Heating by the Circulation of Fluids. 277 



Art. 111. On heating by the Circulation of Fluids. 

 By Robert Mallet, Esq. 



Sir, 



It appears strange that any man should have thrown away 

 his money upon a patent for circulating hot oil; after the 

 thing had been so distinctly pointed out by Mr. Tredgold, and 

 published long since in \he Trans. Hort.Soc, and in the Gard. 

 Mag. Vol. VII. p. 177. Still more unfortunate is it, that, were 

 the patent valid as a patent, the difficulties and danger of bring- 

 ing it into practice are such as would render it useless. Oil 

 possesses, in common with some other fluids, when hot, such a 

 power of exuding through fissures, or the minutest capillary 

 apertures, that it is found almost impossible, if not wholly so, 

 to keep the joints, &c., of apparatus [containing it stanch for 

 any length of time. In addition to this inconvenience, the 

 danger of its inflammation is imminent ; for, the moment the 

 heat becomes sufficient to carbonise the oil (and there is no 

 mode of regulating or preventing this), gas begins to be 

 generated, and conflagration is likely to ensue. Of this there 

 was a lamentable instance at a sugar-baker's in London. 



The advantage proposed in heating by hot oil instead of 

 water, is, that, oil boiling at a temperature about three times 

 as high as water, three times as much heat will be developed, 

 in the same time, from an equal surface of an oil apparatus, 

 as from that of hot water ; therefore, that, to heat a given 

 space by the former mode, only one third the heating sur- 

 face will be required as by the latter ; and that, consequently, 

 the cost of the apparatus will be reduced in about the same 

 ratio : that the apparatus, being smaller, takes up less room, 

 &c. ; and that the combustion of the fuel is more perfect, 

 and therefore more economical, at this elevation of tem- 

 perature than at a lower one. Such, I think, is a fair state- 

 ment of the advantages proposed by heating with fluids at a 

 temperature above 212° Fahrenheit; for effecting which two 

 other modes have also been proposed, namely, by water 

 heated under pressure in close vessels, and by using saline 

 solutions as the medium of heat. 



To the first of these, which is the subject of Mr. Perkins's 

 patent, there are many objections. First, the extreme danger 

 which ever will attend the exposure of metallic vessels to 

 great elastic pressure, however contrived or skilfully arranged 

 and managed. The rapid destruction of those tubes which 

 are placed in contact with the fire ; which, namely, the con- 

 tinued failure of the generators, was one of the causes of the 

 ill success of Mr. Perkins's engine. This destruction of 



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