THE MOLECULAR FORCES IN PLANTS. 245 



the utmost significance in connection with plant life. If salts 

 soluble in water, and containing* potash ammonia or Phosphoric 

 acid, whether they have originated in the soil itself or have been 

 directly added to it from outside, come into contact with the 

 minute particles of the soil, they are absorbed more or less 

 actively, according to the character of the soil. They become 

 chemically fixed, arid we will now proceed to determine by suitable 

 experiments the absorption of one substance, viz. ammonia (Knop's 

 method). 1 



100 gr. of air-dry fine earth are intimately mixed with 10 gr, 

 of powdered chalk, and treated in a flask with 200 c.c. of a solution 

 of Ammonium chloride, containing exactly 1 gr. of the salt in 

 208 c.c. of water. We leave the soil in the fluid for forty-eight 

 hours, frequently shaking it, and then filter off 40 c.c. of fluid, and 

 evaporate this down to about 10 c.c., with addition of a drop of 

 pure Hydrochloric acid. In this 10 c.c. of fluid we determine the 

 quantity of Nitrogen, and also in 40 c.c. of the original Ammonium 

 chloride solution, which has also been similarly concentrated by 

 evaporation to 10 c.c. If the Ammonium chloride solution has 

 been accurately prepared. 40 c.c. of it should contain exactly 40 c.c. 

 of Nitrogen (at C. and 760 mm. barometric pressure). From 

 the results of the Nitrogen determinations, for which we use an 

 Azotometer (see Zeitschrift /. analytische Chemie, Bd. 9, p. 226 

 and Bd. 13, pp. 101 and 383) and brominated soda lye, the quantity 

 of ammonia absorbed by the soil can be easily calculated. The 

 brominated solution (solution of Sodium hypobromite) is prepared 

 by dissolving 100 gr. of caustic soda in 1250 c.c. of water, allowing 

 to cool, and then adding 25 c.c. of Bromine. We use for each 

 experiment 50 c.c. of this fluid to 10 c.c. of the Ammonium 

 chloride solution concentrated by evaporation. To determine the 

 Nitrogen absorbed by 60 c.c. of the generating fluid (50 c.c. of 

 brominated lye and 10 c.c. of water) we employ the table prepared 

 by Dietrich (Zeitsclirift f. analytische Cliemie, Bd. 5). The Azoto- 

 meter may be obtained from Ehrhardt and Metzger in Darmstadt 

 at a price of about 30 mks. 



The apparatus, which is represented in Fig. 91, consists first of 

 a generating vessel divided into two parts by a glass septum not 

 visible in the figure which does not extend to the top. In one 

 compartment we place 50 c.c. of the brominated soda, in the other 

 10 c.c. of the research fluid. The generating vessel is closed with 

 a rubber stopper, and'placed in a cooling vessel, which, like the tall 



