Colouring Matter of Rottlera tinctoria. 301 



Experiment. Calculation. 





i. 



ii. 









Carbon, . 



. 71-47 



71*22 



71-71 



^60 



360 



Hydrogen, 



6-37 



6-21 



5-97 



H 30 



30 



Oxygen, . 



. 22-16 



22-57 



22-32 



°u 



112 



100-00 100-00 100-00 502 



I have added to these the calculation of the formula C 60 H 30 

 14 , which agrees tolerably well with the analysis ; for al- 

 though it is not entitled to much confidence it agrees with 

 the determination of the lead salt, giving the smallest propor- 

 tion of lead. The precipitate in question which was obtained 

 by adding an aqueous solution of acetate of lead to a diluted 

 alcoholic solution of the resin, contained 18*67 per cent, of 

 oxide of lead, while the formula Pb O C 60 H 29 13 requires 

 18*27 ; but on repeating the preparation in the same manner, I 

 could not obtain sufficiently concordant results to entitle me 

 to fix its constitution. Indeed I think it far from improbable 

 that it may be a mixture of several resinous acids. 



The colouring matter of the Rottlera belongs to the class of 

 substantive dyes. It does not require a mordant, all that is 

 necessary being to mix it with water, containing a solution 

 from a fourth to a half its weight of carbonate of soda, and to 

 boil it with the stuff. The Hindoos, in addition to carbonate 

 of soda, which they use in the form of native barilla, employ 

 powdered gum, and before adding water, rub the whole of the 

 materials up with a small quantity of sesamum oil. These 

 additions, however, are not necessary for success, as I obtained 

 a very fine colour without them. It is remarkable, however, 

 that this colour is only produced on silk. Calico, whether 

 with or without a mordant, acquires only a pale fawn colour, 

 and entirely devoid of beauty. On silk, the colour is a rich 

 flame or orange tint, of great beauty and extreme stability. 

 The great brilliancy and permanence of the tint which it pro- 

 duces, and the fact that the material supplied by commerce, 

 contains between 70 and 80 per cent, of real colouring matter, 

 ought to induce the silk dyers of this country to turn their 

 attention to it, the more especially as there is no doubt, that 

 if the matter were placed in the hands of an intelligent person, 

 our Indian empire might supply it in abundance. 



NEW SERIES. — VOL. I. NO. II. APRIL 1855. X 



