70 



CONDUCTIVITIES OF ORGANIC ACIDS 



The bottle containing the alkali was covered with a dark material, 

 since, in the presence of light the tendency of the alkaline solution to 

 become colored is much greater than in the dark. 



One of the greatest difficulties in connection with the alcoholic pot- 

 ash method was that of temperature changes. The coefficient of expan- 

 sion of alcohol is so large that even small changes in the temperature of 

 the laboratory, and consequent changes in temperature of the solu- 

 tion, will change quite appreciably the normality of the alkali. 



It was this difficulty which led us to the use of an 

 aqueous solution of ammonia with coralline as 

 the indicator, instead of the alcoholic caustic FIG. 24. 



potash with phenolphthalein as the indicator. 

 The ammonia was prepared by heating concentrated ammonia and 

 passing the gas which was given off, first over sticks of sodium hydrox- 

 ide, which collected a large part of the water-vapor and any carbon 

 dioxide, and then over sodium, which absorbed the remainder of the 

 water-vapor; and finally into a weighed quantity of conductivity water 

 in a measuring flask until the approximate amount of the gas necessary 

 to make a tenth-normal solution was dissolved. This solution was 

 titrated against standard sulphuric acid to obtain its exact normality. 



Coralline was used as the indicator because it is sensitive to the 

 organic acids, and is not sensitive to carbon dioxide except when the 

 latter is present in fairly large quantity. In order to test whether 

 coralline is sensitive to small quantities of carbon dioxide, another 

 worker in this laboratory measured out two equal quantities of a 

 standard acid, added an equal amount of coralline to each, and then 

 allowed carbon dioxide to bubble through one of these solutions for 

 some minutes. Titrations of both solutions were made, and practically 

 no effect due to the presence of carbon dioxide was found. Equal 

 volumes of a standard acid were again titrated, this time after having 



