468 Intelligence and Miscellaneous Articles. 



The product, as proved by analysis, still contained some 

 monometliylresorcin. 



The preceding data are sufficient^ to my thinking, to prove 

 the usefulness of the modified Dumas' s method of vapour-den- 

 sity determinations ; my efforts will now be further directed 

 to making this modification applicable to cases where both the 

 oil-bath and the mercury thermometer are inapplicable. 



LXII. Intelligence and Miscellaneoiis Articles. 



ON THE MAGNETIZATION OF STEEL TUBES. BY J.-M. GAUGAIN. 



TF into a magnetized steel tube, at the ordinary temperature, a ey- 

 -^ lindrical core of the same metal in the neutral state be introduced, 

 and again taken out after the lapse of a few moments, it will be 

 found to be magnetized in the same direction as the tube. But if, 

 after placing the core in the tube, we heat the system with a lamp 

 so as to raise its temperature to about 300°, let it cool again, and 

 after cooling separate the tube from the core, we find that the tube 

 has lost a great part of its previous magnetism, and that the core 

 has acquired a contrary magnetization. 



I suppose that even at the ordinary temperature the core takes 

 a magnetization the inverse of that of the tube as long as it remains 

 within the latter ; but when we come to take it out, friction is in- 

 evitably produced, the result of which is the reversal of the direction 

 of the magnetization. If things happen otherwise when we operate 

 at an elevated temperature, it is because, on the one hand, the in- 

 verse magnetization developed in the core by the influence of the 

 tube is considerably augmeuted by the heatiug, and, on the other, 

 the direct magnetization developed at the moment of separation of 

 the tube and the core is weakened, the tube having lost the greater 

 part of its magnetism when the separation takes place. In conse- 

 quence of both these circumstances the inverse magnetization re- 

 mains predominant. 



Altogether analogous effects to those just indicated are produced 

 when a magnetized core of steel is introduced into a tube of the 

 same metal in the neutral state : if the operation takes place at the 

 ordinary temperature, the tube is found, when separated from the 

 core, to be magnetized in the same direction as the latter ; but if 

 the system be heated and the tube be not separated from the 

 core until after cooling, the tube will have acquired the inverse 

 magnetization. 



1 or the heaticg of the system to develop this inverse magnetism 

 in one of its parts (tube or core), it is not uidispensable that this 

 part shall be in the neutral state. When the two parts are mag- 

 netized in the same direction, but unequally, and there is sufficient 

 difference between their magnetizations, the feebler of these is 

 reversed when the svstem is heated. 



