228 PHILOSOPHICAL TRANSACTIONS. [ANNO 1797. 



genous gas evolved by this process does not arise from the decomposition of char- 

 coal ; because the same quantity of that substance is contained in the gas after, as 

 before electrization. 3. The hydrogenous gas proceeds from decomposed water; 

 because when this fluid is abstracted as far as possible from the carbonated hydro- 

 genous gas, before submitting it to the action of electricity, the dilatation cannot 

 be extended beyond £ its usual amount. 4. The decomponent of the water is not 

 a metallic substance; because carbonated hydrogenous gas is expanded when in 

 contact only with a glass tube and gold, a metal which has no power of separating 

 water into its formative principles. 5. The oxygen of the water (when the electric 

 fluid is passed through carbonated hydrogenous gas, that holds this substance in 

 solution,) combines with the carbon, and forms carbonic acid. This production 

 of carbonic acid therefore adds to the dilatation occasioned by the evolution of hy- 

 drogenous gas. 6. There is not, by the action of the electric matter on carbo- 

 nated hydrogenous gas, any generation of azotic gas. 7. Carbon it appears there- 

 fore, from the united evidence of these facts, is still to be considered as an 

 elementary body; that is, as a body with the composition of which we are unac- 

 quainted, but which may nevertheless yield to the labours of some future and more 

 successful analyst. 



XIX. Observations and Experiments on the Colour of Blood. By Wm. C. IVells, 



M.D., F.R.S. p. 4l6. 



Dr. Priestley is, I believe, the only person who has hitherto attempted to show 

 by what means common air brightens the colour of blood, which has been for some 

 time exposed to it*. His opinion is, that the air produces this effect by depriving 

 the blood of its phlogiston ; for blood, according to the same author, is wonder- 

 fully fitted both to imbibe and to part with phlogiston, becoming black when 

 charged with that principle, but highly florid when freed from it. Various argu- 

 ments may be brought to prove that this opinion is erroneous, even on the ad- 

 mission of such a principle of bodies as phlogiston. It may be said, for instance, 

 that it is contrary to the laws of chemical affinity, that the same mass should at 

 one time convert pure into phlogisticated air, by giving out its phlogiston, and im- 

 mediately after reconvert phlogisticated into pure air, by imbibing that principle; 

 both which changes are supposed by Dr. Priestley to be induced by blood, on those 

 airs. Again ; it may be urged, that since the neutral salts, and the different al- 

 kalies, when saturated with fixed air, produce the same effect as common air on the 

 colour of blood, if common air acts by attracting phlogiston, those other bodies 

 must have a similar operation. But surely it cannot be thought, that the mild vo- 

 latile alkali, which has been supposed by chemists to superabound with phlogiston, 

 can yet attract it from blood. It appears to me however, unnecessary to bring any 

 further arguments of this kind against the opinion of Dr. Priestley, since the fol- 

 lowing experiments will, I expect, be thought sufficient to show, in opposition ta 



* Phil. Trans, for 1776.— Orig. 



