— of iridium. Iridium is white, very hard, difficult to fuse, nearly 



insoluble in nitro-muriatic acid, and not at all in any 

 Other ; oxidable and soluble by the fixed alkalis ; and 

 its oxide is soluble in acids, giving varied and lively co- 

 lours to its different solutions. These are the red salt;? 

 which colour those of platina. 



— ofesmium. Osmium is a metal not hitherto reducible, of whidh 



the oxide has the form of a black and very volatile pow- 

 der, very odorant, very fusible, soluble in water, and 

 rising with it in vapour, and giving a strong smell and 

 taste to that fluid. Its solution assumes a fine blue co- 

 lour by the smallest quantity of infusion of nut galls. 



The singularity of this composition is no less worthy 

 of remark than the sagacity by which it has been de- 

 veloped. 



Chromium has lately been discovered in the meteoric 

 stones by M. Laugier, and since by Mr. Thenard. 



The discovery of Pacchiani, of the formation of muri- 

 atic acid, by galvanism, is considered as in want of con- 

 muna^lc"°add^ firmation, since Messrs. Biot and Thenard did not find it 

 announced by when they took care to make the experiment without the 

 Pacchiani, can presence of any thing which could afford sea salt. The 

 experiments of Mr. Sylvester, recorded in our Journal, 

 Vol. XV. p. 50, however appear to confirm the fact, 

 and conduce not a little to explain the process, which no 

 doubt must be considered as still enveloped in obscurity. 



In a series of researches upon refraction, undertaken 

 in the first instance for the improvement of astronomy, 

 M. Biot was led to avail himself of this action of bodies 

 upon light as a very happy means of analizing transparent 

 substances. 



It has been long known that the rays of light are re- 

 fracted when they pass from one medium into another of 

 tifi'erent density, and that the refractions of different 

 [ediums correspond with their densities, unless they 

 contain some combustible element. These last increase 

 Ai t.«- ^1,^ refraction much beyond what the simple density 

 would have produced. 



From this antient observation it was that-'Newton 



Tormed ajudgment that the diamond must be combustible, 



and he even arrived at the almost incredibly acute con- 



jccturej^ 



Discovery of 

 chromium in 

 meteoric 

 stones. 

 Whether the 



be depended 

 on. 



Curious and 

 useful re- 

 searches of 

 Biot upon re- 

 fraction. 



