244 Medico-Legal Application of RiencKs Test for Arsenic. 



allowed to cool down, and is afterwards to be brought again into 

 contact with heat, to sublime the arsenious acid. 



The pointed end is first to be heated to approaching redness, 

 care being taken that the aperture be not closed thereby, and the 

 tube is then to be slowly moved through the flame until it warms 

 each part in succession, as far as the enclosed metal extends. 

 The temperature at which the sublimation takes place is 380° 

 Fah., which should not be much exceeded. If the process has 

 been well managed, and arsenic be present, it will be found in 

 the form of arsenious acid, occupying a position around the tube 

 about half an inch beyond the copper strips. The part of the 

 glass surrounding the strips will be stained by a whitish opales- 

 cent film, which when the heat has been carried high becomes 

 green ; it is a salt of copper, as is proved by the action of the fer- 

 rocyanide of potassium. This stain does not in any way interfere 

 with the test. The metallic copper is encrusted with dioxide. 



The arsenious acid of the ring is formed by the action of the 

 oxygen of common air, which as it passes over the heated metal 

 combines with any arsenic present. It collects on the nearest cool 

 place, in the form of minute octahedrons of a remarkable brill- 

 iancy. The crystals are much more characteristic of arsenic 

 than the reduced metal, which may be counterfeited by many 

 substances. The smallest amount of the acid that can be satis- 

 factorily recognized is the T |^ of a grain. In examining it, the 

 tube should be first cut immediately below the ring, and the de- 

 posit viewed with a magnifying glass at the open end near the 

 crystals ; in this way the influence of the refractive power of the 

 tube can be avoided. The production of arsenious acid from 

 the metal is also advantageous, inasmuch as the bulk is increased 

 in the ratio of their equivalents, or as 75.34 to 99.34 (As0 3 ). 

 The field covered by the crystals is also larger than that which 

 would be occupied by the reduced arsenic. There is no subli- 

 mate which can rise under the preceding circumstances, that will 

 in any way embarrass the operator. 



Arsenious acid thus obtained forms a perfect evidence, and 

 none other will be desired by the chemist. But in medico-legal 

 questions it is proper to collect it, and use the other tests, so as 

 to remove all doubt from the minds of the jury. The best 

 way to collect the acid, is to cut the tube with a file, imme- 

 diately above and below the ring, and pound up the whole in a 



