MINERAL OR INORGANIC POISONS 



ARSENIC. 



Forms and Occuprence. — Arsenic is extremely widely dif- 

 fused in nature, the chief sources being the yellow sulphides, 

 orpiment and realgar, and arsenical pyrites, a double sulphide 

 of iron and arsenic. It is, further, present in most natural 

 metallic sulphides. When these are roasted or smelted, 

 volatile arsenious oxide passes off and condenses in the 

 flues, but in part may find its way into the air, into 

 streams, on to the soil, and into herbage. When sulphuric 

 acid is made from sulphur dioxide derived from pyrites, 

 arsenic may be present in the acid, and may pass thence 

 into substances prepared by its means; as, for example, 

 into glucose, and eventually beer, and thus may give rise, 

 as in the Manchester epidemic of 1900, to extensive arsenical 

 poisoning. From smelting furnaces and the refuse of dis- 

 used workings, arsenic may pass into vegetation, or into 

 streams, as in the instance remarked by Dunstan of 

 Liskeard under Lead (q.v.). 



Arsenic enters into the composition of many everyday 

 substances, and is used in certain preparations — e.g., of 

 some of the aniline dyes. 



The most poisonous compounds of arsenic are the hydride 

 and certain organic compounds, such as those of dimethyl 

 arsine {e.g., cacodyl oxide [(CH3)2As]20, and the chloride 

 (CH3)2AsCl), but poisoning by these is unlikely outside 

 the laboratory. There does not appear to be much solid 

 foundation for the widespread idea that the hydride is 

 slowly generated by the action of fermenting paste on wall- 



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