890 Transactions. — Che^nistry. 



plied iodine to the supposed auriferous deposit, when a highly coloured suh- 

 stance 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 mag- 

 nesia 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 

 Toooo of a grain of magnesia can be recognized in but ^ 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. 



