564 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



paste to such an extent that its smooth mixing properties, suspension properties and 

 adhesive quahties are considerably injured. Also it has been shown by a great many 

 complaints which have come to the personal knowledge of the writer during his ex- 

 perience, that a frozen arsenate of lead had been used in the spraying applications 

 and apparently did not control the worms. It has been quite evident from investi- 

 gations made of such complaints, that the trouble was in using the frozen material 

 and the reasons why it was not active, I am inclined to believe, are because of the 

 injured properties of adhesiveness, fineness, spreading power, etc. It is only the 

 physical properties that are injured and not the chemical properties. I have seen 

 frozen arsenate of lead dried out and reground and it seemed impossible to put it 

 back in its original smooth state. 



No less emphatic is the statement made by the horticulturist for a 

 prominent commercial company: 



In reply beg to advise, that the only experience we have had with handling frozen 

 arsenate of lead is that it is rendered physically unfit for use; the paste being exceed- 

 ingly hard to work up after having gone through freezing process. The powdered 

 is not harmed by freezing according to oiu- experience and I think in the case of both, 

 paste and powdered, there is no important chemical change, which would affect the 

 insecticidal properties of material. 



Experimental 



In view of the contradictory statements given above, a few pre- 

 liminary experiments were conducted to determine the effect of freezing 

 on the physical properties of some commercial arsenates of lead. 



Six commercial brands of lead arsenate paste and pure samples of 

 acid and basic lead arsenates were each mixed until uniform and 

 divided into equal portions and placed in glass stoppered salt mouth 

 bottles. One bottle from each paste sample was placed in an ice and 

 salt mixture and left for 24 hours. Evaporation was prevented by 

 the use of ground glass stoppers and as soon as the samples had thawed, 

 the water and lead arsenate was mixed thoroughly until a uniform 

 paste was obtained. Many of the frozen pastes appeared much more 

 granular than the unfrozen duplicates. 



Exactly 10.3 grams of each of the arsenate samples were weighed 

 and suspended in 1000 cc. of distilled water. This is equivalent to ''4 

 pounds to 50 gallons" as used in ordinary practice. Tests were made 

 on these samples to see if freezing had affected the property of the 

 lead arsenate to remain suspended in water. The following photo- 

 graphs on Plates 44, 45 are self explanatory. (The numbers are 

 in duphcate. N.F. = Not Frozen, F. = Frozen.) 



Figures I and II of Plate 44 represent the frozen and unfrozen samples 

 2 minutes after shaking: Samples 1, 2 and 4 show the greatest differ- 

 ence; the frozen arsenates have a curdy appearance and settle much 

 more rapidly. Figures III and IV on Plate 45 represent the samples 

 as they appeared after standing for fifteen minutes. The striking 



