Section III., 1885. [ 7 ] Trans. Roy. Soc. Canada. 



II. — Blowpipe Reactions on Plaster of Paris Tablets. 



Bij E. Haanel, Ph.D., Victoria University, Cobourg. 

 (Read May 25, 1885.) 



I. — Osmium with Hydriodic Acid. 



Osmium gives with hydriodic acid on tablet a characteristic greyish-greeu volatile 

 coating. The colovir of this coating is best observed after the brownish coating, resulting 

 from the decomposition of the hydriodic acid during the operation, has evaporated. The 

 coating is not affected either by ammonia or ammonium sul^jhide. The reaction is sensi- 

 tive. The three hundred and eighty-fourth part of a grain of osmic acid gave a very 

 distinct coating. A specimen of iridosmine from Nishnei Tagilsk gave a coating extending 

 two and one-half inches beyond the assay. 



It is evident that a reaction depending on sight for the recognition of a substance is 

 much to be preferred to one depending on the sense of smell, since the latter is unfortu- 

 nately in very many persons either periodically or permanently impaired. For this reason 

 the reaction of osmium with hydriodic acid will advantageously replace the one now in 

 use in Blowpipe Analysis, which depends on the perception of the odour of the osmic acid 

 evolved, and which has, therefore, always been unsatisfactory. 



II. — Reactions on Tablet for Chromium, Antimony, and Molybdenum with 



Tetrachloride of Tin. 



Manipulation. — Fuming tetrachloride of tin is dropped upon the assay contained in 

 the shallow cavity bored near one end of the tablet. The tablet is held in an inclined 

 position ; and the assay, in the case of examination for chromium is gentl)/ heated with the 

 O.F., in case of examination for antimony and molybdenum it is more highly heated. 



Results. — Chromium and most minerals containing chromium give a peach-blow 

 coating, which disappears entirely and at once when touched with the R. F., but reappears 

 with its former intensity and tint when treated with a good O.F., This disappearance 

 and reappearance may be repeated with the same coating any number of times. The 

 coating is not affected either by ammonium or ammonium sulphide. Its production 

 requires some skill. If the assay be too highly heated, the coating fails to appear. The 

 operation should, moreover, be concluded the instant the coating appears, since further 

 blowing tends to cover the coating with a white opaque film due to the tetrachloride of 

 tin. The solid hydrate cannot be substituted with advantage for the fuming liquid tetra- 

 chloride of tin, — the coating either failing to appear, or being too feeble with the hydrate. 



