24 History of physical Science from [July, 



candle, or when heated before the blow-pipe, it tinges the flame 

 of a fine azure blue, and gives out so strong a smell of horse- 

 radish that the fiftieth part of a grain is sufficient to impregnate 

 the air of a large chamber. Klaproth affirmed that tellurium 

 gives out the same odour ; but Berzelius could not obtain it 

 either from pure tellurium, or from its oxide or its alloys. When 

 he inclosed a little of it in a thin glass globule, and converted it 

 into vapour by the blow-pipe till it forced its way through the 

 globule, he observed the very same odour as that emitted by 

 selenium. 



Selenium combines with the metals, and the union is often 

 accompanied by ignition. Selenuret of potassium has the 

 metallic lustre and a greyish white colour. It dissolves rapidly 

 in water without effervescence, communicating the colour of 

 strong ale, and a taste quite the same as that of sulphuret of 

 potash. The acids disengage from it a gas, having, when 

 diluted, an odour quite similar to that of sulphurated hydrogen; 

 but when introduced even in very small quantity into the nostrils 

 it produces a very painful sensation, followed by inflammation, 

 and the symptoms of catarrh. The effects produced by drawing 

 into the nose a bubble of this gas, not exceeding the size of a 

 pea, remained for several days ; and the sensibility of the 

 schneiderian membrane was so far destroyed that ammonia pro- 

 duced scarcely any effect upon the nose. 



Hydroselenuret of potash dissolved in water becomes covered 

 with a pellicle at first of a cinnabar red colour ; but which, as 

 it increases in thickness, becomes greyish. When the liquid is 

 mixed with muriatic acid, it becomes muddy, and deposits a red 

 powder. Selenium dissolves in the fixed alkalies both by the 

 moist way and by fusion. The alkaline selenurets have a cin- 

 nabar red colour ; those of barytes and lime have the same 

 colour, but they are insoluble. Selenium dissolves likewise on 

 the fixed oils, to which it gives a red colour. These solutions 

 have no hepatic smell, as is the case with similar solutions of 

 sulphur. 



Selenium dissolves in nitric acid when assisted by heat. When 

 the solution is evaporated in a retort, it leaves a crystalline mass, 

 which sublimes easily in the form of crystalline needles, often a 

 foot long. This sublimate is very soluble both in water and 

 alcohol. Its taste is purely acid, it reddens litmus, and forms 

 peculiar salts with the alkalies. It is, therefore, an acid having 

 selenium for its base. Its name, of course, will be seletiic acid. 

 The alkaline seleniates crystallize with difficulty, and attract 

 humidity from the atmosphere. When the seleniate of ammonia 

 is heated, it is decomposed. A little ammonia is disengaged, 

 after which selenic acid sublimes ; but the greatest part of the 

 ammonia is decomposed. Water and azotic gas is disengaged, 

 and the selenium remains in a state of fusion, and may be after- 

 wards sublimed. Seleniate of barytes is soluble in water; but 



