1913] J- E. Greaves 521 



at a depth of three feet, yielded 11 parts per million of total arsenic, 

 30.91 per Cent, of which was water-soluble. 



It may be safely concluded, from the above data, that some 

 virgin soils contain arsenic in large quantities, but that the propor- 

 tion in a soil is no index of the amount which is soluble in water. 

 The latter is probably governed by many factors, e. g., kind of soil, 

 water-soluble salts in it, and form in which the arsenic was applied 

 to the soil. 



The latter factor has been tested by applying the same quantity 

 of different forms of arsenic to different portions of the same soil 

 and then determining the quantity of water-soluble arsenic present 

 in the soil. The soil used was a typical bench soil — a sandy loam — 

 fairly high in content of calcium and iron, and supplied with an 

 abundance of all the essential Clements of plant food with the 

 exception of nitrogen, which was low as is characteristic of the arid 

 soil. The proportion of water-soluble salts in the soil was low. 

 The influence of the soil on the solubility of the arsenical insecti- 

 cide was determined as follows: Quantities of lead arsenate (21.96 

 per Cent, of arsenic), Paris green (47 per cent. of arsenic), zinc 

 arsenite (31.25 per cent. of arsenic) and arsenic trisulfide (60 per 

 Cent, of arsenic), were added to 100 gm. portions of soil in quanti- 

 ties sufficient to give 112 mgm. of arsenic per 100 gm. of soil. The 

 soil and arsenic, together with 2 gm. of dry blood, were placed in 

 sterile tumblers, covered with Petri dishes, the water content made 

 and kept at 18 per cent.; and then each mixture was incubated at 

 28° C. for three weeks. At the end of this time the soil was trans- 

 ferred with 1000 c.c. of carbon-dioxide-free distilled water, to 

 large acid bottles. The mixture was left in these bottles with occa- 

 sional shaking for eight days, then filtered and the arsenic deter- 

 mined in an aliquot part. In another set each quantity of insecticide 

 was mixed with a 100 gm. portion of soil and 2 gm. of dry blood, 

 and the water-soluble arsenic determined as above, without incuba- 

 tion. All determinations were made in duplicate. The data are 

 given in Table 2, as mgm. of water-soluble arsenic in 100 gm. of 

 soil either before or after three weeks' incubation (112 mgm. of 

 arsenic had been added to each.) 



