CHAMBERS'S INFORMATION FOR THE PEOPLE. 



it combines with the carbon and hydrogen of the 

 tissues, producing carbonic acid and water. This 

 combination is attended by the evolution of heat, 

 and is thus the source of animal heat. See 

 HUMAN PHYSIOLOGY. 



The compounds of oxygen have already been to 

 some extent described, and will be further treated 

 of under the elements of which they are oxides. 

 Most common rocks, such as quartz, granite, lime- 

 stone, trap, basalt, &c. are compounds of oxygen. 



Ozone is a remarkable modification of oxygen. 

 It has hitherto been obtained only mixed with a 

 large proportion of common oxygen. Oxygen can 

 be ozonised that is, part of it converted into ozone 

 in various ways ; for instance, by passing elec- 

 tric sparks through it, or by the slow combustion of 

 various substances, as phosphorus. Oxygen pre- 

 pared by electrolysis contains ozone. Ozone can 

 be converted into common oxygen by heat, and 

 also by contact with a great variety of substances. 

 Ozonised oxygen occupies less space than the 

 common oxygen from which it was prepared, 

 and expansion takes place when ozone is recon- 

 verted into common oxygen, thus proving that 

 ozone is denser than common oxygen. Experi- 

 ments seem to prove that the density of ozone is 

 to that of common oxygen as 3 : 2. If this is 

 the case, the molecular formula of ozone is O 3 , 

 as that of common oxygen is O^ Ozonised 

 oxygen has a strong and peculiar odour, and acts 

 as a bleaching and oxidising agent. It is generally 

 present in small quantity in the air, and probably 

 is of use in oxidising offensive and injurious 

 organic matters. 



HYDROGEN is a colourless, tasteless, odourless 

 gas. Its specific gravity is 0-0693; in other words, 

 14^ volumes of hydrogen have the same weight as 

 one volume of air. Light balloons filled with hydro- 

 gen, therefore, rise in the air. Hydrogen is very 

 slightly soluble in water, 100 volumes of water 

 dissolving less than two volumes of the gas. It 

 has not been reduced to the liquid state. 



Hydrogen does not occur free in this planet, but 

 spectroscopic observations (see ASTRONOMY) prove 

 that it exists in large quantity in the atmosphere 

 of the sun. It forms one-ninth part, by weight, 

 of water, and is an essential constituent of all ani- 

 mal and vegetable tissues. It may be obtained 

 i. By the electrolysis of water, or dilute acids (see p. 

 311). 2. By the action of water on certain metals 

 as sodium, at ordinary temperatures, iron or zinc 

 at a red-heat, the metal uniting with the oxygen, 

 and setting the hydrogen free. 3. By the action of 

 some hydrated acids (hydric salts) upon metals 

 as hydrochloric acid on zinc, iron, or tin ; dilute 

 sulphuric acid on zinc or iron ; the metal simply 

 replacing the hydrogen (see p. 312). 



Hydrogen is inflammable that is, it can be set 

 fire to in air or oxygen. In order to set fire to it, 

 the contact of a red-hot body is necessary. If a 

 piece of spongy platinum is placed in a mixture of 

 oxygen and hydrogen, the two gases condense in 

 the pores of the platinum, unite there, and produce 

 sufficient heat to render the metal red-hot, and 

 this sets fire to the hydrogen. As already stated 

 (p. 311), two volumes of hydrogen unite with one 

 volume of oxygen to form water. If the two gases 

 are mixed in this proportion, an explosive mixture 

 is formed. When a flame or a red-hot body is 

 applied to such a mixture, very rapid combination 

 takes place, with violent explosion, caused by the 



320 



! sudden evolution of heat. Hydrogen at a high 



| temperature is a powerful reducing agent. By far 



the most important compound of hydrogen and 



oxygen is water ; its chief chemical properties have 



already been described. 



The only other known compound of these 

 two elements is the peroxide of hydrogen. This- 

 substance is formed when acids act on per- 

 oxide of sodium or peroxide of barium ; thus, 

 BaO ? + 2HCl=H 2 O 2 -fBaCl 2 . Its formula is H-,0,,,. 

 and it contains hydrogen and oxygen in the pro- 

 portion of I : 1 6. It decomposes very readily into 

 water and oxygen gas ; a very slight rise of temper- 

 ature is sufficient to effect this decomposition. In 

 many cases it acts as an oxidising agent, because 

 I of the readiness with which it gives up half of its 

 I oxygen ; but, curiously enough, it sometimes acts as 

 a reducing agent. Thus, when brought in contact 

 with oxide of silver, it not only gives off its own 

 superfluous oxygen, and is reduced to water, but 

 also, if we may use the expression, induces the 

 ! oxide of silver to give up its oxygen too, so that 

 metallic silver is produced. 



NITROGEN is a colourless, tasteless, odourless 

 gas. Its specific gravity is 0-972 ; 100 volumes 

 of water dissolve at ordinary temperatures about 

 \\ volume of the gas ; it has not been condensed 

 to the liquid state. Nitrogen occurs in the atmos- 

 phere, of which it forms about 79-1 per cent, by 

 volume. Atmospheric air consists essentially of 

 nitrogen and oxygen, with comparatively very 

 smaU quantities of other gases carbonic acid r 

 ammonia, and water-vapour. Nitrogen may be 

 prepared from atmospheric air by removing the 

 oxygen ; this can be done in various ways ; of these 

 we may mention : i. Passing air through a long- 

 tube containing metallic copper, heated to redness ; 

 the copper unites with the oxygen, forming cupric 

 oxide, CuO, and the nitrogen passes on. 2. Burn- 

 ing phosphorus (or allowing it slowly to oxidise) in 

 air, the oxygen unites with the phosphorus, form- 

 ing phosphoric (or phosphorous) acid (see p. 326), 

 which can be removed by water, in which it is 

 soluble. 



Nitrogen gas is an eminently inactive substance, 

 and does not readily enter into combination with 

 other elements. In the air, its chief function is to 

 act as a diluent of the oxygen. There are, how- 

 ever, a great many very important compounds of 

 nitrogen which we obtain indirectly from one 

 another. All animals and vegetables contain 

 compounds of nitrogen ; and by the decomposition 

 of dead animal and vegetable matters, and from 

 the excreta of animals, other compounds of nitro- 

 gen are formed, which in their turn form part of 

 the food of plants. Thus, there is a constant cir- 

 culation of nitrogen from one state of combination 

 to another, and with this circulation the great mass 

 of free nitrogen in the air has very little connection. 

 We shall here shortly describe the compounds of 

 nitrogen with oxygen and with hydrogen. 



Compounds of Nitrogen and Oxygen. Of these 

 there are five namely : 



Nitric Acid (anhydrous), NsOj, forming, with water, hydrated 

 nitric acid or hydric nitrate, HaO.NoOj or HNOs; and with 

 bases, nitrates, as K 2 O,N 2 O5 or KNOs, nitrate of potash or 

 potassic nitrate. 



Peroxide of Nitrogen, NOj. 



Nitrous Acid (anhydrous), N-'Os, does not form a stable hydric 

 salt with water, but unites with bases forming nitrites, asv- 

 KsO.NgOs or KNOa, nitrite of potash or potassic nitrite. 



Nitric Oxide, NO. 



Nitrous Oxide, N 4 O. 



