230 Method of separating Small Quantities 



rate very minute quantities of arsenic from gruel, soup, porter, 

 coffee, and other alimentary liquors, but that, by continuing the 

 process a sufficient length of time, I could eliminate the whole 

 of the arsenic in the state of arsenuretted hydrogen, either pure, 

 or, at most, only mixed with an excess of hydrogen. 



If this gas be set fire to as it issues from the end of a jet of 

 fine bore into the common air, the hydrogen, as the more com- 

 bustible ingredient, will burn first, and will produce aqueous 

 vapour, while the arsenic will be deposited either in the metal- 

 lic state, or in that of arsenious acid, according as it is exposed 

 partially or freely to the air. The former condition is brought 

 about by holding a piece of cold window-glass opposite to and 

 in contact with the flame, when. a thin metallic film will be im- 

 mediately deposited on its surface ; and the latter, by receiving 

 the flame within a glass tube open at both ends, which, in half 

 a minute, will be found to be dimmed by a white pulverulent 

 subUmate of arsenious acid. By directing the flame obliquely 

 upon the inside of the tube, it strikes against the glass and deposits 

 the arsenic, partly in the metallic state. In this case, if the tube, 

 while still warm, be held to the nose, that peculiar odour, some- 

 what resembling garlic, which is one of the characteristic tests 

 of arsenic, will be perceived. Arsenuretted hydrogen itself has 

 precisely the same colour, but considerable caution should be 

 used in smelling it, as every cubic inch contains about a quar- 

 ter of a grain of arsenic. 



The requisite apparatus is as simple as possible ; being a glass 

 tube open at both ends, and about three quarters of an inch in its 

 internal diameter. It is bent into the form of a syphon aa, 

 the shorter leg being about five in- 

 ches, and the longer about eight in- 

 ches in length. A stop-cock 6, ending 

 in a jet of fine bore, passes tightly 

 through a hole made in the axis of a 

 soft and sound cork, which fits air- 

 tight into the opening of the lower 

 bend of ihe tube, and may be further 

 secured, if requisite, by a little com- 

 mon turpentine lute. To fix the ap- 

 paratus, when in use, in an upright position, a hole is made 



