34 Mr. Mcikle on Specific and Latent Heat, 



bably, be extended to those nodular concretions, generally 

 considered as contemporaneous with the paste in which they 

 are enveloped, the distinction of which, from conglomerates of 

 mechanical origin, forms, in many cases, a difficulty in geology. 

 What the degree may be, of subdivision required to dispose 

 the particles to act thus upon each other, or of fluidity to ad- 

 mit of their action, remains still to be determined. 

 [To be continued.] 



V. On Specific and Latent Heat, and on Alcoholic Engines. 

 By Mr. Henry Meikle*. 



r INHERE are few subjects on which there has been a greater 

 ■*■ diversity of opinion than on the laws according to which 

 heat is distributed in different bodies, or in the same body un- 

 der different forms. To Dr. Black we are indebted for the 

 first important discoveries on this intricate subject; and from 

 his time, many others, following up his researches, have gra- 

 dually added to our stock of knowledge. That absolute cer- 

 tainty is by no means yet attained on many leading points con- 

 nected with this inquiry, there can be little room to doubt ; 

 and as an instance of primary importance, it need only be re- 

 collected what different opinions are still entertained regarding 

 the scales of thermometers, or whether the influx of heat be 

 exactly proportional to the corresponding expansion : many 

 experiments favouring the notion, that whilst the heat increases 

 uniformly, the expansion, in a variety of bodies, proceeds with 

 an accelerated velocity. 



It had been for some time suspected and even so far sanc- 

 tioned by experiment, that under equal volumes the specific 

 heats of the simple gases are equal; and more lately, Mr. Hay- 

 craft seems to have added considerably to the evidence in 

 favour of the same opinion ; though his mode of operating, 

 probably the most correct yet used, seems to be still a little 

 open to objection. 



by being first separately diffused in water to the consistence of thick cream, 

 and when mixed in due proportion are reduced to a proper consistence by 

 evaporation. During this process, if the evaporation be not rapid and im- 

 mediate, or if the ingredients are left to act on each other, even for twenty- 

 four hours, the flinty particles unite into sandy grains, and the mass be- 

 comes unfit for the purposes of the manufacturer. I am indebted for this 

 interesting fact, which, I believe, is well known in some of the potteries, to 

 my friend Mr. Arthur Aikin. And Mr. Herschel informs me, that a similar 

 change takes place in recently precipitated carbonate of copper ; which, if 

 left long moist, concretes into hard gritty grains, of a green colour, much 

 more difficultly soluble in ammonia than the original precipitate. 

 * Communicated bv the Author. 



Mr. 



