222 
DR. GLADSTONE ON CIRCUMSTANCES MODIFYING 
repeated the experiment in a great variety of ways, and have satisfied my mind that 
the amount of error arising from this cause must be quite insignificant — at any rate 
as far as the ferric sulphocyanide is concerned. The slight differences that do occur 
are rather in the character than in the intensity of the colour. 
Note B. 
Acting upon a suggestion of Professor Stokes, I examined more fully whether this 
apparent diminution of colour on dilution might possibly be due to some peculiarity 
in the manner in which this salt in different states of dilution absorbs certain rays 
and transmits others, and whether it exhibited the same depth of colour when the 
amount of dilution was compensated for by the thickness of the stratum through 
which the light passed. In two flat-bottomed beaker glasses were placed two por- 
tions of the same solution of ferric sulphocyanide, and beneath’them at the distance 
of a few inches was laid a sheet of white paper. The solutions appeared of the same 
depth of colour, as I looked down through them. On adding water to one of these 
and still looking down through the whole liquid, it appeared far lighter in colour, 
and on the addition of much water it assumed the yellowish tint. Meconate of iron, 
on the contrary, when looked through in the same manner, presented the same depth 
of colour, whatever amount of water was added to it. 
The ferric sulphocyanide appears then to be really acted on by water, in a manner 
somewhat analogous perhaps to that in which chloride of copper and several similar 
salts are. 
Note C. 
An experiment was subsequently made by adding different proportions of iodide 
of potas.siu[n to a solution of the double chloride of platinuin and potassium, in hopes 
of obtaining a result undisturbed by the separation of any solid matter. Such how- 
ever was not the case. On mixing single equivalents a precipitate instantly resulted ; 
and a deposit was gradually formed when the iodide of potassium was added in pro- 
portions of 2, 3, 4, or 5 equivalents to one of the double chloride. These solutions, 
as also those containing a larger amount of iodide, were intensely red. It was evident 
that the decomposition was far more complicated than 
PtCl^, KCl-l-2KI = PtI,-f3KCl and PtCl„ KCl-F3KI = PtI„ KI-1-3KC1. 
Note D. 
Changes in the state of combination of an element may be rendered visible by a 
change in the intensity of a colour, even where no change in its character occurs. 
Thus oxide of copper dissolved in acetic acid gives a much more intense blue than 
when the same amount is dissolved in sulphuric acid. This fact was taken advantage 
of in the following experiment, which affords additional evidence of the truth of my 
