IXSECTICIDES 



II 



used in spraying potatoes, apple trees, and most shade 

 trees, at the rate of four ounces to 50 gallons of water. 

 On stone fruits, use half this strength, unless lime is 

 added, although in the case of peaches great care must 

 be used if Paris green is applied. Arsenate of lead 

 is safer. Paris green is a heavy powder, and does 

 not stay long in suspension ; hence it must be kept 

 constantly stirred to prevent its settling to the bottom 

 of the vessel. Buy Paris green in as finely powdered 

 condition as possible, and get a reliable brand. 

 Paris green is sometimes adulterated w^ith arsenious 

 acid, which gives a larger per cent of soluble arsenic 

 than should be present. Gypsum or calcium sulphate 

 is also often used as an adulterant. Most experiment 

 stations are able to give the names of reliable brands 

 of Paris green. 



Color Tests for Paris Green — Upon this subject 

 yiv A. V. Stubenrauch says in a bulletin of the Illinois 

 Experiment Station: 'Terhaps the simplest test to 

 determine whether a green has been extensively adul- 

 terated is the color test. Pure Paris green has a bright 

 green color, a shade or two lighter than emerald. Any 

 samples which have a dull or a pale, w^ashed-out ap- 

 pearance should at once be discarded without further 

 question. By placing a small quantity in, say a 

 homeopathic vial, and tapping the latter gently on the 

 bottom or side, adulterants can be made to separate 

 from the green, and can then be seen as white streaks 

 or patches against the glass sides of the vial. The 

 pure green remains bright green against the glass. 

 In connection with the color test. Professor Wood- 

 worth of the California Station has devised the fol- 

 lowing simple test, which can be made by anyone and 

 w^hich will show immediately if the sample is worthy 

 of any further consideration : Place upon a clean glass 

 plate a small quantity of green, what one can easily 



