BETECTION OF ARSENIC. 133 



the plates mixed with black flux, and surrounding it with a 

 circle of the flux ; the plates are then placed in contact, and 

 being bound together by iron wire are exposed to the heat of 

 a common fire for a few minutes, when cooled and opened, the 

 upper plate is found coated with a brilliant silvery alloy. The 

 objections to this process are, that charcoal gives an appear- 

 ance somewhat similar; oxide of tin is said to produce the 

 same appearance, but the most material objection, says Chris- 

 tison, is that it requires a quantity sufficient to try much better 

 tests ten times over. 



The galoanic circle of Mr. Fischer, of Breslau, is, as has 

 been said, an elegant mode, where the quantity of arsenic is 

 at our control, but is not sufficiently delicate. It requires 

 too long a time for its operation where the quantity of arsenic 

 in solution is very small, which affords an opportunity for the 

 fluid in the tube to pass out by exosmose. When successfully 

 applied, the effect is to reduce the metal upon the negative 

 wire within the tube, or else to throw it down in the form of 

 powder. The inventor says he could detect by this instru- 

 ment the tenth of a grain of arsenic, but not when it was dis- 

 solved in more than five hundred times its weight of water. 

 From all that lias been said, it will now, I trust, be evident 

 that the means are certainly within our power of detecting 

 arsenic under any circumstances, and however minute in 

 quantity. The objections or fallacies to which the tests are 

 liable, are confined respectively to each test, and are not com- 

 mon to them all, so that when all correspond in their results, 

 it is impossible to doubt their indications. The fallacies too, to 

 which they are liable, are owing in each to a different cause, 

 and hence, they can never all deceive, for it is scarcely possible 

 to conceive a case which shall combine every cause of embar- 

 rassment. The chief difficulty, and perhaps, one of the most 

 frequent occurrence is that poison is only suspected after a 

 period when it is almost impossible to collect any of the poi- 

 soned food, or whatever other medicine may have been used 

 for its administration. In such cases recourse must be had to 

 the disinterment of the sufferer, and search may be made in 

 the intestines for the poison. The investigations of Orfila and 

 others, induce us to believe that during the decomposition of 

 the animal structure, combinations may occur, which will 

 render the operation of ordinary tests, not only uncertain, 



