86 Mr Purvis, The absorption spectra of 



1. These photographs were taken immediately after the 

 solutions were made. In both solutions the bands at \ 538 and 

 X565 are of the same width and intensity. The X565 band is 

 very weak in the reproductions, but it is quite visible in the 

 original photographs. The general absorption in both begins at 

 about A, 510. 



2. The second series of photographs were taken after the 

 solutions had been standing for some hours. The band \538 in 

 the dilute solution is more diffuse and weaker than the band in the 

 strono- solution ; otherwise there is no chancre in the two solutions. 



3. After standing twelve hours longer, the bands \ 538 and 

 X565 appear to be very like the last photographs. But in the 

 strong solution a faint band X508 has appeared, which is not 

 visible in the dilute solution. 



4. After standing twelve hours longer, the concentrated solu- 

 tion shows that the bands X 538 and X565 are very like those in 

 the last observations : whilst the band X 508 is more clearly 

 marked. In the diluted solution, the bands X 538 and X 565 are 

 still weaker and more diffuse than the corresponding bands in the 

 strong solution, and X538 is particularly noticeable in this respect. 

 There is no band at X 508 in the diluted solution corresponding to 

 that in the strong solution. 



5. After standing twelve hours longer, the general appearance 

 of the bands is much the same as in the last series of observations. 

 But in the strong solution there is a gradual increase in the amount 

 of light coming through on the more refrangible side of the band 

 X 508 ; and there is no such appearance in the diluted solution. 



6. The solutions wei'e allowed to stand four days longer. In 

 the strong solution the bands X 565, X 538, and X 508 are like those 

 in the last series of observations. In the dilute solution the band 

 X 538 is weaker and more diffuse than the corresponding band in 

 the strong solution. The latter band is as well marked as at the 

 beginning of the observations. In the strong solution the band 

 X 508 is noAv well marked, and is absent in the dilute solution. 

 Besides that, there is less general absorption of light by the strong 

 solution than the. dilute solution. 



7. The solutions were allowed to stand tw^o days longer. The 

 general appearance of the phenomena of the two solutions is very 

 similar to that in the last series of experiments. 



8. After standing four days longer, photographs were again 

 taken, and they showed that the bands were very similar to those 

 in the last series of experiments ; but the general absorption in 

 the strong solution was less than before, whilst that in the dilute 

 solution does not appear to have altered. 



9. Finally, after standing fourteen days longer, the photo- 

 graphs show that in the strong solutions the bands X 538 and X 508 



