252 A New Form of Mixing Calorimeter. 



(on that calculated for gram-molecular proportions) ; an error 

 only one seventeenth as great as that experienced by Thomsen, 

 its average error in duplicate experiments being ±5 cal. from 

 the mean, or a difference of 10 cal. between duplicates (ibid. 



i -P. 21). 



When dealing with very strong solutions it is inadvisable *, 

 and often impracticable, to make the determination in the 

 mixing-calorimeter. 



The method which I have adopted in such cases is very 

 simple. It consists of putting 20 to 50 grams of the liquid 

 into test-tubes on feet, placing these in an air-bath surrounded 

 by a water-jacket till they have attained the temperature of the 

 surrounding air, and then pouring their contents into 600 cub. 

 cent, of water in the calorimeter (a platinum beaker) ; thus 

 the heat of dissolution is determined as in the case of a solid. 

 The chief precaution to be observed here is, that the tubes 

 be left sufficiently long in the air-bath before being emptied 

 into the calorimeter. This is necessary owing to the heat- 

 capacity of a liquid being generally higher than that of 

 a solid, any error in the determination of its temperature 

 making therefore a greater error in the heat of dissolution 

 determined. About three hours in the air-bath at a constant 

 temperature (that is, within o, 05 of the required temperature) 

 were generally allowed, and greater pains were taken to bring 

 this temperature to exactly that of the calorimetric water than 

 in the case of solids. If the temperature of the air in the 

 room is satisfactorily constant, and nearly identical with that 

 in the bath, a comparison of the temperatures of the latter 

 and that of the water in the surrounding jacket will indicate 

 the time when the test-tubes have attained the former (and 

 the latter) temperature; and if left under these constant con- 

 ditions for nearly another hour, satisfactory results will be 

 obtained. Success in this is entirely a matter of practice. 

 The correction which has to be applied to the heat of dissolu- 

 tion, owing to differences in the initial temperature of the 

 solutions and the calorimetric water, averaged only about 

 0°*002, and the heat-capacity of the strong solutions necessary 

 for its calculation need therefore be known approximately 

 only. All splashing on pouring in the solutions is entirely 



* In mixing acids and alkalies the results obtained are more accurate 

 in proportion as the solutions are more dilute. In determining the heat 

 evolved on diluting strong solutions, the experimental errors increase in 

 a very rapid proportion if the determinations are made by diluting the 

 solutions with successively equal volumes of water. Further details will 

 be found in a paper on the Nature of Solutions, in the current number 

 of the Journal of the Chemical Society. 



