XVII. MISCELLANEOUS PRODUCTS USED IN AGRICULTURE 367 



Oxygen is the best natural disinfectant, and free admission of 

 oxygen destroys many micro-organisms. It is by absorption of atmo- 

 spheric oxygen that river water, polluted by putrefying organic matter, 

 purifies itself. Unfortunately the process is slow. 



Ozone, O 3 , the allotropic form of oxygen, is much more powerful 

 in its action, and successful attempts to apply it as a disinfectant 

 have been made. 



Hydrogen peroxide, H.,0.,, is an excellent disinfectant, and, though 

 a powerful germicide, has no influence upon enzymes, e.g., those of 

 digestion. 



When air is brought into contact with oil of turpentine in the pre- 

 sence of water, hydrogen peroxide is formed. Advantage is taken of 

 this in the preparavon of " Sanitas," a preparation made from terpenes 

 and possessing a characteristic odour. 



Sulphur dioxide, S(X. This gas, of well-known properties, is a 

 powerful disinfectant and deodoriser. It is poisonous and very irritant 

 when breathed, 5 per cent in air producing fatal results. 



It dissolves in about -}^ of its volume of water, yielding a weak 

 solution of the unstable sulphurous acid, H.,SO 3 . 



It acts in presence of water as an acid, and therefore unites with 

 ammonia, amines, organic bases, etc. It decomposes sulphuretted 

 hydrogen or ammonium sulphide and reduces many organic substances, 

 generally producing colourless compounds. Hence its use in bleaching 

 wool and straw. 



By pressure, it can be condensed to a liquid and is now commerci- 

 ally obtainable in glass siphons (under a pressure of about three atmo- 

 spheres), each of which will yield about 500 litres of gas. 



The usual plan of generating the gas is by burning sulphur in air. 

 The sulphur is often in the form of " candles," i.e., cylinders provided 

 with a wick, or a cheaper method is to use roll sulphur placed in metal 

 dishes and moistened, when everything is ready, with the very inflam- 

 mable and volatile carbon disulphide ; the ready ignition of the sulphur 

 can thus be ensured. According to the Local Government Board's 

 direction, 1-J Ib. of sulphur should be used for an ordinary room ; this 

 probibly would yield air containing about 2 per cent of SO. 2 . 



In Belgium from 20 to 30 grammes per cubic metre are recom- 

 mended (i.e., from 2 to 3 per cent). 1 Considerable difference of opinion 

 appears to exist as to the value of sulphur dioxide as a disinfectant. 



Carbon disulphide, GS.j, the very volatile, inflammable liquid, with 

 the well-known offensive odour, is poisonous both to animals and 

 micro-organisms. Its proposed use as a means of checking nitrifica- 

 tion in soils in th<3 autumn his already been alluded to. On combus- 

 tion it yields carbon dioxide and sulphur dioxide. With alkaline 

 sulphides it forms thiocarbonates or xanthates (e.g., K,CS 3 ), wh'ch are 

 sometimes used in treating plant diseases. 



Manganate and permanganate of soda or potash, K.,Mn0 4 and 

 KMnO 4 . 



ThiS3 are powerful oxidising agents, but bsing non-volatile, require 



1 Rideal, Disinfection and Disinfectants. 



