REPORT OF THE SOCIETY 73 



Sodium Polysulphide Combinations with Arsenic. 



Lead arsenate cannot be used in sodium polysulphide solutions. Arsenate 

 of lime has been used successfully with sodium polysulphide in the following: 



1 lb. sodium polysulphide. 

 % lb. arsenate of lime. 

 5 lbs. high calcium hydrated lime. 

 50 gallons, water. 



Dusting Sulphur. 



Dusting sulphur depends for its fungicidal value on the S022 formed. 

 Where the temperature gets very high, SO2 may be formed so rapidly as to cause 

 burning. Where the temperature is very low SO2 may be formed too slowly 

 to set as an efficient fungicide. This defect of sulphur dust often shows up 

 in the control of apple scab which is a cool weather disease. The value of sul- 

 phur dust depends largely on the temperature and the uneven results following 

 its use as compared with the more even results of copper are thus explained. 

 In very hot climates, where there is danger of sulphur dust burning, the use 

 ■of ten or fifteen per cent of lime is necessary. In cool climates the use of lime 

 in sulphur dust is a detriment as it neutralizes the SO2 as rapidly as it is formed 

 .and reduces the fungicidal value too much. 



Sulphur Dust and Arsenicals. 



• .' Lead Arsenate is the standard poison for use in sulphur dust. Arsenate of 

 lime is too cautic for use on foliage, even when diluted with sulphur. In spite 

 of this, arsenate of lime is being successfully used with sulphur in certain local- 

 ities. 



Red arsenic, or realgar or arsenic tersulphide, is insoluble in acids and solu 

 ble in alkalis. Red arsenic has been used with safety in pure dusting sulphur- 

 but is too heavy and dense for a good dusting material. 



Copper and Sulphur Cominations. 



It has always been assumed that copper and sulphur neutralized each 

 other completely. There is now some question as to the accuracy of this. How- 

 ever, it is safe to say that the use of copper and sulphur mixed in dusting mater- 

 ials is undesirable and wasteful, although the status of copper sulphide and 

 copper sulphite as fungicides is yet to be established. 



