30 Drs. A. Mattbicssen and C. Vogt on the Influence of 



evaporated to crystallization, furnished a crop of 13 ounces. 

 The mother-liquor, evaporated to dryness, gave 3J ounces more 

 of perfectly pure pulverulent iodide of potassium. The theore- 

 tical quantity required is 17| ounces. 



V. Reply to Mr. R. Sabine's "Remarks on the Influence of Traces 

 of Foreign Metals on the Electric Conducting Power of Mercury. 3 ' 

 By A. Matthiessen, F.R.S. ; and C. Vogt, Ph.D.* 



IN the above (Phil. Mag. June 1862) Mr. Sabine has made 

 some remarks on our paper (Phil. Mag. March 1862) which 

 we cannot leave unanswered. Mr. Sabine says (page 457) "that 

 no formula is given to indicate how the numbers in the seventh 

 columns, headed ' conducting powers calculated/ are obtained.'" 



On referring, however, to our paper(pp. 177,178), the following 

 statement is made : — " From the foregoing Tables it will be seen 

 that mercury, when alloyed with very minute quantities of an- 

 other metal, with the exception of zinc, has a greater conducting 

 power; but when alloyed with larger quantities, has a lower 

 conducting power than the mean of the conducting powers of 

 their relative volumes " f . 



"The mean conducting powers of their relative volumes" ex- 

 presses, we think clearly, the method by which the numbers in 

 the seventh columns were calculated. We may be allowed here 

 to add to the passage above quoted, after the words " with the ex- 

 ception of zinc/ ; gold and silver ; for one of us used in calculating 

 the numbers given in the seventh columns of the gold and silver 

 series, as pointed out by Mr. Sabine (page 458), the values 49*468 

 and 63*333 for the conducting powers of gold and silver, instead 

 of 494*68 and 633*33 respectively. 



Mr. Sabine (page 458) refers to an opinion expressed by Dr. 

 W. Siemens J, "that the conducting power of a fluid metallic 

 mixture is in proportion to the conducting powers of the two 

 metals in their fluid state at the same temperature ." If this 

 opinion be correct, we may deduce the value for the conducting 

 power of the metal alloyed with mercury from the observations 

 made with the amalgams ; and we ought also to find that the 

 values so deduced from each observation are the same, for Mr. 

 Sabine has given, in a Table (page 459), only the means of the 

 conducting powers so found. Let us now see how far the above 

 hypothesis will be correct; and in order to do so, we give in 

 Table I. the values deduced from our experiments for the con- 

 ducting powers of the metals alloyed with mercury. 



* Communicated by the Authors. 



t Unfortunately " values " has been allowed to stand (loc. cit.) as a 

 misprint for "volumes;" we think, however, that no one attentively reading; 

 our paper would find much difficulty in making the necessary correction. 



% Pogg. Ann. vol. cxiii. p. 90. 



