48 



Messrs. Holman, Lawrence, and Barr on the 



between sulphur and gold differ but slightly by the two 

 formulae, thus confirming the former conclusions. It is 

 obvious, therefore, that although either of the two formulae 

 would yield fairly good interpolations for Al, Ag, and Gu, 

 ]ret that a mean between the two would probably quite 

 nearly offset against each other the systematic errors of 

 the respective equations. This is also true in the dangerous 

 process of extrapolation for the platinum melting-point, where 

 the chances of error in the result seem to be probably very 

 much reduced by averaging. The means of the melting- 

 points computed by the exponential and logarithmic equations 

 are, therefore, regarded as the nearest available approxima- 

 tions, and the round numbers of column 9 are adopted as 

 provisional values to represent the results of the work. 



Comparison of the results of the Avenarius formula, 

 column 5, will show that they depart widely from the others 

 in the direction which would have been anticipated from the 

 conclusions of the previous paper, thus further strengthening 

 those inferences. 



In addition to the foregoing, the melting-points of three 

 other samples of copper and one other of gold were measured. 

 The gold was dentists' gold " foil," purchased in Boston. 

 This is usually classed as " very nearly pure," but its analysis 

 was not known. No special interest, therefore, attaches to it 

 beyond the indication that it gives of the sign and order of 

 magnitude of the error (about — dt°) which would be introduced 

 hy the use of such gold in the calibration of the Le Chatelier 

 pyrometer, or in similar ways'*. The melting-point was 

 found to be 1068°. 



The tour coppers yielded the appended results : — 



Table II. 



2*e 





 microvolts. 



Melting- 

 points, C. 



Purity of 

 Metal. 



Description. 



16463 



16448 

 16456 

 16446 



10950 



10943 

 10947 

 1094 2 



0/ _ 



99-99 + 



99 83 

 Unknown. 

 Unknown. 



Electrolytic. Probably Lake Superior 



copper, Buffalo Smelting Co. 

 Orcliuary ingot. Same source. 

 Electrolytic. Probably from Montana, 

 Commercial hard drawn wire from 



Washburn and Moen Co. Sp. Elect. 



Conductivity (referred to Matthiessen 



value) 98*3 per cent. 



* ETolman, Calibration of the Le Chatelier Thermo-electric Pyrometer. 

 See Proceedings of the American Academy, xxxi. (n. s. xxiii.), p. 234. 



