NITEOGEN AND ITS OXIDES. 65 



the form of vapor. There it is condensed into the liquid 

 form. To produce this condensation the receiver is kept 

 cool by a stream of water flowing from the pipe, *, over 

 its surface, a netting being spread over it to distribute the 

 water evenly. As the water accumulates in the vessel, c c, 

 in which the receiver rests, the waste runs off by the pipe, I. 



72. Properties of Nitric Acid. This is a nearly colorless 

 fluid, intensely acid, and very corrosive. It stains the skin 

 yellow the moment that it touches it, and if it continue to 

 be applied, it eats the skin, as it is commonly expressed, or, 

 in chemical language, decomposes it. It also attacks and 

 dissolves most metals. These active properties result from 

 the quantity of oxygen in nitric acid, and the readiness 

 with which it parts with a portion of it. What we call the 

 strength, then, of this substance is really its weakness that 

 is, the weakness with which it holds on to one of its in- 

 gredients. If it held on to its oxygen strongly, instead of 

 parting with a portion of it readily, it would not produce 

 such powerful effects upon other substances. We will pro- 

 ceed to illustrate this explanation of its power by its action 

 on metals, and on certain combustible substances. 



73. Action of Nitric Acid on Metals. If you put a bit of 

 copper (a copper cent will answer) in a saucer, and pour 

 upon it some nitric acid, it will at once begin to dissolve 

 the copper. But you do not really get a mere solution, as 

 salt is dissolved in water. The copper acted upon by the 

 nitric acid is no longer copper. It is chemically changed. 

 What the change is we will explain. The acid immediately 

 in contact with the copper lets go a portion of its oxygen, 

 which unites at once with the copper, forming an oxide of 

 copper. The acid that does this is of course no longer nitric 

 acid, for it has lost a portion of one of its ingredients. It 

 becomes nitric oxide, and passes off in fumes. Observe now 

 what becomes of the oxide of copper that is formed. This 



