146 JUNIOR GRADE SCIENCE 



Properties of hydrochloric acid solution. When a strong solution 

 of hydrochloric acid gas is heated, the gas is at first given off, but it is 

 found that further heating does not drive off the whole of the acid, which 

 continues to be given off till the last drop of liquid has evaporated. 

 On the other hand, a very dilute solution, on being heated, becomes 

 more concentrated up to a certain point, beyond which no further 

 concentration can be effected. 



The solution has a sour taste. It causes effervescence with washing 

 soda, a gas being given off. Chalk dissolves in it with effervescence, 

 leaving a clear solution. It has no action on copper, but gives off an 

 inflammable gas with zinc, iron and magnesium, which dissolve in it. 



70. NITRIC ACID. 



i. Preparation of nitric acid. Into a stoppered retort, such as is used 

 in the distillation of water, place 30 or 40 grams of small ci -\sial-* of 

 potassium nitrate (also known as nitre). Using a funnel, carefully introduce 

 enough strong sulphuric acid to cover the nitre. Replace the stopper. 

 Place the retort on a stand as shown in Fig. 86, and insert its neck in that 

 of a flask which is continually kept cool by water, just as in the distillation 

 of water. Gently heat the retort. Brown fumes are given off in abundant;-. 

 and soon drops of a liuht yellow liquid are seen to fall into the receiving 

 flask. When enough nitric acid has distilled over, remove the laboratory 

 burner, and while the materials in the retort are still liquid, pour them, after 

 removing the stopper, from the retort into an evaporating dish. 



ii. Repeat the experiments performed with sulphuric acid, using nitric 

 acid instead. 



Nitric acid. One of the most important compounds with which 

 chemists are familiar is an acid which has long been known under 

 the name of aqua fortis. It can be prepared by synthesis from its 

 constituents. It is generally prepared by distilling a nitrate with 

 strong sulphuric acid. Either potassium nitrate, which is more 

 familiarly known as " saltpetre " or " nitre," or sodium nitrate, also 

 called "Chili saltpetre," is generally employed. The latter salt is 

 the cheaper, and in addition yields a larger amount of nitric acid for a 

 given expenditure of sulphuric acid, so that it is more commonly 

 employed than ordinary saltpetre in the manufacture of nitric acid. 



Pure nitric acid is colourless. When heated it gives off brown fumes. 

 This happens slowly when the pure acid is placed in sunlight, a fact 

 which accounts for the brown fumes above the liquid in bottles of 

 nitric acid which have been kept for some time. 



When diluted it has a sour taste, and like the other acids examined, 

 it causes washing soda to effervesce, giving off a gas, and it turn* litmus 



