| Explosion of Hydrogen and Oxygen. - EY 
sufficiently small size to arrest explosion. Neither can it be sup- 
posed that the outlet at the extremity of the jet was insufficient 
for the expansion of the exploding mixture, and that in conse- 
quence of that expansion, the inflamed gases were driven back 
into the copper globe. This expansion must have been far 
| greater than 15 or 18 times, as deduced from Davy’s experi- 
ments, to have overcome the force exerted by the gases, which 
at the moment were issuing from the globe, under a pressure 
probably of nearly two atmospheres. 
The expansion of hydrogen and oxygen gases by explosion, 
: has not, I think, been satisfactorily determined; and Davy, 
| Whose results are most commonly adopted, does not appear to 
| have deemed his own conclusive. I have made some experiments 
on the subject, and should not have offered the preceding re- 
marks until more satisfactory results had been obtained, had it 
hot been necessary to defer the investigation to an interval of 
more leisure. 
When water is mechanically suspended in the gases, the dan- 
ger of retraction and explosion is undoubtedly increased, but the 
influence of the small quantity formed in the jet on the occurrence 
of the slight explosions already alluded to, must have been ina 
great measure, if not altogether, counteracted by the elasticity of 
the issuing gases. ; 
The cause of this explosion is certainly mysterious; but in 
Whatever manner we may attempt to explain it, it must be re- 
garded as additional evidence of the danger of employing the 
gases in a state of previous mixture, and of the importance of 
adhering to the use of two separate vessels and the concentric jet. 
With these, although less convenient on some accounts, there are 
other advantages ; their perfect safety, however, is alone suffi- 
“lent to induce us to recommend them, and them alone, to the 
chemical student. 
The trials with the tube of Hemming previous to the occur- 
fence of this explosion, seemed to warrant the statement in Its 
favor which has been made in anote in the edition of my Manual 
of Chemistry, now passing through the press. 
Laboratory of Harvard University, Cambridge, June 5th, 1839. 
