Mr. T. S. Hunt's Description and Analysis of Loyanite. 65 



tions required by the practical formulae of Pambour to suit them 

 to the true mechanical theory of heat. It is proved^ that, from 

 the nature of the steam-engine, we cannot expect to convert 

 more than about one-sixth of the heat expended in evaporation 

 into available power, the remainder escaping into the condenser 

 or the atmosphere. The actual amount so converted is in many 

 ordinary engines less than one-twenty -fourth part. The paper 

 concludes with two tables for practical use, — the first for calcu- 

 lating the pressure of steam from the volume, and vice versa ; 

 and the second for computing the effect of expansive working in 

 steam-engines*. 



Glasgow, September 14, 1850. 



XII. Desaiption and Analysis of Loyanite, a new Mineral 

 Species. By T. S. Hunt, Chemist to the Geological Com- 

 mission of Canada-^. 



THIS mineral occurs at Calumet Island on the Ottawa, in a 

 white crystalline limestone mixed with pale green serpen- 

 tine, phlogopite, pyrites, and rarely crystals of apatite. 



Form very imperfect, but has the appearance of a prism replaced 



* A comparison of the results of those formulae and tables with Mr. Wick- 

 steed's experiments on the Cornish engine at Old Ford is given in the 

 Edinburgh Transactions, vol. xx. part 2, together Avith a method of deter- 

 miniu;^' the proportions of an expansive engine which shall perform a given 

 amount of work at the least possible pecuniary cost. 



Subsequently to the publication of the above letter, I became acquainted 

 with the second part of M. Clausius's paper, the object of which is to adapt 

 the principle knoA\Ti as Carnofs law to the mechanical theory of heat. 

 That law, as modified by M, Clausius and Prof W. Thomson of Glasgow, 

 is as follows : — 



When a machine converts heat into expansive power by communicating 

 heat to a substance at a higher temperature (tj), and abstracting heat from 

 it at a lower (tq), the maximum proportion of the heat converted into expan- 

 sive power to the whole heat received is a function of the two temperatures 

 only, and independent of the nature of the substance. 



I have since succeeded in proving, that Carnot's law is not an indepen- 

 dent principle, but is deducible from the equations given in my original 

 paper ; and that the function of the temperatures of receiving and emitting 

 heat, which expresses the maximum value of the fraction of the whole heat 

 converted into expansive power, is the following : |. 



K being a constant, which is the same for all substances in nature. (Trans. 

 Rov. Soc. Edin., vol. xx. part 2.) 



W. J. M.R. 

 London, Jvme 7, 1861. "^^ 



t Communicated by the Author. 

 Phil. Mag. S. 4. Vol. 2, No. 8. July 1851. F 



