220   Art of Travel.

But, as regards mankind, some means of melting snow into water, for the purposes of drinking, is an essential condition of life in the Arctic regions. Without the ingenious Esquimaux lamp (p. 205), which consists of a circle of moss wicks, fed by train-oil, and chiefly used for melting snow, the Esquimaux could not exist throughout the year, in the countries which they now inhabit.

That eating large quantities of snow should seriously disturb the animal system is credible enough, when we consider the very large amount of heat that must be abstracted from the stomach, in order to melt it. A mouthful of snow at 32° Fahr., that is to say, no colder than is necessary for it to be snow at all, robs as much heat from the stomach, as if the mouthful had been of water 143° colder than ice-cold water, if such a fluid may, for the moment, be imagined to exist. For the " latent heat " of water is 143° Fahr. In other words, it takes the same quantity of heat to convert a mass of snow of 32° into water of 32°, as it does to raise the same mass of water from 32' to 141°+32°=175° Fahr. It takes in practice about as long to melt snow of a low temperature into water, as it does to cause that same water to boil. Thus to raise snow of 5° below zero Fahr. to 32°, takes 37° of heat, and it requires 143° more, or 180° altogether, to melt it into water, Also it requires 180° to convert water of 32° into water of 212°, in other words, into boiling water.

Distilled Water.-It will take six or seven times as long to convert a kettle full of boiling-water into steam, as it did to make that kettle boil. For the "latent heat" of steam is 967° Fahr. ; therefore, if the water that was put into the kettle was 60°, it would require to be raised through (212°60°=) 152° of temperature in order to make it begin to boil; and it would require a further quantity of heat, to the extent of 967° (=about 62 times 152°), to boil it all away. Hence, it is of no use to attempt to distil, until you have provided abundance of good firewood of a fit size to burn quickly, and have built an efficient fireplace on which to set the kettle. Unfortunately, fuel is commonly deficient in those places where there is a lack of fresh water.

Rate of Distillation.-A drop per second is fully equivalent

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