[Vol. 9 



412 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



of Ph 4.2 and did not settle out on standing for 2 months. On 

 drying and weighing, the solution was found to contain 1.6 per 

 cent sulphur. This latter preparation was a typical hycrophilic 

 colloidal sulphur and was more nearly a true "soluble" sulphur 

 than the product obtained from the method of Raffo ar.d Man- 

 cini (11). The first preparation was a mixture of hycrophilic 

 and hydrophobic colloidal sulphur. Oden ('13), in a detailed 

 study of this type of colloidal sulphur mixtures, found them to 

 contain particles of different sizes ranging from the molecular 



to particles easily discernible under the low power of the micros- 

 cope. He was able to obtain suspensions with particles varying 

 from the smallest to the largest by fractional coagulation with 

 sodium chloride. Particles of larger size were more easily coagu- 

 lated than the smaller ones. In colloidal sulphur suspensions 

 of this kind the particles have a tendency to collect themselves 

 into groups, forming larger particles which settle out rapidly. 

 The smaller the particles the slower this takes place and in hy- 

 drophilic colloidal sulphur suspensions only a small amount of 

 settling out can be noted after several months. 



The chemical reactions involved in the formation of colloidal 

 sulphur prepared by this method is given by Oden as follows: 



Na 2 S 2 8 + H 2 S04 = Na 2 S0 4 + H 2 S 2 8 

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



2 H 2 S 2 3 = 2H 2 S + 2SO 

 2 H 2 S + S0 2 = H 2 + S 



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



Further chemical reactions will be given in a subsequent section 

 of this paper. 



The method for the preparation of hydrophilic collodal sul- 

 phur was later varied in accordance with the method used by 

 Freundlich and Scholz ('22). After the filtration through glass 

 wool concentrated sodium chloride was added and the mixture 

 centrifuged. The coagulum was then peptized with 100 cc. 

 of distilled water and the insoluble sulphur centrifuged out. 

 The peptized sulphur solution was treated 3 times with 25 



cc. of saturated sodium chloride and finally peptized in 100 cc. 

 of distilled water. 



Another method for the preparation of hydrophilic colloidal 

 sulphur was that first used by Selmi ('52) and was as follows. Sul- 

 phur dioxide was passed into distilled water until a saturated 



