the soil, it condenses by the cold air into transparent yellow crystals, and into opaque yellow amorphous masses; and these collected by the industry of man, constitute all the supplies of "native sulphur" that are demanded for the production of sulphuric acid, and the manufacture of gunpowder,-the latter an invaluable agent for removing the solid rocks which oppose the "getting" of mineral treasures, but unfortunately too frequently employed as a frightful agent for the slaughter of thousands of our fellow men.

The tremendous and destructive effects of gunpowder are referrible to the sudden and intense combination of the sulphur and charcoal with the oxygen of the nitrate of potash that the composition contains ; and the consequent production and evolution of many thousand times the bulk of the charge of powder, of highly heated elastic gases, and vapours of great projectile force.

Returning to the experiment, from whence these remarks originated :—upon removing the branch of“ arbor vitæ" thus beautifully encrusted with crystals resembling "hoar-frost," it must be observed, that it cannot be kept exposed to the air, as the acid will gradually volatilize; but it may be preserved for a considerable time beneath a glass-shade, in a cold room; and in this situation, if the crystals ultimately drop off, they may be all collected and sublimed again upon the branch, as at first; or upon a bunch of red flowers, either natural or artificial.

It will then exhibit a very close resemblance to the

beautiful phenomenon, that took place on the twentieth of March of the present year; when the beautiful pink and crimson blossoms of almond trees, were suddenly covered with white and delicate crystalline flakes of snow.

At the same time vegetation was exceedingly forward; many trees had put forth leaves, and these exposing great surface for the reception of the snow flakes; the whole feature of the landscape was far more striking than it is ever presented upon leafless branches during the depth of Winter.

The chemist discovers that substances capable of assuming the crystalline form, will generally adhere to porous or rough surfaces in preference to such as are compact or polished; he accordingly introduces sticks and strings into various solutions of salts, and these act as nuclei for the accretion of crystals; the most familiar examples of this kind that can be presented, are crystals of "verdigris" on sticks, and of "sugarcandy" upon strings.

In Nature, the same fact is observable; for during the congelation of water, the crystals of ice form first the stones, grass or moss, at the borders of the pond or stream, and then gradually proceed across the surface.

upon

During the last experiment, the crystals of "benzoic acid" were found to be more abundant upon the rugged branch of the "arbor vitæ" than upon the smooth interior of the glass shade; and in Nature the same thing happens, for the crystals of water or "hoar

frost" are found more plentifully deposited upon leafless branches, and grass plats, than upon stone pavements and gravel-walks; and these two latter surfaces may be perfectly free from "hoar-frost" whilst a few withered leaves, straws, or feathers, lying upon them, will be beautifully encrusted with such crystals.

The delicate and elegant frost-work, resembling trees and landscapes, which forms upon the inside of window panes, results from the congelation of the vapour of water contained in the air of the apartment; and the same beautiful appearance displays itself upon the glasses of a close carriage, from the congelation of the moisture exhaled by the lungs of its occupants.

The appearance of hoar frost upona window-pane, may be artificially imitated by dissolving half an ounce of "Epsom salt," i. e., sulphate of magnesia, in a wineglass full of hot water, and then spreading this solution with a sponge, evenly over the surface of the pane of glass; as it cools, so it will crystallize in very beautiful arborescent or tree-like forms; and by this simple proceeding, window panes are now very commonly

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frosted," in preference to the more expensive and hazardous method of rendering them opaque by grinding.

Two winters ago, at day-break, the flag-stones of the foot pavement of London exhibited the most splendid example of this crystalline form of water; the crystals were arranged, interwoven, and interlaced, in an endless variety of the most delicate and intricate figures that it is possible for the imagination to conceive; a very slight thaw having occurred in the night, the film of water, was suddenly frozen, by the frost setting in at dawn.

Sometimes, during a severe frost, by an occult process in the vast laboratory of Nature, heavy showers of rain suddenly fall; the drops are immediately frozen, and then trees, hedgerows, eaves of houses, and other solid objects, present a most beautiful appearance; they are coated with ice and icicles which reflect and refract the sunbeams in a variety of gorgeous colours.

If the conflagration of a building happen during a severe frost, the water employed to quench the flames, is frequently frozen as it dashes and trickles over the walls, and forms brilliant icicles pendant from the parapet, portico, balconies, and window-frames.

The formation of icicles depends upon the successive congelation of drops, or slender streams of water; and in Nature they sometimes accumulate so greatly upon trees, that the branches break beneath the load, and thus much damage ensues.

The vicissitudes of The Four Seasons are continually changing the physical state of water, yet never altering

its actual composition; for if the chemist experiment upon equal weights of this compound, in its three physical states of liquid, solid, and vapour, he invariably educes from them all, Oxygen and Hydrogen in the definite weights, already stated.

Leaving, for a time, the effect of natural and artificial cold upon water, let us briefly examine the habitudes of this wonderful liquid when subjected to the action of artificial heat, as in the familiar process of boiling.

Why should the heat be invariably applied beneath the vessel containing the water, and never upon the surface of the water? The answer to this apparently simple question involves the greatest refinements of chemical science.

It has been already stated, that water is a non-conductor of heat, and this fact has been experimentally proved in several cases; therefore, if heat were directly applied to its surface, the portions of water constituting such surface would soon become elevated, by mere heat of contact, to the boiling point; and this boiling film, having less specific gravity than that of the colder portions below, would float upon them; whilst they cannot derive heat from it on account of their non-conducting power.

For example, let the iron heater of the tea-urn be heated red hot, and then by means of its hook, held that its end may touch the surface of water contained in a large tall glass; the heat will instantly cause the surface to boil furiously, whilst the beneath water will remain cold; nay, even a piece of ice, tied to a