ON ARSENIC 11 



the retort grew red hot, when the mass began to flow and 

 to boil. This degree of heat was continued till the ebullition 

 was over, when I found that some fuming muriatic acid had 

 gone over into the receiver. After the residuum in the 

 retort was cool, I dissolved it in water ; the solution being 

 filtered and evaporated, yielded crystals of common salt ; 

 but there remained a thick mass, which changed the colour 

 of lacmus to red, and would not crystallise. In Sec. vn. it 

 has been observed that mineral alkali, supersaturated with 

 acid of arsenic, will not crystallise ; wherefore I diluted this 

 magma with distilled water, adding finely powdered chalk, 

 till the solution showed no more mark of acidity ; I then 

 filtered it. After evaporation in the open air, crystals were 

 obtained, perfectly agreeing with the neutral salt (Sec. VIL). 



SECTION XII. UPON SAL AMMONIAC. 



One part of sal ammoniac was distilled with three parts 

 of acid of arsenic. A portion of muriatic acid went over 

 with the water ; I then changed the receiver, and increased 

 the heat, when fuming muriatic acid came over, and the 

 mass entered into fusion. Immediately after this, the receiver 

 was filled with a white smoke, and a white powder was sub- 

 limed into the neck of the retort ; at last a pungent volatile 

 alkali passed over into the receiver ; and a residuum remained 

 in the retort, which was acid of arsenic. The powder sub- 

 limed into the neck of the retort was dissolved in water, 

 and the solution was filtered, when there remained a white 

 powder, which proved to be arsenic. The liquor which 

 passed through the filter contained sal ammoniac. 



I repeated the same experiment, applying only a bladder 

 instead of the receiver. When the heat became so strong 

 as to drive the white powder into the neck of the retort, 



