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[Vol. 9 



GARDEN 



and sulphur. Shaw prepared his pentathionic acid by passing 

 simultaneously hydrogen sulphide and sulphur dioxide into 3 

 liters of distilled water for 32 hours, the sulphur dioxide being 

 kept slightly in excess. This controversy was definitely settled 

 by Debus ('88). His work is summed up by Mellor ('17) in the 

 chapter on the compounds of sulphur and oxygen. 



The properties of pentathionic acid have been more recently 

 studied by Raschig ('20) and Riesenfeld and Feld ('21). The 

 latter state that the action of H 2 S and S0 2 forms the hypothet- 

 ical acid H2S3O4 as an intermediary product and that by its 

 oxidation and reduction pentathionic acid is formed; they give 

 the following reactions: 



2S0 2 + H 2 S = H 2 S 3 4 



HS.O, + 6S0 2 = 2H 2 + H.S.O. > 0xidatlon b ^ l5 ° 



H 2 S 3 04 + 3H 2 S = 6S + 4H.O— Reduction by H 2 S 

 5H 2 S 3 04 = 3H 2 Ss0 8 + H 2 — Polymerization 



They studied the action of acid and alkali and found that the 

 acid was unstable in both conditions. 



It is therefore evident that the hydrophilic colloidal sulphur 

 prepared according to the methods of Selmi ('52), Raffo ('08), 

 Od('n ('13), and others, is pentathionic acid. That this is an ox- 

 idation product of sulphur seems a logical conclusion. The in- 

 fluence of the hydrogen-ion concentration also points toward pen- 

 tathionic acid as being the toxic factor in all of the prececing ex- 

 periments. Flowers of sulphur, hydrophobic colloidal sulphur, 

 and especially hydrophilic colloidal sulphur exhibited toxicity 

 only at Ph 4.2-5.4, because of the fact that pentathioric acid 

 is destroyed when in a solution of higher or lower hydrogen-ion 

 concentration. 



To obtain further proof of the toxicity of pentathioric acid 

 the hydrophilic colloidal sulphur was freed of this acid. The col- 

 loidal sulphur was prepared by the following method, which is 

 only a slight modification of the one used in previous experi- 

 ments: Thirty cc. of a saturated solution of sodium thiosulphate 

 were slowly added to 10 cc. of concentrated sulphuric acid. The 

 mixture was warmed and filtered through glass wool. The fil- 

 trate was then coagulated with sodium chloride and centrifuged. 

 The coagulum was peptized in 100 cc. of distilled water and 

 again centrifuged to remove insoluble sulphur. Coagulation, 



