43'^ teASES IM THE Al'Jl'OS P H E R E. 



to ftkygen. The (ransferring is neceiTary to prevent llie nilrlc 

 afcid formed and combined with the water, from ablorbing 

 the remainder of the nitrous gas to form nitrous acid. 



Metliod with Sulphuret of lime is a good teft of the proportion of ox^'gen 



in a given mixture, provided the liquid be not more than 20 or 

 80 per cent, for the gas (atraofperic air) ; if the liquid exceed 

 this, there is a portion of azotic gas imbibed fomewhat uncer- 

 tain in quantity, 



VoJta's method. Volta's eudiometer is very accurate as well as elegant and 

 expeditious: according to Monge, 100 oxygen require 196* 

 meafures of hydrogen ; according to Davy 192 ; but from the 

 moft attentive obfervations of my. own, 185 are fufficient. In 

 atmofpheric air I always find 60 per cent, diminution when 

 fired with an excefs of hydrogen; that is, 100 common air 

 with 60 hydrogen, become 100 after the explofion, and no 

 oxygen is found in the refiduum j here 21 oxygen take 39 hy* 

 drogeni 



^. Of ihe Weight of the Aqueous Vapour Atmdfphere, 



To find the I have, in a former elTay, (Manchefler Mem. vol. 5. p. 1, 



ous vapour'^in ' P^g^-^-^S-) given a table of the force of vapour in vacuo for 



the armofphere. every degree of temperature, determined by experiment; 



and in the fequel of the efTay, have (lievvn that the force of 



Vapour in the atmofphere i:* the very fame as in VfKuo, when 



they are both at their ulmoflfor any given temperature. To 



ifind the force of aqueous vapour in the atmofphere, there- 



tbrCj we have nothing more to do than to find that degree of 



cold at which it begins to be condenfed, and oppofite to it in 



the table abovemenlioned, will be found the force of vapour. 



JFrom the various fafls mentioned in the efiay it is obvious, that 



I'apour contra6ts no chemical union with any of the gafes in 



the atmofphere ; this fa&. has fince been enforced in the An- 



nafes de Chimie, vol. xlii. by Clement and Deforrhe. 



M. De SaulTure found by an excellent experiment, that dry 

 bir of 64f° will admit fo much vapour as to ihcreafe itsfelaftii 

 city, ^. This I have repeated nearly ih his manner, and 

 found a fimilar refult. But the table he has given Us of 

 aqueous vapour at other temperatures is very far wfohg, efpe- 

 cially at temperatures diftaht from 64i^. The numbers Were 

 not the refult of dire£l experiment, like the one above. IF 

 we could obtain the temperature^; of all parts of the earth's 



furfaCCi 



