DILUTION OF CONCENTRATED SOLUTIONS. 341 



No record is given of a systematic study of the variation in heat of dilution by 

 either of these investigators. 



In order to obtain numerical results, the manner in which the specific heat varies 

 with temperature must first be found. 



The temperature effect on the heats of dilution of hydrogen chloride and lithium 

 chloride were investigated. 



The experiments were more difficult to carry out owing to radiation corrections 

 which now become a greater consideration. Also the range of temperatures for which 

 the heat of dilution experiments were possible is limited. With concentrated 

 hydrochloric acid no temperature above 20 C. could be attempted, and below C. 

 the water employed would, of course, freeze. 



With lithium chloride solutions the maximum concentration employed at air 

 temperatures could not be employed at C. owing to the much smaller solubility of 

 the salt. Since, therefore, only moderately strong solutions could be taken much 

 smaller temperature changes were observed on dilution. Attempts were made to get 

 the heat dilution of these solutions at temperatures above 30 C., but without success, 

 owing to the small heating effect and the large radiation. 



To eliminate the radiation loss the heating coil employed for the specific heat 

 experiments was tried, but it was found impossible to regulate the temperature of the 

 coil with sufficient delicacy. Observations were made, but failed to give consistent 

 results on repetition. 



In each specific heat and heat of dilution experiment, separate radiation-loss 

 experiments were 'made, and these were checked in the following manner. 



The quantity of solution to be experimented with was introduced into the vessel 

 and its temperature raised from about 10 C. (to which it had been previously 

 cooled), by means of the heating coil, by steps of about 5 C. to about 50 or 60 C. 

 The rate of cooling was then plotted against temperature, and gave a curve which 

 closely approximated to a straight line, within the range 10 C. on either side of 

 air temperatures. The points all lay perfectly on the curve, and the curve cut 

 the axis of temperature at a point which was found to coincide exactly with air 

 temperature. 



The regularity of this effect, and the certainty with which it could be measured, 

 made experiments with a relatively large radiation loss quite satisfactory. Thus, in 

 the specific heat determination of lithium chloride solution at a temperature of about 

 70 C., a rise in temperature by heating of 10 '21 C. is observed, while the radiation 

 loss is about 2 C. 



For lithium chloride only one concentration of solution was attempted, as 

 the results only showed a small change in heat of dilution ; and moreover 

 with the concentrations less than that employed the heating effect is so 

 small, since in both solutions it falls off very rapidly as the concentration is 

 diminished. 



