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Just such peculiar quasi-acid, or phenolic substances are Alizarin, and most of the natural adjective dyestuffs, the colouring principles of logwood, cochineal, Persian berries, etc. Hence these substances will be combined and carried down with such precipitated basic salts. The complex compounds thus produced are coloured substances known as lakes.
But let us take the printed piece of cotton and dye that in the Alizarin bath, and then we shall discover the conditions for producing colours with such a dyestuff as madder or Alizarin. Different coloured stripes are produced, and the colours are conditioned by the kind of metallic salts used.
The chemical substances which go to form the bodies of plants and animals remained just such "Dinge an Sich" until organic chemistry undertook to show them one after the other, whereupon the thing in itself became a thing for us, as the coloring matter in the roots of madder, alizarin, which we no longer allow to grow in the roots of the madder in the field, but make much more cheaply and simply from coal tar.
This artificial alizarin yields colours which are purer than those of natural madder, and being derived from what was originally regarded as a waste product, its cost of production is considerably cheaper. We have endeavoured thus far to deal with gas, and tar, the two principal products in the distillation of coal.
For example, if I take a solution containing basic sulphate of alumina, prepared as I have already described, and add to some Alizarin, and then heat the mixture, I shall get a red lake of Alizarin and alumina precipitated. If I had taken sulphate of iron instead of sulphate of alumina, and proceeded in a similar manner, and added Alizarin, I should have obtained a dark purple lake.
Magenta, however, permanently dyes the woollen as it did not the cotton. Alizarin only stains the untreated woollen, whilst the piece treated with alumina is dyed red, and that with iron, purple. If, however, the pieces treated with iron and alumina had been dyed in the Magenta solution, only one colour would have been the result, and that a Magenta-red in each case.
The number of coal-tar colours is thus very great, and the variety also. Adjective Colours. As regards the artificial coal-tar adjective dyestuffs, the principal are Alizarin and Purpurin. These are now almost entirely prepared from coal-tar anthracene, and madder and garancine are almost things of the past.
I myself had toyed with the problem of artificial alizarin and I knew enough about it to foresee that, in no very distant future, the work of the chemist's retort would take the place of the work of the fields. It was finished; my hopes were dashed to the ground. What to do next? Let us change our lever and begin to roll Sisyphus' stone once more.
In this important paper, Porak, after giving some historical notes, describes a long series of experiments performed on the guinea-pig in order to investigate the passage of arsenic, copper, lead, mercury, phosphorus, alizarin, atropin, and eserin through the placenta.
Silk, wool, fur, etc., act like fibre and mordant together, for they absorb and fix the substantive colours firmly. In our experiments we saw that turmeric is one of the few substantive colours fixing itself on both cotton and wool, without any aid from a mordant or fixing agent. Magenta was also a substantive colour, but Alizarin was certainly not one of this class. Adjective Dyestuffs.
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