224- Dr, Schunck on Colouring Matters. 



add an excess of lime, then of course the alizarine also combines with 

 the lime, and the alumina and peroxide of iron having no free body 

 to combine with, remain colourless. The process is thus brought 

 into harmony with our previous knowledge of the relative affinity 

 of acids and bases. It is probable that lime is not absolutely neces- 

 sary for the success of the operation, and that it might be replaced 

 by potash, soda, magnesia or baryta ; but as lime is the cheapest 

 substance that can be used for the purpose, it would be of no prac- 

 tical importance to find a substitute for it. 



I have in the preceding remarks left xanthine out of consideration. 

 During the process of madder-dyeing this substance no doubt be- 

 comes oxidized, and deposits the brown substance mentioned above, 

 on all parts of the cloth. This substance, together with the pectic 

 acid, the rubiacine and the resins, are removed afterwards by passing 

 the cloth through a boiling solution of soap. The alkali of the soap 

 dissolves these substances, which have more affinity for alkalies than 

 alizarine, while the fat acid remains on the cloth in combination with 

 the alizarine, the alumina and the peroxide of iron. 



In order to prove analytically that alizarine is the substance which 

 produces madder colours, I took several yards of cloth which had 

 been dyed purple with madder, but not soaped, and treated it with 

 muriatic acid, which removed the oxide of iron, and left an orange- 

 coloured substance on the cloth. After washing the cloth in cold 

 water until all the acid had been removed, it was treated with caustic 

 alkali. The brownish-red solution thus obtained was supersaturated 

 with an acid, and the reddish-brown precipitate formed was thrown 

 on a filter and well-washed with cold water : it was then treated with 

 boiling alcohol. The alcoholic liquid, which was dark yellow, was 

 spontaneously evaporated, and gave crystals of alizarine mixed with 

 a powder resembling beta-resin, and a few yellow micaceous plates, 

 which were probably rubiacine. There remained a brown residue in- 

 soluble in alcohol, part of which dissolved in boiling water, and 

 proved to be pectic acid. On treating some cloth which had been 

 dyed with madder, and then soaped, with muriatic acid as before, and 

 then with caustic alkali, I obtained a purple solution, in which acids 

 produced a yellow precipitate. This precipitate was treated with 

 boiling alcohol like the other ; it gave a yellow liquid, which on eva- 

 poration afforded crystals of alizarine, together with white masses of 

 fat acid. Hardly any residue remained undissolved by the alcohol. 



The preceding observations have a great bearing on the manufac- 

 ture and treatment of garancine. Garancine is the technical name for 

 a preparation of madder, which is obtained by treating madder with 

 hot sulphuric acid until it has acquired a dark brown colour, then 

 adding water, straining and washing until all the acid is removed. 

 The advantages which garancine has over madder are, that it dyes 

 finer colours, that the part destined to remain white does not acquire 

 any brown or yellow tinge, and that its tinctorial power is greater 

 than that of the madder from which it has been prepared. These 

 effects have been attributed to various causes. It has been asserted 



