﻿12 SEVENTH ANNUAL REPORT 



acid. One pound of the Green uniformly spread over an acre of soil, 

 would amount to sixteen-hundredths of a grain per square foot, or 

 nine-hundredths of a. grain of arsenious acid. If uniformly mixed 

 with the soil to the depth of a foot, it would, of course, be the same 

 to the cubic foot. In actual practice, even this amount does not reach 

 the soil direct or in an unchanged form, since much of it is acted upon 

 by the digestive organs of the fated insects." It is safe to say that 

 •even if the Green retained for all time its poisonous power and purity 

 in the soil, this mere fractional part of a grain might be added annually 

 for half a century without any serious effects to the plants. In real- 

 ity, however, there is no reason to believe that it does so remain. Of 

 the few experiments on record which bear on this point, those made 

 by Prof. W. K. Kedzie, while connected with the Michigan Agricul- 

 tural College, in 1872, are the most interesting and instructive. In a 

 paper read before the Natural History Society of the College, he 

 proved, from these experiments, that where water was charged with 

 carbonic acid or ammonia, a certain portion of the Green was dis- 

 solved, but was quickly converted into an insoluble and harmless pre- 

 cipitate with the oxide of iron which exists very generally in soils. 

 Fleck has shown (Zeitschrift fiir Biologie, Bd. viii, s. 455, 1872) that 

 arsenious acid in contact with moist organic substances, especially 

 starch sizing, forms arseniuretted hydrogen, which diffuses in the air; 

 and it is more than probable that the Green used in our fields will lose 

 its poisonous power, and disappear in these and other ways. The 

 <[uestion as to how the plant is affected by the poison through the soil 

 is, therefore, partly answered by the above facts. Water is both the 

 universal solvent and the vehicle by which all plants appropriate 

 their nourishment ; but in this instance its solvent and carrying power 

 is for the most part neutralized by the oxide of iron in the soil ; and 

 though some experiments by Dr. E. W. Davy, and quoted by Prof. 

 Johnson in the article already cited, would indicate that, under cer- 

 tain circumstances, some of the arsenious acid may be taken up by 

 plants before passing into the insoluble combination ; yet the quantity 

 is evidently very slight. 



Some persons have imagined that the soggy and watery potatoes 

 that have been so common of late years are due to the influence of 

 this poison ; but this idea is proved to be erroneous by the fact that 

 such imperfect potatoes are not confined to the districts where Paris 

 •Green has been used. Indeed, they are much more likely due to the 

 injury and defoliation of the plant by the insect; for no plant can 

 mature a healthy root when its leaf system is so seriously impaired 

 by the constant gnawings of insects. P'inally, we must not forget that 

 both arsenic and copper are widely distributed throughout the inor- 



