NITRIC ACID. 



be made to fit tight by grinding-, us any 

 late is liable to contaminate the product. 



As this acid still holds in solution more 

 or less nitrous gas, it is not, in fact, nitric 

 acid, but a kind of nitrous: it is therefore 

 necessary to put it into a retort, to which 

 a receiver is added, the two vessels not 

 being luted, but merely-joined by paper; 

 and to apply a very gentle heat for several 

 hours, changing the receiver as soon as it 

 is filled with red vapours. The nitrous 

 gas will thus be expelled, and the nitric 

 acid will remain in the retort, as limpid 

 and colourless as water. It should be 

 kept in a bottle secluded from the light, 

 otherwise it will lose part of its oxygen. 



The strongest acid that Mr. Kirwan 

 could procure at 60 was 1.5543, which 

 by his calculation contained .7354 of real 

 acid ; but llouelle professes to have ob- 

 tained it of 1.583. It is observable, that, 

 on comparing the tables of Kirwan and 

 Davy, the aeriform acid appears to contain 

 a considerable portion of water more than 

 that which is combined with soda to form 

 the nitrate. 



Nitric acid should be of the specific 

 gravity of 1.5, or a little more, and co- 

 lourless. It boils at 248, and may be dis- 

 tilled without any essential alteration. 

 Exposed to the air it absorbs moisture. 

 If two parts be suddenly diluted with one 

 of water, the temperature will rise to 

 about 112 ; but the addition of more wa- 

 ter to this diluted acid will lower its tem- 

 perature. It retains its oxygen with little 

 force, so that it is decomposed by all com- 

 bustible bodies. Brought into contact 

 with hrydogen gas at a high temperature, 

 a violent detonation ensues, so that this 

 must not be done without great caution. 

 It inflames volatile oils, such as those of 

 turpentine and cloves, when suddenly 

 poured on them : but, to perform this ex- 

 periment with safety, the acid must be 

 poured out of a bottle tied to the end of 

 a long stick, otherwise the operator's 

 face and eyes will be greatly endangered. 

 If it be poured on perfectly dry charcoal 

 powder, it excites combustion, with the 

 emission of copious fumes. By boiling it 

 with sulphur it is decomposed, and its 

 oxygen, uniting with the sulphur, forms 

 sulphuric acid. Chemists in general agree, 

 that it acts very powerfully^on almost all 

 the metals : but Baume has asserted, that 

 it will not dissolve tin ; and Dr. Wood- 

 house of Pennsylvania affirms, that in a 

 concentrated and pure state it acts 

 all on silver, copper, or tin, though 

 : io addition of a little water its ac- 

 tion on them is very powerful. He does 



not mention the specific gravity of thi* 

 acid : he only says, that it was prepared 

 by first expelling the water of crystalliza- 

 tion from nitre by heat, and then decom- 

 posing this nitre by means of strong sul- 

 phuric acid. 



The nitric acid is of considerable use 

 in the arts. It is employed for etching 

 on copper ; as a solvent of tin to form 

 with that metal a mordant for some of the 

 finest dyes ; in metallurgy and assay ing ; 

 in various chemical processes, on account 

 of the facility with which it parts with 

 oxygen and dissolves metals ; in medicine 

 as a tonic, and as a substitute for mercurial 

 preparations in siphylis and affections of 

 the liver; as also in the form of vapour, 

 to destroy contagion. For the purposes 

 of the arts it is commonly used in a di- 

 luted state, and contaminated with the 

 sulphuric and muriatic acids, by the name 

 cf aqua fortis. This is generally prepared 

 by mixing common nitre with an equal 

 weight of sulphate of iron, and half its 

 weight of the same sulphate calcined, and 

 distilling the mixture : or by mixing nitre 

 with twice its weight of dry powdered 

 clay, and distilling in a reverberatory fur- 

 nace. Two kinds are found in the shops, 

 one called double aqua forlis, which is 

 about half the strength of nitric acid ; the 

 other simply aqua fortis, which is half the 

 strength of the double. 



A compound made by mixing two parts 

 of the nitric acid with one of muriatic, 

 known formerly by the name of aqua re- 

 gia, and now by that of nitro-muriatic 

 acid, has the property of dissolving gold 

 and pkttina. On mixing the two acids, 

 heat is given out, an effervescence takes 

 place, oxygenated muriatic acid gas is 

 evolved, and the mixture acquirts an 

 orange colour. This is likewise made by 

 adding gradually to an ounce of powder- 

 ed muriate of ammonia, four ounces of 

 double aqua fortis, and keeping 1 the mix- 

 ture in a sand-heat till the salt is dissolved; 

 taking care to avoid the fumes, as the 

 vessel must be left open : or by distilling 

 nitric acid with an equal weight, or rather 

 more, of common salt. 



With the different bases the nitric acid 

 forms nitrates. 



The nitrate of barytes, when perfectly 

 pure, is in regular" octacdral crystals, 

 though it is sometimes obtained in small 

 shining scales. It may be prepared by 

 uniting barytes directly with nitric acid, 

 or by decomposing the carbonate of sul- 

 phuret of barytes with this acid. Ex- 

 posed to heat it decrepitates, and at length 

 gives out its acid, which is decomposed^. 



