352 On the Proporiion of 



of nitrous gas, or with twice that portion, but with no' 

 intermediate quantity. lu the former case nitric acid is the 

 result ; in the latter nitrous acid : but as both these may be 

 formed at the same time, one part ot ihe oxygen goinff to 

 one of nitrous gas, and another to two, the quantity of 

 nitrous gas absorbed should be variable; from 36 to 73' 

 per cent, for common air. This is the principal cause ot 

 that diversity which has so much appeared in the results of 

 chemists on this subicct. in fact, all the gradation in 

 quantity of nitrous gas from 36 to 72 may actually be ob- 

 served with atmospheric air of the same purity : the wider 

 the tube or vessel the mixture is made in, the quicker the 

 combination is effected ; and the more exposed to water, the 

 greater is the quantity of nitrous acid, and the less ixi nitric^ 

 thiit is formed. 



To use nitrous gas for the purpose of eudioraetry, there- 

 fore, we must attempt to form nitric acid or nitrous wholly, 

 and without a mixture (-f the other. Of these the former 

 appears from my experiments to be most easily and most 

 accurately efiected. In order to this, a narrow tube is ne- 

 cessary ; one that is just wide enough to let air pass water 

 without requiring the tube to be agitated, is best. Let little 

 more nitrous gas than is sufficient to form nitric acid be 

 admitted to the oxygenous gas; let no agitation be used; 

 and as soon as the dmniniUion appears to be over for a mo- 

 ment, let the residuary gas be transferred to another tube, 

 and it will remain without any further diminution of con- 

 sequence. Then -ry-ths of the loss will be due to oxygen. — 

 The transferring is necessa-y to prevent the nitric acid 

 formed and combined with the watur, from absorbing the 

 remainder of the n.irous gas to form nitrous acid. 



Sulphuret of lime is a good lest of the proportion of 

 oxygen in a given mixture, provided the liquid be not more 

 than 20 or 30 per cent, for the. g:is (atmospheric air) : if 

 the liquid exceed this, there is a portion of azotic gas im- 

 bibed somewhat uncertain in quantity. 



Volta's eudiometer is very accurate as well as elegant and 

 expeditious : accoruing to Monae, 100 oxygen require 1 96 

 measures of hydroi^en ; according to Davv, 192 : but from 

 the most attentive observations of my own, 185 are suffi- 

 cient. In atmospheric air I always tind 60 per cent, dimi- 

 nution when fired with an excess of hvdrogen ; that is, 100 

 common air with Go hydrogen become 100 after the ex- 

 plosion, and no oxygen is found in the residuum : here 21- 

 oxygen lake 39 hydrogen. 



2. Of 



