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been recommended still more recently than Marsh's test — 

 I mean Keinsch's test. This test depends upon the fact, 

 that white arsenic and certain preparations of that substance, 

 when boiled in water with bright copper and muriatic acid, 

 give a coating of metallic, arsenic to the copper, which 

 coating, when heated in a tube, yields characteristic crystals 

 of arsenious acid by sublimation. This test is one which 

 enables us to pronounce with certainty as to the presence 

 of arsenic by an estimation of only three of its properties. 

 " There is no substance in nature with which we are 

 acquainted, capable of causing a bluish stain upon copper, 

 or in some cases, where the quantity is more considerable, 

 an iron gray coating, and which, when heated in a glass 

 tube by a spirit lamp, gives a sublimate of colourless resplen- 

 dant octohedral crystals, soluble in water and precipitable 

 yellow by ammoniacal nitrate of silver, the precipitate 

 becoming of a dirty red colour by exposure to light, except- 

 ing Arsenic." 



It may be observed, that when the quantity operated 

 upon is very small, the white sublimate does not manifest a 

 distinct crystalline form, but even then it will in most 

 cases allow of the peculiar reaction of the ammoniacal 

 nitrate of silver. Two only of the properties above men- 

 tioned cannot be considered as sufficient for the demonstra- 

 tion, because antimony and quicksilver can be deposited 

 upon copper under like circumstances. And with regard to 

 the former metal, — when in small quantity, the stain it 

 produces upon copper is very like that resulting from arse- 

 nic. In no case, however, as far as my own experiments 

 go, can any decided well-developed white crust be obtained, 

 from an antimonial stain. You may, indeed, by the appli- 

 cation of a strong heat produce a small white deposit above 

 that part of the tube where the coated copper has beenplaced. 

 This spurious sublimate, however, is not soluble in water, and 



