186 EXPERIMENT STATION. [Jan. 



percolation gave free arsenic. Avery and Beans,^ working with 

 a sample of perfect structure and of nearly theoretical compo- 

 sition, found that when treated in a stoppered flask, y^ gram 

 to 500 cubic centimeters of water, the arsenic continued to pass 

 into solution for sixteen weeks, the duration of the experiment. 

 Upon breaking the granules of Paris green by grinding in a 

 mortar the disintegration was more rapid until a state of equi- 

 librium was reached. Carbonic acid also increased the solubil- 

 ity of the arsenic. The decomposition was evidently due to 

 hydrolysis, as the arsenic dissolved in much greater proportion 

 of the original content than did the copper. They concluded 

 that any method based on solubility in water was merely arbi- 

 trary, as " the amount of arsenic trioxide in solution appears 

 to depend almost entirely on the length of time of action, the 

 concentration of the solution and the state of division of the par- 

 ticles of Paris green." To distinguish free arsenic from that 

 rendered free by hydrolysis, Avery and Beans recommended 

 boiling 1 gram of green five minutes in 25 cubic centimeters of 

 sodium acetate solution (1 to 2). It was found that the sodium 

 acetate solution readily dissolved the free arsenic and at the 

 same time largely prevented hydrolysis of the green. The Hil- 

 gard method, 1 gram to 1,000 cubic centimeters of water for 

 twenty-four hours with agitation, indicates free and loosely com- 

 bined arsenic, and while such results are invariably higher than 

 the former, the increase for greens of perfect structure, free 

 from broken particles, is comparatively slight. These two proc- 

 esses are now quite generally employed. The Association of 

 Official Agricultural Chemists ^ recognizes the acetate method 

 and the ten days' extraction method recommended by Hay%vood 

 as provisional methods. 



To prevent arsenical injury to foliage, Gillette ^ and Kilgore "* 

 advised mixing Paris green with milk of lime to neutralize the 

 free arsenic, and Weed ^ suggested combining the green with 

 Bordeaux mixture. 



> Jour. Amer. Chem. Soc, 23, p. Ill (1901). 



« Methods of Analysis Bur. Chom. Bui. No. 107 (revised), p. 27 (1908). 



3 Towa. Exp Sta., Bui. No. 10, pp. 410-413 (1S90). 



' N. Car. Exp. Sta., Bui. No. 77b. pp. 4-7 (1891). 



6 Ohio Exp. Sto., Bui. (Vol. 2) No. 7, p. 186 (1889); Ibid., (Vol. 4) No. 2, pp. 39-42 (1891). 



