1824.] Tests for detecting the Presence of Arsenic. 33 



ance; while, however, there exists some resemblance in the co- 

 lours, there are these differences in the effects ; antimony fur- 

 nishes a precipitate immediately, and with more of an orange tint. 



Sulphate of Copper. 



Arsenious acid produces no effect upon a solution of sulphate 

 of copper ; but with the assistance of an alkali, a green precipi- 

 tate of arsenite of copper is readily produced. It has been 

 objected to this test, that a fallacious appearance is produced if 

 the suspected solution be of a yellow colour ; but for this case I 

 have already provided. If the sulphate of copper be impure, 

 owing to the presence of peroxide of iron, a greenish precipitate 

 may also be obtained by simply adding potash to the solution. 

 This test may be employed in two ways ; first, add a few drops of 

 an alkaline solution, as potash or its s«6-carbonate to the suspect- 

 ed solution, and when mixed pour them into the sulphate of cop- 

 per. If arsenious acid be present, a green precipitate will be form- 

 ed ; and there is a mode of removing any ambiguity which, if it 

 does not escape my recollection, has not been previously noticed. 

 To be certain that the sulphate of copper contains no peroxide 

 of iron, add first to the solution some potash ; if pure, a fine blue 

 precipitate will be obtained ; to this add the suspected solution ; 

 and if arsenious acid be present, then it will convert the blue 

 precipitate to a green one. 



Nitrate of Silver. 



To confirm the results obtained by sulphuretted hydrogen and 

 sulphate of copper, nitrate of silver is a test which may be very 

 usefully employed. The first method is simply to add the sus- 

 pected solution to one of nitrate of silver, which should be pre- 

 pared either from the crystallized or fused nitrate (lunar caustic), 

 in order that all excess of acid may be avoided. After the 

 suspected solution has been mixed with that of silver, drop in 

 a solution of ammonia or of potash, liquor ammoniae, or liquor 

 potassae of the London Pharmacopoeia ; if arsenious acid be 

 present, a bright-yellow precipitate of arsenite of silver will be 

 formed, which is readily dissolved by excess either of ammonia 

 or nitric acid ; so that supposing too much ammonia to have 

 been employed, nitric acid will restore the precipitate. Potash 

 does not possess the inconvenience of ammonia in redissolving 

 the arsenite of silver formed : but there is one inconvenience 

 attending the use of silver ; the animal fluids all contain mu- 

 riatic "salts ; and, therefore, the fluid contents of the stomach 

 will probably give a white precipitate of chloride of silver when 

 mixed with the nitrate. If, however, the presence of arsenic 

 has been determined by the use of the preceding tests, then 

 the chloride and arsenite of silver must be precipitated together, 

 Netu Series, vol. vii. j> 



