1868.] Specific Heat of Mixtures of Alcohol and Water. 337 



IV. " The Specific Heat of Mixtures of Alcohol and Water.'' By 

 A. DuPRE, Ph.D.j Lecturer od Chemistry at the Westminster 

 Hospital, and F. J. M. Page. Communicated by C. Brooke, 

 M.A. Received March 26, 1868. 



(Abstract.) 



The authors have examined a number of mixtures of alcohol and water. 

 They show that the specific heat of these mixtures, up to an alcoholic 

 strength of about 36 per cent., is higher than the specific heat of water 

 itself. 



Two methods were employed for estimating the specific heat exactly op- 

 posite in principle. 



The first consisted in heating a metallic weight to a certain temperature 

 in a steam-oven, similar to that employed by Regnault in his researches, 

 and then plunging it into the liquid the specific heat of which is to be 

 estimated. The rise in the temperature of equal quantities of different 

 liquids produced by the introduction of the same weight, heated to the 

 same temperature, is inversely proportional to the specific heat of such 

 liquids. 



Two weights and several calorimeters of different sizes were used. One 

 of the weights was made of brass and weighed 246*49 grms., the other was 

 of copper gilt weighing 614*49 grms. Both weights were made in the form 

 of stout rings, and in the inner cylindrical opening of each a small fan- 

 wheel was inserted. 



These rings, after being heated and let down into the calorimeter, were 

 attached to a strand of worsted, and held freely suspended in the liquid of 

 the calorimeter. The worsted had previously been twisted, and when now 

 allowed to untwist it causes a rapid rotation of the ring. The fan-wheel 

 fixed inside the ring thereby produces a current, which, passing through 

 the ring, not only serves to mix the liquid thoroughly, but also consider- 

 ably facihtates the rapid cooling of the weight. 



The calorimeters, as usual, consisted of cylindrical vessels made of very 

 thin polished brass, supported on stretched silk cords, and surrounded by 

 a double cylinder of tin-plate to prevent, as far as possible, any gain or loss 

 by radiation. 



The temperature of the liquid was taken by a small thermometer, having 

 a bulb 60 millims. long and about 2*5 millims. diameter. Each degree 

 was divided into twenty parts, and by means of a telescope j-^ of a degree 

 could be read off. 



The authors give experiments which prove that the high specific heats 

 observed are not due to evaporation caused by the introduction of the 

 heated metals into the calorimeter. 



The second method used was that generally employed. A certain 

 weight of the liquid, the specific heat of which is to be estimated, enclosed 

 in a suitable vessel, is heated and then plunged, vessel and all, into a 



VOL. XVI. 2 I 



