Mr. L. Thompson on Antimoniuretted Hydrogen, 353 



in their arrangement. It may also be added, that if felspar be 

 dimorphic, how comes it to pass that the granite (abounding in 

 felspar) in which the protogine occurs is buts lightly altered ? 



It appears more probable that a difference in composition 

 in the felspars of these rocks will afford the true solution of 

 this problem, and though the data on which we can at pre- 

 sent reason are very imperfect, yet I am inclined to think 

 that the presence of magnesia in the felspar of protogine may, 

 among other causes, contribute toward the extraordinary 

 change which this rock experience/s. Thus, the magnesia may 

 absorb carbonic acid, as well as the alkali, from the percolat- 

 ing water ; and so great is its tendency to combine with two 

 proportions of this acid, that even one part of the carbonate 

 will attract the acid of the other, so as to pass into a bicar- 

 bonate of magnesia ; in which state being soluble in water, it 

 would be speedily removed. This in some measure explains 

 the origin of kaolin, and it also accounts for the small quan- 

 tity of this earth remaining in the porcelain clay ; indeed I have 

 examined some samples in which I could not detect a trace 

 of magnesia. 



This subject is one of great importance to the geologist, as 

 affording an insight into a first and elementary step in the 

 mighty changes which the crystalline materials of the globe 

 have undergone; and the prosecution of this subject by che- 

 mists would confer a boon on geology, and at the same time 

 cannot fail to be instructive to themselves by leading to a better 

 knowledge of the combinations of alumina. 



LXVIII. On Ajitimonmretted Hydrogen, mth some Remarks 

 on Mr. Marsh's Test for Arsenic, By L. Thompson, Esq.y 



Member of the Royal College of Surgeons, 



To the Editors of the Philosophical Magazine and Journal, 

 Gentlemen, 

 T BEG leave to direct the attention of your readers to a 

 -*- hitherto unnoticed combination of antimony and hydrogen, 

 which acquires great interest from its near resemblance in 

 many respects to arseniuretted hydrogen. The plan which I 

 adopt for procuring this gas in its greatest purity is by fusing 

 together equal weights of antimony and zinc, and acting on 

 the alloy with diluted sulphuric acid ; this process is not per- 

 haps altogether free from objection, but answers very well for 

 general purposes. As thus prepared antimoniuretted hydro- 

 gen is a colourless inflammable gas, exploding violently by 

 the electric spark or lighted taper when mixed with an equal 

 volume of oxygen, chlorine, or atmospheric air ; its odour is 



Third Series, Vol. 10. No. 62. May 1837. 2 Z 



