19 
be inferred from the greatly increased absorbent power im- 
parted to the bichromate by the additional molecule of 
CrOg. I therefore took the cylinder containing the standard 
solution used in the last experiment and divided its contents 
into two equal columns : to one I added a few drops of am- 
monia ; this column became slightly but perceptibly lighter 
than the other, so that I have little doubt some change had 
been effected in the constitution of the dissolved salt ; the 
hypothesis of the liberation of a little chromic acid is, I 
think, strengthened by the fact that a solution of the salt is 
of a deeper yellow than the undissolved salt. I think that 
probably a trace of carbonic acid in the water had liberated 
a little chromic acid. 
To try what the effect of the addition of a little weak 
acid would be, I took a solution containing 1*6 grams in 
500 cub. c. and divided it into two equal parts. To one I 
added a little extremely dilute sulphuric acid. The colour 
of this portion became decidedly deeper than that of the 
other. I also tried what would be the effect of the addition 
of a little ammonia to a strong solution, so I divided the 
solution containing 6*4 grms. in 500 cub. c. into two equal 
portions — one I treated with ammonia; this I thought a 
little lighter than the other, but the difference was very 
slight ; this however we might expect, for any small change 
in intensity would be less noticeable in a strong solution 
than in a dilute one. 
I now made some fresh experiments with chromate of 
potash, a little ammonia being added to both columns. The 
mean of four trials gave for the greater limit 3-35, and the 
mean of four trials gave for the smaller limit 2T8. Hence 
