256 Dr. Fresenius on an improved Method for the 



Dr. Fresenius states the objection to the method of Reinsch 

 to be : — 1. That it does not admit of the detection of arsenic 

 in every form in which it may exist. 2. It does not aid the 

 detection of other poisons. 3. It contaminates the substances 

 under examination with copper. 4. Its success in precipi- 

 tating the arsenic is impeded or altogether prevented by the 

 presence of many substances, nitrates, mercury and other 

 metalHc compounds. 5. Almost insurmountable difficulties 

 in determining the arsenic quantitatively are attached to this 

 method. 



The method of Marsh presents these difficulties : — 1 . It does 

 not admit of the separation of the arsenic under every form 

 in which it may occur. 2. It contributes to the contamination 

 of the substance under examination with zinc and other me- 

 tals. 3. The danger of mistaking antimony mirrors for ar- 

 senic. 4. Mirrors are either not formed at all, or their 

 brilliancy is prevented, and the proof of the existence of 

 arsenic rendered doubtful by the presence of water, of organic 

 substances, and atmospheric air. 



The method of investigating the body in cases of suspected 

 poisoning, for the presence of arsenic, which we propose, is as 

 follows : — 



A. Decoloration and Solution. 



The substances intended for examination are, if they con- 

 sist of solid and coherent lumps, reduced into small pieces, 

 and under all circumstances carefully intermixed. Two-thirds 

 of the whole mixture are then put into a large porcelain 

 basin, the remainder is kept in a well-closed vessel for unfore- 

 seen contingencies. The mixture in the porcelain basin is 

 then drenched with an amount of fine concentrated hydro- 

 chloric acid, either equal or superior to the weight of the dry 

 substance it contains, and with as much water as will give the 

 consistence of a thin pap to the whole. The basin is then 

 heated in the water-bath, and chlorate of potash in portions 

 of about half a drachm added to the mixture at intervals of 

 about five minutes, and until the contents of the basin has 

 assumed a bright yellow, perfectly homogeneous and thin 

 liquid appearance. When this point is attained, about 2 

 drachms more of chlorate of potash is added to the mixture, 

 and the basin is removed from the water-bath. When com- 

 pletely cool, the contents are placed upon white filtering paper 

 or upon a linen filtering cloth, and the fluid allowed to run 

 off: the residue is washed with hot water until the liquid run- 

 ning off no longer manifests any acid reaction : the water 

 used in this washing operation is added to the filtrate. The 



