[ 26 ] [Book VI. 



CHAP. VI. 



NITROUS SALTS. 



GoOfOKin Niti't ; Phenomena attending its Deflagration with injlaniykc.bie 

 ^ubjlancesj Natural Htftory cf Nitre, "Cubic Nitres Union cf 

 nitrous Acid -ivito various Earths *>~-Niiroi<s Ammoniac* 



COMMON NITRE, or nitrat of pot-aih *, confitts 

 of the vegetable alkali and nitrous acid. Nitre 

 was unknown to the ancients ; the fubftance which 

 they diftinguiflied by that name was a foffil alkali, for 

 \ve are told by Pliny that it was detergent, and ufed 

 in making "glafs. It is uncertain when nitre was 

 difcovered, but we find it mentioned in the earlieft 

 chemical writers. Nitre melts in a very gentle heat, 

 and in a greater degree of heat totally evaporates. 

 Cold water diflblves one-fixth of its weight j and hot 

 water about its own weight of this fait. Its cryftals 

 are more regular than thofe of any other fait (being 

 prifms of fix fides) having very little water in their 

 compofhion, and therefore not liable to fpontaneous 

 evaporation. Its mod extraordinary property is its 

 deflagration with inflammable fubftances, which hap- 

 pens from the decompofition of its acid, by which a 

 large quantity of oxygenous gas is fet at liberty. To 

 the production of this air is owing the rapid combuf- 

 tion of mixtures of nitre and inflammable fubftances, 

 as evinced in f gunpowder. When nitre is melted 

 by itfelf, no particular effect takes place j but if 

 charcoal is added to it in its melted ftate, deflagration 



* Commonly known under the name of falt-petre. 

 f The reader will do well to confult what has been faid refpeft- 

 ing gunpowder in Book II, 



Or 



