84 PROPERTIES or OXYGEN 



the atmospiere ;* and on this property, as I shall explain liereafter, the 

 use of charcoal powder as a manure probably in some measure depends. 

 2°. They also separate from water any decayed animal matters or col- 

 ouring substances which it may hold in solution ; hence its use in fillers 

 for purifying and sweetening impure river or spring waters, or for clari- 

 fying syrups and oils. This action is so powerful that port wine is 

 rendered perfectly colourless by filtering through a well prepared char 

 coal. 



In or upon the soil charcoal for a time will act in the same manner, 

 will absorb from the air moisture and gaseous substances, and from the 

 rain and trom flowing waters organized matters of various kinds, any 

 of which it will be in a condition to yield to the plants which grow 

 around it, when they are such as are likely to contribute to their 

 growth. 



3°. They have the property also of absorbing disagreeable odours in 

 a very remarkable manner. Hence animal food keeps longer sweet 

 when placed in contact with charcoal — hence also vegetable substances 

 containing much water, such as potatoes, are more completely preserved 

 by the aid of a quantity of charcoal — and hence the refuse charcoal of the 

 sugar refiners is found to deprive night-soil of its disagreeable odour, and 

 to convert it into a dry and portable manure. 4°. They exhibit also 

 the still more singular property of extracting from water a portion of the 

 saline substances they may happen to hold in solution, and thus allow- 

 ing it to escape in a less impure form. The decayed (half carbonized) 

 roots of grass, which have been long subjected to irrigation, may act in 

 one or all of these ways on the more or less impure water by which 

 they are irrigated — and thus gradually arrest and collect the materials 

 which are fitted to promote the growth of the coming crop. 



§ 3. Oxygen — its properties and relations to vegetable life. 



Oxygen is a substance with which we are acquainted only in the gas- 

 eous or aeriform state. f By the unaided senses it cannot be distin- 

 guished from common air, being void of colour, taste and smell. But 

 if a lighted taper be plunged into it, the flame is wonderfully increased 

 both in size and brilliancy, and the taper bums away with great 

 rapidity. 



The effect of this gas upon animal life is of a similar kind. When 

 a living animal is introduced into a large vessel filled with oxygen, the 

 rapidity of the circulation is increased, all the vital functions are stimu- 

 lated and excited, a state of fever comes on, and after a time the ani- 

 mal dies. 



By these two characters, oxygen is distinguished from every other ele- 

 mentary body. It exists in the atmosphere to the amount of 21 percent, 

 of its bulk, and in this state of air is necessary to the existence of ani- 

 «ials and of plants, and to the support of combustion on the face of the 

 globe. It exists also largely in water, every nine pounds of this liquid 

 containing eight pounds of oxygen. 4^ 



• Thus of ammonia they absorb 95 times their own bulk, of sulphuretted hydrogen 65 times, 

 of oxygen 9 times, of hydrogen nearly twice their bulk, and of aqueous vapour so much as to 

 increase their weight from 10 to 20 per cent. 



t la this state it is readily obtained by heating in a glass retort the red oxide of mercury 

 of the shops, or a white salt known by the name of chlorate of potash 



