190 EXPERIMENT STATION. [Jan. 



the formation of a basic acetate. Sample U showed a coiisidcr- 

 ablt! amoinit of impurities. Any hypothetical comhiuatidu of 

 the various constituents that might be offered would be decid- 

 edly arbitrary, and a discussion seems inadvisable at this time. 

 A careful study of the results would indicate that the slow 

 process green, exclusive of moisture, was at least DO per cent. 

 pure. To be of standard quality Paris green should contain not 

 less than 50 per cent, of arsenous oxide combined with copper, 

 and not more than 3.50 per cent, of arsenous oxide soluble in 

 water. The poisonous character of Paris green is dependent 

 on the arsenic content, but the form in which the arsenic exists 

 largely fixes its value as an insecticide. Adulteration is seldom 

 practiced under the inspection laws now in force. 



Paris green is a dry, impalpable powder that readily passes 

 a 100-mesh sieve, and to the touch resembles flour. A micro- 

 scopical examination is required to determine the size, shape 

 and uniformity of particles as well as the general character and 

 amount of impurities. The latter may consist of Scheele's green 

 that was not transformed or by-products such as arsenic, sodium 

 sulfate, sodium acetate and possibly other compounds not inten- 

 tionally added biit present in the original chemicals. The sam- 

 ple of instantaneous green under examination was of a pale 

 green color, and consisted of very small, irregular, angular par- 

 ticles with considerable impurity. It was cohesive, had a poor 

 '' flow," and the film test ^ on glass appeared whitish. The 

 slow process green, on the other hand, had a brilliant green color 

 of metallic luster, and was composed of minute green spheres 

 of various sizes, together with a small amount of crystalline 

 and fragmentary matter. It had an excellent " flow," and the 

 film test on glass was green. The size of the particles is affected 

 by the concentration, temperature and amount of agitation at 

 the time of formation. The smaller the globules with retention 

 of ]ierfect form and similar size, the more desirable the product. 

 Paris green has a high s]iecific gravity and a low power of 

 suspension. In the station laboratory suspension was deter- 

 mined - in a foot column containing the insecticide at the pro- 

 portion of 1 gram of dry salt to 1,000 cubic centimeters of 



• r. W. Woodworth, Cal. Exp. Sta., Bui. No. 126, p. 13 (1899). 



2 Modification of the California method. G. E. Colby, Cal. Exp. Sta., Bui. No. 151, pp. 33- 

 35 (1903). 



