Page:Pure milk - a lecture delivered in the lecture room of the exhibition, July 30th, 1884 (IA b28525140).pdf/19

 in consequence of the fat being the most variable constituent in milk, and also from the fact that the opacity of the fat globules vary considerably.

The microscope has also been suggested as a ready means of detecting adulteration, but except in highly skilled hands this is even less useful, and may now be considered as obsolete as the other. For one thing, however, the microscope still retains and must retain its position: it is practically the only means by which diseased milk, that is milk obtained from diseased cows, can be detected.

One instrument however has survived, and is in constant use by many milkmen: this is the Hydrometer, or as it is more familiarly called in the trade, the Lactometer. This is a valuable instrument in its way, but the results obtained by its use are apt to be misleading, as it simply gives the relative weight of milk compared with water. One gallon of water weighs io pounds; one gallon of milk about 10&middot;3 pounds; it follows from this that if the milk be admixed with water, the weight of one gallon would be reduced, so that supposing the mixture consisted of half milk and half water, the weight would be 10&middot;15 pounds. Unfortunately, however, the weight of pure milk is not uniform; it ranges between the rather wide limits of 10&middot;28 and 10&middot;35. We therefore get a possible error introduced at the starting point, and this starting point or zero being erroneous, it follows that all calculations based upon it must be likewise liable to error. If, however, this were all, the instrument would still be a very useful one in the hands of a careful man, but experiments will soon show that there is another great drawback. If a sample of milk with a specific gravity of 10&middot;30 be taken, and the cream carefully skimmed off, the specific gravity of the skimmed milk would be increased by the removal of the butter fat, which is lighter than water, so that the weight of the skimmed milk itself may be as much as 10&middot;34 or 10&middot;36 pounds. It will be seen from this that we have two different ways in which the milk can be tampered with,