428 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 9 



Another experiment was conducted to ascertain if aerated 

 flowers of sulphur produces pentathionic acid. Two lots of 50 

 gms. each of flowers of sulphur were placed in wash bottles. 

 The 2 bottles were placed in series each connected with wash 

 bottles containing distilled water to collect any volatile water- 

 soluble compound that might come over. Air was passed through 

 one series and air deprived of oxygen through the other. Aeration 

 was continued for 72 hours. At the end of this time H 2 S was 

 passed into the distilled water wash bottles and permitted to 

 stand for 12 hours. A slight precipitate was noted in the distilled 



water through which air containing oxygen had passed. The 

 series without oxygen gave no precipitate. This afforded definite 

 proof that pentathionic acid is an oxidation product of flcwers of 

 sulphur at ordinary temperatures. A concentrated solution of 

 sodium chloride was added to the aerated sulphur suspensions, 

 and centrifuged; the residue was resuspended in water and again 

 centrifuge! I. Hydrogen sulphide was then passed into the super- 

 natant liquid. A precipitate developed only in the one in which 

 oxygen was present. 



A similar series was arranged using precipitated sulphur con- 

 taining no pentathionic acid. The distilled water cortaining 

 the volatile soluble compound and the aerated suspension were 

 tested for pentathionic acid. The former gave a slight precipitate 

 with £LS after standing. The suspension gave a much heavier 

 precipitate indicating that the pentathionic acid was adsorbed by 

 the sulphur particle and was not easily driven off by slow aera- 

 tion. Without oxygen there was no pentathionic acid produced. 



The precipitated sulphur was much more easily oxidized than 

 the sublimed flowers of sulphur. 



Practical Applications 



Time has not permitted a more extensive study of this phase 

 of the problem. It was necessary in the first place to determine 

 the compound of sulphur that is toxic to fungi and to develop 

 a material that would act as a fungicide over a sufficient period 

 when sprayed on the plant. The fact that flowers of sulphur 

 must be acted upon by some definite external physical factor has 

 limited its use to only a small section of the country. It has been 

 the aim in this work to develop, if possible, a sulphur compound 

 that would exhibit fungicidal properties regardless of climatic 

 factors and w r ould for that reason have a wide usage over a large 



