Natural ice is never seen in the warmest parts of that country. To procure ice by artificial means, they dig, on a large open plain, not far from Calcutta, three or four pits about thirty feet square, and two feet deep each, the bottom of which they cover about each inches or a foot thick with sugar cane or the stems of the large indian corn, dried. On this bed are placed, in rows, a number of small, shallow, unglazed earthen pans, formed of a very porous earth, a quarter of an inch thick, and about an inch and a qual'ter deep, which, at the dusk of evening, they fill with soft water that lIas been boiled. In the morning, before sunrise, the ice-makers attend the pits, and collect what is frozen in baskets, which they convey to the place of preservation. This is generally prepared on some high, dry situation by sinking a pit fourteen or fifteen feet deep, lining it first with straw, aud then with a coarse kind of blanketing. The ice is deposited in this pit, and beat down with rammers, till at length its own accumulated cold agaiu freezes it, and forms one solid mass. The mouth of the pit is well secured from the exterior air with straw and blankets, and a thatched roof is thrown over the whole. The quantity of ice formed by the method above described depends on a light atmosphere, and clear, serene weather. Three hundred persons are employed in this operation in one place. At first sight, this curious process may appear to be an effect of evaporation; but this is not the case ; for it is remarkable that it is essential to its success that the straw in which the vessels arc placed should be dry, whereas, if evaporation were concerned in the congelation, wetting the straw would promote it. When the straw becomes wet by accident, it is obliged to be replaced by dry straw. The earth is continually losing heat by radiation, and it loses most on clear, starlight nights, when there are no clouds to intercept and send back the rays of heat. The straw, like all filamentous substances, is a good mdiator of caloric, and it is in consequence of the heat that is thus given out by it into space on clear nights that the ice is formed. When the weather is windy and cloudy the effect does not take place.American Druggists' Circular.
This article was originally published with the title "Process of Making Ice in the East Indies" in Scientific American 13, 10, 75 (November 1857)