98 Kansas Academy of Science. 



The benzidine hydrochloride solution is made up as follows : 

 Place 8 grams of benzidine in an agate mortar, and add enough 

 water to make a paste. Wash the paste into a one-liter flask, 

 add 10 cc. concentrated HCl, and make up to the mark. Filter 

 if necessary. 1 cc. = .0026 grams SO,. 



This method and the barium chloride method usually em- 

 ployed were used in the determination of sulphates on several 

 hundred waters. The results by the two methods agreed very 

 closely, as the data in the following table shows : 



Com]>a)-iKO)i of results obtained ivitli Barium Clilo)-ide and Benzidine. 



Results expressed in paits per million. 



so , by SO^ by 



Lab. Ko. ]>aCl.,. benzidine. DilVerence. 



6678 80.6 84.5 +3.9 



6682 76.5 80.6 +4.1 



6723 254.2 257.3 +3.1 



6729 87.6 96.0 +8.4 



6742 68.7 76.8 +8.1 



6804 45.4 40.3 —5.1 



6887 584.7 583.7 —1.0 



6942 62.2 63.4 +1.2 



7081 29.6 32.6 +3.0 



7082 173.2 180.5 +7.3 



7084 343.9 341.5 —2.4 



7087 101.2 107.5 +6.3 



7114 51.0 46.0 —5.0 



7128 19.8 15.4 —4.4 



7139 38.8 38.4 —0.4 



7142 24.7 19.2 —5.5 



7144 48 . 46 . —2.0 



7148 16.2 21.0 +4.8 



7155 26.3 25.0 —1.3 



715G 51.8 63.4 +1.6 



Several precautions are necessary in order to obviate diffi- 

 culty in carrying out the method. The precipitate should not 

 be allowed to stand too long, for the silky precipitate turns to 

 flakes on standing, which only dissolve after considerable 

 boiling. The suction should be strong enough to remove the 

 last traces of the mother liquid before any wash water is added. 

 If it is not, too high results will be obtained. 



After transferring the precipitate the water should be 

 heated, preferably until all the precipitation is dissolved. Al- 

 though this is not always necessary, it is sometimes a safe 

 procedure to insure easier splitting ofi" of the HCl groups. 



