1864] 



Dr. Stenhouse on Rubia munjista. 



149 



dyeing vegetable fabrics mordanted -with alumina. If, however, strong 

 ammonia be employed to dissolve the purpurine, considerable heat is pro- 

 duced — a rise of temperature of as much as 20° C. taking place if the 

 bulb of a thermometer be immersed in finely di\aded purpurine and strong 

 ammonia poured on it. 



The purpurine employed in these experiments was prepared by Kopp's 

 process, and I am indebted for it to my friend Professor Grace Calvert. 



The solution of the new substance, pujj)ureine, is filtered to separate dust, 

 &c., as well as a black substance insoluble in dilute ammonia; it is then 

 added to a considerable quantity of dilute sulphuric acid, boiled for a short 

 time, and'allowed to cool. When cold, the impure purpureine is collected 

 on a filter, well washed, and dissolved in a small quantity of hot alcohol. 

 The spirituous solution is again filtered into a quantity of very dilute boil- 

 ing sulphuric acid, about 1 part acid to from 50 to 100 of water ; when cold, 

 the precipitate is collected and again well washed. ^ A crystallization out of 

 boihng very dilute acid now renders it quite pure. This somewhat long 

 and tedious process is necessary to free it from an uncrystallizable black 

 substance, a part of which is separated when the crude purpureine is dis- 

 solved in alcohol, and a part is left behind at the last crystallization. 



This compound being in its mode of formation and physical properties 

 very analogous to orceine, I have called it purpureine. When crystalHzed 

 by the spontaneous evaporation of its alcoholic solution, or from boihng 

 dilute sulphuric acid under peculiar conditions of aggregation, it presents a 

 fine iridescent green colour by reflected light ; whilst under the microscope 

 it appears as fine long needles of a very deep crimson colour. As obtained 

 by the process above described, it has, however, but little of the iridescent 

 appearance, being of a browiiish-red colour with a faint tinge of green. It 

 is almost insoluble in cold dilute acids, and is in great part precipitated from 

 its aqueous solution by common salt, thus greatly resembling orceine. It 

 is almost insoluble in bisulphide of carbon, very slightly so both in ether and 

 in cold water, much more so in hot, and very soluble in spirit both hot and 

 cold and in water rendered slightly alkaline. It is'readily soluble in cold con- 

 centrated sulphuric acid, and is precipitated unaltered by water ; on heat- 

 ing, however, it is destroyed. 



Its aqueous solution gives a deep-red precipitate with chloride of zinc ; 

 with chloride of mercury a purple gelatinous precipitate ; and with nitrate 

 of silver a precipitate of a very dark brown colour slightly soluble in am- 

 monia. I have been favoured with the following optical examination by 

 Professor Stokes : — 



Its solutions show bands of absorption just like purpurine in character, 

 but in some cases considerably different in position. The etherial and 

 acidulated (acetic acid) alcoholic solutions show this strongly. The tint is so 

 different in purpurine and its derivative, that the intimate connexion revealed 

 by the prism would be lost by the eye. A drawing of the spectrum for pur- 

 purine would serve for its derivative (purpureine), if the bands were simply 

 pushed a good deal nearer the red end." 



