186 Chemical Researches on the Blood, 



change by exposure to the joint action of light and air for 

 three weeks. 



4. Finding tliat supertartrate of potash exalted the colour 

 of the blood, I endeavoured to form a compound of it with 

 that substance and oxide of tin, and thus, in some measure, 

 to imitate the process in which cochineal is employed for 

 the production 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, occa- 

 sionally applying the salt of tin as a mordant to woollen 

 cloth, linen, Sec; but the brilliancy of the colour was 

 jl.ever permanent. 



5. Having observed that infusion of galls and decoction 

 of oak bark do not impair the colour of the blood, I con- 

 ceived 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 decoc* 

 tJon of oak bark, and afterwards passed it through an 

 aqueous solution 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 the colouring matter of the blood. The compound 

 was bright red : no spontaneous change took place in it, 

 and on the addition of an alkali a white precipitate was 

 formed, the fluid retaining its former tint. 



From this and other experiments, in which it was at- 

 tempted to combine oxide of lead with the colouring of the 

 blood, it would appear that there is no attraction between 

 those two substances. 



7. The most effectual mordants, which I have discovered 

 for this colourinsr matter, are some of the solutions of mer» 

 curv, especially the nitrate, and corrosive sublimate. 



Ten grains of nitrate of mercury (prepared with heat and 

 containing the red oxide) were dissolved in two fluid 

 ounces of a solution of the colouring of the blood. After 

 some hours a deep red compound was deposited, consisting 

 chiefly of the metallic oxide combined with the colouring 



flatter. 



