44 SELECTED ARTICLES. 
or that a part of the water obtained and weighed has not 
been afforded by the oxide of copper incompletely dried, or 
by the apparatus itself. 
Now, if we have no other means to verify the results ob- 
tained by following this method, it is evident, according to 
this statement, that the method does not satisfy the first 
principle we have laid down, and which is so well established 
by experience. Likewise, it loses the advantages which 
are always found in the application of the second, by causing 
the operator to make his valuations by weight, instead of 
measuring the substances in the gaseous state. 
Always impressed with the necessity of finding some means 
to verify the quantity of free hydrogen which may be found in 
an organic body, I performed, for this purpose, a great num- 
ber of experiments, the results of which I shall now state. 
For example: I had hoped, having first ascertained the 
quantity of lead obtained by the reduction of litharge, then by 
means of the weight given to the organic substance, I should 
know the quantity of reducible matter, from which it would 
only be necessary to deduct the quantity of carbon, to obtain 
exactly the weight of the hydrogen. These calculations 
would be founded on the supposition that 12.48 grains of hy- 
drogen would liberate 1294.50 grains of lead, while 76.44 of 
carbon would give 1294.50x2=2589 of lead. I had to give 
up this mode, because, whether the vessels in which the re- 
duction was made were placed in the same or different fur- 
naces, the results were not the same. 
I attempted, then, to determine the reducing power of 
organic matters by mixing them with the sulphate of potassa 
or baryta, and calcining the mixture in a retort, without con- 
tact with the air. During the calcination, the carbon and 
hydrogen should reduce proportional quantities of the sulphate 
into sulphuret, quantities which it appeared to me could be 
ascertained, in the case of the sulphate of potassa, by esta- 
blishing, by the alcalimeter, the value of the sulphuret formed 
during calcination, and for the sulphate of baryta; by dissolv- 
ing the sulphuret, and regenerating the sulphate of baryta by 
