[Vol. 9 

 430 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



mendation. However, the fact that this substance is slowly 

 oxidized at ordinary temperatures leads to the possibility of its 

 being used effectively when treated with compounds that will in- 

 crease its oxidation. It will also be necessary to add to such a 

 spray an adsorptive material to retain the pentathionic acid as it 

 is produced. Many of the common spreaders now in use may 

 do this. These possibilities are being investigated and will be 

 reported later. 



Since the completion of the experimental part of this work 

 there has come to my attention a number of colloidal sulphur 

 preparations that have proved effective as a general spray. Ram- 

 say and Cooke ('22) have prepared a colloidal sulphur that has 

 been used effectively in Australia. They prepare their compound 

 as follows: Ten gallons of home-made lime sulphur (26° Baume) 

 are diluted with 25 gallons of water in a barrel of 50 gallons 

 capacity. In a suitable vessel 6 pints of strong commercial sul- 

 phuric acid are diluted with 9 parts of cold water and allowed to 

 cool. The cold diluted sulphuric acid is then carefully added 

 to the dilute lime sulphur in the barrel, a pint at a time, stirring 

 well until the typical yellow color of the original lime sulphur 

 disappears and until further addition of more acid produces no 

 further precipitation of sulphur. The precipitated sulphur is 

 allowed to settle for a day or two. Three pounds of cheap glue 

 are dissolved in sufficient hot water to render the glue soluble and 

 while still hot is stirred thoroughly into the sulphur. The glue aids 

 in the keeping qualities of the colloidal sulphur. The mixture 

 so prepared is diluted to 250 gallons (with water). This gives 

 a spray containing approximately 5 pounds of precipitated sul- 

 phur per 100 gallons. 



Thiele ('21) recommends the use of colloidal sulphur in the 

 form of a liquid spray (not dust) for the control of mildews in 

 Germany. He states that it is far more effective than the most 

 finely ground sulphur powder. The colloidal mixtures adhere 

 firmly to the plant and are not blown away by the wind cr washed 

 off by rains, as is the powder. Precipitated sulphur as a control 

 for mildew and related fungi has been recommended by Lederle 

 ('22). He prepared this precipitated sulphur as follows: Solution 

 I: 250 gms. of sodium hyposulphite are dissolved in % liter of 

 hot water. Solution II: 250 gms. of sodium bisulphate are dis- 

 solved in % liter of hot water. Solution III : 10 gms. oi glue are 

 dissolved in V± liter of hot water. Solution III is then stirred 



