38 APPLIED BACTERIOLOGY FOR NURSES 



make a solution 1 : 1000 when one tablet is dissolved in 

 a pint of water. Most of the tablets contain either 

 citric or tartaric acid or ammonium chlorid to prevent 

 the formation of insoluble compounds with albuminous 

 matter. Many of the tablets also contain some harmless 

 blue, pink, or j-ellow coloring-matter to aid in identify- 

 ing the solution. For ordinary use solutions of 1 : 1000 

 will suffice, when brought into contact with bacteria, 

 to kill the vegetative forms within fifteen minutes. 

 Stronger solutions, however, must be employed when 

 much organic matter is present. Mercuric chlorid 

 should not be employed to disinfect metal instmments, 

 as it quickly ruins them by its action. 



Carbolic acid, or phenol, is a white crystalhne sub- 

 stance readily liquefied by heat. It can be kept liquid 

 by the addition of 5 per cent, water or glycerin, making 

 what is sold in the drug stores as "pure carboHc acid." 

 For disinfecting purposes it is ordinarily used in the 

 form of a 5 per cent, solution in water, and, while it is 

 less powerful than mercmic chlorid, it has the advantage 

 of being only slightly affected by albuminous material, 

 and of not acting on metals. Its efficiency is increased 

 by the addition of common salt up to saturation : 1 : 400 

 kills the less resistant bacteria, and 1:100 kills the 

 remainder. A 5 per cent, solution kills the less resistant 

 spores within a few hours, and the more resistant in 

 from a day to four weeks. 



Crude carbolic acid consists mainly of cresols and 

 very little phenol. By saponification of mixtures of 

 cresols and neutral tar oils a product is obtained which 

 makes an emulsion with water. Creolin is a type of 

 numerous preparations of this character. They are aD 



