Page:Popular Science Monthly Volume 25.djvu/814

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F all the projects that have excited the ridicule of the unimaginative of times gone by, perhaps none has appeared more exceedingly funny and chimerical than that of producing at will, by mechanism operated by heat, a freezing cold, and that without the use of ice, or any previously congealed substance, and without regard to atmospheric temperature.

In these days of rapid development of the mechanic arts, it seems hazardous to assert impossibility of any mechanical problem involving the substantial amelioration of man's condition. The manifest need of an improvement seems to be but the condition of its realization and development; sooner or later appears the embryo invention destined to be the theme of long study and continual modification, the perfected product often bearing little or no resemblance to the crude prototype that may have first embodied an idea fraught with lasting good to man. The conception once concretely realized, its beneficent results become a part of the common capital of the race, making possible still further advances in our material well-being.

While the progenitors of the race seem early to have discovered the means of producing heat artificially, for their rude arts and for their bodily comfort, it is not probable that the means of obtaining artificial cold could ever have seemed to primitive man a pressing need. Civilization is a multiplying of needs, and nothing connected with man's development seems more clear than that the adoption of artificial protection from the elements, conducing directly as it has to a material modification of Nature's means of protecting the body and providing for its wants, has not only led to the demand for readily available means of producing artificial heat, but for the means of artificial refrigeration as well.

Since the experiments of Professor Twining thirty years ago, with sulphuric ether, the problem of producing artificial cold has been attacked by many, but the basis of the more important and successful systems employed has been, as in Twining's experiments, the volatilization of a liquid in vacuo, by means of a gas-pump. Of the various substances available in nature for this purpose, ether and ammonia have received the most attention. Various other liquids have also been used, such as sulphide of carbon, methylic ether, chloride of methyl, chymogene, etc., and latterly sulphurous acid as used in the famous Pictet system. Compressed air has also been employed, but the mechanical labor required by this system is too costly to allow it to compete with what may be termed the volatilizing systems.

The object sought has been the most economical method of