Prof. Berzelius's Researches on Molybdcena. 183 



vitrified boracic acid greatly promotes the decomposition 

 which then takes place at a less elevated temperature ; but 

 this acid frequently contains water, and produces a bubbling 

 of the melted matter which raises it in the tube, and causes 

 the vapours to issue by perforating the softened part of the 

 glass. 



M. Berzelius maintains, that the sixth part of a grain of 

 sulphur et qf arsenic is sufficient to make three different trials ; 

 but he adds, that, when we have discovered only very small 

 traces of arsenic, we must take care not to introduce any by 

 means of re-agents, among which, both the sulphuric and the hy- 

 drochloric acid may contain it. The first almost always contains 

 some arsenic when it is not manufactured from volcanic sul- 

 phur, and the second, in consequence of sulphuric acid being 

 used in the preparation of the hydrochloric acid, yields the ar- 

 senic which it contains in separating it from soda. We must, 

 therefore, be certain of the purity of these re-agents. 



When death has been caused by the arsenic, and not by 

 the arsenious acid, the process must be modified, because the 

 sulphuretted hydrogen gas decomposes the arsenic acid too 

 slowly. In this case, we must add hydrosulphuret of ammonia, 

 which reduces the arsenic acid to the state of sulphuret, which 

 is afterwards precipitated by the hydrochloric acid. * 



4. Professor Berzelius's Researches on Molybdcena. 



In studying the properties of molybdaena, M. Berzelius has 

 found that this metal, of which we knew only the purple ox- 

 ide, produced by drying the blue oxide, and molybdic acid, 

 has two salifiable oxides, whose saline combinations were till 



• It is obvious that Berzelius has not Keen Dr Christison's paper on the 

 " Detection of minute quantities of arsenic in mixed fluids." These gen- 

 tlemen agree in precipitating arsenious acid by sulphuretted hydrogen, so 

 as to obtain the yellow sulphuret; but their subsequent methods differ: 

 Berzelius adopts a process which requires all the dexterity of as expert a 

 chemist as himself for conducting it with success. Dr Christison, on the 

 contrary, scrapes the sulphuret from the filtre with a knife, which may be 

 done though a very minute portion of it is present, and obtains metallic 

 arsenic at once by heating it with black flux. We refer for particulars to 

 his paper in the Edinburgh Medical and Surgical Journal. 



