The temperatures here given are Fahrenheit. "When ice or snow are not to be had and it is desired to cool any solid, liquid or gas, a good freezing mixture is the simplest method of accomplishing the object. The following mixtures are the most convenient and efficient:

1. Nitrate of ammonia, carbonate of soda and water, equal parts by weight. The thermometer sinks 57°.

2. Phosphate of soda, 9 parts; nitrate of ammonia, 6 parts; diluted nitric acid, (acid 1 part, water 2 parts,) 4 parts. Reduces the temperature 71° or from 50° to - 21°.

3. Sal ammoniac, 5 parts; nitrate of potash, 5 parts; sulphate of soda, 8 parts; water, 16 parts. Reduces the temperature 46° or from 70o to 24°. This is one of the cheapest, most readily procured, and most convenient of mixtures.

Freezing mixtures are often used when it is required to produce a greater degree of cold than can be obtained by the mere application of ice. When ice is at hand, as it generally is in this country, the following should be used:

1. Finely pounded ice, 2 parts; salt, 1 part. This mixture reduces the temperature to 5°.

2. Finely pounded ice, 2 parts; crystallized chloride of calcium, 3 parts. Reduces the temperature from 32° to - 40°.

3. Finely pounded ice, 7 parts; diluted nitric acid, 4 parts. Reduces the temperature from 32° to - 30°.

In every case the materials should be kept as cool as possible. Thus the ice should be pounded in a cooled mortar with a cooled pestle, and the mixture should be made in vessels previously cooled. By attention to these particulars it is easy to freeze mercury at any time by means of these simple and easily practiced methods, though, of course, the modern laboratory is provided with agencies of far greater cooling power.