Drushel and Elston — Sulphide Sulphur. 155 



Art. XX. — On the Quantitative Estimation of Small Quan- 

 tities of Sulphide Sulphur ; by W. A. Drushel and C. M. 



Elston. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — eclxxx.] 



The methods of estimating sulphide sulphur in common use 

 depend (1) upon oxidation of the sulphur to the sulphate con- 

 dition and weighing it as barium sulphate, (2) upon oxidation 

 by means of standard iodine and titration of the excess of 

 iodine with standard sodium thiosulphate, and (3) upon the 

 precipitation of the sulphur by an excess of standard sodium 

 arseriite as arsenious sulphide and titration of the excess of 

 arsenite with standard iodine. These methods all require con- 

 siderable time for execution, and the first and second methods 

 are not entirely reliable for quantities of sulphide sulphur 

 much smaller than 0-04 per cent. The third method is said to 

 be accurate for quantities of sulphide sulphur as small as O0003 

 per cent, but it is necessary to allow the mixture, after treat- 

 ment with sodium arsenite, to stand for twelve hours in order 

 that the precipitated arsenious sulphide may be removed quan- 

 titatively by filtration before the excess of arsenite is titrated 

 back with iodine. 



The object of the present investigation was to develop a 

 rapid method of estimating very small amounts of sulphide 

 sulphur with a fair degree of accuracy. The method is a 

 colori metric method and consists essentially of the comparison 

 of the depth of color of lead sulphide stains obtained from the 

 sulphide sulphur of a given weight of a sample to be analyzed 

 with a standard series of stains prepared from sulphide solu- 

 tions of known sulphur content. A set of stains varying in 

 depth of color from a faint yellowish brown to black represent- 

 ing from 0'0002 percent to - 00i per cent of sulphide sulphur 

 may be prepared and used indefinitely for comparison. With 

 a set of standard stains at hand the method has the advantage 

 that within the range given the sulphide sulphur of a sample 

 may be determined with a fair degree of accuracy in less than 

 ten minutes. 



Preparation of standard set of sulphide stains. — The appa- 

 ratus used for preparing standard stains and for making analyses 

 is very simple. The inner tube of a Liebig condenser with its 

 larger end about 18 mm in internal diameter was cut off 15 cm in 

 length. The smaller end was drawn down somewhat, rounded 

 and fitted to a sound cork stopper which in turn was fitted to 

 a 100 c '" 3 round-bottom flask. The condenser tube then served 

 as a sort of reflux condenser. To the upper and larger end of 



Am. Jour. Sci. — Fourth Series, Vol. XLII, No. 248. — August, 1916. 

 11 



