22$ Mr. Porrett’s experiments relative to the 
the end of the mercurial trough, in a position declining a little 
from the horizontal one towards the table. The decompo- 
sition was then commenced, by applying the flame of a spirit 
lamp to the empty part of the tube, and bringing it down 
gradually, so as to explode in succession the three strata of 
the mixture. The arrangement of the apparatus at the com- 
mencement of the process, will be instantly seen by an inspec- 
tion of the annexed sketch. 
When the retort tube was cold, it was separated, under the 
surface of the mercury, from the adapting tube, in such a 
manner, that any gas remaining in the latter might pass up 
into the graduated tube ; the volume of gas collected, was 
then ascertained, making the necessary corrections for tem- 
perature, pressure, and the capacity of the retort tube, after 
which a solution of pure potash was passed up into it, and 
the diminution of volume which it occasioned was noticed ; 
from the gas which remained, a deduction was made, for the 
quantity of atmospheric air in the upper part of the retort 
tube before the combustion, and which seldom exceeded ~ of 
a cubic inch ; the residual gas was considered as azote, and 
found to be so by all the tests to which I subjected it. The 
small quantity of solution of potash employed to effect the 
absorption was then examined, and if, besides carbonic acid, 
it was found to contain prussic acid, I concluded that I had 
not employed enough of the red oxide of mercury in the 
