OF VITAL PHENOMENA 63 



The following table gives the surface tension at 15 of .25 

 molecular solutions of some non-electrolytes, according to Traube. 

 It may be seen that sugars and amino acids raise the surface 

 tension, urea is inactive, trihydric alcohols and amides lower it 

 slightly, and monohydric alcohols, ketones, nitrils, and organic 

 acids and their esters lower it very much. In homologous series 

 the effect is greater the longer the carbon chain. According to 

 Traube it requires only one-third the molecular concentration of 

 one member of the series to lower the tension as much as the 

 preceding member. 



.25 mol s. t. at 15° .25 mol s. t. at 15° 



Gane sugar 1.007 Propionic acid 83 



Grape sugar [ Methyl acetate 83 



Mannite J I -°° 4 Propyl alcohol 8 



Glycocoll 1.003 Methyl ethyl ketone 797 



Water I Diethylamine .75 



Urea 1 Piperidine 738 



Glycerine 998 Ethyl ether 73 



Glycol 99 Pyridine 73 



Acetamid 986 Paraldehyde 7 



Methyl alcohol 966 Chloral hydrate 695 



Acetic acid 961 Butyric acid 67 



Aceto nitrile 95 Isobutyl alcohol 61 



Ethyl aloohol 92 Tert. Amyl alcohol .60 



Acetone 88 Ethyl acetate 58— .688 



Ethyl urethane 87 Isoamyl alcohol .42 



Propionitrile 842 



Although small amounts of some substances may reduce the 

 surface tension of water to less than half, no substance raises 

 it very much. The explanation is that the substance which lowers 

 the surface tension becomes very concentrated in the surface 

 film and has its maximal effect, whereas the substance which 

 raises the surface tension is driven from the surface, consequently 

 reducing its effect. 



The salts of mineral acids and alkalis slightly raise the surface 

 tension whereas HC1 and HN0 3 lower it. An electrolyte brings 

 with it the added effects of the ions and molecules. 



Surface tension is reduced by the colloids from organisms, 

 but since we do not know their molecular weight we cannot 

 compare them quantitatively with other organic substances. The 

 colloid concentrated in the surface film becomes very viscous, 

 finally forming a membrane insoluble in water. These so-called 

 haptogen membranes form on the surface between water and 

 air, ether, carbon bisulphide, chloroform and many solids. By 



