CHEMICAL CONSTITUTIONS AND POISONOUS ACTION 273 



named, or to the fact that dilute solutions of alkalies are rapidly converted 

 into carbonates by respiring plants. The ions of mercury, silver, and cyano- 

 gen are, however, certainly much more poisonous than those of either 

 hydrogen or hydroxyl. 



After Wiithrich had compared the poisonous action of equivalent solutions, 

 various authors worked with equimolecular concentrations 1 . The ratio i : 16 or 

 the fraction ^ indicates a solution containing one gramme-molecule in 16 litres. 

 In the case of mercuric chloride, whose molecular weight is 271, the 16 litres would 

 contain 271 grammes of solid. Therefore i cubic centimetre contains 271 -=- 16,000 

 = -0169 of a gramme, which is a 1-69 per cent, solution. It is only when equi- 

 molecular solutions are used that the influence of dissociation and of combination 

 with different radicles can be determined. 



The differences in the detailed results obtained by the above authors are 

 due partly to the specific peculiarities of the plants examined, and partly to the 

 fact that Kronig and Paul observed the concentration required to produce rapid 

 death, whereas the other authors noted that required to stop growth. In the 

 latter case, when the maxima and minima for growth are noted,, the rapidity of 

 penetration as well as the degree of dissociation become of less importance, for 

 during a prolonged experiment a condition of equilibrium will be reached after 

 a time. A large quantity of a slightly dissociated substance can, in time, accumulate 

 within the cell, even when only the ions diosmose, provided that they enter into 

 combination within the cell, so that a continuous inward stream is kept up 2 . 



It is possible that the relation between the poisonous action and the degree 

 of dissociation shows best in the case of acids and alkalies, because these substances 

 readily penetrate the protoplast. Whether the rapidity of absorption is of impor- 

 tance or not, the degree of dissociation is certainly decisive as regards poisonous 

 action. Thus Kahlenberg and True found that the dissociating chloride of iron 

 , is as poisonous in a concentration of i : 22,400, as is colloidal iron in a strength 

 of i : 1,174. Further, sulphate of copper after the addition of cane sugar and 

 potassium hydrate only exerts the same action in a strength of i : 400 as it does 



1 Wiithrich, Zeitschr. f. Pflanzenkrankheiten, 1892, Bd. II, p. 16 ; Kahlenberg and True, Botanical 

 Gazette, 1896, Vol. XXII, p.8i; Zeitscbr. f. physikal. Chemie, 1897, Bd. xxu,p. 474; Heald, Botanical 

 Gazette, 1896, Vol. xxil, p. 125 ; Kronig and Paul, Zeitschr. f. Hygiene und Infectionskrankheiten, 

 1897, Bd. xxv, p. i ; True and Hunkel, Bot. Centralbl., 1898, Bd. LXXVI, p. 289 ; Stevens, Botanical 

 Gazette, 1898, Vol. XXVI, p. 377 ; Clark, ibid., 1899, Vol. xxvin, p. 289. [Equivalent solutions 

 are not always equimolecular. Thus equivalent solutions of sodium carbonate (Na 2 CO 3 ) and sodium 

 bicarbonate (NaHCO 3 ) will contain i gramme-molecule c f Na 2 CO 3 (106 grammes) to 2 gramme- 

 molecules of NaHCO 3 (168 grammes). Similarly equivalent solutions of acids will contain equal 

 numbers of atoms of displaceable H, so that normal or decinormal solutions of HCl contain twice 

 as many molecules as similar solutions of H 2 SO 4 . When diluted these solutions will contain equal 

 numbers of free sodium and hydrogen ions respectively.] 



2 [A good instance of this is afforded when a cell of Elodea is immersed in a solution of veratrine 

 nitrate, for as the nitric acid ions are absorbed and assimilated the insoluble veratrine is precipitated 

 inside and outside the cell. Penicillium, however, can assimilate veratrine, so that if it is grown on 

 an inorganic nutrient solution to which potassium and veratrine nitrates have been added, the 

 solution becomes acid instead of alkaline, some of the nitric ions being set free.] 



PFEFFER. II T 



