144- Dr. Schunck on the Colouring Matters of Madder. 



in a free state, and further, that the brown precipitate produced by 

 acids in a watery extract of madder contains the whole of these two 

 colouring matters in a free state. If then a piece of mordanted 

 cloth be dyed with this brown precipitate, after being freed from all 

 excess of acid, the whole effect is produced by the alizarin contained 

 in the brown precipitate. If, however, a small quantity of lime, 

 chalk, soda, or any alkaline base, either caustic or carbonated, be 

 added to the brown precipitate before dyeing, then its power of 

 dyeing is very much increased. In order to prove this, I took six 

 pieces of mordanted cloth, all of the same size. Nos. 1, 2 and 3 were 

 mordanted in the usual way with acetate of alumina, and Nos. 4, 5 

 and 6 with acetate of iron, Nos. 1 and 4 were dyed with a certain 

 quantity of the brown precipitate; Nos. 2 and 5 with the same 

 quantity of the brown precipitate, to which, however, there had 

 previously been added a very small quantity of lime water; Nos. 3 

 and 6, lastly, with the same quantity of brown precipitate, and a large 

 excess of lime water. The dyeing was performed each time in the 

 same vessel with the same quantity of water, and for the same length 

 of time. Now I found at the conclusion that No. 2 exhibited a far 

 darker, fuller, and more brilliant shade of red than No. 1, and 

 No. 5 a much more intense purple colour than No. 4, whereas 

 Nos. 3 and 6 showed hardly any colour at all. Now I can offer only 

 one explanation of these differences. When a small quantity of lime 

 is added to the brown precipitate, it combines exclusively with the 

 rubiacin, or is transferred during the process of dyeing exclusively 

 to the rubiacin. The first effect of the dyeing is the combination 

 of the alizarin with the alumina and peroxide of iron of the mor- 

 dants. These compounds then attract and combine with the lime 

 compound of rubiacin contained in the fluid, by which means a 

 greater intensity of colour is produced. I repeated this experiment 

 with the pure colouring matters. I took two pieces of mordanted 

 cloth of the same size, and dyed the one with pure alizarin, and the 

 other with the same quantity of alizarin to which rubiacin combined 

 with lime was added, and I found that the latter was much darker 

 than the former. I therefore conclude that madder colours are 

 always double compounds of alizarin, rubiacin, alumina, and an alka- 

 line base, or of alizarin, rubiacin, peroxide of iron, and an alkaline 

 base. 



It follows from this that the maximum of tinctorial power in 

 madder is produced when the alizarin is in a free state, and the ru- 

 biacin is in combination with lime or some alkaline base. If an 

 excess of lime be added then the alizarin also combines with it, and 

 is thus rendered incapable of attaching itself to the alumina and 

 peroxide of iron of the mordants. A slight excess of lime exists in 

 the root when grown on a calcareous soil ; for if a quantity of mad- 

 der which has dyed as much cloth as it is capable of doing and is 

 seemingly quite exhausted of colouring matter, be treated with sul- 

 phuric acid, and the acid be carefully removed by washing, it is 

 found that after being so treated it is capable of again dyeing almost 

 as much mordanted cloth as it did before, a fact long known in 



