1864.1 



Dr. Stenhouse on Rubia mmjista. 



151 



purpureine does to purpurine*. The following is an extract from a letter 

 I received from Professor Stokes : — 



" It would be very unlikely d priori that such a simple process as that 

 of Kopp should effect a perfect separation of two such similar bodies as 

 alizarine and purpurine ; and as I find his purpurine is free from alizarine, 

 it would be almost certain a priori that his * green alizarine ' would contain 

 purpurine, and the two would be dissolved by bisulphide of carbon, and 

 might very well afterwards be associated by being deposited in intermingled 

 crystals, if not actually crystallizing together." 



Action of Ammonia on Munjistine. 



This reaction with munjistine was only tried on a very small scale, but 

 the results were by no means satisfactory. The munjistine was completely 

 destroyed, the greater part being changed into a brown humus-Hke sub- 

 stance, insoluble in ammonia, — the remainder forming a colouring-sub- 

 stance, analogous to purpureine, but not crystalline. It dyed unmordanted 

 silk a brownish-orange colour. 



The combined action of ammonia and oxygen, therefore, on the three 

 colouring-substances alizarine, purpurine, and munjistine, is to change 

 them from adjective to substantive dye-stuffs. I think it not improbable 

 that if this archilizing process were applied to various other colouring mat- 

 ters, they would be found capable of undergoing similar transformations. 

 Action of Bromine on Alizarine. 



A boiling saturated solution of alizarine in alcohol is mixed with about 

 six or eight parts of distilled water, and to this when cold about one or one 

 and a half parts of bromine water are added, when a bright yellow amor- 

 phous precipitate is produced. After standing twelve or sixteen hours, the 

 solution is filtered ; and if the clear filtrate be now carefully heated so as to 

 expel the spirit, a substance of a deep orange-colour is deposited, consisting 

 of very fine needles, which are contaminated with a small quantity of resin 

 if a great excess of bromine has been employed. These needles are soluble 

 in spirit and ether, insoluble in water, and soluble in bisulphide of carbon, 

 from which they crystallize by spontaneous evaporation, in dark-brown 

 nodules. With soda they give the same purple colour as alizarine. They 

 dye cloth mordanted with alumina a dingy brownish red, very different 

 from the colour produced by ordinary crystaUized ahzarine. The follow- 

 ing optical examination is from a letter of Professor Stokes : — 



^'Bromine Derivative of Alizarine " 



" I can hardly distinguish this substance from alizarine. The solutions 



* Since this paper was communicated to the Royal Society, I find by a notice in Kopp 

 and Wills's * Jahresbericht ' for 1862, p. 496, that a similar experiment upon alizarine 

 had been made by Schvitzenberger and A. Paraf. The product of one preparation which 

 they obtained, and to which they have given the name of alizarinamid, yielded a formula 

 C40 NO12, and another preparation gave the formula Cgo H32N3 O24, both being, when 

 dry, nearly blacJc amorphous substances. It appears, therefore, from the results of MM. 

 Schiitzenberger and Paraf s experiments, that these gentlemen were not more successful 

 in obtaining a pure product from the action of ammonia on alizarine than I have been. 



