Intelligence and Miscellaneous Articles. 69 



prives salts of their water of crystallization, could not be verified 

 with oxalate of ammonia and ferrocyanide of potassium. Weighed 

 portions of these salts, placed respectively under blue, white and 

 green glasses, were found at the end of a month to have suffered no 

 change in weight. It has been observed by Hunt, that a solution 

 of bichromate of potash gives a greenish-yellow precipitate with 

 sulphate of copper in the sunshine. This was found to take place 

 almost equally in all the rays, whether in sealed or open vessels, 

 though a little earlier in the former. The action was found more 

 rapid and more complete in dilute than in concentrated solutions. 

 The latter, after having ceased to deposit, give a further amount of 

 precipitate if diluted. There is a considerable effervescence in the 

 liquid, caused by the escape of oxygen gas. The precipitate is at 

 first of a greenish- yellow, but becomes a yellowish-brown when dry, 

 and shrinks greatly in bulk. Solutions of sulphate of copper and 

 of bichromate, exposed separately to the sun, and then mixed in the 

 dark, give the same precipitate ; but if prepared in the dark, no per- 

 ceptible precipitate is obtained, even on long standing. If the mix- 

 ture is boiled, however, a precipitate appears. If the precipitate 

 formed by the action of the sun is removed and the liquid boiled, a 

 precipitate appears of a redder shade, probably identical with Bensch's 

 chromate of copper. I have not as yet obtained a quantity sufficient 

 for analysis, either of this or of the former precipitate. Whether 

 the electric and hygrometric conditions of the atmosphere exert any 

 influence upon actinic decompositions, I have not been able to de- 

 termine with certainty. — From theChemical Gazette for Sept.l, 1852. 



NOTE ON THE INDUCED CURRENTS PRODUCED BY THE TORSION 

 OF IRON. BY G. WERTHEIM. 



It has long been known that an iron wire submitted to the action 

 of terrestrial magnetism becomes permanently magnetic when it is 

 made to suffer a considerable and likewise permanent torsion. An 

 attempt is made to explain this fact by saying that torsion acts in 

 the same manner as any other mechanical impulse, that it facilitates 

 the separation of the two magnetic fluids, and that at the same time 

 it communicates to the iron a certain coercive force. This opinion 

 however is founded upon incomplete observation ; torsion acts in a 

 manner which is altogether special in compelling the molecules to 

 assume a spiral arrangement, and thus communicating to the sub- 

 stance itself the form which Ampere has assigned to the internal 

 currents. Temporary torsion produces temporary magnetic effects, 

 permanent torsion produces permanent magnetic effects, and these 

 effects cannot be reproduced by any other mode of action of mecha- 

 nical forces. 



Temporary Effects. — A bar of iron, magnetized to saturation, is 

 partially demagnetized at the moment it suffers a temporary torsion, 

 and regains its full magnetic properties as soon as the torsion ceases ; 

 in other words, during the torsion it is traversed by an inverse cur- 

 rent, and when the torsion ceases by a direct current, whatever may 

 be the direction in which the torsion is effected. 



I understand by saturation that state of magnetic equilibrium pre- 

 sented by a bar of iron which has acquired the full amount of mag- 



