C. Bar us — Relation of Volume, etc. in case of Liquids. 407 



that the azurite crystals from the "Anson S." mine in Grant 

 county, a neighbor to the 'Copper Glance" and "Potosi" 

 mines, are generally covered with kaolin, when found; and 

 this is true of many of those from the Copper Queen mine. 



In a letter, Mr. Lucas says: — "At a depth of about 40 ft., 

 the green and blue carbonates run out, and the brittle copper 

 comes in, getting better and purer, and increasing in quantity." 



In conclusion, the writer wishes to tender his acknowledg- 

 ments to Mr. Lucas, for his generous courtesy and aid. 



U. S. National Museum, July 2, 1889. 



Aet. LII. — Note on the Relation of Volume, Pressure and 

 Temperature in case of Liquids /* by Carl Barus. 



Many experiments made with alcohol, ether, para-toluidine, 

 diphenylamine, paraffine, thymol, and less completely with 

 naphthaline, vanilline, azo-benzol, a-naphtol, monobrom cam- 

 phor, benzoic acid, caprinic acid, palmitic acid, and monochlor- 

 acetic acid, show that if temperature and pressure vary linearly 

 at a mean rate of about 'll C. per atmosphere there will be no 

 change of volume. My temperatures lie between 30° and 

 300°, and the pressure between 20 atm. and 500 atm. By 

 judicious extrapolation (enclosure of the experimental data, 

 volume, pressure, temperature, between two mathematical 

 functions, one of which is necessarily above and the other 

 below the observed values ; whereas both of the said functions 

 fall within the limits of error, within the interval of observa- 

 tion), the probable contours can be computed to 1000 atm., 

 with results accentuating the above law. The linear relation 

 was predicted from theoretical considerations by Dupre (1869) 

 and by Levy (1884) — considerations soon proved to be inade- 

 quate by Massieu, H. F. Weber, Boltzmann and Clausius. 

 Ramsay and Young (1887) established the relation in ques- 

 tion experimentally for vapors, but not, I think, very fully for 

 liquids decidedly below their critical points. Reasoning from 

 these data Fitzgerald (1887) investigated the consequences of 

 the law, viz : (1) specific heat under constant volume is a 

 temperature function only ; (2) internal energy and entropy 

 can be expressed as a sum of two terms one of which is a vol- 

 ume function only and the other a temperature function only. 

 Thus Pamsay, Young and Fitzgerald arrive substantially at 

 the same position from which Dupre and Levy originally 

 started. 



* The present communication has the assent of Mr. Clarence King, at whose 

 suggestion and under whore instruction the work was done. 



