( 347 ) 



according to him, muft depend on the de- 

 gree of heat to which they have heen ex^* 

 pofed in lubrerranean fires *. 



Leaving unnoticed the laft of thefe ex- 

 periments, as being too equivocal, and con- 

 fiderlng only the two former, I could have 

 wiflied that Dr. Pricftlty had explained 

 himfelf more fully relative to thefe two la- 

 vas ; and afforded us certainty that the two 

 flones on which he made his experiments 

 were really volcanic. 



But fuppofing they actually were fuch, 

 if we oppofe our ten procefTes to the two 

 of Dr. Prleftley, the ccnfequence to be de- 

 rived will be, that volcanic products are not 

 always deftitute of permanent gafes ; which 

 dedud;ion will be found perfectly to agree 

 with obfervaticns we fhall have hereafter to 

 make, and is by no means contrary to thofe 

 already made. In the latter, I have princi- 

 pally fhown that the numerous pores in 

 volcanic products expofed to our common 



'^ Experiments and Obfervaticns on Air, Vol. IV. 



iire. 



