458 CONSIDERATION OF CARBON COMPOUNDS. 



used in solution or as a gas ; hydrogen peroxide, salicylic acid, boric 

 acid, sulphur dioxide, ferrous or cupric sulphate, alcohol, chloroform, 

 thymol, etc. 



The selection of a disinfectant depends on the respective conditions. While 

 the relatively harmless salicylic acid is often used as a preservative for articles 

 of food it is the powerful but strongly poisonous mercuric chloride which is 

 used externally in the operating room. The surgeon disinfects his hands by 

 first scrubbing with soap and water, immersing in a saturated solution of potas- 

 sium permanganate and washing finally in solution of oxalic acid. The latter 

 removes through its deoxidizing and dissolving power that portion of the per- 

 manganate which adheres to the hands. For the disinfection of rooms gases^ 

 such as formaldehyde, sulphur dioxide or chlorine, are indicated. Instruments 

 may be disinfected by heat or by immersion in suitable solutions. 



The term asepsis refers to the absence of living germs of fermentation, putre- 

 faction or disease, while the term sterilization is used for the process of destroy- 

 ing all living micro-organisms in the object or material operated on. Aseptic 

 conditions by means of sterilizing may be brought about either by the use of 

 antiseptic agents or by application of heat. 



Action of chlorine and bromine. These two elements act upon 

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

 they either (rarely, however) combine directly with the organic sub- 

 stance, or remove hydrogen, or replace hydrogen. The following 

 equations illustrate this action : 



C 2 H 4 + 2Br = C 2 H 4 Br 2 . 

 Ethylene. Bromine. Ethylene bromide. 



C 2 H 6 + 2C1 : : G 2 H 4 + 2HC1. 

 Ethyl alcohol. Chlorine. Aldehyde. Hydrochloric acid. 



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



Acetic acid. Chlorine. Monochloracetic Hydrochloric 

 acid. acid. 



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

 ing agents by combining with the hydrogen of the water and liber- 

 ating 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 com- 

 bination with organic bases forming salts, or as an oxidizing agent, 

 or by substitution of nitryl, NO 2 , for hydrogen. As instances of the 

 latter action may be mentioned the formation of nitro-benzene and 

 cellulose nitrate: 



