MILK is an opaque, white fluid, secreted by the mammary glands of the female class illammalia. Among the many instru ments which are used for the detection of adulterations, are the galactometer and the hydrometer. The first is a simple and most reliable method ; it consists of a glass tube—a perfectly straight bottle will answer the purpose—which is marked off into one hun dred parts and filled with milk, which is allowed to stand until the cream has completely separated, when the quality of the milk is shown by the number of parts of cream in the hundred. The hydrometer was invented by Dceffel, and is preferred by chemists ; it simply detects the presence of water, and in the hands of un skilled persons is of little use, as the addition of extra sugar or starch increases the density of the milk and renders the instru ment useless. Investigation finds very few cases of adulteration of milk (except with water). The presence of starch may be tested by dropping a little iodine into it ; if a violet blue color forms, starch is present. Chalk settles, and if these settlings are dissolved in vinegar they will foam up.
MILK (Condensed). The following article is selected as a description of the process of making condensed milk, which, for use on shipboard, in mining camps, and for pleasure parties, is al mcst a perfect substitute for the fresh article, and its preparation is due to the wants of people who cannot obtain a supply of fresh milk. In connection with sugar and carbonate of soda, it is under certain conditions, evaporated till it appears in the form of mealy powder ; it is then pressed into brick-shaped cakes. These must be triturated with warm water when it is to be used. Milk may be dessicated by evaporating to the consistence of dough and then thoroughly drying, after which it is crushed and bottled. Various processes are in use for preserving milk, but the most common is that of condensing. The process of condensing milk
is as follows : When the milk is received at the factory, it is passed through the strainer into the receiving-can, from which it is con ducted through another strainer into cans holding about twenty gallons each, and in these the milk is heated. This is done by setting them in hot water, and the milk is held there till it reaches a temperature of 150° to 175° Fahr. The milk next passes through another strainer into a large vat containing at the bottom a coil of copper pipe, through which steam is passed, and here the milk is heated up to the boiling point. Granulated sugar of the best quality is then added in the proportion of one and a quarter pounds to a gallon of milk. From the steam vat it is conducted to the vacuum-pan, which has a capacity for condensing 3,000 quarts or more at a time. It is now subjected to the heat for about three hours, during which time it will lose 75 per cent. of its bulk, which represents the amount of water evaporated. At this stage it is drawn off into cans holding about forty quarts each, which are set in cold water until the temperature is reduced to about 70° Fahr. It is then poured into large drawing cans furnished with faucets. From here it is drawn into small cans holding about a pound each. These cans are then immediately soldered up. Milk preserved in this way can be kept an indefinite length of time, and is used for any purpose to which fresh milk is adapted. It is generally of excellent quality, for if the milk was tainted or impure the product would not keep. Preserved milk thus made contains about one third of its weight in sugar. A number of factories in this country and Europe are engaged in the industry, which has become of considerable importance.