EXPERIMENT STATION BULLETINS. 379 



It will be noticed that the greatest variation between the computed 

 value and the determined value is 0.13% while in ten out of the fifteen 

 values the variation is under 0.10%. The above determinations were 

 made on 10 oc. samples of the diluted solution. 



SUMMARY, 



Total Sulfur. — The total sulfur is determined by oxidizing the sulfur 

 present to the sulfate form, using sodium peroxide as the oxidizing 

 agent and precipitating and weigliing as barium sulfate. 



Monosulfide sulfur. — The monosulfide sulfur is determined by titra- 

 ting a 25 cc. sample of the diluted solution with decinormal iodine until 

 the yellow color disappears. The number of grams per 100 cc. of the ori- 

 ginal solution is given by the computation, cc. iodine X .0016 X 1000. 



25 



Thiosulfate Sulfur. — The thiosulfate sulfur is determined by continu- 

 ing to add iodine solution after the monosulfide end point has been 

 reached until we have one drop in excess. This additional amount of 

 iodine determines the amount of thiosulfate sulfur. For a 25 cc. sample 

 the grams per 100 cc. of original solution is given by computation, 

 cc. iodine X .0064 X 1000. 



25 



Sulfate and Sulfite Sulfur. — These are determined together by precipi- 

 tation in the cold as barium sulfate after filtering off the sulfur from 

 the solution used for the monosulfide and thiosulfate sulfur determina- 

 tions. 



Total Sulfide Sulfur. — This may be determined by dissolving the sulfur 

 precipitate, filtered off for the sulfate sulfur determination, in concen- 

 trated potassium hydroxide, oxidizing and precipitating as barium sulfate. 



Calcium oxide. — The calcium oxide may be determined by oxidizing 

 the sulfur to the sulfate form and precipitating the calcium as the 

 oxalate. 



It may also be determined by computation from the amount of 

 iodine used in the monosulfide and thiosulfate sulfur determinations 

 and from the amount of sulfate and sulfite sulfur present. The fol- 

 lowing computation gives the number of grams per 100 cc. : (cc. iodine 

 used for monosulfide sulfur) -{-(2 X cc, iodine used for thiosulfate sul- 

 fur) X -.^^^SX^OOO _^ (sulfate and sulphite sulfur) X 1,75. 



ADVANTAGES OF THESE METHODS OVER OLD METHODS. 



1. The use of sodium peroxide as an oxidizing agent is more con- 

 venient than either bromine water or hydrogen peroxide and does not 

 have to be especially prepared for the work as does the hydrogen per- 

 oxide solution. 



2. The necessity of using the ammoniacal zinc chloride solution is 

 avoided by substituting an iodine titration, thus doing away with the 

 laborious task of filtering test portions for determining an end point by 

 means of an external indicator. 



3. The process of dissolving the zinc polysulfide sulfur or sulfur 

 precipitate in order to determine the sulfide sulfur is done away with. 



