1904.J P^of. Deicar on Liquid Hydrogen Calorimetrij. 581 



WEEKLY EVENING MEETIXG, 

 Friday, March 25, 1904. 



Sir Jame.s Crichton-Browxe, M.D. LL.D. F.K.S., Treasurer 

 and Vice-President, in the Chair. 



Professor Sir Ja3Ies Dewak, M.A. LL.D. D.Sc. F.Jt.S. M.R.I. 

 Liquid Hijdroi/eii Ccdorimetnj. 



Ix the determination of quantities of heat, besides the " method of 

 mixtures," the various calorimeters that have been used depend 

 on liquefaction, evaporation, or condensation. One of the earliest, 

 that of Laplace and Lavoisier — a development of Black's method — 

 depended on the liquefaction of ice, care beini,^ taken to isolate the 

 ice which was the calorimetric substance from anv external heat 

 effects, bj means of a jacket of snow. In the middle of last 

 century Bunsen devised an exceedingly delicate instrument in which 

 ice was again the calorimetric substance ; but instead of following 

 liaplace and Lavoisier's plan of measuring the weight of ice melted. 

 Tie took advantage of the reduction in volume of melted ice — namely, 

 about one-eleventh part — to determine with great accuracy the 

 quantity of heat that had been employed. As a unit of heat will 

 melt yV gramme of ice, this will produce a change of volume of 

 about ^-^o cubic centimetre ; and if the index tube of the instrument 

 be half a millimetre in diameter, the unit of heat will be shown by 

 about t> or 7 millimetres on the scale. With such an instrument it is 

 therefore possible to determine very accurately one-tenth of a 

 gramme-calorie. 



Professor Joly's calorimeter depends on condensation. In it the 

 quantity of steam condensed on the body, which is the subject of 

 experiment, is ascertained by weighing the amount of water formed. 

 The body is contained in a chamber of relatively large volume into 

 which the steam is suddenly admitted. It will be noticed, therefore, 

 that the uncondensed steam in the chamber acts as a jacket to the 

 body and prevents the passage of heat between it and external bodies ; 

 in this manner it is isolated from disturbing causes. In Professor 

 Joly's hands, this instrument has been used to determine directly the 

 specific heat of gases at constant volume. 



Other methods have been adopted for the measurement of quan- 

 titiee of heat. Black compared the quantities of heat in two bodies 

 of equal masses and temperatures, by noting the times in which they 

 cooled to the same temperature. Regnault and others have used the 



