602 PHILOSOPHICAL TRANSACTIONS. [aNNO iJSg. 



posite surface to attract or receive it, and if it be supplied, both surfaces will 

 pass off in the positive state; and either surface will give out more electricity 

 than is really induced on it, because the electricity of the opposite surface forms 

 a charge. For the substance of the remainder of this paper, reference may be 

 had to Mr. Nicholson's ingenious Introduction to Natural Philosophy, in 2 

 vols. 8vo. 



XXII J. Experiments on the Transmission of the Fapour of Acids through a 

 Hot Earthen Tube, and further Observations relating to Phlogiston. By the 

 Rev. Joseph Priestley, LL. D., F. R. S. p. 289. 



In Dr. P's former experiments on the phlogistication of spirit of nitre by heat 

 it appeared, that when pure air was expelled from what is called dephlogisticated 

 spirit of nitre, the remainder was left phlogisticated. This he found abundantly 

 confirmed by repeating the experiments in a different manner, and on a larger 

 scale; and he applied the same process to other acids and liquors of a different 

 kind. From these it will appear, that oil of vitriol and spirit of nitre, in their 

 most dephlogisticated state, consist of a proper saturation of the acids with 

 phlogiston, so that what we have called the phlogistication of them, ought rather 

 to have been called their super-phlogistication. 



He began with treating a quantity of oil of vitriol as he had done the spirit of 

 nitre, viz. exposing it to heat in a glass tube, hermetically sealed, and nearly 

 exhausted ; and the result was similar to that of the experiment with the nitrous 

 acid, with respect to the expulsion of air from it, though, the phlogistication not 

 appearing by any change of colour, I did not in this method ascertain that cir- 

 cumstance. The particulars were as follow. After the acid had been made to 

 boil some time, a dense white vapour appeared in quick motion at a distance 

 above the acid ; and though, on withdrawing the fire, that vapour disappeared, it 

 instantly re-appeared on renewing the heat. When the tube was cool, he opened 

 it under water, and a quantity of air rushed out, though the acid had been 

 made to boil violently while it was closing, so that there could not have been 

 much air in the tube. This air, which must therefore have been generated in 

 the tube, was a little worse than common air, being of the standard of 1.12 

 when the latter was 1.04. 



That this air should be worse than common air. Dr. P. could not well explain. 

 But in his former experiments it appeared that vitriolic acid air injures common 

 air; and that in proportion as pure air is expelled from this acid, the remainder 

 becomes phlogisticated, or charged with vitriolic acid air, clearly appeared in the 

 following experiment. Making a quantity of oil of vitriol boil in a glass retort, 

 and making the vapour pass through a red-hot earthen tube, glazed inside and 

 out, and filled with pieces of broken tubes, he collected the liquor that distilled 



