NITROGEN AND ITS OXIDES. 63 



other many times, producing the same results. The brill- 

 iancy of the lighting-up will diminish each time, because 

 the combustion of the taper uses up the oxygen. 



68. Nitrogen in Respiration. As nitrogen can not sup- 

 port combustion, so it can not support life. If we put an 

 animal a mouse, for example into ajar of nitrogen, it will 

 die speedily. But nitrogen does not act as a poison. The 

 air which animals take into their lungs is four fifths nitro- 

 gen, but it does them no harm. The reason that animals 

 can not live in nitrogen alone is simply that they can not 

 live without having some oxygen in the air which they 

 breathe. Because this gas can not support life it is some- 

 times called azote, from two Greek words , privative, 

 and zoe, life. 



69. Compounds of Nitrogen with Oxygen. Nitrogen forms 

 five compounds with oxygen. Those which are of the most 

 interest to us are nitric anhydride, which unites with water 

 to form nitric acid (formerly called aqua fortis, the Latin for 

 strong water), and nitrous oxide, the so-called laughing-gas. 



The following table shows us the names and formulae of 

 these five oxides of nitrogen : 



Names. Formulae. Composition. 



1. Citrous oxide (or laugh-) __ 



ing-gas) . . . ; N ' 28 Parts N ' 16 P artS ' 



2. Nitric oxide N a O a (orNO)* 28 " " 32 " " 



3. Nitrous anhydride N a O 3 28 " " 48 " " 



4. Nitric peroxide N 2 O 4 (or N0 a )* 28 " " 64 " " 



5. Nitric anhydride N 2 O 3 28 " " 80 " " 



This table illustrates the regularity in proportions which 

 prevails in all chemical combinations, explained in Chapter 

 III. 



In order to learn all about these oxides of nitrogen, you 



* For reasons which we can not explain here, the formula? of these bod- 

 ies are of necessity halved as indicated. 



