284 - description of an apparatus for the 



The inflammable gas, which has found its way into the 

 receiver b, is always present in too minute a quantity to 

 compose, with the residuary oxygen, after the removal of 

 the carbonic acid, . a mixture capable of being inflamed 

 by the electric spark. To ascertain its precise quantity, it 

 is necessary to have recourse to another operation. After 

 trying, eudiometrically, the quality of an aliquot part of 

 the gas in the receiver Z», let a similar aliquot part be de- 

 prived of its carbonic acid, and then mixed with a portion 

 of pure hydrogen gas, not exceeding one-third or one- 

 fourth the estimated bulk of the oxygen which it contains. 

 Detonate the mixture, and observe the amount of the di- 

 minution after the explosion ; the products of the com- 

 bustion ; and the quantity of oxygen gas consumed. After 

 subtracting, from the total expenditure of oxygen, half the 

 bulk or'the added hydrogen gas, the remaining number shows 

 how much oxygen has been absorbed by the combustible 

 gas contained in the residue. By the rule of proportion, 

 it may be determined, how much carbonic acid would have 

 been produced, by the oxygenation of the whole of the 

 combustible gas, and what quantity of oxygen it would have 

 saturated. 



The most obvious objection to this method of analysing 

 the compound gases is, that the real proportion of the pro- 

 ducts, resulting from their combustion, may perhaps be 

 disguised, in consequence of the absorption of a part of the 

 carbonic acid by the water, over which the experiment is- 

 made. By frequent trials, however, I find that this is a 

 source of error too trivial to be deserving of consideration ; 

 and that the proportion of carbonic acid, thus generat- 

 ed, exceeds what is composed by the rapid combustion of 

 the same gas over mercury. When the operator has ac- 

 quired sufficient dexterity, the interval of time, between the 

 completion of the combustion and the admeasurement of 

 the residue, is too small to allow an absorption to any 

 notable amount. It must be observed, also, that the car- 

 bonic acid constitutes only a small part of the residue ; and 

 is, for that reason, very little acted on by water, conformable 

 to a principle which I have explained in the Philosophical 



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