its constituents differ from those of the standard given. If, for instance, it is found that the specific gravity and percentage of total solids are both low, the addition of water is plainly indicated. By calculating the amount of whole milk corresponding to the total solids found, it is possible to state just how much water has been added. When it is found that the specific gravity is as it should be, and the total solids are between 12 and 12·5 per cent, it is seldom worth while to continue the analysis further than a determination of the mineral salts, for it would scarcely be possible for these three quantities to be what they should be unless the milk were quite normal. Thus, in a sample of milk recently analyzed by the writer, the specific gravity was found to be 1·033, the total solids 12·077 per cent, the mineral salts 0·598 per cent, and the water 87·923 per cent. Though the solid constituents were somewhat low, the discrepancy was too slight to fancy for a moment that the milk had been tampered with in any way.
Occasionally chalk or lime-water is added to give body to a diluted milk. Its presence will be readily detected by the increased amount of ash, which may be examined by the well known qualitative methods. During the warmer months, the difficulties of keeping milk fresh not infrequently lead to the addition of bicarbonate of soda or borax, but as a preservative the latter salt is an absolute failure. It simply keeps the curd from precipitating, but does not prevent the decomposition of the milk. After standing some time such a milk will be found to emit a very putrid, disagreeable odor.
Though the addition of these adulterants is far from commendable on the part of the milkman, the reflection is not without comfort that they exercise for the most part no injurious influence on the animal economy—a reflection, by the way, which can not be indulged in about the majority of food adulterants.