ii8 Journal of Agricultural Research voI.xv.no. 2 



TITRATION TO A CERTAIN HYDROGEN-ION CONCENTRATION WITH THE 

 HYDROGEN-ELECTRODE APPARATUS 



The general arrangement of the apparatus for determining the hydro- 

 gen-ion concentration by the use of the hydrogen electrode was that 

 given by Hildebrand.^ 



Our outfit contains the following pieces: One Weston D. C. milli- 

 voltmeter and multiplier; one Kohlrausch slide wire bridge with exten- 

 sion coils; one Leeds and Northrup No. 2,500 type R. galvanometer 

 with lamp and scale; two Edison storage batteries. The calomel and 

 hydrogen electrodes were made according to the directions given by 

 Hildebrand. 



For the first part of this work neither this bridge nor the galvanometer 

 were available. The bridge used was a straight-wire bridge such as is 

 commonly found in physics laboratories. Instead of the galvanometer 

 we used the Lipmann electrometer and reading telescope. 



The galvanometer with the lamp and scale, as well as the Kohlrausch 

 bridge, are found exceptionally satisfactory for this class of work. 



As a source of hydrogen we have found that made by the electrolytic 

 process very satisfactory. This can be bought compressed in iron 

 cylinders. As a precaution against impurities the gas is washed in a 

 train of alkaline pyrogallic acid, potassium permanganate, mercuric 

 chlorid, and carbon-dioxid-free water. The hydrogen made from 

 aluminium and sodium hydroxid was found just as satisfactory, but 

 more expensive as to materials and labor. 



METHOD OF DETERMINING THE TITRABLE ACIDITY BY THE USE O? THE HYDROGEN 



ELECTRODE 



Twenty-five cc. of the water or alcoholic extract were pipetted into a 

 wide mouth 250-cc. flask. The calomel and the hydrogen electrodes 

 were inserted through a rubber stopper which fitted the mouth of the 

 flask. As the lower end of the hydrogen electrode was bell-shaped, it 

 was necessary to use a partially split stopper. Through a third hole in 

 the stopper the tip of a burette was inserted so that the N/20 sodium 

 hydroxid could be added without exposing the contents of the flask to 

 the air. Hydrogen gas was then allowed to bubble through the solution 

 with frequent shaking and the bridge adjusted until equiHbrium was 

 obtained — that is, until no current flowed through the galvanometer. 

 At this point the reading of the milli-voltmeter was noted. Next, N/20 

 sodium hydroxid was added from the burette slowly with frequent 

 shaking. It was desired to measure the amount of alkali necessary to 

 add in order to obtain three different hydrogen-ion concentrations: Ph7, 



• HlI,DEBRAND, J. H. SOME APPLICATIONS OF THE H\T)ROGEN ELECTRODE IN ANALYSIS, RESEARCH 

 ANDTEACHING. /n Jour. Amer. Chem. Soc, V. 35, HO. 7, p. 847-871. 15 fig. 1913- 



