THE PHYSICAL CHEMISTRY OF PROTOPLASM 225 



plest possible one; namely, H 2 O. But if the water molecule were 

 really as simple as this, the compound would boil at a very low 

 temperature, would have a very low surface tension, etc.; whereas 

 its actual boiling point, surface tension, etc., are much higher 

 than those of other compounds having a higher molecular weight 

 than is indicated by the formula H 2 O. Actual measurements of 

 the physical properties of water indicate that at the temperature 

 at which water is a vapor its formula is at least (H 2 0) 2 ; while 

 at lower temperatures, at which it exists as a liquid, its formula 

 may be (H 2 O) 3 , or (H 2 0) 4 , or even more complex still. The 

 cause for this association of the compound into multiple molecules 

 undoubtedly lies in the extra valences of the oxygen. In many 

 organic compounds oxygen is undoubtedly tetravalent, and it 

 may be easily conceived that in these complex molecular groupings 

 in the water it exhibits this same property; the possible molecular 

 arrangements being represented by the formulas 



H H 



H v /H H O O H 



>O=:0< and etc. 



W \H H O 0-H 



^ v 



Such molecules may be conceived to break down very easily, 

 leaving the extra valences of the oxygen available to form linkages 

 with other atoms or molecules. This may constitute one of the 

 ways in which water exerts its remarkable effects both as a solvent 

 and as an accelerator of all kinds of chemical reactions. Other 

 organic compounds which contain tetravalent oxygen are exceed- 

 ingly active chemically, and there seems to be much to commend 

 this view of the chemical structure of the water molecule. 



Probably the most remarkable property of water is its power 

 of solution. No other liquid surpasses water as a solvent. This 

 power, as has been pointed out, is supposed to be due to, or in 

 some way correlated with, the extra valences of the oxygen atoms, 

 which may perhaps unite with similar extra valences of other sub- 

 stances with which the water is brought into contact, and so cause 

 the latter to enter into solution. All kinds of substances dissolve 

 in water, and when in solution, or even when only moistened, are 

 much more active chemically than when dry. This property of 



