192 
DR. GLADSTONE ON CIRCUMSTANCES MODIFYING 
This close agreement proves not only the correctness of the two independent expe- 
riments, but also the correctness of this method of reckoning the amount of the 
coloured salt in any given mixture. 
Injiuence of the mass of a substance present in the solution, hut which is not one of the 
constituents of the coloured salt. — It has already been remarked that the addition of 
a colourless salt will reduce the colour of a solution of ferric suiphocyanide. The 
influence of mass in this kind of action remains to be examined. 
A mixture was made of ferric sulphate and suiphocyanide of potassium. The red 
solution that resulted contained of course sulphate of potash. Successive portions of 
a solution of this salt were added, and the amount of decomposition effected was 
determined by means similar to those employed in previous experiments. 
Sulphate of Water added 
potai added. comparative 
^ solution. 
o 1 v i c Water added 
^ P, ® f , to comparative 
potash added, 
5 measures =22 measures. 
10 measures=38 measures. 
15 measures = 52 measures. 
20 measures =67 measures. 
30 measures = 92 measures. 
40 measures=115 measures. 
60 measures=155 measures. 
This action then proceeds in a gradually decreasing ratio. The above results give 
the curve projected in Plate VII. fig. 3, which, like those formerly examined, does 
not belong to the second order. 
These very diversified experiments have put to a rigid test the truth of Berthollet’s 
view. Whatever were the circumstances under which the reactions were tried, they 
invariably showed that the results were dependent both upon the nature and upon 
the quantity of all the substances in solution. 
I have purposely investigated, at considerable length, the reactions made evident 
by the colour of ferric suiphocyanide, both because I desired to prove the matter 
thoroughly, and because the scientific public will probably require (as indeed I did 
when I commenced the investigation) a greater amount of testimony, where it depends 
on the colour of a solution, than if it had depended on substances actually separated 
and weighed. I now proceed to the examination of reactions made evident by means 
of other coloured iron salts ; but I shall not dwell at any length on these, unless there 
be some apparent anomaly to call for more particular attention. 
Ferric Gallate. 
A solution of gallic acid was made of known strength. Equal portions of it were 
added to equal portions of the different ferric salts. 
1 equiv. ferric nitrate with 1 equiv. gallic acid gave 100 parts of black salt. 
1 equiv. ferric chloride with 1 equiv. gallic acid gave 88 parts of black salt. 
1 equiv. ferric sulphate with 1 equiv. gallic acid gave 70 parts of black salt. 
1 equiv. ferric citrate with 1 equiv. gallic acid gave 10? parts of black salt. 
