NITRIC ACID. 295 



tin and iron by the acid very slightly diluted. Poured upon red 

 hot charcoal, it causes a brilliant combustion. When mixed 

 with a fourth of its bulk of sulphuric acid, and thrown upon a 

 few drops of oil of turpentine, it occasions an explosive combus- 

 tion of the oil. Sulphur digested in nitric acid at the boiling 

 point is raised to its highest degree of oxidation and becomes 

 sulphuric acid ; iodine is also converted by it into iodic acid. 

 Most vegetable and animal substances are converted by dilute 

 nitric acid into oxalic, malic and carbonic acids. It stains the 

 cuticle and nails of a yellow colour, and has the same effect 

 upon wool ; the orange patterns upon woollen table covers are 

 produced by means of it. In the undiluted state it forms a 

 powerful cautery. 



In acting upon the less oxidable metals, such as copper and 

 mercury, nitric acid is itself decomposed, and nitric oxide gas 

 produced, which comes off with effervescence. Palladium and 

 silver when they are dissolved by the acid in the cold, produce 

 nitrous acid in the liquor and evolve no gas, but this is very 

 unusual in the solution of rnetals by nitric acid. Those metals, 

 such as zinc, which are dissolved in diluted acids with the evo- 

 lution of hydrogen, act in two ways upon nitric acid ; sometimes 

 they decompose it, so as to disengage a mixture of peroxide of 

 nitrogen and nitric oxide, and at other times they decompose 

 both water and nitric acid at once, in such proportions that the 

 hydrogen of the water combines with the nitrogen of the acid 

 to form ammonia, which last combines with another portion of 

 acid, and is retained in the liquor as nitrate of ammonia. The 

 protoxide of nitrogen is also evolved when zinc is dissolved in 

 very feeble nitric acid, which may arise from the action of hy- 

 drogen upon nitric oxide. Nitric acid, in its highest state of 

 concentration, exerts no violent action upon certain organic 

 substances, such as lignin or woody fibre and starch, for a short 

 time, but unites with them and forms singular compounds. A 

 proper acid for such experiments is procured with most certain- 

 ty by distilling 100 parts of nitre, with no more than 60 parts of 

 the strongest oil of vitriol. If paper is soaked for one minute in 

 such an acid, and afterwards washed with water, it is found to 

 shrivel up a little and become nearly as tough as parchment, and 

 when dried to be remarkably inflammable, catching fire at so low 

 a temperature as 356, and burning without any nitrous odour. 

 (Pelouze.) 



