THE ACTION OF CHEMICAL AFFINITY. 
199 
This irregularity of colour accounts for the extraordinary appearance when suc- 
cessive portions of sulphocyanide of potassium were added to the ferric acetate {vide 
Plate VIII. fig. 2) ; for, it must be remembered, the red colour observed in that 
experiment was due to the colour of the acetate as well as of the sulphocyanide. 
The ferric acetate then confirms Berthollet’s view, but, like the meconate, its 
testimony in respect to the influence of mass is equivocal. 
Ferric Ferrocyanide. 
The ferric ferrocyanide, though insoluble in pure water, is soluble in the presence 
of oxalic acid, giving a deep blue. A mixture was made of a known amount of ferro- 
cyanide of potassium with that acid, and it was added to the various ferric salts. 
The blue from the nitrate, chloride, or sulphate was very intense ; the mixture con- 
taining the acetate was colourless the first minute, but gradually became blue; while 
that containing the citrate also deepened in tint on standing. After remaining about 
two hours, the coloured mixtures were in the following proportions : — 
1 eq. ferric nitrate -1- 3 eq. ferrocyanide of potassium gave 100 parts of blue salt. 
1 eq. ferric chloride 3 eq. ferrocyanide of potassium gave 87 parts of blue salt. 
1 eq. ferric sulphate + 3 eq. ferrocyanide of potassium gave 89 parts of blue salt. 
1 eq. ferric acetate + 3 eq. ferrocyanide of potassium gave 45 parts of blue salt. 
1 eq. ferric citrate + 3 eq. ferrocyanide of potassium gave 60 parts of blue salt. 
The effect of mass was also tried. The addition of more ferrocyanide of potas- 
sium to a mixture of one equivalent of ferric nitrate and three of the ferrocyanide 
produced no appreciable increase of colour. With the citrate, however, the follow- 
ing numerical results were obtained : — 
Ferric Ferrocyanide 
Blue salt 
Ferric Ferrocyanide 
Blue salt 
citrate. of potassium. 
produced. 
citrate. of potassium. 
produced. 
1 equiv. + 3 equivs. 
88 
1 equiv. + 9 equivs. 
113 
1 equiv. + 6 equivs. 
107 
1 equiv. + 15 equivs. 
120 
These numbers give rise to the curve in Plate IX. fig. 5. 
Acetate or citrate of potash added to a mixture of ferric nitrate and ferrocyanide 
of potassium in oxalic acid, produces no pereeptible change at the moment of mix- 
ing; but a decrease of colour becomes apparent after a few minutes, and continues, 
becoming more and more marked for some hours. 
The ferrocyanide then bears a similar testimony to the truth of Berthollet’s posi- 
tion to what the ferric sulphocyanide and gallate do. 
I Ferric Comenamate. 
Single equivalents of cornenamie acid (C 12 Hg N08-f-4H0) were mixed with single 
equivalents of the different ferric salts. With the nitrate, chloride, and sulphate it 
