242 PRINCIPLES OF CHKMJSTRY 



removal of impurities from the air is called ' disinfection.' 47 The accu- 

 mulation of all kinds of impurities in the air of dwellings and cities i& 

 the reason why the air of mountains, forests, seas, and non-marshy 

 localities, covered with vegetation or snow, is distinguished for its fresh- 

 ness, and, in all respects, beneficial action. 



but animal vitality can be sustained in it for a somewhat long time, although the 

 effect of such air is exceedingly painful to even the lower animals. There are mines in 

 which a lighted candle easily goes out from the excess of carbonic anhydride, but in which 

 the miners have to remain for a long time. The properties of air may be considerably 

 vitiated by the combustion of charcoal, wood, and similar substances in it, even when it 

 contains a comparatively small amount of carbonic anhydride. This doubtless depends on 

 the fact that certain gaseous substances are formed in the act of combustion (carbonic 

 oxide, acetylene, hydrocyanic acid, and others) which are positively injurious to breathe. 

 The action of charcoal fumes and smoke is based on this fact. The presence of 1 p.c. of 

 carbonic oxide is deadly even to cold-blooded animals. The air of explosive mines, where 

 explosions are made, is known to produce a state of insensibility resembling that produced 

 by charcoal fumes. Deep wells and vaults not .unfrequently contain similar substances, 

 and their atmosphere often causes suffocation. The atmospheres of such places cannot 

 be tested by lowering a lighted candle into it, as these poisonous gases would not extin- 

 guish the flame. This method only suffices to indicate the amount of carbonic anhydride. 

 If a candle keeps alight, it signifies that there is less than 5 p.c. of this gas. In doubtful 

 eases it is best to lower a dog or other animal into the air to be tested. 



47 Different so-called disinfectants are capable of purifying the air, and of preventing 

 the injurious action of certain of its components by changing or destroying them. Dis- 

 infection is especially necessary in those places where a considerable amount of volatile 

 substances are evolved into the air, and where organic substances are decomposed ; for 

 instance, in hospitals, closets, &c. The numerous disinfectants are of the most varied 

 nature. They may be divided into the following chief categories : oxidising substances* 

 antiseptic substances, and absorbent substances. To the oxidising substances used for 

 disinfection belong chlorine, and various substances evolving it, because chlorine in the 

 presence of water oxidises the majority of organic substances. Further, to this class 

 belong the permanganates of the alkalis, as substances easily oxidising matters dissolved 

 in water ; these salts are not volatile like chlorine, and therefore act much more slowly, 

 and in a much more limited sphere. Antiseptic substances are those which convert 

 organic substances into such as are little prone to change, and prevent putrefaction and 

 fermentation. They most probably kill the germs of organisms occurring in miasmata. 

 The most important of these substances are creosote and phenol (carbolic acid), which 

 occur in tar, and which act in preserving smoked meat. Phenol is a substance little 

 soluble in water, volatile, oily, and having the characteristic smell of smoked objects. Its 

 action on animals in considerable quantities is injurious, but in small quantities, used in 

 the form of a weak solution, it prevents the change of animal matter. The smell of 

 privies, which depends on the change of excremental matter, may be easily removed by 

 means of chlorine or phenol. Salicylic acid, thymol, common tar, &c., are also substances 

 having the same property. They are used in special cases, but naturally not so generally. 

 Absorbent substances are of no less importance than the preceding two classes of disin- 

 fectants, inasmuch as they act regularly and are innocuous. They are such substances 

 as absorb the odoriferous gases and vapours emitted during putrefaction, which are 

 chiefly ammonia, sulphuretted hydrogen, and other volatile compounds. To this class 

 belong charcoal, certain salts of iron, gypsum, salts of magnesia, and such like substances, 

 as well as peat, mould, and clay. Their employment is profitable, not only for removing 

 the odour, but also in the radical destruction of miasmata. The questions both of disin- 

 fection and ventilation appertain to the most serious problems of common life and 

 hygiene. These questions are so vast that we are here able only to give a short outline 

 of their nature. 



