with reference to the detection of Arsenic. ■ 481 



adopted by M. Fuchs for the analysis of crude iron and iron 

 ores* . 



A slip of copper immersed into hydrochloric acid, sp. gr. 

 1*1 72, containing arsenic, was not acted upon, in a closed 

 vessel, after remaining twelve hours at the ordinary tempera- 

 ture; if the acid was diluted with an equal quantity of water, 

 action took place after a few hours, the arsenic being preci- 

 pitated upon the copper; if the solution was exposed to the 

 air the action occurred in a still shorter time, but if heated 

 it took place nearly immediately, whether the acid was con- 

 centrated or diluted. The copper was covered at first with 

 a grayish brilliant metallic coating, which upon increase of 

 temperature, and according to the quantity of arsenic present 

 in the solution, turned black, and finally separated in black 

 scales. 



In order to ascertain the delicacy of this reaction, a solu- 

 tion of one part of arsenious acid was made in 1000 parts of 

 pure hydrochloric acid diluted with water. A portion of this 

 solution (to which one-third of pure hydrochloric acid was 

 added), containing l-100,000th part of arsenic, was acted upon 

 as soon as it was heated ; at first the precipitate had the ap- 

 pearance of iron, but after long boiling it became black with 

 a metallic lustre. With a solution containing l-200,000th 

 part, the copper was distinctly covered with arsenic after a 

 quarter of an hour's boiling. The limit appears to be between 

 l-250th and l-300,000th parts ; and is therefore consider- 

 ably greater than that of any other reagents, and is not likely 

 to be mistaken for other substances. 



If arsenious acid be dissolved in water, and a slip of copper 

 immersed, no action takes place; but if a few drops of hydro- 

 chloric acid be poured upon the copper, the arsenic is imme- 

 diately precipitated. A quantitive estimate of the arsenic 

 may be made by this method, as on boiling the solution 

 nearly the whole of the arsenic is separated from the copper, 

 and the quantity of arsenic may be calculated from the loss of 

 weight sustained by the copper. The arsenic obtained may 

 either be further tested by Marsh's apparatus, or it may be heat- 

 ed in an open glass tube, when brilliant crystals of arsenious 

 acid will be obtained, which may be dissolved in a weak alka- 

 line solution and tested by the usual reagents ; or the slip of 

 copper may be heated in a glass tube with hydrogen gas, 

 when metallic arsenic will be sublimed. 



Antimony. — Copper does not precipitate this metal with 

 the same iron-like appearance as arsenic ; the precipitate has 



* See Phil. Mag. for February 1841. 

 Phil. Mag. S. 3. Vol. 19. No. 126. Dec. 1841. 2 I 



