258 PHILOSOPHICAL TRANSACTIONS. |_ANNO 1782. 



fixed alkali, and the alkali, after the operation, was found crystallized ; but when 

 the tube was exhausted of air, and the experiment repeated, no change whatever 

 was found in the alkali. Essai sur l'Electricite, par M. Le Comte De La 

 Cepede, vol. 1, p. 155. 



Fourthly, if lead and mercury be agitated in a phial, partly filled with 

 common air, this air will be diminished i, and the residuum will be found com- 

 pletely phlogisticated. The diminution will be still greater if the phial contain 

 dephlogisticated air : 4 Pr. 140. The lead is converted into a calx, calcination 

 being the known effect of the amalgamation of the base metals ; and this calx 

 absorbed the fixed air produced, for Dr. Priestley expelled this air from it : 4 Pr. 

 144 ; and hence an amalgama of lead and mercury decrepitates when heated. 

 Whence could this fixed air proceed, but from the respirable air ? For surely 

 neither lead nor mercury contain any. 



If the above experiments be attended to, the answer to the 2d question will 

 be equally obvious. It is certain, that common air does not consist of + of its 

 bulk of fixed air; for if it did, the remaining |- must be dephlogisticated air: 

 and if so, then the absolute weight of a mixture of 4 dephlogisticated air and i 

 fixed air should coincide at least nearly with the absolute weight of an equal bulk 

 of common air ; but in fact it is very far from it : for 4 cubic inches of common 

 air weighed 1.54 gr. ; but a mixture of 3 cubic inches of dephlogisticated air 

 and 1 of fixed air weighs 1 .83 gr. ; neither indeed has so large a portion of 

 fixed air been ever supposed to exist in common air. Besides, if fixed air pre- 

 existed in common air, it might be separated from it by lime-water, at least in 

 some degree. I have mixed 1 part of fixed air with 20 of dephlogisticated air, 

 and also with 20 of phlogisticated air in close vessels, and these mixtures did not 

 fail to render lime-water turbid. But let common air be agitated in lime-water 

 ever so long in close vessels, not the least cloudiness will appear ; nor does 

 quick-lime, in these circumstances, in the least affect common air, as Dr. 

 Priestley has observed. 2 Pr. 184. The spontaneous precipitation of lime-water 

 arises therefore from an accidental diffusion of fixed air through common air 

 and the slowness of this precipitation shows its quantity to be very small. The 

 inference from the above experiments will be much stronger against the pre- 

 existence of fixed air in respirable air, if, instead of common air, dephlogisti- 

 cated air be used ; for there the diminution is so great, and the quantity of fixed 

 air produced so considerable, that it can by no means be supposed to have pre- 

 existed, its properties being so very opposite to those of dephlogisticated air. 



Having synthetically proved the constituent parts of fixed air to be pure 

 elementary air and phlogiston, I shall now endeavour to do the same by its 

 analysis : and, in the first place, that it contains phlogiston, and even in such 

 quantity as to deserve to be classed among the phlogisticated acids, appears by 



