No. 6. DEPARTMENT OF AGRICULTURE. 513 



2. Color Tests. — Tlie color alone can be depended upon to deter- 

 mine whether a green has been wilfully adulterated or not. Pure 

 Paris green has a decidedly bright, light emerald-green color. Any 

 sjtmple which presents a dull, pale or faded color is impure. By plac- 

 ing a small quantity in, say, a homeopathic vial, and tapping the 

 latter gently on the bottom or sides, adulterants can often be made 

 to separate, and can then be seen as w^hite or light streaks or patches 

 against the side of the vial. A pure sample will remain bright green 

 against the glass. Woodworth, of the California Experiment Sta- 

 tion.* has devised the followiug simple but effective test in connec- 

 tion with the color test: Place a small quantity of green, what one 

 can easily pick up on the point of a pen knife, upon a piece of window 

 glass which has been polished clean and dry; tilt the glass at a slight 

 angle and gently tap the edge, just enough to cause the green to flow 

 in a streak across the glass. If the green is of good quality, the 

 streak will be a bright, light emerald-green; if the sample has been 

 adulterated, the streak will have a faded, dull or whitish appearance. 

 Any samples, therefore, which exhibit the latter have been adul- 

 terated or are of too low a grade to be used. 



In connection with this test the writer has found that if great care 

 is taken in cleaning and polishing the glass and the green is allowed 

 to flow only gently across the surface, then by blowing strongly and 

 (iuickly across the surface of the glass, from the side, in the direction 

 of the streak, the particles of Paris green can be blown oft' the plate. 

 Leaving only the adulterants adhering to the glass. If they are pres- 

 ent in large quantity they may then be seen as a dull streak by look- 

 ing through the glass Towards a bright window or a strong light. 

 When the green is exceptionally pure the streak will be nearly im- 

 f'erceptible to the naked eye. AVith the aid of a compound micro- 

 scope the character of the adulterants may be determined. In per- 

 forming this test, great care must be exercised in blowing across the 

 glass. The blowing must be a quick, strong puff, otherwise mois- 

 ture will be condensed and the particles of green will thus be retained 

 on the glass along with the other material. 



3. Ammonia Test. — Pure Paris green is wholly soluble in am- 

 monia. Place a small quantity, say a quarter or a third of a tea- 

 spoonful in a tumbler or other glass vessel, and then pour on an 

 ounce or two of common ammonia water. If after stirring for four 

 or five minutes the solution has assumed a deep blue color, and re- 

 niains perfectly clear, and after standing no residue settles to the 

 bottom, the green fs reasonably pure at least. But if after stirring 

 and allowing to stand an insoluble residue remains, the sample has 

 been adulterated and should be discarded. This test will show the 

 adulteration of the most fraudulent kind, the addition of a foreign 



•Bulletin 126, California Experiment Station, p. 12. 



33—6—1902 



