No. 6. DEPARTMENT OF AGF.iCULTURE. 515 



the clean, green balls, brand this compound as fraudulent, and it can- 

 not be named anything but "bogus/' although the package in which it 

 was bought was labeled "Strictly Pure Paris Green." 



Kequirements of a Good Paris Green. 



The points which go to make a good Paris green have been sum- 

 med up as follows:* 



"1. It should be a wholly dry and impalpable powder. Grittiness 

 and caking are evidences of adulteration. 



"2. It should have a bright, light emerald-green color, which should 

 not whiten or become dull in the streak left in passing a sample 

 across a clean glass plate. 



"3. It should be entirely soluble in. ammonia. Any residue is an. 

 adulterant. 



"4. Under the microscope it should be seen to contain only a trace 

 of foreign matter, and should consist of clean, green spheres, wholly 

 separate from one another. Aggregation into masses is evidence of 

 careless manufacture. 



'•These are all the points which can be readily determined. In ad- 

 dition to the above, should be added the most important point, but 

 one w-hich can be determined only by a chemical analysis, viz: 



"5. Paris green should contain not less than fifty per cent, of ar- 

 senious oxid, of which not more than four per cent, should be in the 

 free state, or uncombined with copper." 



Efect of the Addition of Lime. — Lime is now being added to the 

 mixture of Paris green and water to lessen the injurious action of the 

 uncombined arsenious oxid. This it does by combining with the 

 soluble arsenic to form the insoluble arsenite of lime, which is fully 

 as harmless as Paris green itself. This is true only up to a certain 

 point, however. When the uncombined arsenic is present in large 

 quantities the lime will do no good, and may even be harmful. It 

 has been shownf that lime acts upon white arsenic in such a way 

 when it is in suspension in water that the injurious action upon the 

 foliage is greatly increased. 



Objections to the Use of Paris Green. 



The most serious objection to the use of Paris green as an insecti- 

 cide, outside of the counts against it enumerated above, due to the 

 shortcomings of the manufacturers, is the rapidity with which it 

 settles in the spray tank. Paris green is a very heavy-grained sub 

 stance, and therefore one requiriug continuous effort to keep it in 

 suspension. When the poison is used alone the water throughout 

 the tank must be kept in motion. Merely creating a current around 



•Bulletin 68, Illinois Experiment Station, p. 175. 



tBulletln 10. Iowa Experiment Station, p. 411; also cited by Woodworth Bulletin 126. Cali- 

 fornia Experiment Station, p. 12. 



