The Spraying of Trees. 581 



When the following samples were taken, Oct. 5, the old appli- 

 cation of Paris green was still intact just under the surface, appar- 

 ently as abundant as when first applied, but none of it could be 

 traced in the soil by the eye. 



A. Soil taken at one-half in. below the layer of poison. Much 

 arsenic present. 



B. Sample 1 in. down. Much arsenic present. 



C. Two in. down. Some arsenic found. 



D. Five in. A very little arsenic was present. 



E. Seven in. down. A trace of arsenic found, yet the poison was 

 even here more abundant than it was at 3 in. in the sand (C in Exp. I.) 



F. Eight in. down. No arsenic. 



The questions now occur how the arsenic went down in the soil, 

 and why it went deeper in the clay loam than in the sand. We 

 must first detei-mine if the arsenic went into solution and was 

 carried down by the natural drainage. It will be remembered that 

 at ^ in. under the surface in the loose clay loam (A, Exp. II.), 

 plenty of arsenic was found. A sample of this soil was thoroughly 

 digested in hot water, and the water carefully tested for arsenic, but 

 not a trace of it was found. This shows that the arsenic was in an 

 insoluble condition, and that it was probably carried into the soil 

 simply by the mechanical action of the rain. There are various 

 other considerations which also support this view. We have seen 

 that it evidently followed the remains of the root in one instance 

 (E. F. Exp. I.). It went down farther in the clay loam because that 

 soil was seamy and burrowed by worms. The sand is a better 

 filter. Again, if the arsenic had been dissolved in the soil water, it 

 would have gone much farther down, tor the eleven inches of rain- 

 fall on the moist soil of plot II. (there was no surface drainage 

 possible) must have gone many more inches into the soil, for there 

 were some heavy rains ; and a similar remark will apply to plot I. 

 Again, if the arsenic were in solution in the soil, it would pass 

 laterally, as well as downwards, with the movement of soil water, 

 and the plants which grew on the very edges of the plots would 

 have suffered. 



The gist of the whole matter then, if we may generalize from 

 these tests, is that the arsenites do not leach from the soil. They 

 remain where they fall, the same as sand does, and are carried 

 down only when there are crevices or other openings in the soil, 

 and they then go down as insoluble compounds, and to a slight 



