254: ON SOME BLOWPIPE-REACTIONS. 



fall into tliree groups : (1), Easily soluble, e.g., PbO, BPOs, BaO, &c.; 

 (2), Slightly or partially soluble, e.g., Mn^O* CoO, &c.j and (3), 

 Insoluble, e.g., Fe^O', Ce^^Os, NiO, CaO, MgO, &c. 



VI.— ON THE DETECTION OF BROMINE IN BLOWPIPE 

 EXPERIMENTS. 



When fused witli pliosplior-salt and copper oxide, the bromides, it 

 is well known, impart an azure-blue coloration to the flame, much 

 like that produced by chlorides under similar treatment, althovigh 

 streaked more or less with green, especially at the commencement of 

 the operation. To distinguish these bodies more closely, Berzelius 

 recommended the fusion of the test substance with 6 or 7 volumes of 

 bisulphate of potash in a closed tube. Bromides by this treatment 

 become decomposed, as a rule, and give off strongly -smelling brownish 

 or yellowish-red vapours of bromine. But this process does , not 

 always give satisfactoiy results, as in some instances the bromide is 

 very slightly attacked. In this case, the following method, based on 

 a peculiar reaction of bromide of silver, first pointed out by Plattner, 

 may be resorted to. If insoluble, the bromide is fused with 2 or 3 

 volumes of carb.-soda. A soluble bromide of sodium is thus formed, 

 with separation of the base. To the filtered or decanted solution 

 of the fused mass, a small fragment of nitrate of silver is added, in 

 order to precipitate bromide of silver. This, collected by decanta- 

 tion, is fused with a small quantity of bisulphate of potash in a little 

 flask or test-tube. The bromide of silver will quickly separate from 

 the flux in the form of a blood-red globule, which becomes pale, 

 yellow when cold. The little globule, washed out of the tube by 

 dissolving the fused bisulphate in some warm water, is carefully dried 

 by being rubbed in a piece of blotting or filtering paper, and is then 

 placed in the sunlight. After a short time, it will turn green. Chlo- 

 ride of silver, as obtained in a similar manner, melts into an orange- 

 red globule, which changes to clear-yellow on cooling, and finally 

 becomes white, or nearly so. Placed in sunlight, it rapidly assumes- 

 a dark-gray colour. Iodide of silver, under similar treatment, forms 

 whilst hot an almost black globule, which becomes amethyst-red 

 during cooling, and dingy-yellow when cold. In the sunlight it 

 retains the latter colour. A mixture of chloride and iodide of silver 

 assumes a greenish tint somewhat resembling the colour acquired by 

 the bromide globule. This, however, can scarcely give rise to any 



