228 Messrs. F. Lydall and A. W. S. Pocklington. 



" Magnetic Properties of Pure Iron." By FRANCIS LYDALL and 

 ALFRED W. S. POCKLINGTON. Communicated by J. HOP- 

 KINSON, F.R.S. Received May 4, Read June 16, 1892. 



The following results were obtained at King's College, Strand, for 

 a specimen of very pure iron. The experiments were made under the 

 direction of Dr. Hopkinson. The sample was supplied to him by Sir 

 Frederick Abel, K.C.B., F.R.S., to whom it was sent by Colonel 

 Dyer, of the Elswick Works. It is of almost pure iron, and the sub- 

 stances other than iron are stated to be : 



Carbon. Silicon. Phosphorus. Sulphur. Manganese. 



Trace. Trace. None. 0'013 O'l 



The method of experiment is the same as that described in Dr. 

 Hopkinson's paper before this Society on the " Magnetisation of Iron 

 at High Temperatures," viz., taking a curve of induction at the 

 temperature of the atmosphere, and then at increasing temperatures 

 until the critical point is reached. The temperatures, as in his paper, 

 are calculated from the resistances of the secondary winding, the 

 increase of resistance per 1 C. being assumed to be O00388 of the 

 resistance at 20 C. In brackets are also given the temperatures 

 calculated by Benoit's formula 



Resistance at t C. = resistance at 0C. {1 +0'00367^+0'000000587^}.* ; 

 The dimensions of the iron ring are 



as in the earlier experiments. 



Fig. 1 gives the curve of induction taken at 10'5 C. compared with 

 the sample of wrought iron of Dr. Hopkinson's paper, just referred 

 to, taken at 8'5 C. It shows the very high induction developed in 

 the pure specimen for a moderate magnetising force, and also the 

 small amount of hysteresis. The following are the actual values of 

 induction, B, and magnetising force, H : 



* Everett's ' C.G-.S. Units and Physical Constants,' p. 160. 



