38 Mr. Meikle on Specific and Latent Heat, 



double the atmospheric tension, issued forth against only half 

 that force, it must have expanded considerably; and conse- 

 quently, without some additional heat, its temperature would 

 have been much reduced ; but being at the same time in contact 

 with the stop-cock and pipe, which were still about 248 , there 

 can be no doubt that these communicated heat to it; and 

 therefore, if on condensing in the bucket, this vapour did not 

 heat the water more than an equal weight of steam of half the 

 original elasticity did, the obvious conclusion is, that in the 

 boiler the. same weight of denser steam contained less heat*. 



But this and several other sources of fallacy are deserving 

 of more particular consideration. On account of the high 

 pressure, the aperture through which the steam issued must 

 have been very contracted ; probably, it was but a small part 

 only of the circular hole in the stopper of the stop-cock ; and 

 therefore there was so much the greater chance of the ex- 

 panding vapour absorbing heat from its contact with the hot- 

 ter metal ; especially when we consider that the vapour would 

 enter by such a small opening into the cylindrical cavity of 

 the stopper, where it would have an opportunity of expanding 

 and absorbing heat; and after dashing from side to side 

 of this little chamber would pass out of it by a like narrow 

 aperture diagonally opposite to that by which it entered. On 

 passing this second orifice, it would still further expand and 

 absorb more heat from the hot metallic pipe. Besides, if the 

 velocity of the steam was not ultimately the same in all the 

 three cases, it is reasonable to think, that its elasticity, whilst 

 rushing through the pipe, would, in the high-pressure cases, 

 be even inferior to that of the atmosphere ; otherwise, its mo- 

 mentum, which is independent of refrigeration, would have 

 been sufficient to drive all the water out of the bucket. I should 

 therefore suppose, that if the velocities were greater in the 

 higher temperatures, still the elasticity and momentum taken 

 together, could but little more than balance the atmospheric 

 pressure. If this notion be correct, it will follow that the 

 greater the elasticity and temperature within the boiler, the 

 less would these be in the stream of vapour ; and consequently 



* It has often been observed, that steam issuing from a pipe at 212° is 

 quite transparent till at some distance from the pipe ; but that a stream of 

 high-pressure steam issues opaque from the very orifice. This shows in- 

 controvertibly that a given weight of the high-pressure steam had con- 

 tained less heat than a like quantity of the common sort. Otherwise, such 

 heat would just have enabled it to maintain the transparent elastic form 

 when it expanded into steam of the ordinary atmospheric pressure. This 

 remark is somewhat at variance with M.Clement's result; and perhaps 

 the reason may be, that he had allowed his steam to escape from the boiler 

 through a smaller opening than that alluded to. 



its 



