509 



months, the plants having" grown to fall size, flowered, and fruited, it 

 was found by application of both Marsh's and Reinsch's tests that the 

 arsenic had permeated every i^art of the plants. Being thus satisfied 

 that plants were capable of taking up arsenic during their development, 

 he made some experiments with the use of phosphates containing 

 arsenic. The sulphuric acid employed in their manufacture contained 

 about 2.8 pounds arsenic per ton, and the proportions employed were 

 one ton of acid per two tons of bone. The amount of arsenic in the 

 superphosphate was therefore relatively very small. 



In his next experiment he prepared a soil consisting of one part super- 

 phosphate and four parts garden-mold, into which he transplanted a 

 small cabbage-plant. At the end of three weeks an examination for 

 arsenic, with a small portion of the plant, (113 grains,) gave the " most 

 distinct indications of the presence of that substance." Since, however, 

 he considered the conditions in this case very favorable to the absorp- 

 tion of arsenic, he examined carefullj' different samples of Swedish 

 turnips which had grown in a soil to which superphosphate had been 

 applied at the rate of six hundred weight per Irish acre, and found 

 arsenic in each case. It is also stated that sheep refused to feed freely 

 upon the turnips grown upon soil to which the superphosphate had 

 been applied. 



The results of Professor Davy's experiments do not, however, seem 

 to have been confirmed by the results of later investigations, and, in 

 fact, so far as we have been able to learn, these have been of a decid- 

 edly contradictory character. Thus Mr. E. H. Ogston,* doubting that 

 a saturated solution of arsenious acid could be applied to plants with- 

 out injury to them, and that the amount of arsenic communicated to the 

 soil by the application of superphosphates would be large enough to 

 appear in the plant in sufficient quantity to be detected by the ordinary 

 tests of the laboratory, repeated the experiments by watering some 

 strong cabbage-plants of some weeks' growth with a saturated solution 

 of arsenious acid, and though only two doses were administered in three 

 days, the plants drooped and died in less than a week. Repetition of 

 this experiment with Scotch kale afforded similar results. After a few 

 days all the plants experimented uijon were removed from the ground 

 and various portions of the stems and leaves examined for arsenic by 

 means of the Marsh's test, when the poison was found " only in the por- 

 tions of the stems close to the roots, which were darkened in color in 

 the interior. In no case was the poison found in the stem at more than 

 five inches from the ground." Mr. Ogston experimented with other so- 

 lutions of arsenious acid, but found that when the dilution was suffi- 

 ciently great to prevent injury to the plant, no arsenic could be detected 

 in any portion above ground. 



With regard to the absorption of arsenic in case of the Swedish tur- 

 nips, without any experiments, he reasons that the quantity ajiplied per 

 acre in the superphosphate is not sufficient to render it possible to de- 

 tect its presence in the root. But admitting that the plant will absorb 

 arsenic with the same avidity as phosphoric acid, which, reasoning from 

 the evidences on record, is scarcely i^ossible, close calculation shows 

 that when the quantity which might be introduced to the soil through 

 the medium of the superphosphate is present, enough could be taken 

 up to be detected by the delicate tests at our command. 



The conclusions arrived at by Mr. Ogston seem to be corroborated by 

 the results of the investigations of Daubeny.f In his experiments he 



* Gardner's Chronicle, 1860, 21C. t Jour. (. hem. Soc, XIV, •^:io. 



4A 



