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LXXVIII. Intelligence and Miscellaneoics Articles. 



ON OSMIAMIC ACID. BY MM. J. FRITZSCHE AND H. STRUVE. 



WHEN caustic ammonia is added to a solution of osmic acid in 

 excess of potash, the deep orange colour of the liquid becomes 

 rapidly a bright yellow, and a new salt is produced and separated, 

 either immediately or by evaporating the liquid at a gentle heat, 

 which is a yellow crystalline powder. 



The formation of this new compound does not necessarily depend 

 on the presence of potash or any other oxide, but uniformly upon 

 that of ammonia ; the ammoniacal salt is, however, subject to altera- 

 tion, and decomposes during evaporation. It is better therefore to 

 cause a basic oxide to intervene. 



M. Gerhardt remarks that the formula of the osmiamates which the 

 authors have given requires correction ; they agree, he states, with 

 the formula OS, 03 N (M). 



The properties of the osmiamates are as follows : they decompose 

 by heat with explosion ; and several of them undergo the same de- 

 composition when struck. Among the products of this decomposi- 

 tion are metallic osmium, an osmiate, or a less oxygenated osmic 

 compound. Protosraiamate of mercury volatilizes without explosion, 

 when heated quickly ; and it diffuses a strong smell of osmic acid. 



Osmiamic acid can be obtained only in solution in water. In 

 order to prepare it, osmiamate of barytes is to be cautiously decom- 

 posed by sulphuric acid, or recently prepared and moist osmiamate of 

 silver is to be decomposed by dilute hydrochloric acid. After fil- 

 tration a bright yellow-coloured solution is obtained, which may be 

 preserved for several days, if it be sufficiently dilute ; on the other 

 hand, if too concentrated, it becomes brownish and decomposes with 

 the disengagement of gas, osmic acid is set free, and a black non- 

 explosive substance is deposited which contains osmium. 



The same metamorphosis occurs when the weak acid is evaporated 

 over sulphuric acid. 



Osmiamic acid not only expels carbonic acid from carbonates, 

 but also decomposes chloride of potassium. In fact crystals of os- 

 miamate of potash are obtained, if a crystal of chloride of potassium 

 with a drop of solution of osmiamic acid be exposed to evaporation 

 on a strip of glass. 



Zinc dissolves in solution of osmiamic acid, with the evolution of 

 a little gas ; part of the acid is decomposed, and the zinc is covered 

 with a very adherent black deposit, and flocculi appear in the liquid 

 which possess the odour of osmic acid. When all the undecomposed 

 acid is saturated with zinc, the metamorjihosis ceases. 



In the cold, acids do not decompose osmic acid or the osmiamates : 

 sulphuric, nitric or hydrochloric acid may be added to their solutions 

 without inconvenience ; but decomposition readily occurs when heat 

 is applied, and it is rendered apparent by the disengagement of osmic 

 acid and by the brown colour of the liquor ; the products vary ac- 

 cording to the nature of the acid employed. 



