Laboratory Notes, 



By 



C. C. Knott, D. Sc, F.R.S.E. 



Professor of Physics. 



1. Electric Resistance of Cobalt. 



The manner in wliich the electric resistance of cobalt varies with 

 ]\\(j:]\ temperatures does not seem to have been studied with any great 

 care. The peculiar beha^'iour of nickel and iron as regards their change 

 of resistance with temperature is now well knowri'^ With a view to 

 see if cobalt presented anv similar peculiaritv, I set ^Ir. Omori, one of 

 the graduating students in Physics, to investigate the (juestion. 



The piece of cobalt used was cut from a sheet of rolled cobalt 

 which had been given me by l^rofessor Tait. T)r. E. Divers, F. R. S., 

 kindly determined its composition by an analysis of a very small 

 quantity (about 20 grains) sup])h'ed lu*m. Tlie result of the analysis 

 is as follows : 



Carbon ft)und 0'77 7o ^^"^^.Y ^^ ^^ much as 1-00% 



Silicon 0T5 



Iron 0-73 



with a minute quantity of manganese and perhaps ^vVo *^^ ^ metal 

 undetermined. Dr. Divers regarded it as of remarktd)le purity for a 

 furnace product. 



I) See my pajDer On thn Electric Resistance of Nickel at ITitjh. Temperatures, Trans. Royal Soc, 

 Edin , Vol. XXXIir (1880)— also abstract in the Journal of the Colleije of Science, Tokyo, Vol. I. 



