and some other Animal Fluids. log 
ing it three days afterwards, a small quantity of a bright red 
powder was observed at the bottom of the phial, which proved 
to consist of the colouring principle combined with the metal- 
lic oxide. A portion of this compound which has been kept in 
water for some weeks has undergone no change of colour; but 
when dried by exposure to air, it loses its brilliant tint, and 
becomes of a dull red hue. 
To a compound solution of muriate of tin and colouring 
matter, similar to that employed in the last experiment, I 
added a sufficient quantity of solution of potash to decompose 
the salt of tin. The precipitate thus obtained was collected, 
and dried by exposure to the air of a warm room. It was of 
a dull red colour, and has undergone no apparent change by 
exposure to the joint action of light and air for three weeks. 
4. Finding that 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 com- 
pound is produced, when it is dried at a very moderate tem- 
perature its colour becomes similar to that of the other com- 
binations which I have described. 
These experiments I repeated in various ways, occasionally 
applying the salt of tin as a mordant to woollen cloth, linen, 
&c. ; but the brilliancy of the colour was never permanent. 
5. Having observed that infusion of galls and decoction of 
oak bark do not impair the colour of the blood, I conceived 
that solution of tannin might answer the purpose of a mor- 
dant, as it is effectually employed by dyers in giving perma- 
nence to some of their red colours. 
