THE EEASON WHY. 33 



"As vinegar is to the teeth, and as smoke to the eyes, so is the sluggard to him 

 that sent him." PEOVESBS X. 



system. Animals placed in pure oxygen die in great agony from 

 fever and excitement, amounting to madness. 



33. What is nitrogen ? 



Nitrogen is an elementary body in the form of gas. 



34. Where is nitrogen found ? 



It is chiefly found in the air, of which it constitutes 79 out of 100 

 volumes. It may be mixed with oxygen in various proportions ; 

 but in the atmosphere it is uniformly diffused. It is found in most 

 animal matter, except fat and bone. It is not a constituent of the 

 vegetable acids, but it is found in most of the vegetable alkalies. 



35. What are acids ? 



Acids are a numerous class of chemical bodies. They are gene- 

 ratty sour. Usually (though there are exceptions) they have a 

 great affinity for water, and are easily soluble therein ; they unite 

 readily with most alkalies, and with the various oxides. All acids 

 are compounds of two or more substances. Acids are found in all 

 the kingdoms of nature. 



36. What are alkalies ? 



Alkalies are a numerous class of substances that have a great 

 affinity for, and readily combine with, acids, forming salts. They 

 exercise peculiar influence upon vegetable colours, turning blues 

 green, and yellows reddish brown. But they will restore the 

 colours of vegetable blues which have been reddened by acids ; and, 

 on the other hand, the acids restore vegetable colours that have 

 been altered by the alkalies. Alkalies are found in all the kingdoms 

 of nature. 



37. Could animals live in nitrogen ? 



No ; they would immediately die. But a mixture of oxygen and 

 nitrogen, in equal volumes, constitutes nitrous oxide, which gives a 

 pleasurable excitement to those who inhale it, causing them to be 

 merry, almost to insanity ; it has, therefore, been called laughing 

 gas. 



38. Why does nitrous oxide produce this effect ? 

 Because it introduces into the body more oxygen than can be 



consumed. It, therefore, leranges the nervous system, and being 

 2* 



