always contains more or less of the sulphate and carbonate of lime, and it generally contains a trace of common salt, and the usual proportions of air and carbonic acid
gas. The presence of these is detected by subacetate of lead, which displays the smallest portion of carbonic acid or a carbonate, and nitrate of silver, which detects
the muriates by the formation of muriate of silver.
Water from melted ice is perfectly wholesome, and is drunk during the summer season, wherever the climate will admit of its being collected and preserved at a
moderate expense. In this form, it is a luxury -- almost a necessary -- the middle in
states of this country more particularly, " where," Dr. Dunglison remarks, " there
is not a tavern on the road, on the eastern side of the Blue Ridge, that does not
furnish ice to the traveller in any abundance." When sea-water freezes, the ice does not contain the salts. Consequently, when melted, it affords fresh water, and accord
* The air in ice and snow water contains 34.8 per cent, of oxygen, while that in rain water contains but 32 per cent.
ing to the voyagers in high northern and southern latitudes, the water has been found sweet, soft, and wholesome. River Water. This is a mixture of rain and spring water, and when deprived of the matters which it frequently holds in suspension, is generally of considerable purity. Mountain streams, which generally issue from siliceous rocks, and run over stony or pebbly beds, are, for the most part, comparatively pure and soft.. The river water of New-England, and the other hilly portions of the United States,, is usually of this description, though in the time of floods, and after heavy rains, they contain much sedimentary matter. River water gradually deposits much of its earthy salts as it flows, and becomes purer by exposure ; it therefore generally contains less calcareous matter than spring water; its specific