Physical and Chemical Behavior of Solids. 209 



Table I. 



-Effect of Uniform Pressure on the Melting Points of Certain 

 Metals. 





Latent 





A T per 





Probable 





heat 



Vol. change 



1000 atm. 



AT per 



error 1 of co- 





cal. 



on melting 



cale. from 



1000 atm. 



efficient in pre- 



Metal 



per gram 

 Q 



Vi-V. 



equation II 



observed 



vious column 



Sn 



14-25 



0-003894 



+ 3-45 



+ 3*28 



±0-02 



Cd 



13-7 



000564 



+ 6-10 



+ 6-29 



±0-04 



Pb 



5-37 



0003076 



+ 8-59 



+ 8-03 



±0-03 



Bi 



12-6 



— 0-00342 



— 3-67 



— 3-55 



±0-08 



1 For calculation of the probable error of the coefficient, see Merriman, 

 Method of Least Squares, 6th ed., Chapter on the Precision of Observations. 



The melting point of nearly all substances is raised by 

 uniform pressure. For metals (and in all probability for most 

 substances) this change of melting point is not very large — in 

 the neighborhood of 10° (or less) per 1000 atm.; * but for many 

 oils and organic substances (wax, naphthaline, etc.) the change 

 may amount to 30° or 40° per 1000 atmospheres. Con- 

 sequently, with substances of the latter class whose melting 

 point is close to the ordinary temperature, we should be justi- 

 fied in stating that uniform pressure increases their rigidity. 



In passing it may be observed that by reason of this com- 

 paratively large effect most ordinary oils become solid at high 

 pressures ; consequently pressure transmitted by an oil may 

 cease to be uniform in character at high pressures. For in- 

 stance, Kahlbaum Roth and Siedler,f using castor oil, found 

 that their metal cylinders had been slightly deformed at the 

 highest pressures (above 10,000 atmospheres), though they 

 failed to attribute this to the real cause — a lack of uniformity 

 consequent upon solidification of the oil. Even liquids 

 ordinarily so light and mobile as kerosene or gasolene become 

 thick and viscous at high pressures, the former around 8,000 

 atmospheres, the latter around 20,000 atmospheres.:): 



Uniform pressure may promote chemical reaction between 

 solids under specified conditions characteristic of the particular 

 reaction, but in general it will not do so,§ except in so far as 

 it has an effect on the rate of reaction, which effect is probably 



*It is understood here that the pressure is acting on both solid and liquid 

 phases. If it acted on the solid phase alone, the effect would be many times 

 as great (compare p. 214). 



f Zs. anorg. Chem., xxix, 258 et seq.. 1902. 



\ Bridgman, Proc. Am. Acad., xlvii, 337, 1911. 



§ This statement would require some modification for systems containing 

 an appreciable amount of a liquid or vapor phase. 



