Those extensively engaged in dyeing, or in any other indq- try involving the use of comparatively pure water, find it necraary to study the quality of the water they use, and as a ever, that the ingredient which renders the water hard ia nearly as often magnesia as lime, and quite as often a mixture of both. These .substances are often found in water in the form of carbonates held in solution by carbonic acid. On the contrary, the carbonates 6f lime and magnesia are insoluble in water free from carbonic acid. It follows that any substance which with combine with the carbonic acid present will precipitate those salts, and the water will thus be rendered soft., Lime is also found in water in the form of a sulphate and magnesia in the form of a chloride. As the substances named are the ones most objectionable, so far as the laundry is con- cemed, we will not here enumerate the large list of mineral substances which may be met with in the examination of waters found in various localities. It is obvious that to act intelligently in removing these substances from water, the exact nature of the impurity should be inown. The tests are extremely simple and can be applied easily. The test for the presence of lime is the oxalate of ammonia. A few drops of a solution of this salt poured into water, produces a well- defined milkiness when any of the salts of lime are present. To determine whether the lime thus indicated is in the form of a sulphate or carbonate (or both may be present), boil down a portion of the water in a glass bottle until a pellicle forms • to the fluid in the bottle add hydrochloric acid, and if efferves- (;ence ensues, it indicates the presence of a carbonate of lime or magnesia, or both. If the solution entirely clears up, that Indicates ab sence of sulphate of lime. If it remains turbid sulphate of lime is present. It is not important to distinguish between the carbonates of magnesia and lime, as both can be thrown down by the addition of newly-slaked lime. This should be put in the water, in the form of milk of lime, small quantities at a time, or better, the exact amount of milk of lime necessary may be easily computed. Find by experiment upon small but definite quantities of the water the exact amount of milk of lime of a giventhat can be added to those definite quantities without rendering the water alkaline. This can be tested by the use of red litmus paper, whieh is turned blue by the weakest alkaline reaction. The amount of lime that a pint or a quart of the water will thus neutralize being ascertained, the amount necessary for any quantity can be at once determined. Lime thus added also precipitates organic impurities. In many cases, however, the mere boiling of water will throw down the salts oflime and magnesia, by driting offa portion of the cr.rbonic acid through the agency of heat. “VVhon lime is added the carbonic acid instead of escaping with the steam, as when water is boiled, unites with the added lime, to form a carbonate precipitating in common with the mixture of all the carbonates present. The carbonates of soda and potash will produce sipilar effects, the carbonate of soda (washing soda) being in common use to remove the carbonates of lime and magnesia from water where they are present. An excess of the carbonate of soda, if not too great, will d0 no harm when used for this purpose. This salt also precipitates the sulphate of lime. The chlorides of the earthy metals are not often found in the waters commonly used for domestic purposes in quantities sufficient to injure them.
This article was originally published with the title "Hard and Soft Waters" in Scientific American 21, 14, 217 (October 1869)