NIT 



NIT 



put into an iron spoon, and placed upon 

 burning coals, or held above the flame of 

 u candle, it gradually blackens, and at 

 last melts. At that instant it explodes 

 with a very violent report, and a strong 

 impression is made upon the bottom of 

 the spoon, as if it had been pressed 

 down very violently. This sudden and 

 violent combustion is occasioned by the 

 rapid action of the .sulphur on the nitre. 

 By the application of the heat, the sul- 

 phur and potash form a sulphuret, which 

 is combustible at a lower heat probably 

 than even sulphur. Sulphurated hydro- 

 gen gasj azotic gas, and perhaps also sul- 

 phurous acid gas, are disengaged almost 

 instantaneously. It is to the sudden ac- 

 tion of these on the surrounding air that 

 the report is to be ascribed. Its loudness 

 evidently depends upon the combustion 

 of the whole powder at the same instant, 

 which is secured by the previous fusion 

 that it undergoes ; whereas the grains of 

 gunpowder burn in succession. A mix- 

 ture of equal parts of tartar and nitre, 

 deflagrated in a crucible, is known by the 

 name of white flux. It is merely a mix- 

 ture of carbonate of potash, with some 

 pure potash. When two parts of tartar, 

 nnd one of nitre, are riefiagvated in. this 

 manner, the residuum is called black flux, 

 .from its colour. It is merely a mixture of 

 charcoal and carbonate of po! ash, 



Nkre is much used in medicine, in fe- 

 vers as a cooling remedy, and as a diu- 

 retic in urinary affections. It is employ- 

 ed also in many arts, as in dying- ; and in 

 domestic economy, for the preservation 

 of animal substances used for food. To 

 these substances it imparts a red colour. 

 See NITROUS acid ; also GUNTOWOEB. 



NITRIC acid. The two principal con- 

 stituent parts of our atmosphere, when in 

 certain proportions, are capable, under 

 particular circumstances, of combining 

 chemically, into one of the most powerful 

 acids, the nitric, which consists, according 

 to Mr. Davy, of 70.5 of oxygen, and 29.5 

 of azote, or nitrogen. If these gases be 

 mixed in this proportion in a glass tube, 

 about a line in diameter, over mercury, 

 and a series of electric shocks be passed 

 through them for some hours, they will 

 form nitric acid ; or, if a solution of pot- 

 ash be present with them, nitrate of pot- 

 ash will be obtained. The constitution of 

 this acid may be further proved, analyti- 

 cally, by driving it through a red-hot por- 

 celain tube, as thus it will be decomposed 

 into oxygen and nitrogen gases. For all 

 practical purposes, however, the nitric 

 acid is obtained from nitrate of potash, 



VOL, V, 



from which it is expelled by sulphuris 

 acid. 



Four parts of pure nitrate of potash, 

 coarsely powdered, are to be put into a 

 glass retort, and three parts of concen* 

 trated sulphuric acid cautiously added, 

 taking care to avoid the fumes- that arise, 

 which is best done by standing in a cur- 

 rent of air, to convey them up the chim* 

 ney. Join to the retort a tubulated re- 

 ceiver of large capacity, with an adopter 

 interposed, and lute the junctures with a 

 mixture of pipe-clay, sifted sand, and cut. 

 tow. In the tubuiure fix with fat lute a 

 g'lass tube terminating in another large 

 receiver, in which is a small quantity of* 

 water; and, if you wish to collect the 

 gaseous products, let a bent glass tube 

 from this receiver communicate with a 

 pneumatic trough. Apply heat to the re- 

 ceiver by means of a sand bath. The first 

 product that passes into the receiver is 

 generally red and fuming ; but the ap- 

 pearances gradually diminish, till the acid 

 comes over pale, and even colourless, if 

 the materials used were clean. After 

 this it p.garn becomes more and more red 

 and fuming-, till the end cf Ihe operation; 

 and the whole mingled together will be 

 of a yellow or orange colour. 



In the large way, and for the purposes 

 of the arts, extremely thick cast iron or 

 eai-tben reto Ijy employed, to 



which an eanhen head 'is adapted, and 

 connected with a range of proper con- 

 densers. The strongtli of the acid too is 

 varied, by putting more or less water in 

 the receivers. The nitric acid thus made 

 generally contains sulphuric acid, and also 

 muriatic, from the impurity of the nitrate 

 employed. If the former, a solution of 

 nitrate of barytes will occasion a uhito 

 precipitate: if the latter, nitrate of silver 

 will render it milk}'. The sulphuric acid 

 may be separated by a second distillation 

 from very pure nitre, equal in weight to 

 an eighth of that originally employed ; or 

 by precipitating with nitrate of barytes, 

 decanting the clear liquid, and distilling 

 J 1 .. The muriatic acid may be separated 

 by proceeding in the same way with ni- 

 trate of silver, or with litharge, decanting 

 the clear liquor, and redistilling it, leav- 

 ing an eighth or tenth part in the retort. 

 The acid for the last process should be 

 condensed as much as possible, and the 

 redistillation conducted very slowly ; and 

 if it be stopped when half is come over ? 

 beautiful crystals of muriate of lead will 

 be obtained on cooling the remainder, if 

 litharge be used, as M. Steinacher informs 

 us ; who also adds, that the vessels sb-croU! 



B 



