544

DYEING AND CALICO PRINTING.

Bismuth has two additional disadvantages as compared with tin: its priceis very considerably higher, and it is more liable to be blackened by sulphurettedhydrogen in the atmosphere.

Chromium Mordants.

A variety of chromium compounds have a very decided adtion both uponorganic fibres and upon colouring matters. The most important of these ischromic acid, which is always used in combination with potash. The bi-chromate of potassa, commonly known as bichrome or red chrome, is a salttoo generally known to require any description. Few commercial chemicalsare more generally met with in a state of purity, and it is, we believe, neverintentionally sophisticated. It should show no whitish or yellowish spotsor incrustations. It should be perfe&ly soluble in pure water, leaving nosediment or turbidity. If a little nitric acid is added to the aqueous solu-tion of bichrome, a solution of nitrate of baryta should not occasion any pre-cipitate. If one appears, sulphuric acid is present, in the state of sulphate ofpotassa.

The neutral or yellow chromate of potash is comparatively little used. Itsa&ion is milder, and more easily regulated than that of the red chromate, andwith organic colouring matters it yields a variety of interesting results, manyof which require and deserve further investigation. Against the above-men-tioned advantage must be set the fadt that it is exceedingly variable incomposition, two samples being rarely found quite identical. The results arehence uncertain. Those who wish to experiment upon its adtion on a practicalscale can employ a solution of 15 r parts of bichrome and 143 parts of cleancrystallised carbonate of soda, not effloresced.

The principal use of red chrome is to produce blacks upon wool, along withlogwood, smaller quantities of other wares being added to modify the shade.Chrome-blacks are cheap, both from the low price of the materials and fromthe small amount of time and labour required. The shades produced are,however, inferior both in beauty and permanence to the old logwood andcopperas black.

With other dye-wares red chrome produces a variety of browns, yellow-browns, yellows, oranges, bottle-greens, olives, black-greens, and purples.The a&ion of the chromes upon logwood is exhaustively treated in Dr. Runge’swork, “ Farben-Chemie,” Part III.

Chromic oxide, in combination with acids, is also a mordant, though littleused. The most important of its compounds are the sulphate and the nitrate.It has the disadvantage of imparting, in itself, a pale greenish colour, whichto certain shades would of course be fatal. Its affinity, for many colours atleast, is but feeble, and many dyers complain that the shades produced areharsh and dull.

Chrome-alum, a double sulphate of chromic oxide and of potash, is occa-sionally employed on the Continent. The salts of chromic oxide may be usedto fix aniline blues upon cotton.

From the immense use of bichrome in dyeing it is very possible that certainquantities of this powerful poison may find their way into rivers. In allsanitary legislation its exclusion, even in minute traces, should be rigorouslyinsisted on. +