42 WATER. 



its weight of water ; and bones that have been dried for 

 twenty-five years have produced one-half of their weight 

 of water. The hardest stones ground and distilled dis- 

 cover a portion of water ; and it has been said that even 

 fire itself is not without it. 



The grand reservoir of water is the Ocean : this covers 

 nearly three-fifths of the earth's surface, and extends to 

 an unfathomable depth. The most striking property of 

 sea- water is its saltness, the cause of which philosophers 

 have endeavoured to account for in various ways. Dr. 

 Halley supposed that the sea was originally fresh, and 

 that its saltness proceeded from the salts of the earth 

 conveyed into it by rivers. Others have supposed that 

 there are vast rocks of salt at the bottom of the sea, 

 whence it derives its saltness ; and this is rendered more 

 plausible from the numerous and extensive salt-mines 

 known to exist in different parts of the earth. Others, 

 again, have supposed that the sea was created salt to 

 keep it from putrefaction ; but it appears to be kept from 

 putrefaction by the agitation of the winds and tides, for 

 stagnant salt-water will in time become corrupt. Al- 

 though the sea is universally salt, yet it is salter within 

 the tropics than at the arctic regions ; this is accounted 

 for by the quantity of snow, and the large rivers, that 

 fall into the northern seas ; to which may be added, that 

 evaporation is infinitely less in those seas than between 

 the tropics, consequently a proportionately less quantity 

 of fresh water is" carried off. 



Of the various kinds of water, Snow- water, when col- 

 lected clean, is the purest. .Ram-water may be considered 

 the purest distilled water, but in its passage through the 

 air, it becomes impregnated with putrescent matter, 

 which, while it renders it superior to any other for fer- 

 tilizing the earth, renders it inferior to spring and river 

 water for various purposes. The manner in which rain- 

 water is generally obtained, viz., from gutters placed un- 

 der the roofs of houses, adds to its impurity, and renders 

 it in a short time quite putrid. 



/foyer-water is next in. purity to rain-water, particularly 

 where it runs over a clean, stony bottom, and is superior 

 to it for domestic purposes. River-waters putrefy sooner 





