To ascertain the quantity of this substance, a variety of methods was used, the principal results of which I shall cursorily relate.
2. It would have been in vain, in this instance, to have applied, without any previous step, oxalat of ammonia, the usual test of limes in order to obtain an accurate estimate of the quantity of lime present in the water; for as oxalic acid also acts upon iron, some ambiguity would necessarily have occurred. Indeed that oxalat of ammonia did not, in this case, re-act upon the lime in the manner that it usually does, had been noticed (§ III f, g) in some of the preliminary experiments[1]
- ↑ By adding a considerable quantity of oxalat of ammonia, and concentrating the solutions by heat, the whole of the lime appeared to be precipitated, together with a portion of iron; but in order to obtain the oxalat of lime pure, it was necessary to calcine the precipitate so as to drive of the oxalic acid, to redissolve the residue in muriatic acid, and to precipitate the lime again by oxalat of ammonia. The small quantity of iron present did not than interfere, and this process, however circuitous, proved tolerably accurate.
I was drawn by this part of the subject into an experimental inquiry respecting the action of oxalat of ammonia on solutions of iron, and the unfitness of that test for the precipitation of lime when iron is present, the principal results of which I shall state summarily.
1. If to a strong solution of sulphat of iron, a small quantity of sulphat of lime be added, and then a little oxalat of ammonia, no precipitate or cloudiness appears ; whilst the same quantities of sulphat of lime and oxalat of ammonia added to a bulk of water equal to that of the solution of iron, instantly form a precipitate.
2. If oxalat of ammonia be added to a solution of sulphat of iron, a bright yellow colour is produced, and presently after this a copious white precipitate appears, which, in subsiding, assumes a pale lemon colour. If at the moment the cloud is forming, the vessel be scratched with any pointed instrument, white lines appear, as in the precipitation of magnesia from carbonic acid by phosphoric acid.
3. This precipitate being washed, and gently heated over a lamp, assumes a bright cinnamon colour, and becomes magnetic, in consequence, no doubt, of the carbonization of the oxalic acid, and these changes take place ata heat much inferior to ignition.
4. If a solution of potash be added to the washed precipitate, previous to the application of heat, a strong smell of ammonia arises, and the oxyd passes to a dark greyish colour, showing that the precipitate is a triple salt of oxalic acid, iron, and ammonia.
