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CHEMICAL MEMORANDA. 



By Wm. McMu.iTRFF, Chemist. 



lu a previous monthly report I took occasion to publish the results 

 of some prelimiuary experiments, made principally to determine whether 

 arsenic, when applied to plants in the form of Paris-green for the de- 

 struction of the Colorado potato-beetle, could, when transmitted to the 

 soil, be absorbed and assimilated during growth, and at the same time 

 I gave the results of other experiments in the same direction. My own 

 experiments having been of a somewhat unsatisfactory character, and 

 those of others having furnished such extremely discordant results, I 

 finally determined to follow out the investigation about to be described, 

 to endeavor to settle this question, together with others which subse- 

 quently arose. These subsequent questions were suggested by the fears 

 entertained by some of our correspondents that, when Paris-green was 

 applied to crops year after year, sufficient quantity might accumulate 

 in the soil to poison it sufdciently to destroy its fertility and render it 

 incapable of producing vegetation. 



My investigation was therefore made to determine — 



1st. If applied to the soil, can arsenic or arsenious acid be absorbed 

 and assimilated in the economy of jjlant growth ? 



2d. If absorbed and assimilated, can it be taken up in sufiScient 

 quantity to become prejudicial or injurious to the health of consumers ? 



3d. If not taken up by the plant during growth, does it by its pres- 

 ence in the soil exert a poisonous influence upon the plant itself? 



4th. If it exerts a poisonous influence upon the plant, to what extent 

 may it exist in the soil before it becomes iujurious I 



The experiments were conducted as follows : 



Fifteen common flower-pots, of as nearly uniform size as possible, 

 were selected, and each one filled with a measured quantity of good 

 garden-soil. With the soil of each pot were then thoroughly intermixed 

 quantities of Paris-green, ranging from 100 milligrams to 1 gram. 

 Thus one pot contained 100 milligrams; that next to it contained 

 200 milligrams; the next 300; and this quantity was increased 

 until it finally reached 1 gram. In the other pots the increase 

 was made more rapid, and the other pots contained 2, 3, 4, and 

 5 grams, respectively. After the soil had thus been carefully pre- 

 pared, a given number of peas, all of which were carefully selected, so 

 as to secure as nearly as possible those of the same size and appearance, 

 were planted in each pot. This experiment proved unsatisfactory, from 

 the fact that on one night that portion of the green-house in which the 

 pots had been placed became too cold, and a large number of the seeds 

 failed to germinate on this account. I therefore considered it of some 

 importance to duplicate the experiments, and, without disturbing these 

 further than to remove them to a warmer portion of the green-house, 

 prepared in a similar manner and with the same care another series of 

 pots. At this time the question also arose, what would be the effect 

 of arsenic in combination, as arseniteof potassa and arseniate of potassa ? 

 For the purpose of determining this, I prepared two other series of pots 

 in the same manner as before, and placed them alongside the former. 

 With these experiments my results were extremely satisfactory, and 

 when those plants which had grown well had reached the period of 

 bloom, the three series of pots finally prepared were each placed by 

 themselves in a convenient position and photographed, and from the 



