86 Dr. Stenhouse — Examination of Unhia mmiyisia. [Jan. 14, 



the caution which is necessary in endeavouring to derive the epochs of the 

 decennial period from the magnitude of the diurnal range of the declina- 

 tion-magnet, and the preference due to the variation in the amount of the 

 disturbances in different years. 



January 14^ 1864. 

 Major-General SABINE, President, in the Chair. 

 The following communications were read ; — 



I. "Examination of Rubia munjista, the East-Indian Madder, or 

 Munjeet of Commerce.^^ By John Stenhouse, LL.D., E.R.S. 

 Eeceived December 21, 1863. 



(Abstract.) 



As a portion of this paper has already appeared in the * Proceedings/ 

 vol. xii. p. C33, I shall confine myself in this abstract to briefly noticing 

 the additional observations which I have subsequently made. 



By numerous analyses of munjistine crystallized out of spirits and dried 

 at 100° C, and likewise of sublimed munjistine, I find that its formula 

 is Hg Og. This result has been confirmed by analyses of the lead-salt, 

 the formula of which I find to be 5(C^g Hg Og), 6 PbO, exactly correspond- 

 ing to the purpurine compound described by Wolff and Strecker*. 



A comparison of the subjoined formula of alizarine, purpurine, and mun- 

 jistine. 



Alizarine C^oHgOg, 



Purpurine C^g Hg Og, 



Munjistine C^e Hg Og, 



indicates the very close relationship between these three substances, the 

 only true colouring principles of the different species of madder with which 

 we are acquainted. 



Tinctorial Power of Munjeet, 

 From a numerous series of experiments I have just completed, I find that 

 the garancine from munjeet has about half the tinctorial power of the garan- 

 cine made from the best madder, viz. Naples roots. These, however, 

 jaeld only^about 30 to 33 per cent, of garancine, while munjeet, accord- 

 ing to my friend Mr. Higgin of Manchester, yields from 52 to 55 per cent. 

 The actual amount of colouring matter in munjeet and the best madder are 

 very nearly the same ; but the inferiority of munjeet as a dye-stuff results 

 mainly from its containing only the comparatively feeble colouring matters 

 purpurine and munjistine. The latter in large quantity is positively in- 

 jurious ; so much is this the case, that when the greater part of the mun- 

 jistine is removed from munjeet-garancine by boiling water, it yields much 

 richer shades with alumina mordants. 



* Annalen der Chemie, vol, Ixxv. p. 24. 



