66 SCIENCE PRIMERS. [MATERIAL 



alcoholic solution of gam-mastic. If you add water 

 to mastic varnish, the alcohol takes away the water 

 and the mastic falls out, or precipitates, as a curdy 

 solid composed of very visible whitish particles. But 

 if a drop of the varnish is added to a good deal, say 

 half a pint, of water and well stirred at the same time, 

 the mastic, though it is still precipitated as a solid, is 

 in a state of extremely minute division. No separate 

 solid particles of mastic are visible to the naked eye, 

 but the water assumes a faint milky tinge. 



This milkiness arises from the presence of solid 

 particles of mastic diffused through the water and 

 yet, if the experiment has been properly managed, a 

 drop of the fluid may be spread out as before and 

 examined with the highest magnifying powers, and 

 nothing can be seen of such particles. So far as 

 vision goes it might be a drop of pure water. Now 

 our best microscopes are able to show us anything 

 solid which has a diameter of T^Wo^ 1 f an ^ ncn > 

 quite distinctly ; and probably solid opaque particles 

 of much smaller size would make themselves ap- 

 parent as a turbidity or cloudiness. The particles of 

 mastic must be therefore so much smaller than this 

 that they remain invisible, Hence it follows that 

 if water were made up of separate particles, or 

 droplets. Tpoooooth f an i nc ^ m diameter, and thus 

 had the structure of a mass of very fine shot, no 

 microscope that has yet been constructed would enable 

 us to see even a trace of that structure. " We could 

 not obtain any direct evidence of it. 



