MORDANTS.

283

will contain, after removal of the sulphate of lead by filtration, a variablequantity of basic sulphate of alumina, according to the greater or less amountof sulphuric acid which has escaped precipitation, and also basic acetate ofalumina and free acetic acid, which keeps both these basic salts in solution.When this liquid is printed on cloth it begins speedily to give off volatileacetic acid, and the basic salts are fixed on the tissue, the process being com-pleted by ageing.

According to the direct experiments made by M. D. Kcechlin, the basicsulphate of alumina has been proved to be an excellent mordant. He pre-pared this salt by partial precipitation of a hot and concentrated aqueoussolution of alum, by means of caustic potassa. The salt obtained was dis-solved in a sufficient quantity of acetic acid, and the liquid was used forprinting, and the tissue exposed to ageing. It is quite clear that nothing butsubsulphate (basic sulphate) of alumina could remain on the cloth afterdrying, since the elimination of the acetic acid must have been complete, andthe sulphuric acid could not, under any conditions, leave the base or the cloth.This cloth, after having been dunged, was put in the dye-beck, and gaveexcellent results. This experiment proves that we may admit, at least, thatas regards the ordinary mordants there remains on the cloth, after printing andageing, a certain quantity of subsulphate of alumina, which contains all thesulphuric acid of the neutral sulphate of alumina which has not been combinedto sulphate of lead plus a certain dose of alumina or subacetate of aluminaderived from the acetate of that base decomposed during the ageing process.When exatflly 100 parts of alum and 75 of acetate of lead are employed, abouttwo-thirds of the sulphuric acid of the sulphate of alumina are displaced : thecomposition of the liquid which is the result of this rea&ion is represented bya liquid prepared by dissolving 1 molecule of basic sulphate of alumina in2 molecules of acetic acid. Whether or no the two acids do temporarily eachpartake of a portion of the base present, after the ageing process there willonly be basic sulphate of alumina left on the cloth. These considerations,which somewhat elucidate the true nature of the mordants, do not clash at allwith the use of pure acetate of alumina. What is said is only meant to provethat the subsulphate of alumina, and the sulphates of soda, potassa, andammonia, or also the alkaline acetates, can be mixed along with the acetate ofalumina without injuring its excellent properties as a mordant. We mayalso state here that, as regards the materials to be used, the purest articlesanswer the purpose best in every respedt.

The following prescriptions for red liquors are given by M. D. Koschlin :—

Strong Mordant, No. 1.

30 gals, of water, 6 of which are a decodtion of Lima-wood to “ sighten ”the work; 165 lbs. of alum ; i6£ of soda-crystals ; and 165 lbs. sugar of lead.

Mordant, No. 2.

Water as above; 82^ lbs. of alum ; 8£ lbs. of soda-crystals ; 55 lbs. acetateof lead.

These formulas are old. The following are of more recent date :—

Strong Mordant.

11 kilos, alum ; 82*5 grms. acetate of lead ; 32 litres boiling water.