APPENDIX.

687

on a filter and dried. The yield is 66 per per cent of the weight of thecrude aloes employed. The aqueous solution is used diredlly for dyeing.Lowe digests without heat 1 part of aloes in 8 parts of nitric acid, and afterhaving filtered the solution pours it into a large quantity of water. He alsoprepares chrysammic acid by evaporating a solution like the above down toone-half. He then adds £ part of nitric acid, and concentrates afresh tillcrystals of oxalic acid appear, when he pours the whole into a large amountof water.

If instead of proceeding as above the concentrated nitric solution is mixedwith excess of ammonia and the whole evaporated to crystallisation.chrysammidis obtained in small brilliant crystals.

A cheaper preparation may be made by dissolving 132 parts of aloes in100 parts of boiling water and adding 80 parts of nitric acid. There is abrisk effervescence and a plentiful disengagement of gas. The acid is thenneutralised with about 10 parts of soda-lye, of sp. gr. 1-12. Before makinguse of this preparation the mixture is slightly acidulated with hydrochloricor tartaric acid. The a&ion of any deoxidising agent, especially proto-chloride (muriate) of tin changes red chrysammic acid and violet chrysammidinto blue hydro-chrysammid. All the shades produced upon silk, wool, orcotton, ranging from red to violet or to cinnamon-brown are, in contadt withreducing agents, converted to grey, blue-grey, greyish blue, olive-green, ormoss-green. If silk and wool are plunged into a weak aqueous solution ofchrysammic acid, and the bath is raised to a boil, the silk takes shades varyingfrom rose to corinthe (a colour somewhat approaching that of dried currants),whilst wool is dyed a chestnut-brown, varying in intensity. Cotton unmor-danted is not dyed; if prepared with alumina it takes a violet. If mordantedwith iron it remains undyed. Linder’s aloetic acid produces upon wool, un-mordanted, a deep brown, which may be carried to a velvety black. Lowe’simperfedt chrysammic acid yields upon wool reddish-brown shades. Linder’saloetate of soda (aloetic acid neutralised with soda) imparts to wool, un-mordanted, a fine bluish-grey colour.

Chrysammid dyes silk and wool a grey, light or dark ; with the addition ofpink-salt the tone becomes greenish.

Upon silk chrysammid dyes a nut-brown ; upon wool a yellow beforesteaming, and an olive-green after this operation.

When perchloride of tin is added we obtain a rusty yellow upon cotton,and a cinnamon-brown upon silk and wool.

With alum chrysammid yields, before steaming, a rusty yellow or buff uponsilk and cotton, and a yellow upon wool. After steaming the cotton becomesa pearl-grey, the silk a drab, and the wool a bright “ wood ” colour.

According to Lindner, aloetic acid (aloes purple) is useful for fixing colourswhich in themselves are deficient in solidity. If, for instance, 10 parts oforchil are mixed with £ part of aloes purple, previously dissolved in soda-lye,the colour of the orchil is unaffedted by air and light, without any injury toits brightness. If in dyeing cotton goods with madder or fleur de garance alittle aloes be added to the bath, the garnet-brown shades acquire a peculiarlustre.

41. Rufigallic Acid.—Gallic acid can be transformed into tannin byboiling with a very small quantity of arsenic acid, which undergoes no