of mordanting is not a practical man in the general sense of the term, but a man of the highest scientific attainments and standing, namely, Professor Liechti, who, with his colleague Professor Suida, did probably more than any other man to clear up much that heretofore was cloudy in this region.  We have seen that with aluminium sulphate, basic salts are precipitated, i.e. salts with such a predominance of appetite for acids, or such quasi-acids as phenolic substances, that if such bodies were present they would combine with the basic parts of those precipitated salts as soon as the latter were formed, and all would be precipitated together as one complex compound.  Just such peculiar quasi-acid, or phenolic substances are Alizarin, and most of the natural adjective dyestuffs, the colouring principles of logwood, cochineal, Persian berries, etc.  Hence these substances will be combined and carried down with such precipitated basic salts.  The complex compounds thus produced are coloured substances known as lakes.  For example, if I take a solution containing basic sulphate of alumina, prepared as I have already described, and add to some Alizarin, and then heat the mixture, I shall get a red lake of Alizarin and alumina precipitated.  If I had taken sulphate of iron instead of sulphate of alumina, and proceeded in a similar manner, and added Alizarin, I should have obtained a dark purple lake.  Now if you imagine these reactions going on in a single fibre of a textile material, you have grasped the theory and purpose of mordanting.  The textile fabric is drawn through the alumina solution to fill the pores and tubes of the fabric; it is then passed through a weak alkaline bath to basify or render basic the aluminium salt in the pores; and then it is finally carried into the dye-bath and heated there, in order to precipitate the colour lake in the fibre.  The method usually employed to mordant woollen fabrics consists in boiling them with weak solutions of the metallic salts used as mordants, often with the addition of acid salts, cream of tartar, and the like.  A partial decomposition of the metallic salts ensues, and it is induced by several conditions:  (1) The dilution of the liquid; (2) the heating of the solution; (3) the presence of the fibre, which itself tends to cause the breaking up of the metallic salts into less soluble basic ones.  Thus it is not really necessary to use basic aluminium sulphate for mordanting wool, since the latter itself decomposes the normal or neutral sulphate of alumina on heating, an insoluble basic sulphate being precipitated in the fibres of the wool. (4) The presence of other added substances, as cream of tartar, etc.  The best alumina mordant is probably the acetate of alumina ("red liquor"), and the best iron mordant, probably also the acetate ("iron liquor”) (see preceding lecture), because the acetic acid is so harmless to the fibre, and is easily driven off on steaming, etc.  A further reason is that from the solution of acetate of iron or alumina, basic acetates are very easily precipitated on heating, and are thus readily deposited in the fibre.