89 



properties than when combined with the other compounds, 

 which may be explained by the formation of soluble arsenic 

 in the reactions between the poison and the sulphides. Be- 

 cf;nse of the chemical reactions, the sodium and potassium 

 .sulphides, Avliile more rapid in their poisonous effects upon 

 insects, Avere generally more liable to cause injiiries to the 

 loliage of fruit trees than the calcium and barium com- 

 pounds in combination with arsenate of lead. 



According to their nature and mode of action, various 

 fiubstances are incorporated in spraying mixtures to give 

 penetrating and adhesive proper.ties. The agents that are 

 commonly used are silicate of soda, saceharates, soap, glue, 

 gelatine resin, and commercial oil emulsions. Tests show 

 that glue, soap, glycerine, sodium silicate and oil emulsions 

 of various formulas may lie combined with the sodium and 

 potassium sulphides, and that similar combinations are 

 possible with the calcium and barium sulphides except in 

 the case of soap, oil emulsions and sodium silicate. As to 

 the influence of such combinations or effectiveness, no 

 marked results haA^e been observed, except when soap and 

 oil emulsions were employed Avith the sodium or potassium 

 sulphides against aphides, or oil emulsions Avith the same 

 sulphides for the control of the San Jose scale. The prin- 

 cipal gain in the latter case appears to be in an increased 

 rate of toxicity. The destructive action of the sulphides 

 alone on the scale is apparently sloAver, and Avhile pro- 

 longed over a more extended period may, hoAvever, prove 

 no less efficient. 



Taking all factors into consideration, especially 

 economy and safeness to trees, there appears to be little 

 reason for discontinuing the use of lime-sulphur for prepa- 

 rations containing sulphides of other basic elements. In 

 spite of certain defects, no spraying mixture so Avell meets 

 the need of the commercial orchardist as lime-sulphur 

 solution. 



