406 



Professor W. Chandler Boherts- Austen. [March 26, 



left to itself at the ordinary atmospheric pressure, will not unite ; 

 by " augmenting the number of points of contact in a powder," the 

 result may be very different. The powders of metals may weld into 

 coherent blocks. Let us appeal to his own experiments. The 

 section, Fig. 13, shows the general form of the compression apparatus 

 employed by Spring. 



Under a pressure of 2000 atmospheres on the piston, or 13 tons 

 to the square inch, lead in the form of filings becomes compressed 



Fig. 13. 



The metallic powder is placed under a short cylinder of steel in a cavity in a 

 Bteel block divided vertically, held together by a collar, and placed in a chamber 

 of gun-metal, which may be rendered vacuous. The pressure is applied to a 

 cylindrical rod passing through the stufiSng-box. 



into a solid block in which it is impossible to detect the slightest 

 vestige of the original grains, so that lead filings weld into a block 

 identical with that obtained by fusion. Under a pressure of 5000 

 atmospheres the lead no longer resists the pressure, but flows as if it 

 were liquid through the cracks of the apparatus, and the piston of the 

 compressor descends to the base of the cylindrical hole driving the 

 " flowing " lead before it. This result in the case of lead is hardly 

 unexpected, for BoUey* showed in 1849, that lead prepared in a 

 particular way, so as to be in a state of fine division, may be con- 

 verted under a powerful press into a flexible plate, or may be made 

 to receive a sharp impression. The more interesting results were 



* 'Licbig u. Kopp. Jahresb.' 1849, p. 278, quoted by Dr. Percy, 'Metallurgy 

 of Lead, 1870, p. 9. 



