Intelligence and Miscellaneous Articles. 325 



been made to explain it ; among others, by saying that in a perfect 

 calm, while the issue of vapour is suspended, everything being mo- 

 tionless in the apparatus, and all the dissolved air expelled, the water 

 may accidentally become heated beyond the point corresponding to 

 its pressure, and then if ebullition sets in, it suddenly furnishes a 

 mass of vapour which breaks the envelopes. But the embarrassing 

 circumstance, and the one found in most cases, is that the accident 

 takes place without the heating having been continued, while the 

 workmen and the machine were at rest, and when, from cooling, the 

 pressure in the machine had diminished. These conditions, almost 

 always mentioned with surprise in these accidents, exhibit an un- 

 doubted analogy with the experiments which I have described. Is 

 it not possible that at a moment of repose, and while the heating has 

 been discontinued, the cooling which sets in at first diminishes the 

 pressure of vapour existing in the boiler 1 As water, in virtue of its 

 great specific heat, cools very slowly, it retains for a longer time a 

 temperature which ought to produce ebullition under this diminished 

 pressure. This ebullition doubtless takes place most frequently in 

 proportion as the diminution of pressure permits ; but it may happen 

 that, under exceptional circumstances, a retardation similar to that 

 described above is produced, and then after a longer or shorter delay 

 ebullition sets in, either spontaneously, or in consequence of some 

 foreign disturbance. This ebullition ought to manifest the charac- 

 ters many times observed in my apparatus, where the concussions 

 raised the heavy support to which the retort was fixed. From the 

 large quantity of water contained in a boiler, these strokes might 

 well cause a fracture of the sides, and the disastrous effects of this 

 kind of accidents. 



The explanation which I attempt to give accounts, it is seen, for a 

 boiler-explosion, even when heating has ceased, when all the machine 

 is in a state of cooling, and the pressure has been diminished. Com- 

 paring the details ordinarily noted in this kind of explosion with the 

 conditions of the experiment above mentioned, it is impossible not 

 to observe a striking analogy, if the hints above given are correct ; 

 and it would remain to find out the means of preventing these de- 

 plorable accidents. No solid body by its contact seemed to me to 

 determine ebullition with certainty at the desired point ; and all of 

 them at length and by repeated heating become inactive. Contact 

 of gases, on the contrary, invariably provokes ebullition as soon as 

 the temperature makes it possible. Ilence, as M. Donny has already 

 said, it is desirable permanently to produce gases in the interior of 

 the boiler. Wires or platinum plates which dip in the water, and 

 by which enters the current of even a feeble battery, would very 

 probably be sufficient to prevent retardations of ebullition. 



P.S. — Since writing'this Note, I have read {Cosmos, April 7, 1864) 

 of a fact which agrees very well with this proposed theory of the 

 explosion of boilers. 



This is the explosion at Aberdare, where two boilers burst. The 

 waiter supplied appeared to contain a little sulphuric acid. Some 

 pieces of the sides presented by Mr. Fairbairn to the Manchester 



