20 



rests upon the assumption that calcium is a stronger base than magnesium, and will exert a 

 greater attractive force upon acids, while it ignores the application of the mass law to the dis- 

 tribution of an acid between two bases, which itself accounts very satisfactorily for the facts 

 observed. 



(3) Of sodium sulphate "Wolf (Landw. Versuchsst. , 6, pp. 210, 213) indicates that solutions of more 

 than 0.05 per cent are toxic to roots of the bean {Phaseolus vulgaris). Loeb [Am. Journ. Physiol- 

 ogy, 3, 393 (1900)], found sodium sulphate to be more poisonous than sodium chloride to eggs 

 of a fish (Fundulus heteroclitus). This he attributes to a precipitation of calcium from its ion 

 proteid compounds in the protoplasm, a reaction effected through the sulphions dissociated by 

 sodium sulphate. 



(3) The minimum toxic concentration for sodium chloride, the same plant and the same methods 

 being used, is placed about three times as high (one- sixteenth normal) by True [Amer. Journ. 

 Sci , ser. 4, 9, 187 (1901)]. As the experiments with sodium chloride here described were repeated 

 several times, without variation in the result, no explanation for this discrepancy is apparent. 



Many experiments have been made with sodium chloride as to its elf ects upon plants. It may 

 be of interest to refer to some of those in which limits of endurance have bee a determined, 

 especially as these are in all cases much higher than that given above for rcot tips of Lupinus 

 albus. Storp TBiedermann's Centralbl., 13, 76 (1884)] found that sodium chloride in a solution of 

 greater concentration than 0.01 per cent retarded the germination of seeds. Eschenhagen [Ueber 

 den Einfluss von Losungen verschiedener Concentrationen auf den Wachsthum der Schimmel- 

 pilze (1889)], quoted by Stange in Bot. Zeitung (1892, p. 255), gives the following limits for the 

 active growth of fungi in solutions of sodium chloride and of sodium nitrate: 



Fungus. 



Per cent 

 sodium 

 chloride. 



Per cent 

 sodium 

 nitrate. 



Aspergillus 

 Penicillium 

 Botrytis — 



Richter [Ueber die Anpassung der Siisswasseralgen an Kochsalzlosungen Flora, 75,- 4 (1892)] 

 found th'dit Zygnema stellinum geyiiiinum lived two months in a 6 per cent solution of sodium 

 chloride added to a culture solution, and more than a year when the sodium chloride solution 

 was 2 per cent or weaker. De Freitag [Archiv fiir Hygiene, 11, 68 (1890)] is authority for the 

 statement that Bacillus tuberculosis lived three months, and the typhus Bacillus six months 

 in a saturated solution of sodium chloride. Coupin [Revue Gen. de Botanique, 10, 177 

 obtained the following limits for various plants in solutions of sodium chloride: 



Plant. 



Per cent 

 limit of 

 endur- 

 ance. 



Per cent 

 in dif- 

 ferent 



solution. 



Wheat • 



1.8 

 1.2 

 1.2 

 1.4 

 1.1 



5 



Peas . . , 



25 



White lupine 





Maize . . 





Vetch 









According to W. Sigmund [Landw. Versuchsst., 47, 1 (1896)] the maximum concentration of 

 NaCl solutions endurable by germinating seeds of cereals is 0.5 per cent, of legumes 0.3 per 

 cent, of rape 0.1 per cent Loew [Bui. 18, Div. Veg. Phys. and Path., p. 19] found that Spirogyra 

 suffers in a solution containing 0.5 per cent of sodium chloride. 



(t) Carbonic acid (HCO3) is here regarded as a monovalent acid, so that a gram molecule 

 (instead of one-half of a gram molecule) to the liter has been used in making up normal solu- 

 tions of sodium bicarbonate. To prevent inversion to the normal carbonate (NasCOs) [see 

 Cameron and Briggs, Bui. 18, Div. of Soils, 1900; also Jour. Physical Chem., 5, 537 (1901)] solutions 

 of the bicarbonate were always well charged with carbon dioxide and were tested for 

 hydroxyl with phenolphthaleine before being used in culture experiments, and again at the end 

 of the experiment. It is quite possible, of course, that a small error was thus introduced, as the 

 carbonic acid formed by the dilution of carbon dioxide in water may have retarded somewhat 

 the dissociation or ionization of the sodium hydrogen carbonate. It is improbable that sodium 

 hydrogen carbonate, unaccompanied by the normal carbonate, would ever occur in nature 

 except in the presence of an excess of carbon dioxide, which fact is a further justification of 

 the procedure here described. 



In order to demonstrate that this excess of carbon dioxide was not in itself injurious to the 

 roots of white lupine, the following simple check experiment was made: Carbon dioxide was 

 forced into distilled water until a saturated solution was obtained. Plants were then entered in 

 this solution, which was protected as completely from loss of carbon dioxide as circumstances 

 would permit. After twenty-four hours the solution was tested with barium hydrate, and the 

 heaviness of the resulting precipitate of barium carbonate showed that very much more carbon 

 dioxide still remained than is present in ordinary water. During this period the roots grew 

 nearly as well as in water containing only the normal quantity of carbon dioxide. It might be 

 supposed that a solution of carbon dioxide in water and presumably containing the. hypothet- 

 ical carbonic acid must needs be itself quite toxic, as it would be expected to yield the hydrogen 

 ion which recent investigations have shown to be excessively toxic. In this connection some 

 work of Pfeififer [Ann. Chem. (2), 23, 625 (1884)] will prove interesting. This investigation showed 

 that a solution of carbon dioxide is an exceedingly poor conductor; that in fact the highest con- 

 ductivity observed in such solutions was only about a thousandth of that which Kohlrausch's 

 work showed it should possess. See also Knox [Ann. Phys. Chem., 54, 44 (1895)] and Walker and 

 Cormack [Journ. Chem. Soc, 77, 5 (1900)]. 



It would seem rational, therefore, to consider that carbonic acid does not exist itself, or at 

 least in only minute quantities in solutions of carbon dioxide, but is potentially present in its 

 constituents and only forms in the presence of some added influence, such as a base. And that, 

 therefore, even a concentrated aqueous solution of carbon dioxide would contain no hydrogen 

 ions, or so very small a quantity as to be ineffective against so delicate an indicator as a plant 

 root. 



