DIATOMS— CONGER 337 



Nearly every household iiow-a-days has a jar of diatomite on the 

 kitchen shelf — not, of course, so labeled, but under the name of silver 

 polish. The material is very superior for this purpose. To clean 

 the rust from a piece of iron, it is natural to use a file. To clean the 

 corrosion, or silver-oxide, from a piece of fine silver, it is logical again 

 to select a file, but a much finer file in order that it will not scratch 

 the surface of the silver or cut away any of the precious metal. 

 Precisely the kind and size of file that is needed in this instance is 

 found in the finelj^ ridged and sculptured surfaces of some of the 

 diatoms. Two of these little "files", greatly enlarged to show their 

 rasping surfaces, are illustrated in plate 10, and between them is a 

 photograph of a bit of the earth containing many of these small 

 instruments. They are fine enough to remove the tarnish, but not so 

 fine as to remove much of the surface. For these same reasons they 

 are suitable and widely used also in polishes for automobiles. 



The form just mentioned is adapted not only for polishing, but 

 also for use as a reinforcing or binding material in paints and plas- 

 tics. The liquid plastic or paint fills the pores and the spaces be- 

 tween the ridges on the diatom shells, and when the material hardens, 

 the whole mass locks together in a very tenacious texture that resists 

 cracking. It is the same principle that is used in putting hair, fiber, 

 or other binder in plaster, but on a much smaller scale ; the intricate 

 sculpturing on the diatom shell presents a great amount of irregular 

 surface for the firm attachment of the matrix. Even concrete is 

 made stronger by the incorporation of these little shells. It is a case 

 of many small forces working together. 



The same effect is obtained when diatomite is mixed with tar for 

 roofing. The diatoms are small and mix easily, yet they bind firmly. 

 Also, they make the tar dry and prevent its running when it becomes 

 warm and soft in the sun, and render it less sticky; and the combi- 

 nation makes a firm roofing material that is resistant to cracking 

 or checking. A homogeneous mixture of the diatomite with the tar 

 is readily obtainable, which is easy to apply to the roof, and is at the 

 same time very adhesive. Longer fibers are no better and are more 

 troublesome to handle. 



When the bright sun shines on an exposed hillside of very pure 

 diatomaceous earth, the substance glares with the whiteness of new 

 fallen snow (pi. 7), so that workmen in the neighborhood find it 

 necessary to wear smoked glasses. The diatom shells themselves are, 

 of course, of glasseous silica and actually transparent; the whiteness 

 is due to complete and total reflection of the sunlight by the fine, 

 intricate structure of the diatom shells, for, as is well known, sunlight 

 when totally reflected and completely diffused is white. Thus we see 

 that even the color is a product of the structure. 



