ARMATURE LAMINATIONS 27 



in the Standardisation Rules for the Testing of Sheet Iron, drawn 

 up by the Verband Deutscher Elektrotechniker. These rules read 

 as follows : 



1. The total loss in the iron shall be measured by means of a 

 watt-meter on a sample made up of at least four different plates. 

 The sample shall weigh at least 10 kgs., and the loss in watts 

 per kg. shall be determined at a given temperature for a 

 maximum induction of 10,000 lines per sq. cm. and a periodicity 

 of 50 complete cycles per second. 



2. As normal thickness, shall be taken 0*3 mm. and 0'5 mm. ; 

 deviations from the normal thickness shall not exceed 10 per cent. 

 (By this is meant deviations of appreciable extent, and not pitted 

 places or small protuberances which are unavoidable in the manu- 

 facture of sheet iron.) 



3. The measurements shall be made on a magnetic circuit 

 composed exclusively of iron of the quality to be tested, and built 

 in accordance with the conditions here set forth. 



4. As specific weight of the iron, 777 shall be taken in all cases 

 where more precise data is not available. 



5. In disputed cases, the determination of the Physical- 

 Technical Imperial Institute shall be accepted, and the deter- 

 mination shall be made at an iron temperature of about 30 Cent, 

 when no other temperature has been specified. 



Specification for the Test. 



As normal form for determining the iron loss, a unii'ormly- 

 wound ring may be employed. As, however, for practical 

 conditions, certain disadvantages are associated with the use of 

 a ring, the Standardising Commission for Iron Testing re- 

 commends that either the apparatus of Epstein or that of 

 Mollinger shall be employed. In guarantee determinations, it is 

 recommended that the iron loss be determined by means of one of 

 these two types of apparatus. 



For tests by means of the Epstein apparatus, the following 

 instructions should be observed : 



The magnetic circuit is constructed of four cores, each having 

 a length of 500 mm., a breadth of 30 mm., and a weight of at least 

 2'5 kgs., thus making a total weight of at least 10 kgs. for the 

 four cores. The individual sheets are insulated from one another 

 by Japanese paper in such a manner that they are at no point 

 in contact with one another. The four cores constitute a rect- 



