11)01).] PUBLIC DOCUMENT — No. 31. 65 



Of the treatments shown in this table, Kos. 1, 3, 4 and 11 

 gave the quickest, most effectual and permanent results. Nos. 

 5, 6 and 12 proved about as effective, but in this experiment the 

 effect was not so permanent. The arsenic sulfide in this case 

 was dissolved in an alkaline solution of potassium sulfide. Ob- 

 servations made one year after treating the various plots showed 

 that there was little or no permanent injury to vegetation in 

 any case. The nitrate of soda, when applied at the strength 

 given, was not permanently injurious, and what injury was 

 caused to grass at first was quickly followed by a marked change 

 in color and greatly stimulated growth. jSTeither were the ef- 

 fects produced by sodium sulfide, copper sulfate and niter cake 

 of any value from the point of view of permanency. 



It was not the purpose of this experiment to test the relative 

 poisonous effects of these substances on vegetation; nor would 

 this method be accurate enough for the purpose. It should 

 also be borne in mind that one test can only be an indication of 

 the relative merits of the chemicals used ; moreover, there was 

 considerable difference in the purity of the chemicals used. 

 There are many different grades of crude chemicals on the 

 market, and with the exception of corrosive sublimate every- 

 thing which we used was a crude commercial chemical. These 

 in some instances differ in their composition. It is, therefore, 

 impossible for us to state whether Nos. 1, 3, -l and 11 would 

 always prove to be superior to Nos. 5, G and 12. It would 

 require a series of exjjeriments under similar conditions to 

 establish reliable data, but in all probability there is very little 

 important difference in the relative efficiency of these arsenic 

 compounds as regards their toxic effect on vegetation. Some of 

 the proprietary poisons on the market for killing weeds are 

 arsenic compounds, probably in most cases arsenate of soda. 

 Their purity may not in all cases be as high as some of the 

 grades we used, but this is not an objection and may be an 

 advantage, since the crude forms are cheaper, and are efficient 

 enough for all practical purposes. 



The writer has used many chemical substances for extermi- 

 nating weeds in lawns, walks, on tennis courts, railroad tracks 

 and other places, and is well aware that a variety of results is 

 obtained from the use of the same substances under different 



