MORDANTS.

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33 0 Baume = sp. gr. 1-275 to i-2g8 = about 50° to 55° Tw. From no to 115parts of this solution are precipitated by 100 parts of acetate of lead previouslydissolved in 30 parts of water: the resulting liquor has, after filtration, astrength of from rn6 to 1-125 S P- g r - = about 21 0 to 23i° Tw., and containsfrom 18 to ig per cent of acetate of alumina. This is the highest strengthattainable; and the liquor yields, when employed as a mordant, the sameresult as that obtained from alum, provided the sulphate be quite free fromiron. It has already been observed that, instead of acetate of lead, acetate oflime is frequently used in this process : 100 parts of alum, 100 of water, and150 of crude acetate of lime solution, sp. gr. 1-087 = about 15J 0 Tw., yielda red liquor having a strength of sp. gr. 1-095 = about 18° Tw. Excess oflime must be avoided, since it renders the colours dull.

M. E. Kopp has called attention to the use of hyposulphite of alumina as amordant. This salt is perfedtly soluble in water, and the solution is decom-posed at a boiling heat into sulphurous acid, sulphur, and alumina. None ofthese compounds can affedt the strength or quality of the fibre to which it isapplied. Pure hyposulphite of alumina may be prepared by the doubledecomposition of crystallised sulphate of alumina and crystallised hyposulphiteof lime. Of the first-named salt take 4-167 kilos., and after solution inwater there is added a solution of 4-875 kilos, of the latter salt. The preci-pitate of sulphate of lime is removed by filtration through stout flannel, andthe precipitate strongly pressed : there is thus obtained a perfectly clearsolution, which can be preserved for a long time, even in contadt with air. Asolution of hyposulphite of alumina of -1-20 sp. gr. contains as much aluminaas a solution of acetate of no sp. gr. The solution of hyposulphite isreadily thickened in the cold by means of gum, torrified starch, or British gum.The hyposulphite solution resembles the acetate solution in this respedl, also,that it is better for being not quite pure and more advantageously used whenmixed with a certain proportion of alkaline salts : 6 kilos, of alum are com-pletely decomposed by the use of4'65 kilos, of hyposulphite of soda,or 4-85 kilos,of crystallised hyposulphite of lime, so that 2 kilos, of this last salt can replace3 kilos, of acetate of lead, which latter is obviously a far more expensive salt.

Since there is some difficulty in thickening sulphates with starch, M. Koppadvises to prepare first hydrochlorate of alumina, which, in the state of athickish syrup, is incorporated with cold starch paste. To this mixture is nextadded hyposulphite of soda, in such proportion as to decompose two-thirdsor three-fourths of the hydrochlorate of alumina. In order to prepare a hydro-chlorate of alumina suitable for this purpose, it is proper to decompose 6 kilos,of ammonia-alum in aqueous solution, by means of 2-78 kilos, of dry chlorideof calcium (not chloride of lime). The liquid, after being drawn off from theprecipitated sulphate of lime, is evaporated to the consistency of a syrup in aleaden vessel. On cooling, there are formed crystals of sal-ammoniac; themother-liquor is drawn off, and evaporated at 150° until a pellicle formson the top of the liquid, which, on cooling, becomes a solid, white, deli-quescent mass. M. Kopp prepares hyposulphite of lime by the adtion ofsulphurous acid gas upon a previously boiled mixture of basic oxysulphide oflime (soda waste), with 10 per cent of its weight of pulverised sulphur andwater. As soon as the liquid shows an acid readtion it is neutralised and allowedto stand till clear, and evaporated at a gentle heat. In this way beautiful