114 ESSAY VI. 



went over. It had the smell of volatile sulphureous acid ; 

 no arsenic was sublimed. (&) Vitriolated fossil alkali, or 

 Glauber's salt, was likewise decomposed, but seems not to 

 require so much heat as vitriolated vegetable alkali. 



SECTION X. NITRE. 



I distilled a mixture of one part of purified nitre and 

 three parts of acid of arsenic. As long as there remained 

 any humidity in the acid, pure water went over into the 

 receiver; but when the mass grew dry, nitrous acid rose, 

 and the matter in the retort flowed clear. When no more 

 acid came over with this degree of heat, I let the retort 

 cool. The nitrous acid I obtained was not so volatile 

 as that which is obtained from arsenic and nitre. The 

 residuum, dissolved in water and evaporated, yielded crystals, 

 perfectly agreeing with the neutral salt obtained by Macquer, 

 together with a little undecomposed nitre. 



Arsenic certainly could not decompose nitre, except by 

 the power of a double elective attraction, viz. in consequence 

 of the alkali of the nitre uniting with the acid of arsenic, 

 and the acid combining with the phlogiston of the arsenic, 

 by which this acid is rendered very volatile. If muriatic 

 acid had a greater affinity with phlogiston, arsenic would 

 likewise decompose common salt, as really happens with 

 cubic nitre. Macquer obtained no neutral salt in the 

 crucible, but alkali of nitre containing a little arsenic. I 

 have found that this salt may likewise be prepared in a 

 crucible. Let nitre be melted for this purpose in a crucible, 

 which is to be red hot only at the bottom, then let as much 

 as will stand on the point of a knife of powdered arsenic 

 be added, and, after the red vapours and effervescence are 

 over, as much more arsenic is to be added, and so on till 



