9 



with the proteids of the protoplasm of plants and animals, which "ion 

 proteids" play a liighl}^ important part in life jjrocessesand phenomena. 

 This aspect of the subject will be treated particularly in discussing 

 the significance of the experiments with mixed solutions. 



METHODS OF EXPERIMENT. 



SALTS EMPLOYED. 



In the selection of a series of salts for investigation the experience 

 of members of the Division of Soils in field and laboratory served as 

 a guide. Salts were used which have been determined as forming 

 definitely injurious components of alkali soils and as occurring in 

 sufiicient quantity to be of practical importance. In about the order 

 of their general abundance in the Western United States these are 

 sodium chloride (NaCl), sodium sulphate (NaoS04), sodium carbonate 

 (NajCOg), sodium bicarbonate (NaHCOg), magnesium chloride (MgCla), 

 magnesium sulphate (MgS04), and calcium chloride (CaClg). Inci- 

 dentally, experiments were made with gypsum (CaS042H20), calcium 

 carbonate (CaCO.^), calcium bicarbonate [Ca(HC03)2], and with 

 magnesium carbonate (MgCOg), and bicarbonate [Mg(HC03)2], ^^ 

 well as with an aqueous solution of carbon dioxide (CO^), the last in 

 order to test a theory that suggested itself during the experiments 

 with carbonates and bicarbonates. 



In preparing and standardizing the solutions much assistance was 

 rendered by Mr. Seidell, of the Division of Soils. 



The solutions were invariably made with salts manufactured by 

 Baker & Adamson, and found to be practically chemically pure, dis- 

 solved in distilled water. ^ They were made up in each case on the 

 basis of a normal solution — i. e., of a gram-equivalent per 1,000 c. c. of 



^ The water used in all experiments was distilled through a tin worm and waa 

 collected and stored in Winchester quart bottles of practically insoluble glass. 

 A. conductivity test showed this to be an unusually pure water, but in order to 

 establish this point beyond doubt, a portion of this same water was redistilled 

 from glass, the first and last portions being of course discarded. A test of the 

 distillate showed it to possess about twice as great conductivity as that which 

 liad been distilled only once from the tin. A comparison of cultures of lupines 

 in the water which had been only once distilled with that which was redistilled 

 showed practically no difference in the amount of growth made by the roots. As 

 Galeotti has lately shown [Biol. Centralbl. , 21, 329 ( 1901 )] , the oligodynamic action 

 of relatively concentrated ' ' colloidal " solutions of metals disappears in the presence 

 of weak solutions of electrolytes. Thus a solution of copper containing 1 gram- 

 atom of metal per 126,000 liters of water produced no effect upon Spirogyra in 

 the presence of a 0.01 per cent solution of sodium chloride, and a solution of 1 

 gram-atom of copper per 68,000 liters of water acted only after twenty-four hours, 

 although in the absence of the electrolyte the toxic effect of the colloidal copper 

 solution is manifested at a dilution of 1 gram-atom of copper per 126,000,000 liters 

 of water. (See footnote, p. 50.) Hence it is practically certain that in the 

 experiments described in this report no complications were to be feared from the 

 possible presence of a trace of metals in the water used. 



