1922] 



YOUNG — THE TOXIC PROPERTY OF SULPHUR 425 



By the action of remaining sulphuric acid, 



H 2 SO* + 5H 2 S 2 3 = 2H 2 S 6 0a + 3 H 2 



The pentathionic acid then joins with sulphur (S p) and water 

 to form the hydrophilic colloid of the following structure : 



SsOe H2 SsO 



6 



H 2 



The possibility of such a structure is based on the fact that a 

 compound containing so many oxygen ions must necessarily have 

 a great affinity for water. Moreover, a molecule containing so 

 many sulphur atoms would, because of its residual valence, ac- 

 count for its combining with other atoms of sulphur. This being 

 true, pentathionic acid would have the property of combining 

 between molecules of sulphur and water. In other words, it is 

 an adsorptive medium for both these substances. A similar phe- 

 nomenon is described and illustrated by Langmuir ('17) in his 

 studies of secondary valences in mixtures of fats and water. 



Having no such adsorption medium present in hydrophobic 

 colloidal sulphur, the S A absorbs water and forms the grouping 

 S A.' H 2 0, which is a typical suspension colloid, poorly hydrated 

 and gradually settling out. 



The chemical nature of pentathionic acid has been very thor- 

 oughly studied. It was discovered by Wackenroder ('46) in 

 1845. He prepared the acid by passing H 2 S into a saturated 

 solution of S0 2 , always keeping the excess of the latter. By 

 calculations he arrived at the formula of H 2 S 5 O a . For quan- 

 titative determinations he precipitated the acid with an alkali, 

 in much the same way as reported by Freundlich and Scholz 

 ('22) for hydrophilic colloidal sulphur. He also found that salts 



precipitated it. 



After the discovery of this acid considerable controversy arose 

 as to its existence in a pure state. Spring ('82) states that it is 

 his opinion that the so-called pentathionic acid consists of a solu- 

 tion of sulphur in tetrathionic acid and that salts obtained from 

 this solution are simply tetrathionates containing admixed sul- 

 phur. That this conclusion was partially correct was proved by 

 Shaw ('83). He could produce pure pentathionic acid, but at 

 times such an admixture as obtained by Spring would be obtained. 

 A close relationship undoubtedly exists between pentathionic acid 



