NEW CONCEPTIONS IN SCIENCE 



into enough parts to be present, in large numbers, 

 in every drop of the water; it must have been 

 broken up into millions of millions of parts. 



The subtle substance known as fluorescein, dis- 

 solved in water, makes the water fluorescent- 

 makes it shine with a pale light after it has been 

 illuminated. A gram of this substance will pro- 

 duce fluorescence in a hundred tons of water- 

 that is, in a hundred million cubic centimetres. 

 The substance must be evenly distributed through 

 every minute fraction of a cubic millimetre; it 

 must have been split into billions of pieces. 



This same process of molecular division is taking 

 place constantly under our eyes, as, for example, 

 in all things which burn, when solids like coal, 

 liquids like kerosene, go off in more or less invisible 

 gases ; or when water and other liquids evaporate 

 or go off as steam. One might easily think that 

 this conversion of a solid or a liquid into a gas car- 

 ries the process of division much further than in 

 the examples I have cited, but this is not always 

 so. Water going over into steam occupies, at or- 

 dinary atmospheric pressure, only about seventeen 

 hundred times its volume as water. Liquid air 

 evaporating into common air gives only about 

 eight hundred volumes. This is very small in com- 

 parison with one volume of fluorescein dissolved in 

 a hundred million parts of water. 



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