PARIS GREEN. 329 



rendered soluble by prolonged treatment. Two methods for 

 determining soluble arsenious oxide have been adopted pro- 

 visionally by the Association of Official Agricultural Chemists, 

 in one of which sodium acetate is used as the solvent, while in 

 the other the green is treated with water for ten days. Investiga- 

 tions with these methods have shown that the sodium acetate 

 method gives more closely the true percentage of free arsenious 

 oxide, while the water-extraction method gives in addition some 

 arsenic caused by the decomposition of the green by water. From 

 a practical standpoint the portion of the green that is so loosely 

 combined would in all likelihood soon break up and scorch the 

 foliage quite as badly as would free arsenious oxide. The water- 

 extraction method would seem, therefore, to indicate more 

 accurately the probable effect of the green on foliage. 



The provisional method of the A. O. A. C. requires treatment 

 with water for ten days, but it has been pointed out that the usual 

 practice among horticulturists is to mix the green with water 

 not very long before they wish to use it. For this reason certain 

 Stations, for instance New York, California and New Jersey, 

 have adopted a one-day extraction period, which it is believed 

 gives results more in harmony with actual practice. This Sta- 

 tion has likewise adopted this method in the present work, and 

 analyses by both the one-day and ten-4ay extractions are given 

 in the table for comparison. The analyses clearly show that, 

 if the ten-day method is to prevail as a standard, but three of 

 the samples would fall within the usual legal limit of three and 

 one-half to four per cent, of soluble arsenious oxide. With the 

 one-day method, but one sample, 18569, contains an excessive 

 jimount, 5.85 per cent. This sample varies greatly in composi- 

 tion from a duplicate sample from the same manufacturer, and 

 under the microscope clearly shows the presence of white arsenic. 

 The use of this sample would be exceedingly dangerous to foli- 

 age. 



Copper Oxide. The amount of cupric oxide found in the 

 samples varied from 26.56 to 30.27 per cent., with an average of 

 28.65 P^r cent. In pure copper aoeto-arsenite the ratio of 

 arsenious oxide to copper oxide is as 1.87 is to i.oo. This ratio is 

 of value in assisting to determine whether white arsenic has been 

 used to fortify the green, for arsenious oxide cannot be added 

 without increasing the ratio. In the samples analysed, the ratio 



