MATTES 21 



been measured. It is evident that the diameter of the 

 molecules of water and soap cannot exceed the thick- 

 ness of the film. Regarding the molecule of soap as 

 made up of fifty atoms, — for example, sodium pal- 

 mitate, the formula of which is C15 H31 C O2 Na, exact- 

 ly fifty atoms; then, if the black film of soap bub- 

 ble contains only one layer of molecules of soap 

 together with sufficient water to make the thickness 

 fifty atoms, the size of the atoms, or, rather, the 

 average distance from center to center of atoms, would 

 be 1 /4a,m,wo of a centimetre. Of course, it is impossible 

 to tell the number of atoms or molecules contained in 

 the thinnest part of a soap bubble. The only definite 

 conclusion is that the diameter of the molecules in the 

 particular case cannot exceed the thickness of the 

 film, and that the diameter of the atoms must be con- 

 siderably less than the thinnest part of the film. 



Thus far I have spoken of simple substances and of 

 the size of atoms and molecules. It is evident that, 

 if there are but seventy simple substances known, 

 most things with which we are acquainted must be 

 compounds. 



A compound is produced by the union of two or 

 more simple substances. For example, thoroughly 

 mix 32 parts by weight of sulphur with 56 of iron 

 filings, and ignite the mixture with a burning match. 

 The whole mass, even in the absence of air, will soon 

 glow with heat and light. The weight of the result- 

 ing mass is equal to that of the sulphur plus that of 

 the iron. 



The heat and light were produced by the chemical 

 action of the sulphur and iron on each other. The 

 atoms of the two substances rushed together with 

 such enormous velocity that intense heat and light 

 were generated by the concussion, as is done when the 

 motion of a cannon ball is arrested by a steel-clad 



