Phijsical and Chemical Papers. 97 



THE DETERMINATION OF SULPHATES IN WATER. 



The Use of Benzidine Hydrochloride. 



Hy K. ^\'. r.KIMKMll.I.KK. 



THE majority of the waters of Kansas often contain con- 

 siderable quantities of calcium sulphate, whose exact and 

 quick determination is very often necessary. Especially is this 

 true in the examination of boiler waters. The usual procedure 

 for this determination is to precipitate the calcium sulphate 

 as barium sulphate, filter, and weigh. This operation requires 

 from four to twelve hours to complete, depending upon the 

 quantity of calcium sulphate in the water. Where the content 

 in calcium sulphate is desired to be known on short notice, 

 therefore, this method will not meet the demand. The benzidine 

 method, however, will, as the results herein contained show. 



The method consists in precipitating the sulphates by means 

 of benzidine hydrochloride — C,.,H,(NH.) ,-21101 — as benzidine 

 sulphate, which being insoluble in water is filtered off, sus- 

 pended in water, and titrated in the hot with standard alkali, 

 using phenolphthalein as indicator. This titration is possible 

 by the very weak basic properties of benzidine. The whole 

 operation can be completed in from fifteen to thirty minutes. 



The method is not original with me, having been proposed 

 by Raschig (Zeit. angew. Chem. 1903, 16:617) and investigated 

 by Friedam and Nydegger (Zeit. angew. Chem. 1907, 19:9), 

 whose suggestions I have followed and adapted and modified 

 to suit water-analysis conditions. 



After a few trial experiments the following method was de- 

 cided upon as the best procedure for water analysis : To 

 250 cc. of water (less if the SO, content is greater than 500 

 parts per million) add 10 cc. of a 1 per cent solution of hydro- 

 xy lamine hydrochloride (more if the iron content of the water 

 is very high) and 20 cc. of benzidine hydrochloride. Stir 

 vigorously and allow the silky white precipitate to settle. Filter 

 on a disc of black ribbon filter paper in a Gooch crucible, tvith 

 uction. Wash with cold di.stilled water twice (about 25 cc), 

 ■and drain precipitate thoroughly. Transfer the precipitate 

 to the original beaker, add water, and heat to boiling. Titrate 

 with N 20 NaOH, using phenolphthalein as the indicator. 

 Parts per million SO, -- 9.6 ~ ' cc. N '20 NaOH. 

 —7 



