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SELECTED ARTICLES. 
dation of lead possesses the following advantages: In the 
determination of the oxygen by the combustion of hydrogen, 
uncertainties arise, both from the impurities of the latter gas, 
and from the destruction of some of the nitrogen. 
Chemists are not agreed as to the proportion of oxygen gas 
in common air, as indicated by the eudiometer of Volta. 
Humboldt and Gay Lussac made it 21 per cent.; Dalton 20.7 
or 20.8; Henry is doubtful whether it be 20 or 21; while 
Thompson makes it 20. Allowing for the accidental errors 
inevitable in the use of Volta's apparatus, the chief difference 
between the results above cited, appears to depend on the dif- 
ferent doses of hydrogen, which had been mixed with the 
atmospheric air for detonation. Humboldt and Gay Lussac 
made use of equal volumes of air and of hydrogen, obtaining 
thereby, as above stated, 21 per cent, of oxygen. Other au- 
thors use a half volume of hydrogen, but my own experiments 
with this proportion have furnished a result indicating but 
20.6 per cent, of oxygen, under the same circumstauces in 
which the other operation gave 21 per cent. It may be proper 
to remark, that the mixture of two parts of common air with 
one of hydrogen, has the advantage of extending very much 
the use of Volta's eudiometer, for the analysis of impure airs 
in experiments on respiration and fermentation; for 100 parts 
of corrupted air, which contain 88 of azote and 12 of oxygen, 
may be analyzed by a single detonation, if we use 50 parts of 
hydrogen; whereas, 100 of air, which contain 84 of azote and 
16 oxygen, cannot be inflamed by the electric spark, if we add 
so much as 100 parts of hydrogen. It may be also remarked, 
that the adding of oxygen to the air, previous to the analysis, 
only complicates the operation, requires a separate previous 
analysis of the latter to ascertain its purity, and consequently 
lacks precision in the result. 
The method by oxidating lead introduces no new gaseous 
ingredient into the air under trial; whereas the residue of a 
detonation with hydrogen is vitiated by the latter, even after 
the total combustion of the oxygen. 
The phosphorus eudiometer has the disadvantage of leav- 
