1922] 



YOUNG — THE TOXIC PROPERTY OF SULPHUR 411 



colloidal sulphur." The other form of colloidal sulphur is that 

 first prepared by v. Weimarn and Molyschew ('11). This last 

 has a very low degree of hydration and will be designated in 

 this paper as hydrophobic colloidal sulphur. A more detailed 

 description of these forms will be given in a subsequent section. 



The hydrophilic colloidal sulphur was prepared according to 

 the methods of Raffo and Mancini (11) and Oden ('13) with 

 certain modifications. Fifty gms. of pure crystalline sodium thio- 

 sulphate were dissolved in 30 cc. of distilled water; 70 gms. of 

 concentrated sulphuric acid, sp. gr. 1.84, arsenic free, were 



;hed into a gla 



The cylinder 



was placed in a vessel of cold water and the saturated solution of 

 sodium thiosulphate added very slowly with occasional stirring. 

 The mixture was then allowed to cool and 30 cc. of distilled water 

 added. It was then placed on the water bath and warmed at 

 80° C. for 10 minutes, and filtered through glass wool to re- 

 move insoluble sulphur. The filtrate was cooled and allowed 

 to stand for 12 hours. It was again warmed, filtered through 

 glass wool, and the filtrate cooled. This warming, filtering, and 

 cooling was repeated until no more insoluble sulphur came down. 

 The final filtrate was a slightly turbid yellowish solution. This 

 was centrifuged for 30 minutes at 1500 revolutions per minute. 

 A portion of the colloidal sulphur was thrown out of solution. 

 The supernatant liquid was a clear yellowish solution and was 

 saved for further purification. The residue was washed in cold 

 distilled water and again centrifuged for the same length of time 

 and at the same speed. The supernatant liquid was again yel- 

 lowish and was saved. The washing and centrifuging of the res- 

 idual colloidal sulphur were repeated until the residue peptized 

 in water gave a reaction of Ph 4.2. This colloidal suspension was 

 faintly yellow and upon standing 1 week some of the particles 

 settled out, the solution retaining its faint yellow color. Upon 

 drying and weighing, the suspension gave a percentage of sulphur 



of 3.4. 



The supernatant liquids collected from the above were treated 

 with a concentrated solution of sodium chloride, whereby the 

 yellowish colloidal sulphur was coagulated. The sodium chloride 

 was added until no more coagulum seemed to form. The coag- 

 ulum was easily centrifuged out and repeptized in 10 cc. of dis- 

 tilled water. The color of this solution was a deeper yellow and 

 onlv verv sliehtlv turbid. This colloidal suspension gave a reaction 



