TH£ EAKTH, 119 



most genuine we know is mixed with exhalations and dissolu- 

 tions of various kinds ; and no expedient that has been hitlier- 

 to discovered, is capable of purifying it entirely. If we filter 

 and distil it a thousand times, according to Boerhaave, it will still 

 deposit a sediment ; and by repeating the process we may eva- 

 porate it entirely away, but can never totally remove its impuri- 

 ties. Some, however, assert, that water, properly distilled, will 

 have no sediment-' and that the little white speck which is 

 found at the bottom of the still, is a substance that enters from 

 without. Kircher used to show, in his Museum, a phial of 

 .\'ater that had been kept for fifty years, hermetically sealed ;* 

 during which it had deposed no sediment, but continued as trans- 

 parent as when first it was put in. How far, therefore, it may 

 be brought to a state of purity by distillation, is unknown ; but 

 he very well know, that all such water as we every \vhere see, 

 is a bed in which plants, minerals, and animals, are all found 

 confusedly floating together. 



Rain-water, which is a fluid of Nature's own distilling, and 

 which has been raised so high by evaporation, is nevertheless u 

 very mixed and impure substance. Exhalations of all kinds, 

 whether salts, sulphurs, or metals, make a part of its substance, 

 and tend to increase its weight. If we gather the water that 

 falls, after a thunder-clap, in a sultry summer's day, and let it 

 settle, we shall find a real salt sticking at the bottom. In win. 

 ter, however, its impure mixtures are fewer, but still may be 

 separated by distillation. But as to that which is generally 

 caught pouring from the tops of houses, it is particularly foul, 

 being impregnated with the smoke of the chimneys, the vapour 

 of the slates or tiles, and with other impmities that birds and 

 animals may have deposited there. Besides, though it should 

 be supposed free from all these, it is mixed with a quantity 

 of air, which, after being kept for some time, wiU be seen to 

 6e])arate. 



Spring- water is next in point of purity. This, according to 

 Dr Halley, is collected from the air itself; which being sattid 



1 Hill's History of Fossils. 



2 Hermetically sealing a glass vessel, means no more than heating tlio 

 mouth of the phial red hot ; and thus when the glass is become pliant, squeez- 

 ing the mouth together uitli a (tair of pincers, and then twisliug it six ot 

 Eevtrn timea round, which etiectually closes it up. 



