54 ESSAY V. 



in number as long as there was any liquid remaining. Their 

 taste was very much like the taste of vitriolated magnesia 

 (Epsorn salt). Mr. Westfeld pretends that they are alum ; 

 but they resemble alum in no other respect, except in con- 

 taining the same acid. 



SECTION III. EFFECTS OF PHLOGISTICATED VITRIOLIC ACID. 



I dipped, according to Stahl's prescription, some rags 

 into a solution of fixed alkali of tartar, and, after saturating 

 them with the acid of burning brimstone, I put them into a 

 retort, poured some acid of tartar upon them, and luted on a 

 receiver which contained water and levigated manganese. 

 The retort was put into a sand-bath, and, after a warm 

 digestion of one day, the liquid of the receiver had become 

 as clear as water, and a little fine powder was precipitated 

 to the bottom, consisting for the most part of siliceous earth. 



SECTION IV, EFFECTS OF PURE NITROUS AciD. 1 



(a) I poured 1 oz. of pure colourless nitrous acid upon 

 2 drms. of levigated manganese. After this compound had 

 been kept in a heat of digestion for several days, the 

 menstruum was found to have lost nothing of its acidity, 

 nor was there any appearance of effervescence. I abstracted 

 the acid by distillation, poured the distilled liquor again 

 upon the residuum, and distilled it over again, but very 

 slowly. The residuum was but very little dissolved. I 

 again poured the distilled acid upon it, and afterwards added 



1 Under the name of pure nitrous acid I understand colourless nitrous 

 acid the fuming acid distilled in a gentle heat, till the mass remaining 

 in the retort appears colourless, and yields white vapours when heated. 

 Nitrous acid of this quality must be preserved in a glass vessel, furnished 

 with a ground stopple, in a dark room. 



