and the Constiiuents of Well- and River -waters. 63 



present. The constituents of Thames water which are supposed 

 to be a fertile source of disease, escape from the water even at the 

 common temperature, and it follows as a positive certainty, that 

 during the evaporation of the water in order to obtain the solid 

 residue, the greater part, and probably the whole of those con- 

 stituents which are inducive of disease, are expelled with the steam. 

 The organic matter remaining with the mineral constituents of 

 the water, is small in quantity and of an inert character. I 

 therefore regard it as unimportant, except so far as it may serve 

 in some measure as an index of the quantity of malarious matter 

 originally present in the water ; but the loss of weight experi- 

 enced on igniting the residue of a gallon of Thames water is not 

 even a reliable index of the quantity of organic matter actually 

 in the residue, since other constituents present are volatile at a red 

 heat, and in consequence untrustworthy results are obtained. 



In selecting a water for the supply of a town, providing the 

 water be not what is called a decidedly hard water, tlie relative 

 quantities of mineral salts are of little consequence ; but the 

 question whether it contain putrescible organic matter, and if 

 so, in ivhat quantity, and of what nature, is the first to be deter- 

 mined, and its paramount im])ortance is universally recognized. 

 A water containing such matters is supposed very justly — indeed 

 we have abundant evidence — to pjromote, if it does not originate, 

 malarious diseases in populations condemned to drink it; such 

 populations, as is well known, being much more prone to cer- 

 tain zymotic maladies, than those who enjoy a supply of water 

 which is free from putrescible organic contaminations. 



By allowing Thames water to remain in contact with a large 

 surface of iron for twenty-four or forty-eight hours, the ivhole 

 of the putrescent impurities appear to be removed. This re- 

 markable action of iron ap])ear8 to be due in a great measure 

 to the formation of nitrous acid, which oxidizes and destroys 

 every particle of destructible matter which may be present in 

 the water. The experiments I have made, and of which the pre- 

 ceding pages afford but an imperfect outline, have occupied me 

 more than twelve months. I am now engaged in making an 

 extensive series of experiments on large quantities of Thames 

 water, in the hope of contributing to the elucidation of the ma- 

 larious gas(;s which escape spontaneously, and which are, in con- 

 sequence of their volatile, character, expelled with the steam in 

 the ordinary methods of analysis. The results of these expei-i- 

 ments, which are approaching completion, I hope shortly to 

 communicate. 



