644
THEORY AND PRACTICE OF ENGINEERING.
Book II.
arc either exactly double, triple, or some multiple by a whole number of the smallestproportion in which the body enters into combination with the other substance. Fourteenof nitrogen can only combine with 8, 16, 24, 32, or 40 of oxygen, but with no inter-mediate proportion.
Oxygen is an invisible and permanently elastic gas, without taste, colour, or smell; itsspecific gravity, as compared with air, is 1 -111 to I *000; compared with hydrogen as 16 to 1,hydrogen being unity. At mean temperature and pressure 100 cubic inches of oxygen weigh34*60 grains. When water is freed from air 100 cubic inches will absorb 3*5 cubic inchesof oxygen; it forms $ of the weight of the atmosphere, | of the weight of water, and is soabundant a principle in the mineral kingdom, that in silex it forms 50 per cent., in alumina47, in lime 28, in magnesia 40, in potash 17, and in soda 25 per cent.; in the sulphateand carbonates of lime, the two most abundant acids, it is the essential ingredient. Oxygendoes not occur in nature except in combination with other bodies, and it is then said thatthe body so containing it is oxidised, or is in a state of oxidation; its combining numberis 8.
Hydrogen is the lightest form of matter known, its specific gravity, as compared withoxygen, being as 1 to 16; 100 cubic inches of pure hydrogen gas at a mean temperatureand pressure weigh 2*1318 grains, and as compared with atmospheric air its specific gravityis as *0694 to 1. It does not form a very important element in the composition of rocksthough it occurs in the animal and vegetable kingdoms in abundance. It is one of theelements of water, constituting about 11 per cent, of that compound, or £ of the w*ater of theglobe. Pure water, when exposed to the action of voltaic electricity, is resolved into twovolumes of hydrogen, disengaged at the negative pole, and one volume of oxygen at thepositive. Water therefore, consisting of one volume of hydrogen, and half a volume of
oxygen, their relative weights are as 1
l to 8.
Equivalent.
Volumes.
Hydrogen - 1
1
11*1
1 *0
Oxygen - - 1
8
88*9
0*5
1 9 1000
Pure water , at the temperature of 62°, has its specific gravity equal to 1 000; a cubicinch weighs 252*5 grains, and a cubic foot 998*217 ounces avoirdupois, so that the specificgravity of any substance in reference to water is nearly the absolute weight of 1 cubic footof such substance in ounces avoirdupois.
Water is about 815 times the weight of atmospheric air, and at 32° it freezes, ice beingof the specific gravity of 0*94. It boils at 212°, when the barometer is at 30° : ICO cubicinches of steam weigh 19,062 grains, the specific gravity of steam being *6249. At a meanpressure, and at a temperature of 212 3 , the bulk of steam is 1700 times greater than thatof water.
Pure hydrogen condenses half its bulk of oxygen when detonated by the electric spark,and is much employed by the chemist as a deoxidating agent; it refracts light powerfully,and is an imperfect conductor of electricity.
Water has the power of absorbing many of the gases, 500 cubic inches absorbing of
Sulphuretted hydrogen
_
_
.
Volumes.- 233
Carbonic oxide
.
.
_
- 100
Nitrous do. -
_
-
.
- 76
Olefiant gas -
.
.
.
- 12*5
Oxygen
-
-
-
3*7
Hydrogen
-
-
-
1*56
Nitrogen
-
-
-
1*56
Water absorbs oxygen and nitrogen from the air, condensing more of the former than thelatter, and air at the surface of the earth is always found to contain water, but is scarcelyever in a pure state.
Peroxide of Hydrogen , or oxygenated water, is liquid, transparent, and inodorous; itsspecific gravity is 1 *45, and it is decomposed by all metals except iron, tin, antimony, andtellurium. Silver and oxide of silver decompose it as well as platinum and gold. Leadand mercury more slowly disengage the oxygen.
Hydrogen
- 1
Equivalent.
1
5*9
Volume.
1
Oxygen -
- 2
16
94*1
1
1
17
100*0