ON ARSENIC 107 



small quantity of arsenic, and that only in proportion to the 

 water contained in the acid ; the fuming nitrous acid dissolves 

 still less; but muriatic acid has a strong attraction for 

 arsenic, and the less water it contains the more it dissolves 

 and carries over into the receiver. The above-mentioned 

 quantity of muriatic acid is necessary, in order to keep the 

 arsenic dissolved with the aid of heat. Now, if to such a 

 solution nitrous acid be added, the arsenic will be calcined, 

 because its phlogiston is taken away by that acid, as 

 sufficiently appears from the red elastic vapours ; whence 

 likewise the attraction of the muriatic acid, for the now 

 dephlogisticated arsenic is diminished, so that it is capable of 

 dissolving more arsenic. Aqua regia might be poured upon 

 arsenic at first, but then the great effervescence carries the 

 arsenic up to the surface, and thus prevents it from being 

 perfectly attacked by the menstruum. After all the acid 

 has been distilled over, the fire ought to be increased, in 

 order, if there should be any aqua regia remaining in the 

 mass, to expel it entirely ; the remaining acid weighs nearly 

 as much as the arsenic employed for the experiment. One 

 would hardly believe that it was an acid, because it has no 

 taste ; but after some days it grows moist in the air, 

 and at last deliquesces, and then it has the appearance of 

 vitriolic acid. As the deliquescency of this acid is very 

 slow, I dissolve it in a certain quantity of water, when 

 a small quantity of white powder remains undissolved, 

 which comes from the retort, which is found much corroded 

 after the process, and is therefore nothing but siliceous 

 powder. This powder ought to be carefully separated from 

 the acid, which may be effected by filtration ; and in order to 

 prevent the glue of the blotting paper from mixing with the 

 acid, which might lead to a different result, the paper ought 

 to be, as I said above, previously lixiviated with hot water. 



