( yy ) 



CHAP. XXI. 



EXPERIMENTAL ENQUIRIES RELATIVE 

 TO THE NATURE OF THE GASES OF 

 VOLCANOS, AND THE CAUSES OF 

 THEIR ERUPTIONS. 



The perfeEl refemhlance of the effecis produ- 

 ced by fame gafes of volcanos and thofe of 

 others generated in lavas ^ and other fimilar 

 fubjiances^ -when re- melted in our common 

 Jire^ may enable us to difcover the nature 

 of the former^ by invefigaiing that of the 

 latter — Matrajfes of clay^ filed to a cer- 

 tain height with volca?iic products^ expofed 

 to the fire of a chemical furnace^ and com- 

 municating nsoith a pneumatic-chemical ap- 

 paratus prepared 'with mercury — Experi- 

 ments made in this manner on the fpotted 

 glafs of Lipari— Phenomena obferved 

 njuithin the matrafs during ignition — No 

 gas appeared above the mercury — Ebidli- 

 ent Jlate in which the glafs was found 



when 



