Chemical Weather Glass

This curious instrument appears to have been invented more than a hundred years ago, but the original maker is not known. It is simply a glass vial about ten inches long and three quarters of an inch in diameter, which is nearly filled, and hermetically sealed, with the following mixture:—Two drachms of camphor, half a drachm of nitrate of potassium, half a drachm of chlorate of ammonium, dissolved in about two fluid ounces of absolute alcohol mixed with two ounces of distilled wat
r. All the ingredients should be as pure as possible, and each vial filled separately. When the instruments are made in numbers and filled from a common mixture, some get more than the due proportion of the solid ingredients, and consequently such glasses do not exhibit that uniformity of appearance and changes, that undoubtedly should accompany similar influencing circumstances. It is in consequence of a want of precision and fixed principle of manufacture, that these interesting instruments are not properly appreciated, and more generally used.

The glass should be kept quite undisturbed, exposed to the north, and shaded from the sun. Camphor is soluble in alcohol, but not in water, while both water and alcohol have different solvent powers, according to the temperature; hence, the solid ingredients being in excess for certain conditions of solution, depending upon temperature chiefly, and perhaps electricity and the action of light also, appear as crystals and disappear with the various changes that occur in the weather.

The various appearances thus presented in the menstruum have been inferred to prognosticate atmospheric changes. The following rules have been deduced from careful study of the glass and weather:—

1. During cold weather, beautiful fern-like or feathery crystallization is developed at the top, and sometimes even throughout the liquid. This is the normal state of the glass during winter. The crystallization increases with the coldness; and if the structure grows downward, the cold will continue.

2. During warm and serene weather, the crystals dissolve, the upper and greater part of the liquid becoming perfectly clear. This is the normal state of the glass during summer. The less amount of crystallization, that is, the greater the clear portion of the liquid (for there is always some of the composition visible at the bottom), the greater the probability of continued fine dry weather.

3. When the upper portion is clear, and flakes of the composition rise to the top and aggregate, it is a sign of increasing wind and stormy weather.

4. In cold weather, if the top of the liquid becomes thick and cloudy, it denotes approaching rain.

5. In warm weather, if small crystals rise in the liquid, which still maintains its clearness, rain may be expected.

6. Sharpness in the points and features of the fern-like structure of the crystals, is a sign of fine weather; but when they begin to break up, and are badly defined, unsettled weather may be expected.

Admiral FitzRoy, in The Weather Book, writes of this instrument as follows:—“Since 1825, we have generally had some of these glasses, as curiosities rather than otherwise; for nothing certain could be made of their variations until lately, when it was fairly demonstrated that if fixed undisturbed in free air, not exposed to radiation, fire, or sun, but in the ordinary light of a well-ventilated room, or, preferably, in the outer air, the chemical mixture in a so-called storm-glass varies in character with the direction of the wind—not its force, specially (though it may so vary in appearance, only from another cause, electrical tension).

“As the atmospheric current veers toward, comes from, or is only approaching from the polar direction, this chemical mixture—if closely, even microscopically watched—is found to grow like fir, yew, fern leaves, or hoar-frost—or like crystallizations.

“As the wind, or great body of air, tends more from the opposite quarter, the lines or spikes—all regular, hard, or crisp features—gradually diminish, till they vanish.

“Before, and in a continued southerly wind, the mixture sinks slowly downward in the vial, till it becomes shapeless, like melting white sugar.

“Before, or during the continuance of a northerly wind (polar current), the crystallizations are beautiful (if the mixture is correct, the glass a fixture, and duly placed); but the least motion of the liquid disturbs them.

“When the main currents meet, and turn toward the west, making easterly winds, stars are more or less numerous, and the liquid dull, or less clear. When, and while they combine by the west, making westerly winds, the liquid is clear, and the crystallization well-defined, without loose stars.

“While any hard or crisp features are visible below, above, or at the top of the liquid (where they form for polar winds), there is plus electricity in the air; a mixture of polar current co-existing in that locality with the opposite, or southerly.

“When nothing but soft, melting, sugary substance is seen, the atmospheric current (feeble or strong as it may be) is southerly with minus electricity, unmixed with, and uninfluenced by, the contrary wind.

“Repeated trials with a delicate galvanometer, applied to measure electric tension in the air, have proved these facts, which are now found useful for aiding, with the barometer and thermometer, in forecasting weather.

“Temperature affects the mixture much, but not solely; as many comparisons of winter with summer changes of temperature have fully proved.

“A confused appearance of the mixture, with flaky spots, or stars, in motion, and less clearness of the liquid, indicates south-easterly wind, probably strong to a gale.

“Clearness of the liquid, with more or less perfect crystallizations, accompanies a combination, or a contest, of the main currents, by the west, and very remarkable these differences are,—the results of these air currents acting on each other from eastward, or from an entirely opposite direction, the west.

“The glass should be wiped clean now and then,—and once or twice a year the mixture should be disturbed, by inverting and gently shaking the glass vial.”