COLORIMETRICAL EXPERIMENTS. 43 



experiments it would appear that with considerable ad- 

 ditions of ammonia the results with disks outside were much 

 improved. "Why the results were not equally good with 

 disks inside may, I think, be accounted for, and will be 

 considered further on. I also compared the solution con- 

 taining 4000 with the one containing 1 600 ; standard 

 solution 1600 in 500 cub. c, length of column 21 "2 : — 



ABO 



4000 8 4.240 



The number under B was the mean of eight trials. The 

 theoretical length was 8-5. With the standard solution on 

 the left hand this length seemed to give a similar tint ; but 

 with standard solution on right it seemed a little darker. 

 And now I remarked for the first time, or, if I had previ- 

 ously remarked it, had not thought it worthy of notice, 

 that even an apparently so trivial circumstance as altering 

 the positions of the cylinders from right to left had a per- 

 ceptible influence in the determination of colour. I after- 

 wards made some experiments to test this. Next I com- 

 pared solutions containing 1600 and 600; standard so- 

 lution 1600 in 500 cub. c, length of column 21-2 : — 



ABC 



6000 5"! 6684 



The number under B was the mean of eight trials. The 

 result is not so satisfactory as the others. I also tried 

 these solutions with white surfaces inside ; standard so- 

 lution same as last : — 



ABC 



6000 3*9 8697 



— a widely remote result, and much further from the real 

 value than with disks outside ; also a disk placed in the so- 

 lution at the depth assigned by calculation seemed too dark. 



