of Atmospherical Air, Se. 151 
The rusting of iron in the habitual temperature 
of the atmosphere, seems likewise to be owing to a 
decomposition of water, since no rust can take 
place without moisture. Iron confined in dry oxy- 
genous gas will never rust: From this fact, we 
learn, why finery cinder, which has been made in a 
high temperature, will not rust in the ordinary tem- 
perature of the atmosphere. Being already com- 
bined with a large portion of oxygen, its remaining 
attraction for it is too feeble to decompose water. 
But in order to prove that the addition of weight 
to the iron (in the decomposition of water by red-hot 
iron).is really caused by oxygen, we are called upon 
to exhibit it in the form of dephlogisticated air, or of 
some other substance into which oxygen is allowed 
to enter.—I confess that, as far as I know, this has 
not yet been done; but, though we have not hitherto 
nitric acid. If, for instance, the sulphate of potash, or of 
soda, be dissolved in-equal parts of strong nitric acid ina 
sufficient heat, nitrate of soda, or of potash, is found in the 
mixture when itis become cold. But Scheele has observ- 
ed, that only one third of the sulphate is decomposed in this 
way. That the weaker substance should thus displace the 
more powerful one, is a paradox in the doctrine of affini- 
ties, and cannot be satisfactorily explained. Probably the 
excess in quantity makes up for the defect of the power of 
attraction, Thus Margraaf decomposed completely the ni- 
trate of soda by muriatic acid, when he distilled one part 
the former with eight parts of the latter. This process is 
analogous to the entire decomposition of the red oxyd of 
mercury by caloric, 
