COMBUSTION.] 



CHEMISTRY. 



315 



for the exercise of a comprehensive view when we 

 attempt to explain or predicate the result of chemical 

 affinities. The metal zinc also illustrates the varying 

 rapidity and effects of oxidation ; for if it be exposed to 

 air and moisture, a superficial coat of oxide will form, 

 which will protect the mass of the metal from further 

 action ; whilst if the same metal be burned in a jar of 

 oxygen, or thrown into a ladle containing melted nitre, 

 its oxidation is most rapid, and dense fumes of the 

 oxide are given off from its surface. Even if some 

 melted zinc be cast into a fire, its combustion will be 

 very vivid, and the oxide will be produced in abundance, 

 being attended by the production of a brilliant blue 

 flame. 



The process of combustion generally results in the 

 production of an acid, when carbonaceous or organic 

 matter is present. Thus, in experiment 11, in which 

 charcoal was burned in oxygen gas, the resulting product 

 would be carbonic acid ; and, in most cases, it matters 

 not whether the combination takes place rapidly or 

 otherwise. Thus the act of breathing, or of inspiring 

 air into the lungs, is attended by the combustion of 

 carbon in the blood of the individual, as presented by 

 the surface of the lung to the oxygen of the inspired 

 air. In tlds instance, a very slow but complete com- 

 bustion results, and carbonic acid is afforded. The act 

 of breathing, and the rapid combustion of fuel, may be 

 fctkm as extreme instances of the kind ; but between 

 tbew a gradation exists, in which the production of heat 

 and carbonic acid is afforded. Thus, when the atmo- 

 sjili < has access to substances containing carbon of the 

 fatty or oily kind, and in contact with fibrous matter, a 

 slow combustion progresses. If circumstances are 

 favourable, the rate of this combustion rapidly increases ; 

 and, eventually, spontaneous combustion ensues. To 

 this we owe the frequent destruction of buildings in 

 which hemp, jute, and cotton waste are stored. Even 

 if these substances be in a damp state, the same result will 

 occur. During fermentation or germination, the changes 

 produced are of a similar nature to those we have 

 mentioned. Oxidation, in fact, proceeds ; and, as is well 

 known, such is always, in these instances, attended with 

 the production of heat. The heat set free at the dung- 

 heap, and in the processes of malting, are cases which 

 illustrate these observations. 



We have previously remarked, that all sources of 

 artificial heat depend on the presence of oxygen as 

 necessary to combustion. Almost every material em- 

 ployed by man for the production of heat, contains 

 carbon in some form or other ; and, according to the 

 rapidity with which the oxygen in the air is caused to 

 unite therewith, so the intensity of combustion is in- 

 creased. This is effected in the stove, fire-place, and 

 steam-engine furnace, by means of chimnies which 

 produce a strong draught, and so cause a rapid flow of 

 oxygen with the air through the fire-bars. In the 

 locomotive engine, the combustion of fuel is rapidly 

 effected by means of the blast-pipe of the cylinder which 

 conveys the waste steam into the funnel. In the iron 

 smelting furnace, and in other metallurgical processes, 

 intense heat is produced by an engine, etc. ; and the 

 domestic bellows is a similar class of article, and used 

 for the same purpose. In some phases of combustion, 

 oxygen is supplied in a latent state. This occurs in 

 gunpowder, in which the nitre is the source of oxygen, 

 anil affords it in great quantities. In such cases, bodies 

 can burn without access to the atmosphere ; and, in most 

 mixtures of the chlorates or nitrates with dry organic 

 bodies, this readily takes place on heat being applied. 



The general effect of oxygen in nature, is that of a 

 life-giving principle. It breaks up the rocks, and con- 

 verts the sterile hind into a fruitful country. Through 

 Hs action on the organic substances in plants, they bud 

 forth into leaf, and produce the flower and seed. Every 

 leaf is AS a lung to a tree, and thereby plants are 

 enabled to breathe and to exist. In animals, oxygen 

 oxidises tko carbon of tho food, producing animal heat, 

 is we have already shown ; and thus its agency is o 

 universal as to leave no object out of its influence. 



It is desirable that the student should become fully 

 acquainted with its general properties and character, as 

 throughout the following pages we shall have frequently 

 to refer thereto. A careful repetition of the experiments 

 we have named, will therefore prove of great use in this 

 respect. 



OZONE. 



IT was discovered some years ago, by M. Schonbein, 

 that a peculiar result was produced when water was 

 decomposed by means of voltaic electricity ; and many 

 were the guesses of chemists and others as to its causes. 

 When a little dilute sulphuric acid is submitted to the 

 action of a voltaic battery having two platina poles, a 

 strong odour is soon produced, which has almost exactly 

 the same smell as may be noticed when a few sticks of 

 phosphorus are put into a glass bottle with some water. 



Ozone so called from its smell is thus produced, and 

 it has lately been considered as having an individual 

 character and properties. It has, however, never been 

 detected in such a form as to be submitted to any pro- 

 cess except that of testing for its presence ; and hence, 

 although we are acquainted with some of its chemical 

 effects, those of a physical character h".ve yet to be dis- 

 covered. It has decided bleaching properties ; promotes 

 putrefaction, and produces chemical decomposition. It 

 is considered to be either a product of oxygen, the active 

 principle of oxygen, or a new element. 



The tests for the presence of ozone are salts of man- 

 ganese, and the iodide of potassium. The best mode of 

 detecting its presence, is that of employing white blotting 

 or filtering paper, which has been moistened with a 

 solution of iodide of potassium and starch, such as arrow- 

 root, itc. If free ozone be present, the iodide is at once 

 decomposed, the iodine is set free, and the starch becomes 

 of a blue colour. 



Although but little is known of ozone, it has con- 

 siderable interest attached to it, in a sanitary point of 

 view. It has been found, that air charged with animal 

 matter never exhibits ozone in a free state ; and that, 

 generally speaking, the more there is of free ozone in an 

 atmosphere, the healthier it is for the purpose of animal 

 existence. Any one who has once smelt ozone, will 

 readily detect its presence in the air which chiofly 

 occurs during clear and frosty weather. Occasionally, it 

 may be noticed before the change of weather, and in 

 small patches or districts of country. As we speak of 

 our own experience only, it may happen that many of 

 our readers nay not be so sensitive to its action on the 

 nasal organs. Such, however, may easily resort to the 

 starch-paper test. 



Some very interesting experiments were made, some 

 time ago, in reference to the, presence of free ozone. 

 Whilst it could be instantly detected by the manganese 

 test, in the middle of an open thoroughfare ; the sides of 

 the road next to houses, and courts and narrow open- 

 ings running therefrom, indicated an absence of ozone. 

 This fact shows that some intimate relationship must 

 exist between the functions and products of animal 

 vitality, and the presence of the substance. At the 

 present time, the amount of free ozone present in the 

 air, is registered at most meteorological observatories ; 

 and the reports of medical officers also embrace the same 

 subject. The indications are measured by the relative 

 discoloration which the iodide and starch paper undergo ; 

 a set of test-papers, of graduated tints, being kept 

 as a standard of comparison. This subject will be again 

 referred to, under the head of Meteorology. 



CHLORINE. 



FOR a long time, it was considered by chemists, that 

 hydrochloric or muriatic acid had oxygen as one of its 

 constituents ; and until Sir Humphry Davy discovered 

 chlorine to be an elementaiy, and, indeed, for some time 

 afterwards, that opinion was maintained. At the present 

 day, however, chlorine is placed amongst the elementary 

 bodies, and is one of the most active agents in its chemical 

 relations, next to oiygen, with which we are acquainted. 



