322 APPENDIX. 
Effervefcence, or Fire; as alfo of common 
Air impregnated with the like Fumes, is 
principally owing to thofe Fumes or Vapours, 
as mentioned in Experiment CXVI. Vol. I. 
and not to a rebating of the Degrees of its 
Elafticity, for that we fee is exaftly the fame 
with that of common Air. 
It is obfervable that though there was 
a very great Etfervefcence made by many of 
the abovementioned Mixtures in vacuOy yet 
no elaftic Air was generated by feveral of 
them, and but little by many others, not near 
fo much as would probably have been made 
in the Bolt-head Fig. 34. p. 1(38. Vol. L 
where I have given many Inftances of much 
greater Quantities of Air being generated by 
efrervefeent Mixtures ; the Reafon of which 
Difference feems to be this, viz, that the 
Affion and Reaffion of the common Air with 
the effervefeent Mixture in the Bolt-head, 
contributed to throw off more Air into an 
elaftic State, than was done in vacuo where 
there was none of that Air, 
Expe- 
