﻿136 M. C. Marignac on the Specific Heats, Densities, 



The variation of temperature produced in the liquid by the 

 immersion and agitation of the heated thermometer was mea- 

 sured by a very sensible thermometer, the divisions on which 

 corresponded to -^ of a degree, and which was read by means 

 of a horizontal telescope. 



The saline solutions were contained in a silvered brass cylin- 

 drical vessel, of which the value in water had been determined 

 by previous experiments, and found to be 13 grammes, including 

 the thermometer. However, even a notable error in this value 

 would only involve a scarcely perceptible one in the result of the 

 experiments, since it would affect equally the specific heats of 

 water and the solution compared with it. 



For strongly acid liquids I used a vessel of very light glass, of 

 which the equivalent in water was 14*9 grammes. 



To avoid as much as possible accidental and variable external 

 influences, these vessels were suspended by their spread upper 

 brim, by means of a tin plate perforated with a circular hole, in 

 the middle of a large cylinder of the same metal, itself immersed 

 in water at the surrounding temperature. 



For the experiments to be perfectly comparable, it is neces- 

 sary to wait, before commencing them, till the temperature of 

 the liquid in the calorimeter is quite stationary under the influ- 

 ence of the external radiation and of the superficial evaporation. 

 This makes the first experiment of a day rather long; but it is 

 easy afterwards, by following the course of an exterior thermo- 

 meter, to bring the liquid immediately to such a temperature 

 that it will not vary sensibly during a much longer time than 

 the duration of a determination. 



When about to commence this investigation, 1 thought it 

 would be sufficient for me to determine by a series of trials made 

 upon water an empiric relation expressing, for each difference 

 between the temperature of the heated thermometer and the 

 temperature of the bath, the ratio of the quantities of heat given 

 up by the first and gained by the second. But I had to abandon 

 this idea, and to compare directly the experiments made on each 

 solution with similar experiments, made immediately before and 

 after, on water. 



In fact, I have remarked that, while all the determinations 

 made in one and the same day, or sometimes in two consecutive 

 days when the atmospheric conditions have not changed, are in 

 general very accordant, it is not quite so satisfactory when ex- 

 periments made at periods somewhat more distant are compared, 

 even when the conditions of temperature are the same. This 

 may be due either to atmospheric influences other than the 

 temperature (for example, the hygrometric state of the air), or 

 to the fact that, at periods a little distant, one does not preserve 



