DETONATION OF HYDROCYANIC ACID AND OXYGEN. 303 



acid broken to pieces by being violently shaken. The acid is 

 thus wholly converted into gas and constitutes with the oxygen 

 a detonating mixture. 



This being done, the bomb is placed in the calorimeter, and 

 thermal equilibrium established ; we note the progress of the 

 thermometer and then proceed to detonate the mixture. 

 After the detonation, we again follow the progress of the 

 thermometer. The gas is then extracted by means of a mercury 

 pump, and caused to pass first through a drying apparatus, and 

 then through tubes containing potash. The bomb is then 

 purified by filling it several times with dry air, which is also 

 passed through the same tubes, so as to extract the whole of the 

 carbonic acid. 



This can thus be weighed, which affords a valuable check on 

 the combustion. 



Special trials showed that the quantity of nitrous compounds 

 formed in the combustion was negligable, but that a trace of 

 hydrocyanic acid always escaped. The latter was determined 

 each time in the potash, after the weighing; it amounted to 

 between half a hundredth and a hundredth of the original weight. 

 This was taken into account. 



These points having been settled, the heat disengaged was 

 calculated in two ways ; either by considering it in relation to 

 the weight of hydrocyanic acid employed (minus the trace 

 which is not oxidised), or to the weight of carbonic acid 

 obtained (with the same deduction). The list of results observed 

 may be given. The heat absorbed, owing to the tension of the 

 aqueous vapour in the bomb at the temperature of the experi- 

 ment, was taken into account ; also + 0'4 was added to all the 

 results obtained, in order to allow for the fact that the detona- 

 tion was effected at constant volume. The heats of combustion 

 given below are supposed to be obtained at constant pressure. 

 We will now give the heat disengaged by the combustion of 

 27 grms. of gaseous hydrocyanic acid (HCN = 27 grins.), effected 

 by means of free oxygen at constant pressure. 



According to the final weight According to the initial weight 



of the hydrocyanic acid. of the carbonic acid. 



158-9 163-4 



160-0 161-3 



154-2 155-6 



159-0 160-4 



160-1 160-3 



Mean ... 158-4 Mean ... 160-2 



The general mean, 159'3, of the two calculations will be 

 adopted. Thomsen, according to results which he published 

 after those just given, obtained by ordinary combustion 

 -j- 159*5, a value agreeing with that of the author as closely as 

 could be expected. 





