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plates of copper, and heated for a few minutes, the copper 

 plates became coated with a silvery white alloy. Other 

 metals, such as tin, mercury, and antimony, are capable of 

 producing nearly the same effect; this plan, therefore, inde- 

 pendently of its want of delicacy, is altogether abandoned. 

 Galvanic arrangements have been employed for the 

 purpose of detecting arsenic. Thus, the suspected sub- 

 stance has been placed in a platinum vessel, and zinc brought 

 in contact with the solution and platinum, and metallic 

 arsenic has been deposited upon the latter. This method 

 has been recommended by Dr. Clendenning, but I am not 

 aware that it has ever been extensively used. Other gal- 

 vanic arrangements have been employed; it will not be 

 however necessary to particularize them, as they are neither 

 so certain in their results nor so delicate in their action, as the 

 processes now in use. Dr. Christison was the first, I 

 believe, to recommend the test of reduction in tubes, about 

 twenty years ago. The metallic arsenic which was obtained 

 upon the glass, forming a dark steel-coloured looking crust. 

 Dr. C. states, that these crusts have been distinct when not 

 weighing more than 2 ie part of a grain, — and Berzelius 

 has stated that the ^ gr. of white arsenic is quite suffi- 

 cient to yield a distinct crust by the process of reduction. 

 There can be no doubt that this process is one of very great 

 delicacy, sufficiently so, in experienced hands, for every 

 practical purpose. At the same time it must be admitted, 

 that in cases where the arsenic is not unmixed with other 

 substances, but, on the contrary, contaminated with large 

 quantities of animal or vegetable matters, the difficulty 

 of separating the arsenic in a form which will admit of its 

 subsequent reduction to the metallic state, is greatly in- 

 creased. It is, indeed, only in the separation of small 

 quantities of arsenic from complex organic mixtures, that 

 the skill of the analyst can be said to be brought to 

 trial, a very little experience sufficing to enable any one to 



