240 Dr. p^ iestley ’ s Obfervaiions on 
than its acquiring phlogifton. gaber, for inftance, ob- 
ferves, that blood becomes black when u begins to pt 
trify, as it does alfo whenever it is dried and haidenec 
near the fire. Father becc ari a alio found as I have ob- 
ferved, that red blood continued (and h e could iaib y a 
to obferve alfo, that it became) black in vacuo, where it 
could not have imbibed plilogilton. This I found to be 
the cafe when the blood was covered two inches and a 
half with ferum ; but it regained its florid coloui w ten 
it was expofed to the open air. 
In general, however, it cannot be expedked, that when 
blood has become black without having received phlo- 
gifton ab extra , it will recover its florid colour by icing 
expofed to the air. For the delicacy of its texture and 
confequently its capacity of being eafily affefted by phlo- 
gifton, may be effentially altered by internal cauies ot 
blacknefs. This is even the cafe when blood has become 
black by being expofed to nitrous and inflammable air, 
though this change is probably effeaed by its mibi mg 
Expofed pieces of the fame mafs of red blood to thefe 
two kinds of air, and alfo to fixed air at the lame time. 
They all became black ; but that which was in the in- 
flammable air was the leaft lb, and none of them reco- 
vered their florid colour in the open air. But at anotlici 
time, a piece of craffamentum, which had become black 
in fixed air, did, in fome meafure, and very flowly, reco- 
ver its florid colour in dephlogifticated air. Perhaps 
the pieces that had loft their colour in the nitrous and 
