The Evolution of the Sciences 



crystallisable molasses will only diffuse with 

 extreme slowness. This is the principle of the 

 purification of sugar juice introduced by 

 Dubrunfaut and used in all sugar houses. This 

 observation may be generalised. We may follow 

 the English physicist Graham and say that all 

 natural bodies are divided into crystalloids, 

 which diffuse readily, and colloids, which diffuse 

 slowly. 



This classification is easily explained if we 

 consider that organk substances not easily 

 crystallised that is to say, colloids have un- 

 doubtedly a much larger molecule than crystal- 

 lised bodies. Thus Hofmeister attributes to 

 the albumen of the blood the formula C 450 H 720 

 N Il6 S 6 O I40 ; the albumen molecule is therefore 

 built up of 450 atoms of carbon, 720 atoms of 

 hydrogen, 116 of nitrogen, 6 of sulphur and 140 

 of oxygen. It weighs ten thousand times more 

 than an atom of hydrogen and 250 times more 

 than a molecule of salt ; it is therefore natural 

 for it to be much larger and less capable of slip- 

 ping through the pores of membranes. 



On the other hand, there are great differences 



between these membranes; some are much 



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