[ 57 ] 



VI. Note on the Examination of certain Alloys by the Aid of the 

 Induction-balance. By W. Chandler Roberts, F.R.S., 

 Chemist of the Mint*. 



[Plate VI.] 



SOME weeks since, Prof. Hughes showed me that equal 

 volumes of various -metals give widely different indica- 

 tions with the induction-balance. It appeared probable that 

 a careful examination of a definite series of alloys would prove 

 to be of interest; and as Prof. Hughes at once gave me the 

 most generous assistance, teaching me the manipulation and 

 controlling the results, I am able to submit the following ob- 

 servations to the Society. 



The relative values of different metals as indicated by the 

 induction-balance were given by Prof. Hughes in a paper read 

 before the Royal Society on the 15th of May last. They do 

 not accord with the values usually accepted as representing 

 the relative conductivity of the respective metals ; and this 

 being the case, it became important to ascertain what relation 

 the indications given by alloys, when under the influence of 

 the induced current, bear to their electric conductivities, which 

 afforded Matthiessen a basis for dividing them into groups f . 



A series typical of each group was therefore taken ; the con- 

 stituent metals were melted together in the requisite propor- 

 tions; and the thoroughly mixed alloys were carefully rolled 

 to a uniform thickness, usually 1*3 millim. Disks 24 millims. 

 in diameter were then cut with the same punch; and these 

 disks were placed in succession on one side of the balance, so 

 that their bases lay exactly on a line midway between the pri- 

 mary and secondary coils, this having been found to be the 

 plane of maximum force. The respective values of the alloys 

 were ascertained either by introducing the sonometer into 

 circuit, or by superposing a graduated wedge-shaped scale of 

 zinc over the opposing coil of the balance, as has already been 

 explained by Prof. Hughes. 



The alloys of Lead and Tin were selected as an example of 

 Matthiessen's first group. The results are recorded in the fol- 

 lowing Table, and are graphically indicated in the curve No. 1, 

 Plate VI. The readings are those of the zinc scale J. 



The Gold- Silver alloys, representing the second group, pre- 

 sented no difficulty of manipulation; and the observations 

 were made on disks 1*3 millim. thick and 24 millims. in dia- 



* Communicated by the Physical Society. 



t British-Association Report, 18G3, p. 37. 



% The use of a scale of greater accuracy than the one employed may 

 slightly alter some of the figures, hut it can hardly change the general 

 nature of the curves. 



