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SCIENCE. 



305 



water." * " Solutions of hydrochloric, nitric 

 and sulfuric acids are practically completely 

 dissociated when an amount of these com- 

 pounds in grams equal to their molecular 

 weights divided by the number of H atoms 

 (one gram equivalent) is added to one liter 

 of distilled water."+ 



These statements are contradictory. Though 

 the former states HCl is nearly completely 

 dissociated at h/1000 and the latter states 

 that the same acid is practically completely 

 dissociated at a normal solution, yet both are 

 incorrect ; but to be exact it is also practically 

 completely dissociated at a concentration four 

 times n/1000 dilution. n/250 = 98.94 



Other weaker compounds may have some 

 undissociated ions — e. g., NaCl at a certain 

 dilution is 80 per cent, dissociated; that is, 

 if there were 100 molecules of NaCl and 80 

 per cent, of them were dissociated there would 

 be 80 CI ions and 80 Xa ions and 20 NaCl 

 ions. 



The degree of dissociation increases as the 

 dilution increases until a dilution is reached 

 when the dissociation is practically complete. 



Since the degrees of dissociation in com- 

 pounds capable of dissociation vary with the 

 dilution, it is necessary to find the degree of 

 dissociation before it is possible to determine 

 the exact toxic effect of each kind of ions in 

 the various solutions — e. g., if a seedling just 

 lives in a solution of KOH 1/128 gram 

 equivalent dissolved in distilled water and 

 made up to 1,000 c.c, and dies in a NaOH 

 solution of the same dilution, one of two 

 things must be true, — either the degree of dis- 

 sociation in KOn is less than the degree of 

 dissociation in KaOH at the above-named 

 dilution or the Na ions have an appreciable 

 toxic effect at this dilution, but it has been 

 stated by MacDougal§ that at such weak di- 

 lutions sodium salts have no appreciable in- 



• Kahloiil)(>rg and True. ' On toxic action of 

 ilissolvpfl salts and tboir plectrolytic dissociation,' 

 Rnt. Onzcttr. 22:81, 1800. 



+ MaoDoiigal's ' Text-Book of Plant Physiol- 

 op>-,' 1901, p. 5.3, par. 78. 



t -Arrhenius, 'Text-Book of Elcctro-Cliemistrv,' 



p. i.ri. 



? 'Text-Book of Plant Pliysiologj-,' 1901, p. 53, 

 par. 78. 



rtuence, hence the difference in the toxic effect 

 of the two solutions must be due to the differ- 

 ence of dissociation. 



It has been stated that it is the H ions and 

 those containing H which are fatal.* 



It is the object of the following experiment 

 to find in what dilution KOH, NaOH, HCl 

 and HjSO, seedlings of Indian corn (Zea 

 Mais) will be killed, and deduce facts con- 

 cerning the toxic influence of II and OH ions 

 upon these seedlings. 



In order to be clearly understood in regard 

 to terms used it might be well to give some 

 quotations regarding them. 



Gram-Molecule (Arrhenius, p. 9). — " Thus, 

 for example, the molecular weight of HCl is 

 36.46, and consequently 1 gram-molecule of 

 this (HCl) is .36.46 grams, tliat is, the equiv- 

 alent weight in grams; a gram-molecule of 

 sulfuric acid is 98 grams, i. e., twice the gram 

 equivalent." 



Gram-equivalent (Arrhenius, p. 9). — "By a 

 gram-equivalent of zinc we mean 32.7 grams 

 of this metal; a gram-equivalent of a sub- 

 stance whose equivalent weight is E is E 

 grams." Thus we see that a gram-equivalent 

 of a monobasic substance is equal to its 

 molecular weight, and of a dibasic sub- 

 stance is equal to one half its molecular 

 weight. 



Normal Solution (Sutton, p. 28), — " Nor- 

 mal solutions are prepared so that one liter 

 of solution at 16° C. shall contain the hydro- 

 gen equivalent of the active reagent in grams 

 (H = 1)." Fresenius (p. 687) : " Solutions of 

 such strength that 1,000 c.c. contains an 

 amount of acid or base equivalent to one gram 

 of hydrogen are normal solutions, e. g. 



Mol.wt. W(. in i,oooc.c.or>olutian. 



HCl 3C,.H\ 36.46 



H,SO 98.00 49.00 



Nu,.('o, 106.08 53.04 



The normal solutions used in this experi- 

 ment were made according to the definitions 

 of normal solutions by Sutton and Fresenius. 



Tests in this exiK?rimcnt were made with 

 each of four different dilutions of four dif- 

 ferent solutions, two of alkali, KOH and 



* I., c, p. 53, par. 78. 



