Some Physical Properties of Nitric Acid Solutions. 95 



It will be observed that the differences in the values of the constant 

 are considerable, with the exception of the slight variation at 4 per 

 cent., upon which it is not desired to lay stress ; further, the values 

 of the constant are fairly simple integers. 



The Descending Branch consists of five segments, (i) a rather flat 

 portion from 54 to 63 per cent., (ii) a steep portion from 63 to 70 

 per cent., (iii) a more steep portion from 70 to 78 per cent., (iv) an 

 abrupt descent from 78 to 95 per cent., and (v) a curved portion from 

 95 to 100 per cent. 



The values for the constant a are summarised in the following 

 table : 



It will be observed that the difference in value for the portions V 

 and VI is not considerable. 



As to Segment IX, or curved portion, it was thought at the earlier 

 stage of the inquiry that the apparently irregular results obtained 

 with acids of percentage strengths from 95 to 100 per cent, might 

 arise from experimental errors, the possibility of which is greatly 

 increased in the case of solutions difficult to manipulate and of high 

 coefficient of expansion. With a view of deciding the matter, fresh 

 samples of acids were prepared de novo after an interval of about 

 fifteen months ; concordant results were obtained in the case of two 

 samples of different past history and of approximately the same 

 concentration, namely, 92'34 and 92 - 66 per cent, respectively, which 

 pointed to an absence of any substantial error in the earlier work. 

 Further determinations made with samples of concentration inter- 

 mediate between those formerly made gave intermediate values. 



The results are illustrated by certain curves, for a description of 

 which the reader is referred to pp. 100-105. 



Effect of Temperature, Though the mean straight lines representing 

 the observations are not parallel with one another for the three 

 temperatures, yet within the limits 4 24 - 2 there does not appear 

 to be any great variation in the percentage, composition corresponding 

 to the critical points as conditioned by temperature. It is very 

 probable that at higher temperatures such variations would occur, 



