DECOMPOSITION OF ORGANIC COMPOUNDS. 255 



putrefy have been stated above, and the non-fulfilment of these 

 conditions enables us to prevent decomposition artificially. 



Thus, we freeze substances (meat) ; or expel all water from or 

 dry them (fruit, etc.), in order to prevent decomposition. The 

 action of the ferments is counteracted either by the so-called 

 antiseptic agents (salt, carbolic or salicylic acid, etc.), which 

 are incompatible with organic life, or by excluding the air, and 

 with it the ferments, by enclosing the substances in air-tight 

 vessels (glass jars, tin cans, etc.), which, when filled, are heated 

 sufficiently to destroy any germs which may have been present. 



Action of chlorine and bromine. These two elements act upon 

 organic substances (similarly to oxygen) in three different ways, 

 viz. : the} T either (rarely, however) combine directly with the 

 organic substance, or remove hydrogen, or replace hydrogen. 

 The following equations illustrate this action : 



C 2 H 4 -f 2Br = C 2 H 4 Br 2 . 



Ethylene. Bromine. Ethylene 



bromide. 



C 2 H 6 O + 2C1 = C 2 H 4 O + 2HC1. 



Ethyl Chlorine. Aldehyde. Hydrochloric 



alcohol. acid. 



C 2 H 4 2 + 2C1 = C 2 H 3 C10 2 + HC1. 



Acetic acid. Chlorine. Monochlor- Hydrochloric 



acetic acid. acid. 



In the presence of water, chlorine and bromine often act as 

 oxidizing agents by combining with the hydrogen of the water 

 and liberating of oxygen; iodine may act in a similar manner 

 as an oxidizing agent, but it rarely acts directly by substitution. 



Action of nitric acid. This substance acts either by direct 

 combination with organic bases forming salts, or as an oxidizing 

 agent, or by substitution of nitryl, NO 2 , for hydrogen. As in- 

 stances of the latter action, may be mentioned the formation of 

 nitro-benzine and uitro-cellulose : 



C 6 H 6 + HN0 3 = C 6 H 5 N0 2 + H 2 O. 



Benzine. Nitric acid. Nitro-benzine. Water. 



C 6 H 10 O 5 + 3HNO 3 = C 6 H.3(NO 2 ) -f 3H 2 O. 



Cellulose. Nitric acid. Trinitro-cellulose. Water. 



