418 



NITRIC ACID 



gases, confined over water or an alkaline solution, has a series of electrical explo- 

 sions passed through it. In this way the salubrious atmosphere may be converted 

 into corrosive aquafortis. When a little hydrogen is introduced into the mixed gases, 

 standing over water, the chemical agency of the electricity becomes more intense, and 

 the acid is more rapidly formed from its elements, with the production of some 

 nitrate of ammonia. The formula of the hydrated acid is HO.NO* (HNO S ) ; its equi- 

 valent being 54. 



Nitric acid is usually made on the small scale by distilling, with the heat of a sand- 

 bath, a mixture of 3 parts of pure nitre, and 2 parts of strong sulphuric acid, in a 

 large glass retort, connected by a long glass tube with a globular receiver surrounded 

 by cold water. By a well-regulated distillation, a pure acid, of specific gravity 1 - 500 

 may be thus obtained, amounting in weight to about two-thirds of the nitre employed. 

 To obtain the whole nitric acid equal weights of nitre and concentrated sulphuric 

 acid may be taken ; in which case but a moderate heat need be applied to the retort. 

 The residuum will be bisulphate of potash. When only the single equivalent propor- 

 tion of sulphuric acid is used, namely 48 parts for 100 of nitre, a much higher heat is 

 required to complete the distillation, whereby more or less of the nitric acid is decom- 

 posed, while a compact neutral sulphate of potash is left in the retort, very difficult to 

 remove by solution in water, and therefore apt to destroy the vessel. 



Aquafortis is manufactured upon the great scale in iron pots or cylinders of the 

 same construction as are described under HYDBOCHLOBIC ACID. The more concen- 

 trated the sulphuric acid is, the less corrosively will it act upon the metal : and it is 

 commonly used in the proportion of one part by weight to two of nitre. 



Commercial aquafortis is very generally contaminated with sulphuric and muriatic 

 acids, as also with alkaline sulphates and muriates. The quantity of these salts may 

 be readily ascertained by evaporating in a glass capsule a given weight of the aqua- 

 fortis ; while that of the muriatic acid may be determined by nitrate of silver ; and of 

 sulphuric acid, by nitrate of baryta. Aquafortis may be purified, in a great measure, 

 by redistillation at a gentle heat ; rejecting the first liquid which comes over, as it 

 contains the chlorine impregnation ; receiving the middle portion as genuine nitric 

 acid ; and leaving a residuum in the retort, as being contaminated witli sulphuric acid. 



Since nitrate of soda has been so abundantly imported into Europe from Peru, it has 

 been employed by many manufacturers in preference to nitre for the extraction of nitric 

 acid, because it is cheaper, and because the residuum of the distillation, being sulphate 



A Table of Nitric Add, by Dr. Ure, 



