DIATOMS— CONGER 333 



sible to say at what moment, or in what connection, the study of the 

 structure of these minute plant forms may be turned to practical use. 



The luxuries and comforts of modern life and the innumerable 

 appliances devised through the ingenuity of man to secure and in- 

 crease them, have created such a demand for raw materials for his 

 uses, from the most common and abundant substances to the rarest 

 and most unusual elements, that scarcely any material escapes his 

 vigilant eye. Mankind has developed a new realization of the poten- 

 tialities of materials and a new interest in researches upon their prop- 

 erties. Thus whenever any kind of substance is found to occur in 

 considerable quantity, its possibilities are recognized and investigated, 

 and sooner or later it is likely to find one or many uses of human 

 importance. Frequently this usefulness is based upon some appar- 

 ently insignificant or unique property of the material. 



Such has been the history of the use of diatomaceous earth, which 

 30 years ago was known to only an occasional scientist and to but a 

 very small group of industrialists, but which today has been heard 

 of by most people and has found its application in some phase of 

 almost every industry, affecting every angle of our daily lives. Com- 

 paratively few people yet know what it is, and fewer still have in- 

 quired into the full significance of its unusual properties. 



Diatomaceous earth is typically a fine whitish earth composed 

 largely, often practically purely, of the fossil remains, or shells, of 

 diatoms, accumulating by slow deposition in quiet waters over long 

 periods of time, the resulting deposits being exposed through subse- 

 quent rising or upheaval of the land. Luxuriant growth of these 

 little plants in undisturbed waters, free from inwash of sand or other 

 foreign matter, has resulted in the formation of many large deposits 

 of very pure diatomaceous earth (pi. 7). These deposits are to be 

 found widely scattered and over vast areas of the earth's surface 

 previously covered by oceans, lakes, and other bodies of water in ages 

 past. Quick decomposition of organic matter and leaching out of 

 soluble materials has left almost nothing save the very insoluble and 

 highly indestructible shells of the diatoms, insoluble because they con- 

 sist of silica and comparatively indestructible because they are so 

 small that they easily slip in among other particles without being 

 crushed. 



The very fine porous structure of these shells and their character- 

 istic shape give to diatomaceous earth certain peculiar properties 

 which make it valuable. Chief among these are high porosity, ex- 

 treme lightness of weight, and great amount of surface with com- 

 paratively small amount of actual material. If we were to fill a 

 room from floor to ceiling with tiny cardboard boxes of various shapes 

 we should have an arrangement homologous to diatomaceous earth. 



