WATER—ITS IMPURITIES.
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steam whilst standing in suitably-construdted vats. A precipitate of peroxideof iron is thus formed, insoluble in water and neutral or alkaline liquids. Withthe exception of mineral waters, properly so called, salts of potash and sodaare seldom present as carbonates in sufficient quantity to produce any markedeffeft upon dyeing, whilst their existence as chlorides or sulphates is unim-portant ; and, moreover, the quantity of any of these salts usually found inwater is but small. Silica is frequently met with in water, but is notusually considered to be injurious in dyeing. The experiments of Mr. O’Neill,of Manchester, tend to prove, however, that pure hydrated silicic acid isinjurious in madder dyeing, although not strikingly so.
Organic Matter in water, that frightful bete noir to so many people, is by nomeans to be overlooked in its relations to dyeing and printing; it is especiallydetrimental to bleaching and clearing. Crenic and apocrenic acids, the variousforms and modifications of humin, ulmin, and that series of substances whichmay be generalised as peaty matter, are often decidedly deleterious in eitherdyeing, bleaching, or clearing, imparting a yellow tinge not easily removable.These forms of organic matter may be tested for by mixing about a pint ofthe water with half a fluid ounce of a perfectly clear filtered solution of hypo-chlorite of lime (bleaching-powder), sp. gr. i'Oi4, and heating in a glass flaskto about 160° F. (71° C.) Should the fluid so treated become yellow andprecipitate a buff-coloured deposit, the water is unfit for clearing goods by theold method. It may, however, serve for clearing by the padding machine andsteam box method, as that does not require nearly so much water. Dyeingand printing works are seldom so situated as to be able to use water withoutsome purifying process. The most common purifying agents are exposure toair and light, and the separation of suspended matters by filtration ; butthere is one method to which we here call attention by which the worst watermay be greatly improved even when largely impregnated with animal andvegetable matter. This consists in adding successively to each 1000cubic metres ( = 35,316 cubic feet, or 220,096 gallons) of water, whichshould be contained in a suitable tank, about 67 lbs. of dry perchlorideof iron, and 186 lbs. of crystallised carbonate of soda, both previouslydissolved in as pure water as can be obtained, to the volume of about220 gallons (35 cubic feet). By this process most of the organic matter isremoved, and some of the lime salts greatly lessened in quantity, being carrieddown with the flocculent sediment; this begins to fall slowly immediatelyafter the addition of the iron and soda, which should be well mixed with thewater by vigorous stirring. The chloride of sodium added by this processamounts only to j W i un th, too small a quantity to be in any way deleterious.
Water has not the same degree of solvent adtion upon all substances, and someremain insoluble under its influence; as a rule hot water dissolves moresubstance than cold, and does so more quickly, but the excess dissolved whenhot frequently separates in crystals when cooled. This is a point whichdeserves notice, for a liquid which, when warm, is of the proper strength,may be too weak when cold. This happens very frequently with solutions ofsalts that are but moderately soluble, such as chlorate, bitartrate (so-calledcream of tartar), and sulphate of potash. Crystallisation is also troublesomein steam colours, which though good enough when freshly made, become filled' with small crystals on cooling, and work rough in the machine.