1892. J Formation and Decomposition of Nitrous Acid. 45 



The greatest difference occurs in the third value, which is rather 

 less than 2 per cent., which can readily be accounted for by errors of 

 experiment in dealing with a substance so susceptible of decomposi- 

 tion as nitrous acid. -The curve which represents the concentration 

 of the acid in terms of time is a portion of a hyperbola, the differential 

 equation of which is 



dC = _C? 

 dT M' 



rhich expresses the rate at which equivalent masses react, whether 

 it be of the nitric with the nitrous acid, or the nitrous acid with 

 itself; in each experiment 1/M is the amount of each unit mass 

 rhich reacts with the other per unit time when an unit mass of each 

 ibstance is present. 



If Clemente Montemartini's equation dcjdT = &C is correct, there 

 should be two reacting substances, one of constant concentration 

 throughout the reaction. It is, however, to be observed that the 

 ralues given for the constant ~k in his results differ widely among 

 themselves, often as much as 25 per cent, between the maximum and 

 minimum. Further, all the results in each set of experiments are 

 jferred to the first, the C of equation (ii), though there is no 

 jpecial reason that this analytical determination should be more 

 exact than those subsequent to it. With the general purport, how- 

 rer, of Montemartini's paper I cannot but completely agree, namely, 

 that the rate of decomposition of nitrous acid is dependent upon the 

 tension of the superincumbent nitric oxide, without, however, neces- 

 sarily committing oneself to the view that herein is presented a " true 

 case of dissociation." 



It is worthy of remark that the curve representing the decomposi- 

 tion of nitrous acid is exactly identical with that of a previous case 

 of chemical change investigated by myself, namely, the decomposition 

 of formic acid into carbonic oxide and water,* in which the method of 

 observation was precisely the reverse of that adopted in this research. 

 For, herein, the concentration is determined at equal intervals of 

 time, but in the previous case observations were made of the times 

 required for equal diminution of concentration. The results of other 

 series of experiments are given below, the observed and calculated 

 values for the concentration of the nitrous acid being compared in 

 each instance. 



* ' Phil. Trans.,* 1888, A, p. 290. 



