436 GASES IN THE ATMOSPHERE. 



Specific gravl- Xhefe may be feen in the following Table. 

 ties of gates. A . r 1 • • 



Atmofphenc air - - - . - l.OOO 



Azotic gaz >..... .966" 



Oxygenous gaz - . _ - . 1.127 



Carbonic acid gas - - - - l .500 



Aqueous vapour i - - - - .700 

 Hydrogenous gas - _ - - .077* 



Kirwan and Lavoifier are my authorities for thefe numbers j 

 except oxygenous gas and aqueous vapour. For the former 1 

 am indebted to Mr. Davy's Chemical Ref'earches j his number 

 is fomething greater than theirs: I prefer it, becaufe, being 

 determined with at leaft equal attention to accuracy with the" 

 others, it has this further claim for credit, that 21 parts of gas 

 of this fpecific gravity, mixed with 79 parts of azotic gas, 

 make a compound of exaAIy the fame (peciitc gravity as the 

 atmofphere, as they evidently ought to do, felting afide the 

 tinfounded notion of their forming a 67/e7?iic'a/ compound. The 

 fpecific gravity of aqueous vapour I have^ determined rayfelf 

 both by analytic and fynthetic methods, after the manner of 

 De SauflTure; that is, by abftrading aqueous i^apour of a 

 known force from a givfen quaaitity of air, and weighing the 

 water obtained — and admitting a given weight of water to 

 dry air and comparing the lofs with the increafed elafticity. 

 De Sauflure makes the fpecific gravity to be ,71 or ,75 ; but 

 iic ufed cauftic alkali as the abforbent, which would extract 

 the carbonic acid as well as the aqueous vapour from the air. 

 From the experiments of Pi6let and Watt, I deduce the fpe- 

 cific gravity of aqueous vapour to be ,61 and ,67 refpedively. 

 Upon the whole, therefore, it is probable that ,7 is very 

 nearly accurate. 



We have now fufficient data to form tables anfvv^ering lo the 

 two firft objedts of our enquiry. 



* The fpecific gravity of hydrogen muft be rated too low : if 

 100 oxygen require i85 hydrogeri.by ineal'ure, according to this 89 

 oxygen would require only H hydrogen to form water; whereasf 

 io require 15. Hydrogen ought to be found about -~^ part of the 

 x^eight of common air* 



1. Tabd 



