Condensed Milk.
| Brand. | Water. | Fat. | Cane and Milk Sugar. | Caseine. | Salts. |
| per cent. | per cent. | per cent. | per cent. | per cent. | |
| American | 52·07 | 15·06 | 16·97 | 14·26 | 2·80 |
| New York | 56·71 | 14·13 | 13·98 | 13·18 | 2·00 |
| Granulated Milk Co. | 55·43 | 13·16 | 14·84 | 14·04 | 2·53 |
| Eagle | 56·01 | 14·02 | 14·06 | 13·90 | 2·01 |
Analysis.
The principal adulterations of milk (watering and skimming), are detected by taking its specific gravity, and making quantitative determinations of the total milk solids, the fat, and the milk solids not fat. Of these criteria, the last-mentioned is the most constant and reliable.
Physical Examination.
a. Specific Gravity.—The instrument employed by the New York health inspectors for testing milk is a variety of the hydrometer, termed the lactometer, and its use, which is based upon the fact that under ordinary conditions watered milk possesses a decreased density, is certainly of great value as a preliminary test. The Board of Health lactometer indicates specific gravities between 1·000 (the density of water) and 1·0348. On its scale 100° represents the specific gravity of 1·029 (taken as the minimum density of genuine milk), and 0 represents the density of water; the graduations are extended to 120°, equivalent to a specific gravity of 1·0348. In taking an observation with the lactometer, the standard temperature of 15° should be obtained, and the colour and consistency of the milk noted. If these latter properties indicate a dilution of the sample, and the instrument sinks below the 100° mark, it is safe to assume that the milk has been watered. The scale is so constructed that the extent of the dilution is directly shown by the reading, e. g. if the lactometer sinks to 70° the sample contains 70 per cent. of pure milk and 30 per cent. of water. As the standard of specific gravity (1·029) selected for the 100° mark of the lactometer is the minimum density of unwatered milk, it is evident that the readings of the instrument will almost invariably indicate an addition of water less than has actually taken place. It would therefore appear that, under normal circumstances, the standard adopted by the New York Board of Health errs on the side of too much leniency toward the milk dealer. Cream being lighter than water, a sample of skimmed milk will possess a greater specific gravity than the pure article, and it is possible to add from 10 to 20 per cent. of water to it and still have the resulting admixture stand at 100° when tested by the lactometer. Vehement attempts have been made in court and elsewhere to impeach the accuracy of the indications afforded by the lactometer. These have been mainly founded upon the fact that a sample of milk unusually rich in cream will have a lower density than a poorer grade, so that it is quite possible that milk of very superior quality may show a gravity identical with that of a watered specimen. Great stress has been laid upon this by the opponents of the measures to control milk adulteration adopted by the public sanitary authorities. They have contended that a chemical analysis should be made. Recourse to this method would, however, involve a greater amount of time than it is usually practicable to devote to the examination of the numerous samples daily inspected; moreover, the process is resorted to whenever the indications of the lactometer leave the inspector in doubt. With the exercise of ordinary intelligence this contingency seldom arises, as the proportion of cream required to reduce the specific gravity to that of a watered sample would be more than sufficient to obviate any danger of mistaking the cause of the decreased density. In this connection it should be stated, that the average lactometric standing of about 20,000 samples of milk, examined by the New York State Dairy Commissioner in the year 1884, was 110°, equivalent to a specific gravity of 1·0319.
The following table shows the value of lactometer degrees in specific gravity:—
Value of Lactometer Degrees in Specific Gravity.
Chemical Examination.