Spraying Kotes. 267 



A 'biig-Mlling contest. — A test of the insecticidal value of these 

 materials was made on potatoes. The results are fairly representa- 

 tive of their value as insecticides, for if the materials will kill potato 

 slugs their poisonous properties are assured. 



Two strengths of the materials were used : Jib. perbbl. (48 gals.), 

 the strength at which Paris green is usually applied for potato slugs, 

 and ^ lb. per bbl. The spraying was done July 10 and 17, each 

 strength covering about seventy-live rods of rows. The physiologi- 

 cal effects of the arsenites are recorded in Table I. Slugs were not 

 numerous, but were plentiful enough for a fair test. Both strengths 

 of Paris green, Paragrene, XX, and Green Arsenoid killed all the 

 slugs. A very few sick ones were found when both strengths of 

 Pink Arsenoid, Green Arsenoid ^o. 53 and Green Arsenite had 

 been sprayed, yet it would pass for a clean sweep. 



III. The Composition of Arsenites. 



The analyses of the insecticides used in these experiments con- 

 sisted chiefly in determining the amount of arsenic, the arsenic 

 soluble in water, and the copper. The arsenic soluble in water was 

 found by shaking the insecticide in water for one hour, at the rate 

 of one pound to one hundred gallons, and determining the amount 

 of arsenic dissolved. Comparing Table II with Table I it will be 

 seen that in proportion as the amount of soluble arsenic in an 

 insecticide increases, its injury to foliage likewise becomes greater. 

 At the rate arsenites are commonly used (J lb. per bbl.), the burning 

 is not noticeable with insecticides having less than 3|- per cent of 

 soluble arsenic. 



Anybody but a chemist is likely to become confused over the 

 nomenclature of poisons. Arsenite is a general term for all com- 

 pounds of arsenioLis oxid (As^ O3), the active element in all these 

 materials. Arsenoid is a trade name, not a chemical compound, 

 and simply means arsenic-like. An arsenate is a compound of 

 arsenic acid (Asg O5). None of the materials mentioned here is an 

 arsenate. When the term arsenic is used in connection with insecti- 

 cides, we mean what is ordinarily called white arsenic (As2 O3) and 

 not the metal arsenic (As). In the table copper is given as copper 

 oxid (Cu O), lead as lead oxid (Pb O) and lime as calcum oxid (Ca O). 

 The sulfmic acid (S O3) has no insecticidal effect. 



