EXPERIMENT.
Place a flat saucer containing about a pound of oil of vitriol under the receiver of the air-pump, and set in it a watch glass containing a little water, supported on a stand with glass legs. Exhaust the receiver, when the water will evaporate, but without boiling; and the vapor being absorbed as it forms by the oil of vitriol, the vacuum is preserved, and the evaporation continues, until the vapor has abstracted so much caloric from the remainder of the water that it is all at once converted into ice.
In most elementary works on chemistry may be found a long table of freezing mixtures, as they are called, some with and others without ice or snow. We have selected a few from each division.
WITH ICE OR SNOW.
| { | Snow or powdered ice | 2 parts. |
| Powdered common salt | 1“ | |
| { | Snow | 5“ |
| Powdered common salt | 2“ | |
| Powdered sal ammoniac | 1“ | |
| { | Snow | 3“ |
| Dilute sulphuric acid | 2“ | |
| { | Snow | 2“ |
| Crystallized muriate of lime | 3“ |
WITHOUT SNOW OR ICE.
| { | Sulphate of soda | 3 parts. |
| Dilute nitric acid | 2“ | |
| { | Nitrate of ammonia | 1“ |
| Water | 1“ | |
| { | Phosphate of soda | 2“ |
| Dilute nitric acid | 1“ | |
| { | Sulphate of soda | 2“ |
| Muriatic acid | 1“ |
The effects of most of these mixtures may be considerably increased by previously cooling the ingredients separately in other freezing mixtures.
In connection with this branch of science, and especially with chemistry, the youthful philosopher should practice the art of decanting air from one jar to another standing over water, beginning by passing it from a small to a larger jar, then with two of equal size; and when he can accomplish the transfer without permitting even one bubble to escape, he may essay the much more difficult task of transferring the air from a large to a smaller jar.
He should also practice using the blowpipe until he can keep up a steady and uninterrupted flame for ten minutes or a quarter of an hour, without stopping for breath. It is quite possible to replenish wind in the mouth, which alone ought to be used, without interrupting the breathing for an instant, but it requires some practice.