228 Dr. yiARCtT Ofj an Aluminous Chalybeate Spring 



2. With a view to repeat and vary the last experiment, another 

 portion of residue, also weighing 50 grs. M^as thrown into a 

 solution of neutral carbonat of ammonia, the quantity of the latter 

 being more than sufficient to saturate any acid present, and to dissolve 

 the magnesia suspected to exist in that residue. A considerable 

 effervescence took place. The mixture, after this, was gently 

 heated and filtered. The residue left in the filter was of a pale 

 yellowish-brown colour. The clear solution deposited on standing 

 a small quantity of precipitate similar to the residue left in the filter, 

 to which residue this precipitate was added. The contents of the 

 filter were then treated with potash, in the manner before descrlhed 

 (§ VIII. 1), in order to separate the alumine, after which the residue 

 (now supposed to contain nothing but carbonat of lime and iron) 

 was treated with dilute muriatic acid, which dissolved it with effer- 

 vescence. From this solution, the lime was precipitated by oxalat 

 of ammonia, and the remaining liquor, now containing nothing but 

 muriat of iron, was treated with carbonat of amm.onia, so as to pre- 

 cipitate the whole of the iron, which, in subsiding, assumed a pale 

 reddish colour. The clear fluid being decanted off, and the pre- 



the affinity of the combustible matter for oxygen ; but in an experiment which I made 

 some years ago to ascertain that point, (the particulars of which may be seen in my 

 account of the Brighton chalybeate) this process appeared to bring the iron to the state 

 of peroxyd ; for 100 parts of iron gave 147,6 parts of oxyd, proportions which are 

 now considered as constituting the red oxyd of iron. And as a confirmation of this, I 

 observe that Dr. Thomson in his valuable paper on the oxyds of iron, published in the 

 twenty-seventh volume of Nicholson's Journal, states (page 379) that some of the red 

 oxyd being mixed with oil and heated to redness till it became black and magnetic, no 

 diminution of weight took place. Indeed I have always obtained by this process, not a 

 black, but a brown oxyd, which in cooling passes to a red-brown colour, somewhat 

 varying in shade, but mostly resembling powdered cinnamon, and being more or kss 

 magnetic. 



