NITROBENZOIC ACID. 275 



7. The formation of dinitrobenzene from its elements 



C 6 (diamond) + H 4 + N 2 + 4 = C 6 H 2 (N0 2 ) 2 (dissolved) 

 gives off 12-7 for 168 grms. 



8. The heat of complete combustion of dinitrobenzene 

 (= 168 grms.)- 



C 6 H 4 N 2 4 + 10 = 6C0 2 + 2H 2 + N 2 , 



gives off + 689 '3 Cal. for 168 grms., which amounts, for 

 1 grm., to 4103 cal. All these calculations were made for 

 dinitrobenzene obtained without heat ; in the action of dinitro- 

 benzene on nitric acid, and without having regard to the mixture 

 of isomeric substances produced in this case. The observations 

 which have been published 1 tend, moreover, to show that 

 various isomeric substances of the same chemical function are 

 formed, causing disengagements of heat almost identical. 



3. Chloronitrdbenzene, C 6 H 4 C1(N0 2 ). 



The formation of this compound takes place according to the 

 following equation : 



C 6 H 5 C1 + HN0 3 = C 6 H 4 C1(N0 2 ) + H 2 0. 



It was found that this reaction gives off + 36*4. 



We know that several isomeric substances are formed. The 

 heat of solution in a mixture similar to that formed in the 

 reaction was determined. 



The details of these experiments may be omitted, as they are 

 similar to those already described. 



The heat of chlorination of benzene being unknown, it is not 

 possible to calculate the heat of formation of the above sub- 

 stance from its elements. 



4. Nitrobenzoic Acid, C 7 H 5 (N0 2 )0 2 . 



The formation of this compound takes place according to the 

 following equation : 



C 7 H 6 2 + HN0 3 = C 7 H 5 (N0 2 )0 2 + H 2 0. 

 This reaction gives off -f 36*4. 



We see that this value is nearly constant for the nitration 

 of benzene and all its immediate derivatives. The formation of 

 nitrobenzoic acid from its elements is easily calculated if we 

 admit for the heat of formation of benzoic acid the value -f 54 

 (Kechenberg). We then get 



C 7 (diamond) + H 5 + N + O 4 = C 7 H 5 (Isr0 2 )0 2 - + H 2 (liquid) 

 gives off + 63 Cal. for 167 grms. 



The "heat of complete combustion of the same substance 

 = 761-5 Cal. for 167 grms., or 3772 cal. for 1 grm. 



1 " Bulletin de la Soci&e* Chimique," 2 e sfrie, torn, xxviii. p. 530. 



T 2 



