MORDANTS .

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Manganese Mordants.

Manganese has a very powerful affinity for organic fibre, both animal andvegetable. This is most strikingly shown with the solutions of permanganateof potash. If a slip of calico is plunged into such a liquid it rapidly takes adeep brown colour, permanent as far as light is concerned, but not capable ofresisting treatment with acids. The intensity of the colour thus produced woulddisqualify it as a mordant, except for some of the darkest shades. As thecompound of manganese thus fixed upon the fibre is a hydrated peroxide, andas the protoxide is white, or exhibits at most a faint pinkish tinge, it may beused as a mordant by bringing a powerful deoxidising agent to aft upon it eitheralong with or immediately before the colouring matter.

The use of the sulphate and chloride of manganese in producing certainso-called bronze effects upon cotton, independent of any organic colouringmatter, is not a case of mordant action, and is, moreover, nearly obsolete.

Zinc Mordants.

The affinity of oxide of zinc for organic fibres is very feeble. With themajority of colouring matters, also, it shows little disposition to form lakes.Hence its uses as a mordant are unimportant. Some experimentalists haveobtained a scarlet from sandal wood with a mordant of chloride of zinc.With murexide salts of zinc produce a yellow, which, though good, has nodistinctive feature to recommend it in preference to similar shades morecheaply producible. Chloride of zinc, on account of its deliquescent nature,is sometimes added to printers’ colours with the objeCt of preventing themixture from drying up. It is also employed to fix the alumina of “ alkalinepink mordant” upon the fibre. Certain manufacturers of mordants maintainthat if a solution of zinc—nitrate, chloride, or sulphate as the case may be—is added to a tin spirit, it causes the tin to be thrown better upon the fibre,and by being thus more thoroughly utilised it enables a smaller quantity toanswer the same purpose. We know of no faCts to substantiate thishypothesis, which we are inclined to suspeCt may have been devised to justifywhat was at one time a not uncommon mode of adulterating the preparationsof tin, and is probably not yet extinCt. The aCHon of chloride of zinc uponalkaline pink mordant, as above mentioned, depends obviously upon a principlewhich cannot apply here.

Arsenic Mordants,

Arsenious acid occurs in a great number of printing receipts, its functionbeing often very doubtful. In some cases it plays the part of an alterantrather than of a true mordant. Arsenite of soda mixed with the acetate ofalumina is employed as a mordant for printing aniline colours upon cotton.Arsenious acid, boiled with decoCtions of the woods, fixes a variety of brownsupon cotton and woollens, which are, however, more curious than practicallyimportant. The poisonous nature of the arsenical compounds undoubtedlytends to restrict their tinctorial applications.

Copper Mordants.

Certain preparations of copper are rather extensively used in dyeing andprinting, although their function is less that of mordants, strictly so-called,than of alterants, or oxidising agents.

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