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These waters may be considered under three varieties : 

 First. Rain water, which includes water derived from rain, dew, hail, 

 enow, or frost. When secured before it has coine in contact with the 

 earth, or any substance that can impart impurities to it, this is the purest 

 natural water. It contains only a small quantity of air, carbonic acid, 

 and ammonia. Not holding in solution any of the earthy salts, its ten- 

 dency to dissolve other material with which it may come in contact is 

 very greatly increased. For this reason, as ordinarily secured, it is far 

 more deleterious than any water in use. Thus, falling upon tin roofs, 

 and being conveyed by tin conductors, with lead sold ring, to cisterns, 

 a very perceptible quantity of the poisonous compounds of the latter 

 metal, derived from the soldering, are invariably found dissolved in the 

 water. This I have found to be particularly the case with the water 

 collected from roofs that have been painted with white lead. Collected 

 from shingle or gravel roofs, the evil does not exist to the same extent; 

 yet, in being conveyed through tin conduct oi-s, with lead soldering, or 

 lead pipe, is clearly perceivable. I do not hesitate to say that rain wa- 

 ter, collected in the ordinary mode, used as an habitual drink, must 

 prove highly injurious to health. 



Second. River water. This stands next in purity to rain water. 

 When its source is considered, it must be evident that the water of all 

 rivers must be very far from being pure. The watei* of all our rivers, 

 lakes, ponds, and oceans, has at one time existed in the air in a state of 

 vapor, from whence it has been precipitated, in a pure state, as rain or 

 snow. This water, coming in contact with the earth's surface, and fre- 

 quently penetrating its strata, becomes impregnated with the soluble 

 matter of each particular stratum. For instance, in leaching through a 

 limestone or chalk formation, it would become charged with lime; or, in 

 passing over a magnesian limestone, with lime and magnesia. Thus it 

 will be perceived that this second variety of water must contain varia- 

 ble ingredients; and that a knowledge of the composition of the water 

 becomes an index to the geology of a district, and a knowledge of the 

 geology an index to the composition of the water. 



Third. Spring or well water. Inasmuch as all the water of spi-ings 

 and wells has come in contact with, and leached through the earth, and 

 usually very little time has been allowed for the separation of the clay, 

 sand, &C.J held mechanically in suspension, this vaiiety may be consid- 



