﻿54 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE. 



Of all the arsenicals tested, acid lead arsenate and zinc arsenite 

 were the most adhesive and Paris green the least adhesive on potato 

 foliage. The use of lime with arsenicals applied to potato foliage did 

 not increase their adhesiveness. 



The suspension properties of the powdered arsenicals are of value 

 in differentiating "light" from "heavy" powders, as determined by 

 their apparent densities. 



The physical properties of the commercial powdered arsenicals 

 could not be satisfactorily determined by sieving, as they are generally 

 amorphous and pack in the sieve on shaking. Arsenious oxid samples 

 sometimes contain or consist of relatively coarse crystals, so that 

 sieving may provide valuable data. 



Microscopic examination gave little information concerning the 

 desirable physical properties of the amorphous or seemingly amor- 

 phous powdered arsenicals. Differences in size of crystals present in 

 the arsenious oxid samples were detected under the microscope. 



The toxicity findings are based on the use of equivalent quantities 

 of arsenious and arsenic oxids. Higher percentages of toxicity were 

 found for acid lead arsenate than for basic lead arsenate. The differ- 

 ent samples of calcium arsenate tested varied widely in toxicity. 

 When lime or Bordeaux mixture was added to arsenicals, the toxici- 

 ties were reduced. The average toxicity of the three samples of 

 Paris green and that of one zinc arsenite tested was slightly more 

 than that of an acid lead arsenate and a sodium arsenate. Of the 

 four samples of arsenites, the Paris green samples gave the highest 

 values, zinc arsenite being much less toxic. Based on equivalent 

 metallic arsenic percentages, the Paris green samples gave values no 

 higher than that of the acid lead arsenate tested. Several new arse- 

 nates tested did not show as high toxicities as did acid lead arsenate. 

 Of the various bases tested, lead oxid showed some insecticidal value, 

 while the oxids of zinc, magnesium, and copper showed little and 

 lime no value. Arsenic acid, acid lead arsenate, and one sample of 

 calcium arsenate gave high and practically equal toxicities. Arse- 

 nious oxid (white arsenic) gave lower and variable results. The per- 

 centages of water-soluble arsenic in the original arsenicals had little 

 or no influence on the toxicity, except in the case of those arsenicals 

 which were entirely or largely water soluble. These had high per- 

 centages of toxicity. 



The determination of reaction in terms of the pH value of water 

 extracts from the bodies of various insects fed all of the different 

 arsenicals, and also from the bodies of control insects, showed uni- 

 formly a slight acidity. These results indicate that the arsenic 

 compounds fed did not affect the pH values as determined on dead 

 insects. 



The minimum dosage of metallic arsenic required to kill a honeybee 

 is approximately 0.0005 milligram, while 0.0273 milligram (or 54 

 times as much) is required to kill a full-grown silkworm. Honey- 

 bees, confined in cases, void none of the arsenic eaten, whereas silk- 

 worms void 90 per cent of the amount ingested. Thus, in reality 

 about 6 times, rather than 54 times, as much arsenic is fatal to a 

 silkworm as is required to kill a honeybee under the somewhat 

 unnatural living conditions. 



