THE ACTION OF CHEMICAL AFFINITY. 
219 
. ferric phosphate in hydrochloric acid; yet even here a partial decomposition in all 
probability ensues. The only instructive numerical results which I have obtained 
were by mixing- a saturated solution of oxalate of lime in hydrochloric acid with 
various proportions of acetate of potash or soda. The hydrochloric acid combining 
with the alkali caused a deposition of oxalate of lime, since that salt is not soluble in 
the acetic acid that was liberated at the same time. The following were the results, 
every separate term of which was of necessity a separate experiment, though con- 
ducted at the same time and under similar circumstances. 
Acetate of soda series. 
Acetate of potash series. 
Salt added. 
Oxalate of lime deposited. 
Salt added. 
Oxalate of lime deposited. 
3 measures. 
6 measures. 
9 measures. 
12 measures. 
18 measures. 
30 measures. 
45 measures. 
90 measures. 
0’075 grm. 
0*10 grm. 
O'll grm. 
0‘13‘5 grm. 
0’14"3 grm. 
0*11 grm, 
0‘14‘5 grm. 
0*19 grm. 
20 measures. 
40 measures. 
80 measures. 
120 measures. 
160 measures. 
240 measures. 
0'359 grm. 
0’345 grm. 
0'410 grm. 
0’445 grm. 
0'503 grm. 
0’564 grm. 
Notwithstanding certain irregularities in these series of numbers, it is sufficiently 
evident in both instances that the amount of oxalate deposited increased with the 
amount of acetate added, though not in direct ratio. In the series of experiments 
with the potash salt each portion of the original hydrochloric acid solution contained 
0730 grm. of oxalate of lime, therefore even in the last term of the series, where 
240 measures of acetate were added, there still remained 0T66 grm. in solution. 
Plate IX. fig. 8. exhibits these results. 
Supposed exceptions and limitations . — With this mass of evidence, and that of a 
very diversified character, the question arises, — Are we justified in concluding that the 
principles, which are so general, are universal in their application ? Are there no 
exceptions ? Is there no limitation ? 
As to exceptions, in the whole range of my experiments upon this subject, I have 
never met with a single instance of two substances having so strong an affinity for 
one another, that they combined to the exclusion of other bodies of like kind and 
present in the same solution, even if in large excess*. Sometimes this rests not on 
demonstrative but upon moral evidence, as for instance when sulphocyanide of 
potassium and dissolved ferric ferrocyanide are mixed, where unquestionably the 
amount of ferric sulphocyanide produced must be quite inappreciable, yet that some 
is produced may be safely inferred I think from the fact, that sulphocyanide of 
potassium does give a red with the ferric acetate, and acetate of potash is capable 
of decomposing the ferric ferrocyanide to a well-marked extent. 
* Oxybromide of iron certainly appeared to resist even citric acid ; but then it is not a binary compound. 
Anomalous results too were sometimes obtained on examining the solubility of such substances as phosphate 
of iron in mixtures of salts and acids, but the fihenomena were always of an obscure character. 
MDCCCLV. 2 H 
