TOXIC EFFECT OF HYDROCHLORIC ACID 53 



A comparison of the effects of a substance when dissociated 

 into simple ions, and into complex ions is afforded by copper in 

 the form of a sulphate, and in a modified Fehling's solution. The 

 root of lupine will not survive in a solution of copper sulphate more 

 concentrated than ^y^ -g- gram molecule per liter while it will live 

 in a modified Fehling's solution (copper sulphate, sodium hydrate 

 and sugar) of a concentration of .-^fa gram molecule per liter. 1 



78. Toxic Action of Substances in an Ionic Condition. The 

 toxic action of a substance in an ionic condition may be deter- 

 mined by testing the effect of two dissociable salts in which it oc- 

 curs. Thus if a dilute solution of sodium chloride is harmless 

 while one of hydrochloric acid is fatal, the poisonous action is 

 plainly due to the hydrogen present, since it is known that chlo- 

 rine ions are harmless in such solutions. Then again if sodium 

 nitrate is harmless in dilute solutions and nitric acid is fatal, the 

 action of the latter is to be ascribed to ionic hydrogen. 



Solutions of hydrochloric, nitric, and sulphuric acids are prac- 

 tically 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 ; and since the Cl, NO 3 and SO 4 ions are rela- 

 tively harmless when combined with sodium salts, it may be con- 

 cluded that the toxic effect of such solutions is due to ions of 

 hydrogen, and that this effect will be generally the same in the 

 three acids (See 75, normal solutions). 



79. Toxic Effect of Hydrochloric Acid. Germinate some seeds 

 of Lupinus albus by soaking in distilled water for a day, then place 

 in cotton wool until the roots are about 2 cm. in length. Prepare 

 a few small beakers of glass by cleaning them thoroughly and 

 washing with distilled water. Fit to each beaker a cork plate 

 which sets over the top like a lid. Push through the cork a clean 

 glass rod which reaches half way to the bottom of the beaker. 

 Fit on this rod a second cork of half the size of the upper one. 



1 Kahlenberg and True. On the toxic action of dissolved salts and their electro- 

 lytic dissociation. Bot. Gazette, 22 : 8l. 1896. 



