370 



Mr. E. Wilson. 



its magnetic properties : it is referred to as Pure Iron II. The sub- 

 stances other than iron in this specimen are stated to be — 



Carbon. Silicon. Phosphorus. Sulphur. Manganese. 



Trace Trace None 0'013 01 



This ring has an internal diameter of 3*2 cm , an external diameter 

 of 4 5 cm., a depth of 2*6 cm., and is wound with sixty-one turns for 

 the secondary coil next the iron, and forty-nine turns for the primary 

 or magnetising coils. The method of test* employs a ballistic galva- 

 nometer, and is that in use in the Siemens Laboratory, King's 

 College, London, where the present experiments were carried out. 

 The currents in the primary circuit were supplied by storage cells 

 and measured by balancing the potential difference due to such 

 currents in a standard resistance against a Clark's cell. The 

 current meter in the circuit was only used for convenience of 

 adjustment. 



Quoting from the communication above referred to, Pure Iron I 

 gives the following induction curve at atmospheric temperature : — 



B.... 



34 



118 



467 



2,700 



7,060 



10,980 



14,16( 



15,590 



16,570 



17,120 



17,4 M) | 



, H • • . 



o -is 



0/38 



0-60 



1-06 



2 11 



3-77 



7-48 



13 36 



23 '25 



33 65 



- i 



44-66 j 



Pure Iron II has been tested under two conditions : (a) as received 

 and (6) after careful annealing. The results are given in Table I, 

 which also contains the results obtained by Professor Ewing from a 

 sample of transformer plate rolled from Swedish iron.f The figures 

 of Professor Ewing relating to magnetic hysteresis are exceptionally 

 low, and al chough annealing has considerably improved the Pure 

 Iron II, it is still slightly inferior to the transformer plate. On the 

 other hand, the permeability fx of this pure iron after annealing is 

 exceptionally high, having a value 5490 for B — 9000. The coercive 

 force for maximum B = 15,270 is 1*13 C.Gr.S. units. 



The figures in Table I relating to Pure Iron II after annealing- 

 have been obtained by interpolation from the actual observed data 

 given in Table II. An induction density of 15,270 for H = 9'24 is 

 higher than the author remembers having seen. In fact, for values 

 of H below about 10 or 12 this specimen is exceptionally good, as is 

 shown by the very high permeability. 



* ' Roj. Soc. Proc.,' vol. 53, p. 352. 



t ' Proceedings Institution of Civil Engineers/ vol. 126, p. 185. 



