224 
solution is increased, into crimson, and finally into violet. I 
also made some experiments with a blue solution. For this 
purpose I used an ammoniacal solution of sulphate of copper. 
The tinctorial power of this salt is not as great as I expected, 
and I made no experiments with a standard solution contain- 
ing less than 150, On diluting 15 cc.of an ammoniacal solution 
with sufficient water to make 500 cc., I noticed after a little 
time that the solution was somewhat turbid. This was 
owing to the copper forming an insoluble compound, either 
hydrate or a subsalt ; further addition of ammonia was 
necessary to clarify the solution. Standard solution 150 
in 500, depth 8 '3. 
A 
B 
C 
200 
5-7 
218 
220 
5-3 
235 
240 
5T 
244 
260 
4*8 
259 
280 
4*5 
277 
300 
4-1 
304 
350 
3-4 
366 
400 
3*0 
415 
450 
2*6 
479 
Some experiments were made with solutions of known 
strength, by sinking the disc to the depth assigned by 
theory, to see if the given tint was attained, instead of 
moving the disc about until the tint was estimated to be 
the same and then reading off the result. A solution of 
bichromate of potash containing 50 in 500 cc., and depth 
8 ‘3, was used as a standard. Solutions containing 60, 70, 
80, 90, gave similar tints at the calculated depths. Solutions 
containing 150, and increasing quantities gave tints a little 
too deep at the calculated depths. Also a standard solution 
of permanganate of potash, containing 4*8 in 500 cc. of 
water, and depth 8 -3, was taken. Solutions containing 6 
and 7*2 gave a similar tint at the depths assigned by the 
calculation. Solutions containing 9, 9*6, and higher quan- 
tities, gave tints a little too deep at the calculated depths. 
