CHEMICAL RESEARCHES ON THE ANIMAL FLUIDS. 135 



4. Finding thnt supertartrate of potash exalted the colour Attempt to 

 of the bloodj I endeavoured to form a compound of it with ^°|^^ superar- 

 that substance and oxide of tin, and thus, in some measure, to trate of potash, 

 imitate the process in which cochineal is employed for the pro- ^P^ °^"^^ "^ 

 duction of scarlet dye ; but although a bright red compound is 

 produced, when it is dried at a very moderate temperature its 



colour becomes similar to that of the other combinations which 

 I have described. 



These experiments I repeated in various ways, occasionally The experi- 

 applying the salt of tin as a mordant to woollen cloth, linen, rnents varied, 

 &c. J but the brilliancy of the colour was never permanent. 



5. Having observed that infusion of galls and decoction of Oak bark used, 

 oak bark do not impair the colour of the blood, I conceived ^^ ^ mordant, 

 that solution of tannin might answer the purpose of a mordant, 



as it is effectually employed by dyers in giving permanence to 

 some of their red colours. 



I accordingly impregnated a piece of calico with decoction 

 of oak bark, and afterward passed it through an aqueous solu- 

 tion of the colouring matter of blood. When dry, it was 

 of a dirty red colour, nearly similar to that which would have 

 been obtained, had no mordant been applied : when, however, 

 an alkaline solution of the colouring matter was employed, the 

 colour was equal to that of a common madder red, and as far as 

 I have been able to ascertain, it is permanent. 



6.. A solution of superacetite of lead was impregnated with Oxide of lead, 

 the colouring matter of the blood. The compound was bright 

 red : no spontaneous change took place in it, and on the addi- 

 tion of an alkali a white precipitate was formed, the fluid re- 

 taining its former tint. 



From this, and other experiments, in which it was attempted 

 to combine oxide of lead with the colouring matter of the 

 blood, it would appear, that there is no attraction between these 

 two substances, 



7. The most effectual mordants, which I have discovered for Solution of 

 this colouring matter, are some of the solutions of mercury, "^^'■<^"''y« 

 especially the nitrate, and corrosive sublimate. 



Ten grains of nitrate of mercury, (prepared with heat, and Nitrate of the 

 containing the red oxide) were dissolved in two fluid ounces of '^^^ °^' ^' ^" . 

 a solution of the colouring matter of the blooJ, After son:>e 

 hours a deep red compound was deposited, consisting chiefly of 



the 



