Jan., 1915. Annual Report of the Director. 



391 



show signs of disintegration, were thoroughly treated with shellac and 

 further decay checked. In connection with the rearrangement of the 

 structural collections in this Hall, that of the study collection was car- 

 ried on and considerable interchange of specimens made. About one- 

 quarter of the entire exhibit, which occupies fifteen cases, was com- 

 pletely reinstalled in order to bring the series to a satisfactory condition. 

 To the economic collections in Hall 34 a large number of specimens has 

 been added and a considerable amount of reinstallation performed. In 

 several of the cases the exhibits were entirely removed in order to allow 

 painting of the interiors. These interiors are now all a uniform black. 

 New series installed in this Hall include a number of rare earths; a series 

 illustrating the manufacture of tungsten wire; a series of minerals 

 resembling gold; several series illustrating the uses of cobalt, nickel, 

 zinc, and tin; a number of additions to the building stone collection, 

 including several marble slabs; and a model of a log washer for iron ores. 

 The large specimens of ores in this Hall, which had hitherto rested 

 directly on the floors of the cases and the finish of which they injured 

 on account of their weight and jagged surfaces, have been provided with 

 individual wooden supports placed so as not to be visible. Further 

 injury to the cases has thus been averted. Additions to the collections 

 illustrating the uses of cobalt, zinc, and nickel compounds have been 

 prepared in the Museimi work-rooms and placed on exhibition. These 

 include the pigments which have these metals for base. They are 

 shown as varnished coatings on blocks of wood four inches square. 

 Beside each block is placed a tube of the pigment in oil partly emptied 

 into a small watch glass, in order to show its color in quantity. Besides 

 the zinc pigments there have been added to the collection illustrating 

 uses of zinc, a dry cell with the zinc exposed to illustrate electrical uses 

 of zinc; a zinc etching block and a print from it; a jar of zinc ointment, 

 and powdered willemite used as a fluorescent screen in X-ray and 

 radioactive work. A beginning has been made of a collection to illus- 

 trate uses of the rare earths and others of the less familiar elements. A 

 Nemst lamp illustrates uses of zirconia, and a Welsbach mantle shows 

 an important application of thoria and ceria that has made monazite 

 valuable. A series of specimens shows all stages of the evolution of the 

 filament of the tungsten electric light from the mineral scheelite to the 

 wire ready to place in the lamp. One of the most interesting uses of 

 titanium is shown in an example of the yellow enamel used by dentists. 

 In order to obtain space for these additions, a collection of exhibited 

 antimony ores was reduced. There has been added to the gold series a 

 group of specimens illustrating the appearance of those minerals which 

 are most frequently mistaken for gold. The series consists of two 



