180 METALLOIDS. 



from arsenious acid, by heating with a 

 large proportion of carbon, as in the 

 Case of phosphorus, before described. 

 Beside mixing with carbon, it is best, 

 also, to cover with the same material, 

 and heat from above, downwards. The metal passes 

 off as vapor, and condenses in the cooler part of the 

 tube, or other vessel in which the experiment is per- 

 formed, as a steel grey incrustation. 



ARSENIOUS ACID. 



441. RATSBANE. The ordinary white 



What are the , J 



properties of arsenic of the shops, also known as rats- 

 arscnious bane, is a white and nearly insoluble sub- 

 stance, possessed of a slightly sweetish 

 taste. It is not properly arsenic, but arsenious acid. It 

 contains three atoms of oxygen, to one of metal. Al- 

 though sweet, it is called an acid, because it possesses 

 the chemical characteristic of an acid, viz : the ca- 

 pacity of uniting with bases to form salts. 

 Howisitpre- 442. PREPARATION. Arsenious acid is 

 pared? prepared from metallic sulphurets, many of 



which contain a certain proportion of arsenic, by 

 roasting in the air, and thus burning out their arsenic, in 

 the form of arsenious acid. The fumes are condensed 

 in high chimneys, from which the incrustation of the 

 solid acid is afterward removed. Mispickel, which is 

 a double sulphuret of iron and arsenic, and certain 

 ores of nickel and cobalt, are much employed for the 

 production of arsenious acid. 



