Determination of Temperatures with the Meldometer. 363 



remedy for this is to dust the ribbon lightly with finely 

 powdered talc. This, however, is not very satisfactory, and 

 interferes somewhat with the observations ; but with care, 

 fairly good results can be obtained, as the following numbers 

 show: — 



With talc. Without talc. 



NaCl 799° 792° 



K 2 C0 3 .... 883 880 



KC1 752 762 



Ba(N0 3 ) 2 ... 583 575 



It was then found that the melting-point of potassium 

 sulphate is very little different from that of gold, viz., 7 

 degrees higher or 1052°; and this salt was afterwards used 

 instead of the gold ; thus there is no need to use talc. 



Some melting-points are sharply marked, others are not. 

 In these cases the lowest point was taken at which spreading 

 over the ribbon could be detected. 



For purposes of comparison determinations by other ob- 

 servers are given; some determined the melting-points {e.g., 

 Carnelley, and Meyer, Riddle and Lamb), others the freezing- 

 points (Carnelley, Le Chatelier, Heycock and Neville, and 

 McCrae). The data are taken from the following references: — 

 Carnelley (calorimetric method): J. C. S. Trans. 1876, 



p. 489 ; 1877, p. 365 ; 1878, p. 273. 

 Le Chatelier (thermo-electric method, assuming melting- 

 point of gold as 1045°): Bull. Soc. Chim. t. xlvii. p. 301 ; 

 C. R. t. cxviii. pp. 350, 711, and 802. 

 V. Meyer, Eiddle and Lamb : Ber. xxvii. (1894) p. 3129. 

 — In this method the salt has been previously fused in a 

 platinum tube with a wire down its centre, and to this 

 wire is attached a weight passing over a pulley. "When 

 the salt melts, it is pulled out by the weight, and the 

 temperature is determined at the same moment by an 

 air-thermometer. 

 J. McCrae (Wied. Ann. lv. p. 95), relying on Holborn and 

 Wien's results, standardized his thermo-element with 

 boiling diphenylamine (304°) and boiling sulphur 

 (444°*5). For his thermo-element he used platinum 

 against an alloy of platinum rhodium, and also against 

 an alloy of platinum and iridium. The numbers in 

 brackets given below refer to the latter, and the others 

 to the former. It will be noticed that they do not agree 

 perfectly. This may, of course, be due to his metals not 

 being of the same purity as those of Holborn and Wien. 

 The latter also from their observations find that the iridium 

 alloy is not as well suited as the rhodium alloy. 



