Dr. Schunck on Rubian and its Products of Decomposition. 217 



with cold water, I was enabled to ascertain under what circum- 

 stances and by what means the tinctorial power of the liquid is 

 destroyed, and consequently what is the general character of 

 the substance or substances to which it is due. I found that by 

 adding sulphuric or muriatic acid to the extract and heating, 

 the liquid, after neutralization of the acid, was no longer capable 

 of dyeing. The tinctorial power was also destroyed by the ad- 

 dition of bydrate of alumina, magnesia, protoxide of tin and 

 various metallic oxides, but not by carbonate of lime or carbonate 

 of lead. In all cases in which the property of dyeing in the ex- 

 tract was destroyed, I invariably found that its bitter taste and 

 bright yellow colour were lost. Now in my former papers on 

 this subject, I have shown that the intensely bitter taste of mad- 

 der and its extracts is due to a peculiar substance, to which I 

 have given the name of Rubian ; and as it appeared from these 

 preliminary experiments that this substance, though itself no 

 colouring matter, is in some way concerned in the changes 

 whereby a formation of colouring matter is induced in aqueous 

 extracts of madder, I proposed to myself to examine its properties 

 and products of decomposition more in detail than I had hitherto 

 done. 



The first step necessary to be taken for the attainment of this 

 object, was of course to find a method of procuring this sub- 

 stance in quantities sufficiently large for the purposes of exami- 

 nation. I was at the commencement however far from appre- 

 ciating the difficulties with which its preparation in a state of 

 purity is attended. The process which I had formerly described, 

 by precipitation with sulphuric acid, is not well adapted to the 

 purpose, since rubian in a state of perfect purity is not pre- 

 cipitated by sulphuric acid, besides which it is easily decomposed 

 by an excess of that acid. Neither is it precipitated by any 

 metallic salt, with the exception of basic acetate of lead, which, 

 from the circumstance of its precipitating also other substances 

 from the extract, is not applicable to the purpose. It is decom- 

 posed by alkalies and alkaline earths. Even bicarbonate of 

 lime exerts a decomposing effect on it in conjunction with the 

 oxygen of the atmosphere. These substances must therefore 

 be discarded in its preparation. Besides its great tendency to 

 decomposition, there is another circumstance which presents 

 obstacles to almost all attempts to prepare rubian in a state of 

 purity. There is no investigation of madder which does not 

 make mention of a substance, which when its solution in water 

 is mixed with sulphuric or muriatic aeid and boiled, gives rise to 

 the formation of a dark green powder. To this substance, which 

 - no bitter taste, and is in fact devoid of any characteristic 

 property except the one mentioned, i have restricted the name 



