332 



Mr. J. Joly. 



" On the Method of Condensation in Calorimetry." By 

 J. Joly, B.E., Assistant to the Professor of Civil Engi- 

 neering, Trinity College, Dublin. Communicated by 

 Professor Fitzgerald, F.R.S. Received June 28. Read 

 November 18, 1886. 



[Plates 6 and 7.] 

 Introduction. 



This paper is devoted generally to experimental verification of a 

 method of condensation applied to the determination of specific heat. 

 The extension of the method to the calorimetry of latent heat of 

 gasification has been the subject of some experiments, but the further 

 delay necessary to complete these compels me to defer their con- 

 sideration. Similarly its application, theoretically practicable, to the 

 direct determination of the specific heats of gases at constant volume, 

 is not here considered. 



In another paper (p. 250) some results bearing on the possible value 

 of the method in physical mineralogy and in determinative mineralogy 

 are given. The method was originally devised in the hope that it 

 might be of service in this branch of investigation. 



On the subject of this paper a couple of brief notices only have up 

 to the present been published. One of these arose out of an 

 informal notice brought before the Royal Dublin Society;* the 

 second from a verbal account laid before the Dublin University 

 Experimental Science Association.! 



To the facilities extended to me by Prof. Fitzgerald, in the Physical 

 Laboratory of Trinity College, the whole of the experimental veri- 

 fication of the method is due. I have not attempted to acknowledge 

 anywhere adequately how much is due to his advice and suggestions. 



Theory of the Method. 



If W grams of a substance at the temperature t± of its surround- 

 ings be immersed in an atmosphere of saturated vapour, steam sup- 

 pose, the temperature of which at the prevailing atmospheric pressure 

 is t 2 °, the substance experiences a rise iu temperature of t% — t-f, and 

 absorbs a number of calories, WS(t 2 ° — ^°), where S is the specific heat 

 of the body. Also if X is the latent heat of steam at the temperature 

 ? 2 °, a quantity of steam weighing w grams is condensed, so that 



WS(* a °-*i°) = wX. 

 If in this equation X be known, the value of S may be found by 



* ' Irish Times,' February 17, 1885. 



f ' Dublin University Review,' June, 1885. 



