36 LAWS OF AVOGADRO AND VAN'T HOFF. chap.
a solution which contains 3 gram-molecules of glycerol in the litre is isotonic with a solution of potassium nitrate containing 178 gram-molecules in the litre.
��Glycerol . . Glucose . . Cane sugar . Malic acid Tartaric acid Citric acid Magnesium sulphate Potassium nitrate Potassium chloride Sodium chloride
�Potassium iodide
�Sodium nitrate .
�Sodium iodide .
�Sodium bromide
�Potassium acetate
�Potassium bromide
�1 -Of)
�Potassium sulphate
�Calcium chloride
�S
�Potassium citrate ,
�n
�«
��Bonders, Hambui-ger, and Hedin (7) have obtained analogous results using blood corpuscles. When the red corpuscles are introduced into a solution, which is so con- centrated that it abstracts water from them, the corpuscles sink. If, on the other hand, the corpuscles absorb water from the solution, they at the same time lose part of their colouring matter, and the solution becomes red. In this way it is easy to determine the concentration of a solution which is isotonic with the corpuscles.
Bonders and Hamburger investigated blood corpuscles from the various vertebrates, from the frog to the ox, and always obtained the same results, which, moreover, agreed with those arrived at by De Vries.
Experiments in which living cells are used have the disadvantage that isotonic can only be proved between such solutions as have the same osmotic pressure as the cell. The osmotic pressure of the cells, however, does not vary very much, for most of the cells available for investigation show a pressure of about 4 atmos. Young cells have a higher pressure than older ones, on which fact their power of development depends.
In certain species of l)acteria the osmotic pressure rises to as much as 10 atmos., which high pressure is closely connected \vith their power of destroying other organisms of
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