520 BEroEX— 1888. 



I Effects of Pressure — Sulids. 



The effects of great pressure on solid bodies in the state of powder 

 have been examined by Spring in a series of investigations extending 

 over several years, accounts of which have been published from time to 

 time.' 



The bodies being taken in the state of powder, and the apparatus used 

 being capable of exerting a pressure of about 10,000 atmos., experiments 

 were made on various bodies, elementary and compound. The effects 

 may be classed under two heads, mechanical and chemical. 



As to the mechanical effects, the following metals — lead, bismuth, tin, 

 zinc, aluminium, copper, antimony — taken in the form of powder or filings, 

 when subjected to pressures up to 6,000 atmos., were completely welded 

 into a homogeneous mass of the specific gravity of the metals in block, 

 sometimes with crystalline fracture, but with no trace of powder or filings 

 visible ; spongy platinum gave a block with shining metallic surface 

 exhibiting a dull fracture, and perfect union was not obtained at any 

 pressur ■ ; similarly with amorphous carbon ; while gi-aphite powder was 

 welded at 5,500 atmos. into a compact mass of solid graphite. Similar 

 results in general were obtained with metallic oxides, sulphides, salts, e.g., 

 chlorides, bromides, iodides, sulphates, nitrates, carbonates, thiosulphates, 

 phosphates, and on other bodies ; with most of these, though not with all, 

 the welding process took place, although in not a few cases the welding 

 was incomplete. It was found in subsequent experiments that welding 

 requires time, and that the completion of a welding process was favoured 

 by several conditions, such as amount of pressure, the time during which 

 pressure was applied, and temperature, a rise of temperature favouring 

 the process. A substance difficult to weld was found, on bi-eaking it up, 

 to be most imperfectly coherent in the interior; and on powdering it 

 again and renewing the pressure again and again the welding can be 

 made complete. Generally, the harder the substance the more difficult it 

 is to weld it ; if a body exist in allotropic modifications — as, e.g., sulphur — 

 the effect of pressure is to produce a coherent mass having specific gravity 

 equal to that of the densest variety. The welding of a powder is in some 

 respects analogous to the liquefaction of a gas by pressure ; the particles 

 of the powder are brought into closer contact and within each other's 

 sphere of cohesion, and then unite like drops of water. Although the 

 temperature is hardly raised in the experiments, some metals at very high 

 pressures flow and ooze out of the joints of the apparatus. It will some- 

 times happen that no welding takes place at a very high pressure, but on 

 still further increasing the pressure the process is effected. 



As to the formation ot alloys by pressure, it was found that Woods' 

 metal was formed by submitting to a pressure of 7,500 atmos. a mixture 

 of filings of bismuth, cadmium, and tin in the required proportions. 

 Rose's alloy of lead, bismuth, and tin was obtained in a similar manner. 



' Wied. Ann. [5], 22, 170 ; Bull Acad. Belg. 1880 [2], 49, 323 ; Ahs. Jahr. f. Min. 

 1882, ], i?. 42 ; Bnr. 1882, pp. 15, 595, Ber. 1883, pp. 16, 324, 999, 2723; Ber. 1884, 

 17, pp. 1215, 1218 ; Bidl. Soc. Chim. 44, p. 166 ; 46, p. 299 ; Btr. 1885, 18, B. 597 ; 

 Ber. 1886, B. 728 ; Ber. 1887, 20, B. 358 : Zeitschr. f. phys. Chem. 1, 231. And 

 abstracts in C. S. J. 1881, p. 498 ; 1882, pp. 273, 921 ; 1883, pp. 650, 904 ; 1884, pp. 256, 

 949,959; 1887, p. 332. 



