MANOANATES 199 



with their perfectly innocuous character, adapts them admirably for disinfecting pur- 

 poses. Their action is certainly superior to that of chloride of lime and alkaline 

 hypochlorites ; for although these are also oxidising disinfectants, they act indirectly 

 by decomposing water, from which the chlorine takes hydrogen to form hydrochloric 

 acid, thus liberating oxygen for the supply of the putrefying matter. The manga- 

 nates and permanganates, on the contrary, are agents of direct oxidation, yielding 

 up, as they do, part of their own oxygen to the combustible elements of putrescible 

 compounds. The manganates thus supply one-fourth, the permanganates no less than 

 three-eighths, of the oxygen they respectively contain, peroxide of manganese being 

 in both cases precipitated, and the alkaline base remaining in solution in the form of 

 carbonate. 



Their Efficacy as Disinfectants. Dr. Hofmann has had many opportunities of 

 satisfying himself of their efficacy as disinfectants. Waters taken from stagnating 

 ponds highly charged with organic matter in a state of most active putrefaction, and 

 emitting the most repulsive odour, were instantaneously deodorised by a compara- 

 tively small quantity of permanganate, or even nmnganate of potassium or sodium. 

 After the brown precipitate of peroxide of manganese had been allowed to subside, 

 the waters examined by Dr. Hofmann had become perfectly clear and colourless, 

 having permanently lost their offensive smell and taste. The taint of some of these 

 waters had survived the action of even very considerable quantities of the usually- 

 applied metallic salts. Their deodorisation by chloride of lime was likewise rapid 

 and permanent ; but, though entirely deprived of their original putrid odour, the 

 chlorine-treated waters retained a faint, peculiar smell, probably due to the chloride 

 of nitrogen, generated by the action of free chlorine upon their ammoniacal consti- 

 tuents. 



For freeing river or other waters from ammoniacal impregnations, the disappear- 

 ance of the colours of the manganates and permanganates, in proportion as their 

 oxidising action goes on, particularly adapts them. By the fading of the colour 

 (emerald, if manganate is used ; purple, if permanganate) the operator can follow 

 the process of oxidation, and graduate his additions with the xitmost accuracy. By 

 careful manipulation he may completely free the water from organic impurity, intro- 

 ducing into it, in exchange, only a minute quantity of an alkaline carbonate. This 

 is rarely an objectionable, frequently rather a serviceable, addition ; especially in the 

 case of hard waters, which are thus softened. 



Their minor applications, The innocuous character of these substances has already 

 been referred to ; and it is not the least valuable of their properties. It permits 

 of their being used for a variety of purposes to which disinfectants have hitherto 

 been almost entirely inapplicable. Among them are some of great value, such as 

 disinfection of all parts of the living animal body (deodorisation of the breath, dis- 

 infection of ulcers, wounds, &c.). Scarcely less important is the service they are 

 capable of rendering to the vegetable organism when suffering from blight and 

 similar pernicious influences. They may also be advantageously employed for the 

 purification of tainted provisions, &c. It may be of some interest to the smokers of 

 tobacco to know that by rinsing out the mouth with a dilute solution of permanganate 

 of sodi'.im every trace of the odour of tobacco is almost instantaneously got rid of. 

 Among the numerous applications of minor importance which Mr. Condy suggests 

 for the manganic disinfectants is their use by wine-tasters for refreshing their palates 

 when engaged in the important duties of their profession. They are also said to 

 subdue the irritation caused by the bites of gnats and other still more disagreeable 

 insects. 



The manganic disinfectants are thus seen to possess a combination of properties 

 which in many cases may render their application preferable to that of the hypo- 

 chlorites. These latter, however, have the superiority as atmospheric disinfectants, 

 on account of their exhalation of chlorine gas, in a more or less dilute state, when 

 acted on by acids, or acid salts, or even by the atmosphere itself. _ This^ property of 

 chloride of lime will always secure it a field of application, in which it is not likely 

 to be superseded by non-volatile disinfectants of any kind. 



Their Manufacture. It only now remains to say a few words concerning the manu- 

 facture of the alkaline manganates and permanganates, which is accomplished by a 

 very simple and easy process. 



For laboratory purposes the potassic permanganates are usually preferred to the 

 corresponding sodic compound, on account of the superior crystallising properties of 

 the former salt, and the facilities thus afforded for its purification. For industrial 

 purposes, on the other hand, where cheapness is far more important than perfect 

 purity, the manganate and permanganate of sodium are always used. Mr. Condy 

 manufactures manganates of sodium simply by mixing caustic soda with finely- 

 divided peroxide of manganese, and exposing tho mixture in shallow vessels, for 



