THE ACTION OF CHEMICAL AFFINITY. 
203 
other substances had any influence in the dilution of meconate of iron. Solutions 
were taken of pure ferric meconate ; and of mixtures of ferric chloride with meconic 
acid ; of the same with meconate of potash, both in large excess and otherwise ; of 
ferric nitrate with meconic acid ; of the same with meconate of potash ; and of ferric 
citrate with meconic acid. On repeated dilution with equal amounts of water, no 
notable difference was observed in the relative depths of colour of these several solu- 
tions, except in the case of the citrate, which, on standing for some hours after dilu- 
tion, lost colour considerably. The red also was of a more pure crimson where there 
was nitric acid. 
Pyromeconate of iron prepared by double decomposition was affected in colour by 
dilution in a similar manner to the meconate. Water, too, seemed to have the same 
effect on the blue ferrocyanide as on ammoniacal sulphate of copper. In these cases, 
however, the salts compared were not of precisely the same tint. 
Relative strength of affinity. — Having considered the evidence borne by eight 
coloured and soluble ferric salts as to the truth of certain views of the laws that regu- 
late chemical combination, we have found their testimony on the main points uni- 
form. We may now go further, and by examining the results above given determine 
the relative degree of affinity exerted by the different acids for sesquioxide of iron as 
compared with potash. Thus it is evident that citric acid has a much stronger 
affinity for ferric oxide, or a weaker affinity for potash, than nitric acid has ; and 
again, it is evident that an equivalent amount of ferrocyanide of potassium removes 
the greater proportion of ferric oxide from citric acid, while sulphocyanide of potas- 
sium takes only 01 94 part from the nitrate. 
The following is the order of affinity of the different acids experimented with for 
sesquioxide of iron and an equivalent amount of potash. 
Least affinity for sesquioxide of iron as compared with potash 
Hydrosulphocyanic aeid 1 
Nitric acid . 4 
Hydrochloric acid 5 
Sulphuric acid 7 
Gallic acid 10? 
Pyromeconic acid ? 
Meconic acid ? 
Acetic acid 20 ? 
Hydrobromic acid 
Comenamic acid 
Citric acid 100 
Hydroferrocyanic acid 170? 
Greatest affinity for sesquioxide of iron as compared with potash. 
MDCCCLV. 2 F 
