196 On the Decomposition of the Earths. | [MArcit, 
of an explosion from the reservoir. An accident of this kind oc- 
curred while I was engaged with Professor Cumming in making 
experiments. There had been four pretty loud detonations, owing 
to the explosions of the gas in the safety cylinder; until at length 
the oil at A B was driven out, and the wire-gauze in the cap above 
C was broken. Presently, as Professor Cumming was turning the 
stop-cock of the jet, the whole of the apparatus exploded, and the 
consequences might have been very serious, if we had not been 
protected by the skreen which [ described upon a former occasion. 
The operator should also constantly bear in mind the indispensable 
caution of never opening the stop-cock, below the piston, before 
he has withdrawn the handle of the piston, when he proposes to 
introduce a fresh supply of gas into the reservoir. Using these 
precautions, the apparatus is perfectly safe. 
Having thus briefly described the means by which I have been 
enabled to increase the powers of this blow-pipe, and to add to its 
security, I shall subjoin a statement of the few additional experi- 
ments made with it which may be worth your notice. The interest 
which has been excited by the accounts already published of the 
results thereby obtained is mainly due to you; but it has given rise 
to repeated inquiries respecting the person to whom the invention is 
due, of burning the two gases in a state of condensation from a 
common reservoir. I have already mentioned* that their first ap- 
plication to aid the operations of the blow-pipe was made in 1802, 
by an American ; but, in their first application, the gases were pro- 
pelled from different reservoirs. I believe I may now add, that so 
long ago as the period above alluded to, you made use of these 
gases yourself, for the same purpose ; condensing them by means 
of a column of water, and igniting them in a compressed and 
mixed state, as propelled from a commovs reservoir; and that the 
frequent explosion of your apparatus put a stop to your experiments. 
You will correct me if there be any error, therefore, in considering 
you as the first person who made use of the mixed gases, as I have 
now used them. ‘The proportion, observed in the mixture, is all 
that I can lay claim to; which instead of consisting of hydrogen in 
slight excess with oxygen,t or of the gases in equal parts, has always 
been, by bulk, éwo parts of hydrogen, at the least, to one of oxygen; 
and, in some instances, | have made the excess greater ov the side 
of the hydrogen; using it in the proportion of ihree to one. It is to 
this excess on the side cf the hydrogen, that I am to attribute the 
decomposition of the earths, and their reduction repeatedly, to the 
metallic state. For the truth of their decomposition, I may appeal to 
the testimony of the most experienced chemists now resident in this 
* Journal of the Royal Institution, No. IIT. p. 105, note. ; 
+ The mixture of Aydrogen in slight excess with oxygen, was tried by Sir H. 
Davy (see Journal above cited, p. 127). He considered it as producing a more 
intense heat from combustion than any other flame he had examined, It is, how- 
ever, greatly inferior to the heat produced by burning these gases when mixed in 
the proportion for forming water; as the results have proved. 
