378 



reported in waters, respecting which strong opinions are 

 expressed by chemists. Accustomed to deal with thousands 

 of tons, and having, perhaps, never seen grain weights, or 

 perhaps seen them as the mere spangles used for apportioning 

 doses of the most powerful medicines, the engineer who 

 sees three-quarters of a grain mentioned as present in a 

 pint, may be excused if he is tempted to consider such 

 a fraction not only unimportant, but insignificant. But 

 let this three-quarter grain per pint be deposited from 

 one thousand gallons, without being removed, and it will 

 amount to nearly fourteen ounces avoirdupois, — a very tan- 

 gible quantity. 



The carbonate of lime deposited from natural waters 

 may have been dissolved in either or both of two ways ; 

 either as carbonate dissolved by excess of carbonic acid, 

 which is driven off by boiling ; or lime present, as sulphate or 

 muriate, if carbonate of soda be also present, will form 

 carbonate by decomposition, when the solution becomes con- 

 centrated. 



Sulphate of lime may also exist in water, as sulphate, in 

 a larger quantity than will be found at present ; or it will be 

 formed of muriate of lime and sulphate of soda, reacting on 

 each other. As soon as the solution is concentrated to such 

 a point that the water present is insufficient to hold the whole 

 dissolved, the excess will be deposited. But much may be 

 separated in the solid form, during the brisk boiling of a 

 solution far from saturated. I described, many years ago, 

 in print, how this takes place. When a bubble of steam 

 arises, the salt of any description, which it held dissolved, 

 either is really, or, to render our explanation clearer, may be 

 supposed to be for a moment, left behind in the solid form. 

 If the salt is abundantly and rapidly soluble, like sulphate 

 of soda, it is so instantaneously re-dissolved, that practically 

 the case is as if it never had separated. 



