1 48 Dr. Priestley’s Experiments on the 
than on the phlogiftic hypothefis, whatever be the conftitu* 
tion of phlogifticated air. 
As, in the experiments above mentioned, heat without light 
gives colour to the nitrous acid, and the reflection or refraCtion 
of light is always attended with heat, it may perhaps be heat 
univerfally that is the means of imparting this colour, though 
the mode of its operation be at p refen t unknown. And in thefe 
experiments, as well as the former, it is the vapour that firft 
receives the colour, and imparts it to the liquid when it is 
fufficiently cold to receive it. 
The rufhing out of a quantity of turbid white air from a 
tranfparent tube, quite cold, is a ftriking phenomenon in thefe 
experiments. It may be worth while to examine of what it is 
that this remarkable cloudinefs of the air confifts. There is 
the fame appearance, as I have more than once obferved, in 
the rapid production of any kind of air, which is perfe&ly 
tranfparent as it palies along the glafs tube through which it is 
tranfinitted, till it comes into contaCt with the water in which 
it is received. 
P. S. Not to multiply my communications on the fubjeCt of 
phlogijion unneceffarily, I would beg leave to obferve, at the 
clofe of this article (in reply to what has been objected to my 
former experiments, as being liable to exception from the 
phlogifticated air which could not be excluded from the de- 
phlogifticated air when it was decompofed by means of inflam- 
mable air) that I have found the procefs I made ufe of to have 
no tendency whatever todecompofe phlogifticated air. Indeed, 
nothing that we have hitherto known concerning this kind of 
air could make it probable, that mere heat , in contaCt with 
dephlogifticated or inflammable air ? could have this effeCt. And 
1 it 
