The red obtained from this substance created a great deal of interest among printers and dyers on its introduction in 1857, or thereabouts. For purity and brilliancy of shade it was not excelled by any other colour, but not being able to stand the effects of air and light, its employment was limited. We are not aware that murexide has yet been brought forward as a pigment, and judging from its character as a dye, it would scarcely enrich the palette. Dyes and pigments have much in common, and a fugitive dye cannot be expected to furnish a permanent pigment. Murexide is produced by the action of ammonia on alloxan, which is itself derived from the uric acid of guano by treatment with nitric acid, and was known nearly forty years back to stain the fingers and nails red. The first murexide sent into the market was a reddish-purple powder, dissolving in water with a fine purple tint, leaving a little residue undissolved. Owing to improvements in manufacture, it is now capable of being prepared almost chemically pure, and with that green metallic reflection peculiar to several coal-tar salts and the wings of certain insects. When sulphuretted hydrogen is passed through a concentrated solution of murexide, it is immediately decoloured; a fact which renders it likely that murexide pigments would be as liable to suffer from an impure atmosphere, as from exposure to light and air. When an alkaline solution of murexide is precipitated by an acid, a light shining powder results, called purpuric acid. This dissolves in alkalies, and combines with metalline bases to form various coloured compounds, termed _Purpurates_. Among them may be mentioned a red purpurate of lead, a purple-red and a rose-coloured purpurate of mercury, a purple-red purpurate of silver, a dark red-brown purpurate of strontia, a crystalline red purpurate of cobalt, a scarlet purpurate of platinum, a yellow purpurate of zinc, and a green purpurate of baryta. All of these, however, being more or less soluble in water, and owing their colours to murexide, would be ill adapted for pigments. 107. _Paille de Mil,_ Or African Cochineal, is a substance obtained from Africa. Whether it has received its name of cochineal from its appearance or origin is not clear, but it behaves more like galls and sumac than cochineal, though it does give a kind of red with alumina mordants. The colours it yields are deficient in brightness, and it has otherwise been reported unfavourably of. 108. _Peganum Harmala,_ The seeds of which afford a red colour, has been investigated by the French, but described as inferior to existing reds both in brilliancy and stability. 109. _Persulphomolybdates._