42 DR. JAMES BOTTOMLEy's 



the mean result of four trials. Also with shorter columns 

 of the standard liquid, namely 15-2, io-2, and 5-2 centims., 

 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 disks inside ; standard solution 

 same as last : — 



ABO 



6000 12*3 6894. 



The number under B was the mean of 15 trials ; thus 

 the result with disks inside was not so good as with disks 

 outside. Also 14*1 centims., the theoretical depth_, when 

 tried, seemed slightly too dark with disks inside. I re- 

 peated the experiment with a solution containing 2400, 

 using one containing 1600 as a standard. In preparing 

 these solutions, to the stronger I added 12 additional cub. 

 0. of ammonia, and to the weaker 8. With external white 

 surfaces the results were as follows; standard solution 

 1600 in 500 cub. c. of water, length of column 21 '2 cen- 

 tims. : — 



A B 



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 disks inside the results were as follows; standard 

 solution same as last : — 



A B 



2400 I a 2824 



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

 value got with disks inside is not so good as with disks 

 outside. Also the theoretical depth 14*1 centims., when 

 tried, seemed to be slightly too great. From the foregoing 



