Physical and Chemical Behavior of Solids. 225 



various investigators are in substantial agreement as regards 

 the pressure requisite to consolidate the dry material. These 

 pressures are in the nature of flow pressures, bscause they rep- 

 resent the force required to deform the individual particles and 

 to cause them to flow or weld together. The actual magnitude 

 of the observed welding pressures has little significance because 

 it depended in all these cases upon a number of factors not 

 under control; but it is worth while to make a rough classifi- 

 cation according to the relative ease with which the dry sub- 

 stance welded at ordinary temperature. This is done in the 

 following summary of results, taken mainly from the papers of 

 Spring, Hallock, and Jannettaz;"* in part also from scattered 

 sources, including a few results obtained in this laboratory. 



Summary of the Results on the Relative f Ease of Welding of 

 Various Substances. 



(a) Hard and compact blocks were produced by pressure : 

 with all the metals investigated (including bismuth and anti- 

 mony): with NH 4 C1, NaCl, KC1, KBr, KI, KNO„ NaJSTO,, 

 PbCl 2 , HgCl 2 , Hgl 2 , ZnS, PbS, As 2 S 3 , Mn0 2 , A1P0 4 ;$ with 

 oxalic acid, sulphur, graphite ; with wax, paraffin, and similar 

 substances ; with camphor, resin, starch, and peat. 



(b) Soft and easily destroyed blocks were obtained (using 

 pressures up to 10,000 atmospheres) with : red phosphorus, 

 HgO, HgS, FeS, A1 2 (S0 4 ) 3 , CaS0 4 , (dry) Na 2 C0 3 , ZnC0 3 , 

 iceland spar, borax, sugar. 



(c) Very little or no effect was observed with : amorphous 

 carbon, silica, alumina, magnesia, powdered glass, chalk, PbCO„ 

 dry cotton. 



In the above summary there is some doubt as to the class in 

 which certain of the substances should be placed ; besides which 

 there is, of course, no sharp line of demarcation between the 

 classes. All are in agreement, however, that with the highest 

 pressures hitherto attained in such work (15,000 atm.) abso- 

 lutely no effect is produced with dry silica, alumina, magnesia, 

 or powdered glass. With the exception of the glass (which 

 being a subcooled liquid has no melting-point) these substances 

 are precisely those which, of all the substances mentioned 

 above, melt at the highest temperatures. Further examina- 

 tion of the above summary demonstrates the existence of a 



*Bull. soc. chim., xl., 53, 1883: Bull. soc. geol. France (4), xii, 227-36, 

 1884. 



f Because of the very approximate character of the data, no effort has been 

 made to arrange the substances in each group according to the ease with 

 which they weld together. 



X Furthermore, with hydrated salts and with many salts when moist ; in 

 connection with this see p. 216. 



