DIFFUSION AND OSMOSIS 



<5i 



through the gelatine, and the result after a time is the 

 production of a beautiful purple rosette. The gelatine must 

 he carefully covered to prevent its drying until the diffusion 

 is complete. The preparation may then be dried and mounted 

 as a lantern slide, and will give the most brilliant effect on 

 projection. If the gelatine has been treated with a drop of 

 potassium ferrocyanide solution instead of salicylate of sodium, 

 a few drops of FeS0 4 will give a blue pattern. Or we may 

 treat the gelatine 

 with ferrocyanide 

 of potassium and 

 salicylate of sodium 

 mixed, and thus 

 obtain an inter- 

 mediary colour on 

 the addition of 

 1VS() 4 . We may, 

 indeed, vary indef- 

 initely the nature 

 and concentration 

 of the solution, as 

 well as the number 

 and position of the 

 drops. The results 

 have all the charm 

 of the unexpected, which adds greatly to the interest of the 

 experiment. 



These experiments are not merely a scientific toy. They 

 show us the possibility, hitherto unsuspected, that a vast 

 number of the forms and colours of nature may be the result 

 of diffusion. Thus many of the phenomena of life, hitherto 

 so mysterious, present themselves to us as merely the conse- 

 quences of the diffusion of one liquid into another. One 

 cannot help hoping that the study of diffusion will throw still 

 further light on the subject. 



If a number of spheres, each capable of expansion and 

 deformation, are produced simultaneously in a liquid, they will 

 form polyhedra when they expand by growth. This is the 



Fig. 7. — Pattern produced in gelatine by the diffusion 

 of drops of silver nitrate and sodium carbonate. 



