270 COMPOUNDS DERIVED FROM NITRIC ACID. 



water of the calorimeter, being pushed along by means of the 

 large calorimetric thermometer, which also served to agitate the 

 water at the same time. The progress of this thermometer was 

 followed, also that of the small thermometer immersed in the 

 acid. At the end of six minutes, the two thermometers gave 

 readings agreeing within about one-tenth of a degree, which 

 difference represented the excess of the temperature of the acid 

 over the water in the calorimeter ; the variation of temperature 

 in the two experiments being 170 and 3-45 respectively. 

 Lastly, the rate of cooling was noted. 



The following data were then known. On the one hand, the 

 weights of the water, the platinum, and thermometer reduced to 

 units of water, and also their variation of temperature ; on the 

 other hand, the weights of the acid and benzene, and also the 

 thermal variation involved by their combination, which had 

 converted the benzene into nitrobenzene, with the simultaneous 

 production of water. 



The heat communicated to the water, platinum, and thermo- 

 meters may easily be calculated. But an exact calculation of 

 the heat communicated to the mixture of acid and nitrobenzene 

 would require a knowledge of its specific heat. Now, it is 

 sufficient to know that this specific heat approximates pretty 

 closely to '47, which is the same as that of the acid employed. 

 Thus, in the two experiments in question, the mass of acid and 

 nitrobenzene, reduced to units of water, will be from about 8*5 

 to 9 '5 grms., amounting to about one-sixtieth of the entire 

 heated mass. This fraction is so small as to be of slight im- 

 portance in the calculation of the heat disengaged. Thus the 

 latter can be estimated within the limits of experimental 

 error without its being necessary to measure more exactly 

 the specific heat of the mixture. 



We may thus make a complete calculation of the heat dis- 

 engaged in the reaction that has taken place in the calorimeter. 

 It is brought by calculation to an equivalent of nitrobenzene, 

 i.e. Q, for the weight, C 6 H 5 N0 2 = 123 grms. 



The compound formed under these conditions is really nitro- 

 benzene. To make sure of this, it was precipitated, after the 

 experiment, by means of water, and its density taken, which 

 was found to be equal to 1194 at 14. Now, Kopp has 

 given the value 1187 at the same temperature. The differ- 

 ence, therefore, is so slight that the reaction may be accepted as 

 true. This reaction, however, under the conditions of the 

 author's experiment, is complicated by two circumstances, 

 which must be taken into consideration. On the one hand, the 

 nitrobenzene remains dissolved in the excess of acid ; and on 

 the other, the reaction itself gives rise to water which must give 

 off a certain amount of heat, owing to its combination with the 

 excess of acid. In order to be able to bring in this last factor, 



