236 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1925 



tice possible to crystals belonging to that class. The connection 

 between the chemical i)i-o))erties and the crystalline structure still 

 remains indeterminate, although it must be very intimate. 



There are many reasons why the chemical study of solids should 

 receive greater attention. In metallurgy, although metals and 

 alloys may, and most frequently do, pass through a molten stage in 

 the course of their manufacture, they may undergo many important 

 changes of structure and constitution at temperatures far below 

 that at which the last li(|uid portions have completely solidified, 

 a nil these changes may be so far-reaching as to convert an alloy 

 into one seemingly of an entirely different class, although the gi-oss 

 chemical composition has not altered. The petrologist, especially 

 when dealing with igneous and metamorphic rocks, has to consider 

 reactions which proceed in the midst of solids of high rigidity. 

 Several industries, such as that of cement, are based on reactions 

 of the same kind as those with wdiich the petrologist has to deal. 

 Sintering is not alwa3'S due to the pi'csence of small quantities of 

 molten material between the solid particles, and it is now certain 

 that union of solid masses under pressure may occur without actual 

 melting. This was shown by Spring 40 years ago, but for long, 

 although frequently quoted, his results received little consideration. 



The most striking application of the principle is seen in the metal- 

 lurgy of tungsten. This metal was formerly described as very hard 

 and brittle, and it is not jiossible, b}^ casting it and then annealing, 

 to bring it to a ductile form. The method now adopted is to prepare 

 it in the form of a ]:)ure powder, and then to bring it to a comjiact 

 state by compressing, heating, and hammering while very hot, and 

 finally drawing. As this process is continued, and as an originally 

 thick rod becomes extended into a slender wire, the brittleness pro- 

 gressively disappears, and at last the tungsten is obtained in those 

 beautiful filaments, drawn to extreme fineness, with which we are 

 familiar in our electric light bulbs and wireless valves. A somewhat 

 similar example is that of the adhesion of an electrolytically de- 

 posited metal to its support, which is sometimes so perfect as to 

 ai:»proach the breaking strength of one of the metals, although 

 interpenetration of crystals is not to be seen under the microscope. 



There is another aspect of the chemistry of solids which will make 

 an appeal to some who are not chemists, but amateur students of 

 nature. The great beauty of natural crystals has attracted the atten- 

 tion of poets and artists as well as men of science. Mucli of this 

 beauty dejiends on the varying habit of one and the same crystal 

 species. Even with such a common minei-al as (juai-tz, it is possible 

 on entering a mineral collection to ])oint to some of the crystals 

 exjiosed, and to name their locality, when once the foiin has become 

 familiar. Tl'he same is true of other niinerals. AVhy should there 



