22 



Keratin Sulfur and Cystin Siilfur 

 Summary: Found (percent) 



[March, 



The substance so obtained is acid in reaction, is very hygro- 

 scopic, and gives, with lead acetate, a precipitate which is soluble in 

 an excess of the reagent, and in lead acetate sol. The substance 

 gives the biuret reaction. Its aqueous Solution gives, on treatment 

 with alcohol, a milky turbidity which, on evaporation, deposits small 

 crystals. The material is very stable and, on heating with mineral 

 acids, is decomposed with the formation of sulfuric acid. To 

 determine its basici'ty the aqueous sol. was titrated with 0.0983/iV 

 soda sol., with lacmoid-naphthol-green as the indicator. 



XVII. 1.3 c.c. of the soda sol. was required to neutralize 0.1053 

 gm. of the substance dissolved in water. For a monobasic acid 

 (CioHi7N3S06)3, 1.2 c.c. would be necessary, but it must be con- 

 sidered that the ash of the substance contained a large amount of 

 silicic acid. 



B. In Order to ascertain the sulfur-distribution among the oxi- 

 dation products of cystin, I have oxidized, with potassium perman- 

 ganate, cystin prepared from human hair. About 2.3 gm. of cys- 

 tin, containing 0.61 gm. of sulfur, were oxidized with i 1. of per- 

 manganate sol. All of the filtrate, together with the washings, was 

 evaporated and the contained sulfuric acid determined (XVIII). 



XVIII. I obtained 2.0931 gm. of barium sulfate (0.2875 S^- 

 of sulfur). Therefore, 47 percent of the total sulfur was changed 

 to sulfuric acid in the oxidation. 



