158 REPORT OF NATIONAL MUSEUM, 1899. 



are utilized for industrial purposes, it might at first thought appear 

 that they should be grouped according to the uses to which they 

 are put, as is commonly done at expositions. Such a plan, however, 

 involves a great amount of repetition, since many of the materials, as 

 diatomaceous earths, the clays, steatite, etc., are used for a variety of 

 purposes. On this account the method of installation, or grouping, 

 adopted is somewhat loose, the materials being grouped (1) by kinds, 

 and under kinds so far as possible (2) by uses. Further than this the 

 character of the material has in many instances rendered it necessary 

 to install those closely related and used, it may be, for quite similar 

 purposes in cases of quite different type as is shown in the hydrocar- 

 bon series, the coals, asphalts, etc., being in the deep- wall cases while 

 the petroleums, in bottles, are exhibited in the upright portion of the 

 rail cases. 



