132 Dr. Traitt on the Detection of Arsenic. [Feb. 



The trouble and delay of preparing a coated tube induced me 

 long ago to attempt the reduction in a thin glass tube, with the 

 naked fire, or with the blowpipe ; and the facility thus obtained 

 made the reduction much less irksome. But your happy sug- 

 gestion of the spirit-lamp has rendered the process still more 

 easy — even elegant ; and has euabled me to produce unequivocal 

 metallization of arsenic from portions of the white powder far 

 more minute than what has been mentioned — a circumstance of 

 no small moment, as it affords the most unexceptionable test of 

 what may affect the life of a human being. 



The following simple apparatus is all that is requisite ; and 

 after many trials, I give the process about to be described the 

 preference. 



Take a thin glass tube 2i inches long, and about 0*4 inch 

 wide, closed at one end, with a slightly dilated mouth ; like the 

 common test tubes of the blowpipe apparatus. A piece of cop- 

 per wire, loosely twisted round its upper end, serves to attach it 

 to any convenient support, at an angle of about 30° or 40° ; while 

 the flame of a spirit-lamp is applied to the closed end of the tube 

 containing the mixture to be reduced. 



I employ either the black flux, or a little subcarbonate of soda 

 or potash mixed with charcoal powder. Either of these should 

 be at least equal to thrice the weight of the substance to be 

 ascertained ; but a small excess of them is safer than the oppo- 

 site extreme. Where the quantity is not very minute, it is 

 unnecessary to grind the whole ingredients together, but mixing 

 them on a piece of glass, or of writing paper, with the point of a 

 knife, before they are introduced into the tube, will be sufficient. 

 The tube should be dry and clean ; and its orifice may be 

 slightly stopped with paper. Where the quantities are very 

 minute, 1 usually grind them in an agate mortar; but as every 

 such manual operation, however simple, is embarrassing to those 

 little habituated to experiment, I consider it very useful to sim- 

 plify the whole process by omitting this operation, and substitut- 

 ing an addition of charcoal powder, after the mixture is intro- 

 duced into the tube. The flame of a spirit-lamp will speedily 

 raise the closed end of the tube to a dull red heat ; and in less 

 than two minutes, a shining metallic crust will invest the upper 

 side of the inclined tube, about half an inch from the flame. 

 When the tube is cold, 1 shake out the loose materials from 

 the bottom, and then scrape off the metallic crust from its sides 

 with a knife. This saves the tube for further use, a matter of 

 some consequence in the country. By this process I have 

 reduced less than one-eighth, and even than one-tenth of a grain 

 of arsenious acid, or, as it is sometimes called, the white oxide, 

 to the metallic state. The metallic crust afforded by one-tenth 

 of a grain, was perfectly distinct to the naked eye, and very con- 

 spicuous when a lens was employed. The scrapings of the tube 

 in this case glistened strongly, with a metallic lustre, on the 



