136 Dr. T. Ewan. On the 



The ammonium salt volatilises on heating. The ammonia was 

 therefore determined. 



]STH 3 found 7'69 per cent. \ 



]STH 3 calculated for C 6 H 3 (]N"0 2 ) 2 ONH4 7'76 J 



As I could find no satisfactory way of analysing the dilute solutions 

 of these salts, I made them by dissolving a weighed quantity of the 

 carefully purified salt in water. The solutions so obtained were fairly 

 clear. The values of e (the extinction coefficient for the dissolved 

 body for 1 cm. layer and 1 gram molecule per litre concentration) are 

 given in the following table. The experimental numbers are given 

 in the same way as before in the Appendix Table III. 



The numbers given in Table VIII are obtained from the numbers 

 in Table III of the Appendix by graphical interpolation. The con- 

 centrations are in gram molecules per litre. 



The two most concentrated solutions used give somewhat smaller 

 numbers than the others, which may probably be attributed to the 

 electrolytic dissociation being incomplete in the stronger solutions. 

 The numbers obtained with the other solutions vary irregularly - 

 by taking their mean the following numbers are obtained. 



A. K salt. ]^H 4 salt. 

 530 2-195 



520 4-19 3-995 



510 10-82 10-85 



500 26-26 25-1 



490 67-23 74-5 



480 194-3 173-4 



470 398-5 368-0 



The absorption increases so extremely rapidly between the wave- 

 lengths 470 and 500 that a small error in the measurement of the 

 wave-length can make a great difference in the value of e obtained. 

 Taking this into account the absorption spectra of the potassium and 

 ammonium salts may be regarded as the same. These salts dis- 

 sociate electrolytically into the ions K> or NH 4 + and C 6 H 3 (N0 2 ) 2 . 

 The mean of the above numbers may therefore be taken as represent- 

 ing the absorption spectrum of the ion C 6 H 3 (N0 2 ) 2 0. 



DinitropTienol. 



The behaviour of the solutions of the free dinitrophenol is of some 

 interest. The solutions in benzene or ether are brownish-yellow, but 

 the colour is faint, and unless they are fairly concentrated they 

 appear colourless. An alcoholic solution is much more strongly 



