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as Potassium, Zinc, &c, but there is no metal with which 

 we are acquainted, volatile at so low a temperature as 

 arsenic, with the exception of quicksilver, but quicksilver 

 at 60° F. is a liquid, and arsenic a solid — therefore, there is 

 no metal solid at 60° F., and volatile at 356° F., saving 

 arsenic. But, it may be said, that tins single property of 

 arsenic only distinguishes it from all metals, while the me- 

 tallic nature of tbe substance under experiment is still not 

 demonstrated. Now, it is obviously impossible to submit 

 excessively minute quantities of the so-called metal, arsenic, 

 to those tests by which the metallic nature of a body is said 

 to be demonstrated. It must, however, be bome in the 

 recollection, that although this property of arsenic does not 

 demonstrate its metallic nature, it nevertheless proves that 

 it cannot be any one of the hitherto discovered metals, and 

 therefore, as far as they are concerned, this property estab- 

 lishes a rigid distinction — nor again would such property, 

 as far as we may be supposed to know, distinguish arsenic 

 from every other body, simple or compound, with which 

 we are acquainted. In order to do this, some fresh pro- 

 perty or properties of arsenic must be looked for, until 

 we obtain a set, entirely proper to arsenic, and not 

 possessed by it in common with any other known body, sim- 

 ple or compound, metallic or non-metallic — and I shall 

 have occasion to shew presently, a very few additional pro- 

 perties are required to enable the chemist to distinguish 

 arsenic from all known substances. In all toxicological 

 enquiries it is a matter of veiy great importance, to be en- 

 abled to demonstrate the presence of any particular sub- 

 stance from the effect of as few re-agents as possible upon 

 it ; for this reason, that we are commonly greatly limited 

 as respects quantity of material, sometimes we may have 

 not more, nay even less than the w part of a grain to 

 operate upon, and it is clear, that if the exact nature of this 

 small quantity is only to be demonstrated by applying a 



