RICHARDS. ■ — THE ELIMINATION OF THERMOMETRY LAG. 7 



As has been said, each experimenter must of course determine this 

 value for his own exact conditions ; therefore it is impossible here to 

 apply a suitable correction to previous investigations, although all must 

 have been more or less affected by this cause of error. The Rumford 

 method of eliminating the error from radiation is little better than the 

 Regnault method in this respect ; for the rising thermometer just before 

 the beginning of the reaction will always give too low a reading, while 

 the conditions at the close of the reaction are highly uncertain. 



On account of this phenomenon of thermometric lag, and because of 

 the uncertain application of Newton's law of cooling to systems suffering 

 sudden changes of temperature, it seemed highly desirable to devise a 

 method of wholly eliminating both irregularities. It appeared probable 

 that this object might be accomplished by artificially changing the tem- 

 perature of the environment of a reacting system at the same rate as the 

 system itself changed in temperature.* Thus a given reaction might be 

 made really adiabatic, neither losing nor gaining heat from its equally hot 

 surroundings at any time during the reaction. 



Obviously there are several ways in which the outside water jacket in 

 a calorimeter might be heated in order to accomplish this purpose. The 

 simple device of pouring in hot water might be employed, or the water 

 might be warmed by an electrically heated resistance coil, or the jacket 

 itself might be made the scene of a chemical reaction of the same speed 

 and thermal intensity as that within the calorimeter itself. 



Of these and other methods which suggested themselves the last named 

 seemed the most convenient and suitable for a chemical laboratory. It 

 has the special advantages that before the beginning of operations all the 

 apparatus and material employed may be at the temperature of the room ; 

 that the maximum temperature attained may be easily calculated with great 

 nicety ; that no point in the system can ever exceed this maximum tem- 

 perature, if the reaction is suitably chosen ; and that the speed of the re- 

 action may be simply regulated by a stop-cock admitting one of the 

 reacting substances. 



The following sections of this paper show how this suggestion has al- 

 ready proved serviceable in two important investigations in this labora- 

 tory, and serve to give an approximate idea of the conditions necessary 

 for its satisfactory fulfilment. 



* After the present paper had gone to press it was found that S. W. Ilolman 

 had suggested this, although without in any way testing the suggestion in practice. 

 These Proceedings, 31, 252 (1895). 



