246 Dr. Priestley’s Obfervations on 
Except ferum, milk is the only animal fluid that I have 
tried, through which the air can adt upon blood: for 
black blood became red when it was plunged in milk, in 
the fame manner as if it had been covered with ferum. In 
urine, indeed, black blood becomes inftantly red; but 
this is not owing to the action of the air, through the 
urine, but to the faline nature of that fluid. 
In fome cafes, care mull be taken to diflinguifh the 
floridnefs with which fome detached parts of a quantity 
of blood are tinged, from that which penetrates the folid 
parts of it. In faliva , and in water impregnated with 
alkaline fait, fixed or volatile, and alfo in fpirit of wine, 
the extreme angles and edges of pieces of craflamentum 
and fmall detached parts, floating in thofe liquors, will 
appear of a very florid red, while the compact mafs of 
blood continues dark. The florid colour of the promi- 
nent and detached parts, in thefe cafes, feems to be the 
mere effedt of the minute divifion of the parts of the 
craflamentum in the fluid in which thofe parts float; 
when at the fame time it has no fuch effedt on thofe 
parts which remain compadt, nor has the air the lead: 
power of adting on the blood through the liquor. 
I had imagined, that fince black blood contains more 
phlogifton than red blood, that difference would have 
appeared in the air produced from them, either by being 
Amply diffolved in fpirit of nitre, or when dried and 
made into a pafte with that acid. But the difference: was 
too fmall to be fenfible to this kind of teft. For this 
purpofe, however, I had fome blood drawn from the vein 
of 
