1864.] 



Dr. Stenhouse on Rubia munjista. 



147 



All the specimens were prepared at different times, except IV. and V., 

 wliicli are analyses of the same specimen. The lead compound therefore 

 seems to approach nearly to the somewhat anomalous formula 5(C^g 0.) 

 4- 6PbO, being a basic lead-salt ; it is, however, perfectly analogous to the 

 lead compound of purpurine, 5(0-^^11-0^) +6PbO, described by Wolff 

 and Strecker*. 



From these analyses of the lead compound and also from the ultimate 

 analyses of munjistine itself, it is pretty evident that its true formula is 



Neither sublimed munjistine nor that obtained by crystallization from 

 alcohol, when dried at the ordinary temperature in vacuo, loses weight at 

 1 10° C. It is not improbable, however, that the gelatinous uncrystallizable 

 precipitate, which separates on the cooling of boiling saturated aqueous 

 solutions of munjistine, is a hydrate. 



From some experiments made on a considerable scale, I find that ordinary 

 madder does not contain any munjistine. In order to ascertain this fact, a 

 considerable quantity of garancine from Naples Roots, and likewise some 

 which had been subjected to the action of high-pressure steam according to 

 Pincoff and Schunck's process, were treated with boiling bisulphide of car- 

 bon, and the product obtained on evaporating the bisulphide repeatedly 

 extracted with large quantities of boiling water ; the solution, when acidu- 

 lated with sulphuric acid, gave an orange-red precipitate from which I was 

 unable to obtain any munjistine. Professor Stokes succeeded, however, in 

 detecting the presence of alizarine, purpurine, and rubiacine in it f . 



The production of phthalic acid from alizarine, purpurine, and munjistine, 

 together with a comparison of their subjoined formulae, 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. 



Alizarine CggHgOg, 



Purpurine C^g Hg Og, 



Munjistine ^isMe ^e- 



Two other very convenient sources of phthalic acid are — first, the dark 

 red resinous matter, combined with alumina, which is left undissolved by 

 the bisulphide of carbon in the preparation of munjistine ; secondly, the 

 large quantity of green-coloured resinous matter which remains behind 

 after extracting the alizarine from Professor Kopp's so-called "green ahza- 

 rine " by means of bisulphide of carbon. I have repeated Marignac's and 

 Schunck's experiments of distilling a mixture of phthalic acid and lime ; 

 and, like both of these chemists, I observed a quantity of very aromatic 

 benzol to be produced, which, by the action of strong nitric acid, readily 

 yielded nitrobenzol, and from this, by the action of reducing agents, anihne. 

 The only impurity in the benzol from phthalic acid appears to be a minate 



* Annalen der Chemie, Ixxv. p. 24. 



t He has since informed me that he has succeeded in demonstrating the absence of 

 munjistine. 



