Medico-Legal Application of Riench's Test for Arsenic. 241 



gal questions, and from an extensive series of experiments, I be- 

 came convinced of its great value, and have communicated this 

 paper with a view of introducing to the notice of the profession, 

 the simplest, and as I believe the most effectual method of collect- 

 ing arsenic out of suspected fluids. 



The principle on which the test is founded, is that pure hydro- 

 chloric acid exerts no action upon bright copper — but when certain 

 metallic solutions are present, as an adulteration in the acid, it then 

 attacks the copper, and there is thrown down the reduced metal 

 of the solution. Many metals will thus precipitate themselves, 

 but some do so when in minute quantities, whereas others fall 

 down only when in large amount. Some salts of mercury are 

 reduced without hydrochloric acid, whilst arsenic in no proportion 

 can tarnish copper, unless the acid be present. 



Before Riench's process could be adopted by physicians, it was 

 necessary to ascertain how far organic matters, such as may exist 

 in the contents of the stomach, &c. were calculated to embarrass 

 the operator. The existence of medicines, in the suspected fluids, 

 might also destroy the value of the test. These enquiries, and 

 the hope of simplifying, and rendering the process more certain, 

 caused me to enter upon a full examination of the matter. 



There are three stages in the manipulation : 1. The collection 

 of the arsenic in Riench's test ; 2. Its sublimation ; 3. Its sepa- 

 ration from other substances. 



1. The collection of the poison out of a solution, in which no 

 other active metallic agent is present, is most easily effected by 

 the following process. A piece of copper, in the form of wire or 

 sheet, is to be filed bright, and introduced into the suspected fluid ; 

 to this is then added a small quantity of pure hydrochloric acid, 

 and the whole boiled together in a glass flask. Upon examining 

 the copper after a few minutes' ebullition, when arsenic is present 

 its surface will either be found coated with a film of the color 

 and lustre of rolled zinc, or a deep black with slight polish ; or 

 covered with scales of a black color. These various appearances 

 depend upon the quantity of the poison present, and the extent of 

 the surface of copper. If the boiling be continued after the scales 

 are produced, they drop off, and are lost in the fluid, so that the 

 collection becomes imperfect. All the arsenic present can be 

 separated in this way, therefore the copper not only reduces it, 

 but also affords us an accurate measure of the amount in solution. 



Vol. xliv, No. 2.— Jan.-March, 1843. 31 



