^3 



Detectioji and Qtmntitative Determination of Arsenic. 259 



c conducts the carbonic acid into the reduction-tube C (which 

 is sketched in fig. 2 of its natural size). This reduction-tube 

 must be made of difficultly fusible glass. 



When the apparatus is prepared, the little basin with the 

 sulphuret of arsenic (vide D.) is again weighed, one-third of 

 its contents taken off and put upon a watch-glass ; the exact 



weight of this abstracted part is de- 

 termined by substituting weights 

 for it. The basin containing the 

 two-thirds remaining is carefully 

 kept. The abstracted third in- 

 tended for reduction is rubbed in 

 a smtill basin, previously heated in 

 the water-bath, together with 

 about 12 parts of a mixture con- 

 sisting of 3 parts of dry carbonate 

 of soda and 1 part of cyanide of po- 

 tassium (prepared according to 

 Liebig's method) ; the completely 

 intermixed powder is put upon a 

 small strip of card-paper bent into 

 the shape of a gutter. This is put 

 into the reduction-tube up to the 

 pointyj and the tube is then turned 

 half round its axis. 



In this manner the mixture is 

 placed at a of the reduction-tube 

 without soiling any other part of 

 the tube, the strip of card paper 

 is then cautiously withdrawn from 

 the tube, so as to leave the mix- 

 ture undisturbed. The reduction- 

 tube is then, by means of the cork 

 e, fixed to the gas-evolution appa- 

 ratus ; a moderate stream of car- 

 bonic acid gas is evolved by pour- 

 ing hydrochloric acid into the 

 funnel tube («, fig. 1), and the 

 mixture most carefully dried by 

 very moderately heating the tube 

 along its whole length by means 

 of a small spirit-lamp. When 

 every trace of water has disap- 

 peared from the tube, and the gas 

 stream has become so slow that 

 the bubbles pass through the sul- 

 S2 



