1824.] M. Lewenan on Selenium. 105 



the water ill the Woulf's bottle soon became reddish-yellow. 

 When the action of the acid had moderated, a pound and a half 

 more was added ; the same phenomena occurred again, and were 

 followed by a fresh introduction of acid. Next, to complete the 

 action of the acid, and get rid of the now inert liquid, it was dis- 

 tilled over into the receiver, with a gentle heat ; the distillation 

 was accompanied by the disengagement of a reddish-yellow gas; 

 towards the end of the process, the neck of the retort was lined 

 with small yellow stellated crystals, very probably a binary 

 compound of selenic and muriatic acid, which disappeared on 

 increasing the heat. When almost the whole of the exhausted 

 liquid was thus separated, the remainder of the acid was intro- 

 duced, in separate portions, as before. The action was always 

 very violent on each addition of fresh acid, and it was necessary 

 several times to change the water in the flask, as it became satu- 

 rated with the acid vapours. At last, all the liquors were 

 returned into the retort and redistilled. The insoluble residuum, 

 and the sides of the retort, appearing of a deep-red colour, as if 

 occasioned by pure precipitated selenium, the solubility of which 

 in fuming nitric acid had been demonstrated by direct experi- 

 ment, a pound and a half of that acid was introduced into the 

 retort, and distilled with a gentle heat till no supernatant liquid 

 remained, but without entirely reducing the residuum to dryness. 

 Distilled water was affused over the residual mass at the bottom 

 of the retort, made to boil, and the whole then poured out and 

 filtered, and the residuum washed, till the washings passed off 

 perfectly insipid. The filtered liquid had a light-yellow colour ; 

 that which had been distilled into the receiver was found to be 

 slightly seleniferous. 



" In order to separate the selenium from the filtered liquor, in 

 which it existed as selenic acid, without regard to the metals it 

 might contain, sulphite of ammonia, recently prepared, was 

 employed, which threw down the selenium, in the form of large 

 flakes, of a cinnabar-red colour. The colour was proportionately 

 brighter, as the quantities precipitated were smaller. The pre- 

 cipitation was instantaneous, and preceded by slight turbidness 

 for a few moments, when a concentrated solution was acted on ; 

 but if the solution was diluted, precipitation did not ensue for 

 some time, although a large excess of sulphite of ammonia were 

 added, and, which is advantageous in all cases, the liquor, at 

 first clear, became coloured (sometimes at the expiration of 

 many hours), and at last turbid, and deposited selenium. In a 

 certain state of dilution, the precipitate was black or dark-grey. 

 The selenium thus obtained was washed with cold distilled 

 water, till the washings ceased to precipitate muriate of barytes; 

 five or six washings are commonly necessary ; the selenium was 

 then dried in the shade. 



" To obtain the small portion that might still remain in the 



