FOOTNOTES:
[103] Na3AsO3 + H2O + 2I = Na3AsO4 + 2HI. The acid is at once neutralised.
[104] Mr. Thomas Gibb is the originator of this ingenious process.
[105] By taking hold of the water present, it may prevent the dissociation of arsenious chloride.
[106] It is difficult to get ferric chloride free from arsenic; but the following treatment will remove 80 or 90 per cent. of the arsenic contained in the commercial material:—Dissolve 2 or 3 lbs. of ferric chloride with the smallest amount of water that will effect solution with the addition of 100 c.c. of hydrochloric acid; add a solution of sulphurous acid in quantity sufficient to reduce 2 or 3 per cent. of the iron to the ferrous state; allow to stand a week; and then boil, to remove the hydrochloric acid added. Nitric acid, which is prejudicial, is also removed by this treatment.
[107] When the amount of arsenic to be estimated is small (as in refined coppers), it is better to use a weaker solution of iodine. This is made by diluting 200 c.c. of the standard solution with water to 1 litre. Each c.c. will equal 0.1 per cent., if 1 gram of the metal has been taken for the assay.
[108] The constitution of these phosphates may be thus illustrated—
Magnesic meta-phosphate MgO.P2O5.
Magnesic pyro-phosphate 2MgO.P2O5.
Magnesic ortho-phosphate 3MgO.P2O5.
[109] The composition of which is—
MoO2 90.74,
P2O5 3.14,
(NH4)2O 3.57,
H2O 2.55=100.00.
[110] This is made by adding 27 grams of magnesium carbonate (a little at a time) to a solution of 270 grams of citric acid in 350 c.c. of warm water; and, when dissolved, adding 400 c.c. of dilute ammonia, and making up the bulk to 1 litre; 20 c.c. of the solution is sufficient for 0.1 gram of P2O5, although more will be required if much iron or alumina is present.
[111] For the details of the titration, the student is referred to the same place.
[112] N2O5 + 6FeO = 3Fe2O3 + 2NO.