29f> Agricultural Chemistry. 



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the conclusions: "That Paris green is not injurious to pota 

 foliage if applied in moderate quantity with lime water or B 

 deaux mixture evenly distributed;" and "That sodium arsenite 

 should not be applied to potatoes except with Bordeaux mix- 

 ture." 



Adulteration and the manufacture of impure Paris green were 

 more or less prevalent previous to the passage of insecticide laws. 

 Gypsum or sulphate of lime was one of the most common adulter- 

 ants. This has little if any insecticidal value and was added 

 to increase the bulk. Other impurities may result from the use 

 of crude materials or careless methods in preparation. Wood- 

 worth has given some simple tests to detect common forms of 

 adulteration. 



The ammonia test is performed by taking an amount of Paris 

 green that can be held on a five cent piece, transferring it to a 

 drinking glass and adding about six tablespoonfuls of household 

 ammonia or "spirits of hartshorn." Keep the contents of the 

 glass well stirred for five minutes. If the "green" is pure, it 

 will then form a clear, dark-blue solution and leave no solid 

 residue. If gypsum is present, it will form a white suspension 

 in the liquid and finally settle to the bottom of the glass. This 

 is not a conclusive test since impurities soluble in' ammonia may 

 be present. 



The glass test often enables one to distinguish adulterated 

 samples not detectable by ammonia. Take such an amount of 

 Paris green as can be picked up readily on the point of a pen 

 knife and place it on a small rectangular piece of clear glass. 

 Holding the glass in an inclined position, gently tap the lower 

 edge and the Paris green will move down the inclined plane leav- 

 ing a track of dust behind. In the case of a pure "green," the 

 dust will be of a bright green color. If the sample is impure, 

 it may leave a white, pale-green or other-colored streak, depend- 

 ing upon the color of the adulterating substance. This test is 

 best used for comparing unknown samples with a sample known 

 to be pure. Like the ammonia test, it is not infallible. Varia- 



