CHEMICAL PHENOMENA IN LIFE 



extremely small quantities of material. Especi- 

 ally useful are the cryoscopic methods which allow 

 us to determine the number of ions in the volume 

 unit from the depression of the freezing-point in 

 comparison with that of pure water. The chief 

 source of ions for plants is the moisture of 

 the soil taken up by the roots. It contains, 

 in a very diluted state, salts of sodium, potas- 

 sium, lime, magnesium, iron, also hydrochloric, 

 sulphuric and phosphoric acid. Practically only 

 ions of .these substances pass into the living 

 plant cells. Some of these ions must dis- 

 appear in reactions Very quickly. Thus in 

 living cells we cannot find potassium in the well- 

 known reactions with platinum chloride. Traces 

 of potassium salts immediately furnish the yellow 

 deposit of platinum potassium chloride, but this 

 result cannot possibly be obtained in living cells. 

 When we burn the tissue to ashes and try the 

 reaction again, success is certain. We may 

 draw the conclusion that potassium salts are prob- 

 ably transformed in living cells into non-ionic 

 compounds of potassium. 



Very important is the formation of Complex 

 Ions in metabolism. Iron salts, for example, are 

 certainly not present in living protoplasm, but the 

 presence of iron is always easily shown in plant 

 ash. We can see what kind of transformation 

 may be taking place from the reaction of copper 

 sulphate in the presence of organic compounds. 

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