424 NOYAU 



volume. Another compound of chlorine and binoxide of nitrogen always appears 

 simultaneously with this in variable proportions. Its composition is NO ! C1 (WOC1), 

 and may be represented as nitrous acid, NO 3 , in which one atom of oxygen has been 

 replaced by its equivalent of chlorine. It is a vaporous liquid, possessing similar 

 properties to the other, but having a much greater vapour-density. 



The theoretical vapour-density of the chloro-nitric acid is r74> and that of the 

 chloro-nitrous acid 2'269. 



The vapours of both these compounds are decomposed, when conducted into water, 

 into hydrochloric acid and hyponitric acid or nitrous acid. They are also decom- 

 posed by mercury ; the chlorine combining with the metal, leaving pure binoxide of 

 nitrogen. 



Various proportions of nitric and hydrochloric acids are used in making aqua regia; 

 sometimes two or three parts, and sometimes six parts of hydrochloric acid to one part 

 of nitric acid ; and occasionally chloride of ammonium, instead of hydrochloric acid, 

 is added to nitric acid for particular purposes, as for making a solution of tin for the 

 dyers. An aqua regia may also be prepared by dissolving nitre in hydrochloric 

 acid. 



NITROUS ACID (NO 3 [W 2 O S ] ; equivalent, 38), is obtained by mixing four 

 measures of binoxide of nitrogen with one measure of oxygen ; they unite and form an 

 orange-red vapour, which, when exposed to a temperature of Fahr., condenses to a 

 thin mobile green liquid. It is decomposed by water, and is converted into nitric acid 

 and binoxide of nitrogen. 



3NO S + HO =HNO" + 2N0 2 (3KT 2 O 3 + H 2 O = 2HNO 3 + 2N 2 O 2 ). 



On this account it cannot be made to unite directly with metallic oxides ; the salts 

 of this acid are therefore obtained by an indirect process. Nitrate of potash, when 

 exposed to a high temperature, is decomposed, losing oxygen and becoming nitrate of 

 potash ; some caustic potash is also formed at the same time. To obtain it pure, this 

 is dissolved in water, and while boiling we had nitrate of silver, when we obtain first 

 of all a dark precipitate of oxide of silver, caused by the caustic potash ; which is 

 separated by a filter, and on cooling the liquid the nitrate of silver crystallises in 

 white needles, which may be purified by recrystallisation. From this salt the pure 

 nitrites may be obtained ; for instance, by adding to a solution of nitrite of silver 

 chloride of potassium we obtain the potash salt. 



Hyponitric Acid (NO 4 [N 2 O 4 ] ; equivalent, 46), is best procured by distilling, in a 

 coated glass retort, perfectly dry nitrate of lead. Hyponitric acid and oxygen pass 

 over into a receiver, surrounded with a freezing mixture ; the former condenses into 

 a liquid, while the oxygen passes off by the safety tube, and only oxide of lead 

 remains in the retort. This hyponitric acid or peroxide of nitrogen is a liquid, 

 colourless at 4 Fahr., but is at higher temperatures yellow and orange. It boils at 

 82 Fahr., gives off a dark red vapour, which becomes almost black when further 

 heated. A beautiful lead-salt of this acid has been discovered by M. Peligot. It is 

 formed by digesting a dilute solution of nitrate of lead with finely-divided metallic 

 lead at a temperature between 150 and 170 Fahr. See "Watts's ' Dictionary of 

 Chemistry.' 



NOBLE METALS. This was a division formerly adopted : it included those 

 metals which can be separated from oxygen by heat alone ; these are mercury, silver, 

 gold, platinum, palladium, rhodium, iridium, and osmium. 



XTOXXiS is the term used in the worsted trade for the short wool taken from tho 

 long staple by the process of combing, and is used to give apparent solidity or 

 thickness in the handling of cloth. 



NON-INFLAMMABLE FABRICS. Bee MUSLIN, non-inflammable. 



NOPAL is the Mexican name of the plant Cactus opuntia, upon which the cochineal 

 insect breeds. 



NORDHAUSEN ACID. Brown fuming sulphuric acid, used as a solvent of 

 indigo. See SULPHTJHIC ACID. 



NORIUIVT. The name of a metal which was thought to be always associated with 

 zirconium. It is, however, doubtful if it has any existence. 



NOTATION. In 1815, Berzolius, the chemist, proposed a system of notation in 

 which the use of initial letters was adopted to signify tho elementary bodies. This 

 idea has been continued and improved upon by modern chemists. Tho modern 

 system of notation endeavours to express by initial letters, figures, and a few simple 

 signs, not merely the elements, but their combinations. The modern system of 

 notation will be best studied in Watts's 'Dictionary of Chemistry.' Sec FOKMUL.S:, 

 CHEMICAL. 



NOYAU. A liquor flavoured with the kernels of peach-stones. An inferior kind 

 is flavoured with the essential oil of bitter almonds. 



