Demonstration of the various Strata of Earth which cover the Globe.
In a middling-sized glass bottle, three parts full of clear water, infuse pure alumine precipitated by ammonia, till the bottle is nearly filled.—Expose the bottle to the cold air in frosty weather; or, at other times, to artificial frost. At the moment when the frigorific effect ensues, the alumine will divide all over the surface of the water, and form itself into separate and very regular strata.
To freeze Water in the Midst of Summer, without the Application of Ice.
Take eleven drachms of muriate of ammonia, ten of nitrate of potash, and sixteen of sulphate of soda; reduce each of these salts separately to a fine powder, and mix them gradually in a glass, or rather in a thin metal vessel, with five ounces of water (the capacity of the vessel should be only just large enough to hold the materials): the result will be, that, as the salts dissolve, cold will be produced, and a thermometer immersed in the mixture will sink at or below freezing. A little water, about half an ounce, in a test tube, when immersed in the mixture during its solution, becomes frozen in about ten minutes.
The salts employed in this experiment may be recovered from the solution, if the sulphate of soda be omitted, by evaporating the water, to serve again any number of times. Five parts of muriate of ammonia, five of nitre, and eight of sulphate of soda, mixed with sixteen of water, at the usual temperature, sink the thermometer from 50 to about 10 degrees.
The salts, to produce their fullest frigorific effect, should be recently crystallized in fine powder, and contain as much water of crystallization as possible, but they should not be damp.
If to three parts of ice thus procured, you add four parts of potash, the thermometer will sink from 32° to 61° below Zero, or the freezing point; giving 93 degrees of cold. Snow or common ice, mixed with potash in the same proportions, would serve equally well; but the above experiments are given under the supposition that they are difficult to be procured.