THE ACTION OF CHEMICAL AFFINITY. 
193 
The mixture containing the citrate could not be accurately compared on account 
of its greenish hue. That made from the acetate was of an intense blue. 
When single equivalents of nitrate of iron and gallic acid were mixed, a solution 
resulted in which the gallic acid had to such an extent combined with the sesquioxide 
of iron, that the addition of several equivalents of either one of the constituent sub- 
stances caused a scarcely perceptible increase of colour. 
The ferric chloride was then tried. 
Ferric Gallic 
chloride. acid. 
Black salt 
produced. 
Ferric Gallic 
chloride. acid. 
Black salt 
produced. 
1 equiv. -f- 1 equiv. 
88 
1 equiv. -4- 4 equivs. 
128 
1 equiv. q- 2 equivs. 
108 
1 equiv. -j- 6 equivs. 
133 
1 equiv. + 3 equivs. 
120 
These numbers are represented by the dotted curve in Plate IX. fig. 1. 
The citrate afforded a better opportunity of obtaining a numerical result represent 
ing the influence of the mass of one of the constituents. The following are two ob- 
servations made by means of it. A difficulty was experienced from the greenish hue 
of the mixture of single equivalents gradually changing to black as fresh acid was 
added ; hence the observations given below do not commence at unity. 
Ferric 
citrate. 
Gallic 
acid. 
Black salt 
produced. 
Ferric 
citrate. 
Gallic 
acid. 
Black salt 
produced. 
1 equiv. + 
4 equivs. 
88 
1 equiv. 4-12 
equivs. 
256 
1 equiv. -|- 
6 equivs. 
133 
1 equiv. 4- 16 
equivs. 
310 
1 equiv. 
8 equivs. 
176 
1 equiv. 4 - 18‘6 
equivs. 
346 
1 equiv. 4-10 equivs. 
220 
These numbers are represented by the broken line in Plate IX. fig. 1. 
Ferric 
citrate. 
Gallic 
acid. 
Black salt 
produced. 
Ferric Gallic 
citrate. acid. 
Black salt 
produced. 
1 equiv. 4- 
5 equivs. 
155 
1 equiv. 4-13 equivs. 
297 
1 equiv. 
7 equivs. 
200 
1 equiv. -1-17 equivs. 
353 
1 equiv. 4- 
9 equivs. 
237 
1 equiv. 25 equivs. 
445 
1 equiv. 4-11 equivs. 
270 
1 equiv. 4- 33 equivs. 
509 
This is represented by the continuous line in the same Plate. 
Experiments were also tried with gallate of potash in the place of gallic acid. 
1 eq. ferric nitrate + 1 eq. gallate of potash gave 100 parts of black salt. 
1 eq. ferric chloride + 1 eq. gallate of potash gave 97 parts of black salt. 
1 eq. ferric sulphate -p 1 eq. gallate of potash gave 68 parts of black salt. 
1 eq. ferric citrate + 1 eq. gallate of potash gave a blue solution. 
1 eq. ferric acetate + 1 eq. gallate of potash gave a precipitate. 
A mixture of single equivalents of gallate of potash and ferric nitrate gave nearly, 
but apparently not quite the same depth of colour as when an equivalent of gallic 
acid was mixed with the same iron salt. 
