Art. LIV.—The Dimorphisim of Magnesia.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 13, 1880, Page 389

Art. LIV.—The Dimorphisim of Magnesia. By William Skey, Analyst to the Geological Survey Department. [Read before the Wellington Philosophical Society, 4th December, 1880.] While trying to electro-deposit gold from sea-water, so as to verify Sonstrad's observation regarding gold in sea-water, and if possible to estimate it, I ap-

plied iodine to the supposed auriferous deposit, when a highly coloured substance formed. This I at first took for palladium-iodide, but soon found it to be magnesium oxy-iodide, or at least a substance made up of the three substances—mag-nesia, oxygen, and iodine. Afterwards I found that magnesia, prepared at a certain temperature, behaved just like this electro-deposited magnesia, that is in absorbing iodine. At a high temperature, about 1,000° F. both these forms of magnesia lose this absorbent property. Certain aniline dyes and cochineal, also, are absorbed by this modified magnesia. From these facts I make the deduction that magnesia can exist in two forms, and this receives confirmation by the fact that it is made denser by ignition. Further I find that magnesia may be exhausted out of ammonaical solutions by an electric battery of two cells, and this really forms a capital way for separating and estimating it in analysis. The alkalies are then in due course left pure for easy estimation. The phosphoric acid, which is now used to effect this, and which complicates the process so much, being thus rendered unnecessary. But not only is quantitative analysis thus aided in this case, but the detection of magnesia by means of the battery and iodine becomes a very simple matter, and especially to be recommended for use when but small quantities of test substances are to be had. I find that by these means the 1.10000 of a grain of magnesia can be recognized in but 1.2 a grain of liquid. It is therefore far more delicate than the old tests. I should state that lime, baryta, alumina, do not when electro-deposited, give a chromatic reaction with iodine. The compound iodide described, is easily decomposed by acetic acid, or an alkali. And very slowly decomposed by water. The iodine being in each case detectable in the solution by means of the starch test.