118 ESSAY VI. 



the bladder was distended. The air it contained is entirely 

 the same with that of which I spoke (Sec. vui. (e)). Hence it 

 follows that part of the arsenical acid has combined with 

 a portion of the phlogiston of the volatile alkali, and that 

 the arsenic sublimed into the neck of the receiver has been 

 thus produced. Hence, too, the bladder was necessarily filled 

 at the same instant with that air which arises from the 

 decomposition of volatile alkali. Heat expels the volatile 

 alkali from arsenical sal ammoniac (Sec. VIIT. (c)) ; and as 

 any acid converted into vapour, when it meets with volatile 

 alkali, always produces a smoke, it is evident why the bladder 

 at the end of the process was filled with it. 



SECTION XIII. VITRIOLATED LIME (GYPSUM), AND 

 SPATHUM PONDEROSUM. 



(a) One part of powdered gypsum was mixed with two 

 parts of dry acid of arsenic and exposed to a red heat, when 

 some vitriolic acid came over, with a strong smell of volatile 

 sulphureous acid, and the mass entered into fusion. After 

 the distillation was over, it had the appearance of a milky 

 glass, (b) Spathum ponderosum produced the same pheno- 

 mena, only the vitriolic acid was not expelled till the retort 

 melted. The residuum was a little reddish. See Sec. xx. 



SECTION XIV. UPON FLUOR MINERAL. 



One part of powdered fluor was mixed with four parts 

 of acid of arsenic and distilled, a little water being put into 

 the receiver. When the retort grew red hot, first a yellow, 

 and afterwards a red substance was sublimed. Volatile 

 sulphureous acid went over, but no acid of fluor. The 

 residuum, which was of a grey colour, was divided into two 



