Page:Proceedings of the Royal Society of London Vol 1.djvu/438

Rh retained its red colour to the last; but when quite dry, it became of a dirty red colour.

Sulphuric acid, diluted With eight or ten parts of water, being poured upon the colouring matter, if no heat be applied, remains perfectly colourless; but, by the assistance of heat, it forms a lilac solution, which remains unaltered for a great length of time, though exposed to light; but if heat be applied, so as to evaporate part of the water, the colour is destroyed in proportion as the acid becomes more concentrated.

The effect of nitric acid is to destroy the colour in greater or less time, in proportion to the quantity employed.

Acetic acid dissolves the colouring matter, with appearances similar to those of the muriatic solution.

The solution in oxalic acid is of a brighter red than any other hitherto noticed. In tartaric acid the solution approached to scarlet.

The alkalies also, or their subcarbonates, dissolve the colouring matter; and the solutions may be evaporated nearly to dryness With- out Iosing their red colour.

The next object of Mr. Brande was to ﬁnd such combinations of the colouring matter as would he insoluble, and might therefore afford a permanent dye. When combined with alumina it is red While moist, but becomes brown when dried. With oxide of tin it may also be combined, but becom of a dull red by drying; neither does supertartrate of potash give permanent brilliancy to the colour. But when a piece of calico has been previously dipped into infusion of oak-bark, and afterwards steeped in an alkaline solution of the colouring matter, it acquires a redness nearly equal to that given by madder, and tolerably permanent. But the most effectual mordants appeared to be some of the solutions of quicksilver. Pieces of woollen cloth, calico, or linen, steeped ﬁrst in a solution of corrosive sublimate, and afterwards in a solution of the colouring matter, acquired a permanent red tinge, which remained unaltered by washing with soap.

The author has, therefore, considerable hopes that this substance may be of some utility in the art of dyeing; and he remarks, that blood has, in fact, been already employed by the Armenian dyers, along with madder, to ensure the permanency of the colour.

The author ﬁrst gives us, in detail, the succession of appearances that he has observed respecting this comet and its various parts, consisting of a planetary body, perceptible only by the best telescopes, in the luminous spherical head, which to the naked eye appears as a nucleus. The head is surrounded by an envelope that is hemispherical on the side towards the sun, but extends in an opposite direc-