184 
DR. GLADSTONE ON CIRCUMSTANCES MODIFYING 
formed. The solution containing the ferric citrate was still green; that containing 
the acetate was red, but by no means deep in colour, and of a yellowish tint ; while 
those containing the sulphate, nitrate, or chloride were of an intense red. The follow- 
ing are the relative amounts of dilution required to bring these four last-mentioned 
solutions to the same tint ; — 
3 equivs. sulphocyan. potassium + 1 equiv. ferric nitrate diluted to 100 parts. 
3 equivs. sulphocyan. potassium-1- 1 equiv. ferric chloride diluted to 89'4 parts. 
3 equivs. sulphocyan. potassium -h 1 equiv. ferric sulphate diluted to 65*2 parts. 
3 equivs. sulphocyan. potassium -j-l equiv. ferric acetate diluted to 20 parts. 
The numbers 100, 89’4, 65*2, and 20 therefore represent the relative amounts of the 
ferric sulphocyanide contained in these several mixtures*. 
In reference to the mixture of ferric citrate with sulphocyanide of potassium, the 
question presents itself, — Does absolutely no interchange take place between them, 
or does a partial though very minute formation of ferric sulphocyanide occur in 
accordance both with the law of Berthollet and the analogy of the other cases ? 
The latter conclusion will appear probable from the following observations. Al- 
though the yellowish-green tint of the citrate still remains after the addition of three 
equivalents of the sulphocyanide, six equivalents almost remove it, and a larger quan- 
tity renders the solution colourless. No red colour ever appears in a very dilute 
solution, but this destruction of the green appears to point to the presence of a suffi- 
cient amount of the complementary colour to neutralize it ; and if sulphocyanide of 
potassium be added in large excess to a strong solution of citrate of iron, an unmis- 
takeable red ensues. 
Similar experiments were tried in which the same ferric salt was employed, but 
different sulphoeyanides. Two portions of nitrate of iron, each representing one 
equivalent, were mixed, the one with six equivalents of sulphocyanide of barium, the 
other with a corresponding amount of the potassium salt. A deep red resulted in 
both instances, but 1000 gr. meas. of the solution containing the potassium compound 
required the dilution of that containing the barium salt to only 880 gr. meas. to bring 
it to an equality of colour. The solution of sulphocyanide of mercury produced a 
scareely perceptible reddening when added to the ferric nitrate. 
These experiments suffice to show, that on mixing together solutions of soluble sul- 
phocyanides and of ferric salts, the amount of sesquisulphocyanide of iron formed 
depends in a great measure on the nature of the substances previously combined with 
the sulphocyanogen and with the metallic oxide. The question naturally arises, — 
Does the eonverse of this hold good ? If a solution of sesquisulphocyanide of iron be 
mixed with some other salt, not capable of forming a precipitate with it, will that also 
cause the distribution of the elements into four salts, manifesting itself by a diminu- 
tion of the colour? and if so, will that vary according to the nature of the other salt? 
* See Note A. 
