140 
of the standard, the lengths would be 15 '8, 15, 15*2, numbers 
not far removed from 15 ‘5, which was got by observation. 
I repeated the experiment with fresh solutions, the bulk of 
the liquid being 500 cc. Standard solution 4000 in 500 cub, 
a, length of column 2T2. 
ABC 
6000 14-1 6000 
The number under B is the theoretical quantity, and was 
the mean result of four trials. Also with shorter columns 
of the standard liquid, namely 15*2 cm., 10'2 cm., 5*2 cm., 
the corresponding lengths of the stronger liquid gave similar 
tints. At the same time lengths differing a little from the 
theoretical would also satisfy. With these solutions I also 
tried an experiment with discs inside. Standard solution 
same as last : 
ABC 
6000 12*3 6894 
The number under B was the mean of 15 trials, thus the 
result with discs inside was not so good as with discs out- 
side. Also 14*1 cm. the theoretical depth when tried 
seemed slightly too dark with discs inside. I repeated the 
experiment with a solution containing 2400, using one 
containing 1600 as a standard. In preparing these solu- 
tions to the stronger I added 12 additional cub. c. of 
ammonia, and to the weaker 8. With external white sur- 
faces the results were as follows : — standard solution 1600 
in 500 cub. c. of water, length of column 21*2 cm. 
ABC 
2400 13-8 2458 
The number under B was the result of fifteen trials. Thus 
we get a good approximation to the real quantity. With 
discs inside the results were as follows. Standard solution 
same as last : 
ABC 
2400 12 2824 
The number under B was the mean of twelve trials. The 
