464 NITRATES. 



Antiseptic properties of nitric oxide. Nitric oxide is thought to 

 be an antiseptic. Dr. Priestly says that it renders bladders in which 

 it has been kept imputresible. 



He tried many experiments on the preservation of meats by this 

 gas. It generally saved them from putrefaction, and even stopped 

 the progress of putrefaction already begun, but meats preserved in it 

 had always a bad taste. 



NITRATES OF ALKALIES. 



A highly important and interesting class of salts ; the principal ni- 

 trate, that of potash, having been known from remote antiquity. 



GENERAL CHARACTERS. 



1. Soluble, and crystallizable by the cooling of the hot solution. 



2. At a red heat, detonating with combustibles. 



3. Decomposed by sulphuric acid, nitric or nitrous acid being 

 evolved. 



4. Producing chlorine and dissolving gold leaf, when decomposed 

 by muriatic acid. 



5. Totally decomposed by heat, and (nitrate of ammonia except- 

 ed,) affording oxygen, mixed more or less with other gases. 



NITRATE OF POTASSA. 



1. SYNONYMES. 



Nitre salt petre. The nitre of the scriptures is carbonate of 

 soda.* 



2. HISTORY. Known to the Romans; to the Chinese, from re- 

 mote antiquity, and to the earliest chemists. 



(b.) Roger Bacon, in the thirteenth century, mentions it under 

 the name of nitre. Although the subject of experiments for many 

 centuries, Hooke and Mayhow, in the 17th century, having come 

 very near discovering its real character, and Hales, in the beginning 

 of the 18th, having extracted from it by heat, a great quantity of gas, 

 its nature was not understood till the era of the modern chemistry. 



3. PREPARATION. By saturating pure nitric acid with potassa, 

 or its carbonate, and then evaporating and crystallizing. But it is 

 not necessary to prepare it, as it is found abundantly in commerce, 

 and sufficiently pure for most purposes in chemistry. 



4. PHYSICAL PROPERTIES. 



(a.) The most common form of the crystals is that of the six 

 sided prism, with a wedge-shaped termination. 



* The word nitre is mentioned only twice in the sacred writings, viz. Prov. xxv, 

 20. and Jeremiah, ii, 22. It has been already mentioned (p. 251, Soda,) that in the 

 first intsance, allusion is made to an effervescence produced by an acid, and in the 

 second to a detergent, or cleansing property ; neither of which belong to nitrate 

 of potash, but both of them to the carbonate of soda the natron of the Greeks 

 the nitrum of the Latins. With this understanding, the allusions are appropriate 

 and beautiful ; otherwise unmeaning ; and this use is sustained by Pliny, and other 

 ancient authors. The carbonate of soda is used largely in Great Britain in washing. 



