EXPERIMENT STATION BULLETINS. 377 



the iodine itself. The starch solution prevents the rapid settling of 

 the sulfur precipitate. 



Sulfate and sulfite sulfur. — As has been customary in the past, these 

 have iDeen determined together. After the titration with iodine for the 

 monosulfide and thiosulfate sulfur the solution is allowed to stand until 

 the sulfur settles. It is then filtered, acidified and the sulfate and sul- 

 fite (now sulfate) sulfur is precipitated in the cold. 



TJie total sulfide sulfur* — ^This form of sulfur may be determined by 

 placing the filter containing the sulfur that has been filtered off pre- 

 liminary to the determination of the sulfate sulfur, in a beaker dissolv- 

 ing by heating with 25 cc. concentrated potassium or sodium hydroxide, 

 oxidizing wath sodium peroxide, as in the total sulfur determination, 

 and precipitating and weighing as bariumi sulfate. However, as this 

 is rather a long process, it has been customary to determine the sulfide 

 sulfur by difference, that is by subtracting the thiosulfate, sulfate and 

 sulfite sulfur from the total sulfur. 



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

 off 10 cc, of the diluted solution and oxidizing the sulfur exactly as in 

 the total sulfur determination. After acidifying extra care must be 

 taken to boil off all the gases in solution, for if any carbon dioxide is 

 present a portion of the calcium will be precipitated as the carbonate 

 upon making the solution alkaline. The solution after being boiled is 

 made alkaline and filtered if a precipitate appears. The calcium may 

 then be precipitated with ammonium oxalate in the usual wa3\ 



An estimation of the calcium oxide in solution may be had from the 

 iodine titration, Tartar^ and Bradley have shown that there isi no cal- 



* Since this manuscript was prepared, Mr. O. B. Winter of this laboratory has 

 done a considerable amount of work on the determination of the sulfide sulfur 

 by weighing the free sulfur separated out by the iodine titration. This was sug- 

 gested by Tarter and Bradley but they recommended for more accurate results, 

 dissolving the sulfur in potassium hydroxide and estimating in the same way as 

 for total sulfur. This of course, means a much greater amount of work than 

 where the sulfur is weighed directly. 



The method of weighing the free sulfur gives slightly higher results than other methods 

 and also more closely agreeing duplicates. A comparison of results by the two methods 

 is here given 



These differences may be explained in two ways, either some of the iodine 

 is occluded in the free sulfur precipitate causing it to be too high, or on the 

 other hand the barium sulfate precipitate may be slightly soluble in the solution 

 containing rather high concentrations of potassium and sodium chloride, causing 

 low results. Otto Folin, Jour. Biol. Chem., Vol. I, Nos. 2 and 3, shows that the 

 presence of potassium chloride does give low results for sulfur. This was verified 

 by determining the sulfur in 40 cc. of approximately N/5 H.SOi in the presence 

 of an excess of potassium. 



(1) Jovmal of Ind. and Eng. Chemiatrj'. Vol. 2, p. 271. 



