132 ESSAY VI. 



iron plate, heated nearly red hot, in a dark place, it burns 

 with a blue flame and a white arsenical smoke, and leaves 

 a white powder behind; it is consequently^for the most part 

 regulus of arsenic. The effervescence soon ceases, because 

 each particle of zinc is surrounded with the regulus, which 

 hinders the acid from having any effect upon it. (6) In 

 order to ascertain what kind of air it is which rises during 

 the solution, I tied an empty bladder to the phial in which 

 the mass was contained. The air which I obtained had the 

 following properties : (1) It would not unite with water, nor 

 did it precipitate lime-water. (2) Mixed in a glass vessel 

 with two-thirds of common air, it was not absorbed. (3) 

 When a burning candle was brought to the mouth of the 

 vessel, the air in the vessel was inflamed with detonation ; 

 the flame took its direction towards the hand, which was 

 thereby coloured brown : the matter that produced this 

 colour proved to be regulus of arsenic, and left a disagreeable 

 arsenical smell behind ; the internal surface of the vessel too 

 was covered with a brown pellicle. The air, therefore, which 

 holds the regulus of arsenic in solution is of the inflammable 

 kind, (c) One part of filings of zinc was mixed with two 

 parts of dry and finely powdered acid of arsenic and distilled. 

 When the bottom of the retort began to be red hot, a violent 

 inflammation, accompanied with a very bright light, took 

 place in the retort, which burst with an explosion. In the 

 neck were found regulus of arsenic and flowers of zinc, (d) 

 Zinc dissolved in mineral acids is not precipitated by the 

 acid of arsenic, but its solution in vinegar is precipitated. 

 Neutral arsenical salts decompose all the solutions, and a 

 white precipitate is obtained, which, when well edulcorated , 

 fuses in a retort on the application of a strong heat, 

 and, when mixed with charcoal powder, yields regulus of 

 arsenic. 



