Dr. Schunck on Colouring Mailers. 223 



brown, while the white was yellowish. No. 6 was equal to No. 1, 

 but not darker, and in no respect superior. No. 7 was about equal 

 to No. 4. No. 8 had almost no colour at all ; the red, the purple 

 and the black were mere tinges of colour, such as might probably 

 have been produced by the tenth part of the quantity of alizarine 

 employed, if nopectic acid had been present. No. 9 was again equal 

 to No. 1. No. 10 was lighter than No. 1, the purple especially being 

 pale and reddish, while the white parts were yellowish. No. 1 1 was 

 equal to No. 1, but not superior. No. 12 was exactly the same as 

 No. 10, the purple having a disagreeable reddish cast, while the 

 white parts were yellowish. No. 13 was again equal to No. 1. 

 No. 14 and 15 did not differ from one another, and were equal to 

 No. 1. Hence we may draw the following conclusions : — Alizarine 

 produces the greatest effect in dyeing when used alone. The ad- 

 dition of lime, even in very small quantities, does not increase its 

 tinctorial power, but on the contrary neutralizes the effect of that 

 portion with which it combines. Rubiacine, the alpha-resin and the 

 beta-resin, in a free state, when used in conjunction with alizarine, 

 are injurious in about the same degree : they weaken the red, the 

 black, and especially the purple, while they render the white part 

 yellowish. In combination with lime these substances do not in- 

 crease the tinctorial power of alizarine, they merely allow it to act 

 without hindrance. Pectic acid almost destroys the effect of aliza- 

 rine. Pectate of lime is perfectly indifferent. Rubian in a free 

 state, and in combination with lime, has neither a beneficial nor an 

 injurious effect. Of all the substances therefore contained in madder, 

 none is of use in dyeing but alizarine, while all the others are inju- 

 rious when in a free state. That which is the most hurtful is pectic 

 acid. When alizarine and pectic acid are present together in the 

 dye-bath, the pectic acid having most affinity for bases, combines 

 with the alumina and peroxide of iron, and the alizarine crystallizes 

 out when the bath cools, as I noticed in performing the experiment 

 No. 8. The same is without doubt the case when using rubiacine or 

 the resins. The alumina and peroxide of iron combine with these 

 substances to the exclusion of the alizarine ; and these compounds 

 are either colourless, or have a poor and unsightly colour. The 

 use of lime is therefore easily explained ; it serves, not to increase 

 the tinctorial power of the colouring matter, but to combine with 

 and render harmless the substances which are injurious in a free 

 state. Now if we treat madder with muriatic or sulphuric acid, we 

 remove all the lime and magnesia from it ; the pectic acid, the rubia- 

 cine and the resins become free ; and if we wash with water, the 

 muriatic or sulphuric acid is certainly removed ; but those sub- 

 stances being but little soluble in cold water, remain and destroy the 

 effect of the alizarine in dyeing. But if previous to dyeing we add 

 lime, the pectic acid, the rubiacine and the resins being more electro- 

 negative than alizarine, combine with the strongest base, which is the 

 lime; and the alizarine, which is less electro-negative, combines with 

 the weakest bases, viz. the alumina and peroxide of iron. If we 



