Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/451

438 438 INFLUBNCB OF MAGlfBTISM ON CRTSTAXJJEATIOJT

magnet, ground to fit accurately upon each other, and on its poles, were provided. These bemg of dijSerent lengths, I was enabled to lengthen each arm of the magnet from two to six inches. This being firmly fixed on a mahogany stand, furnished with levelling screws, as shewn in the figure, enabled me to place on the poles a plate of glass or metal, edged widi wax or clay, capable of holding several fluid ounces of any solution.

9. It being absolutely necessary that everything like a current should be prevented, the slightest motion towards any particular point distort- ing the delicate curve lines as they are forming, and consequently dis- turbing the whole result, the levelling*screw and a spirit-level are re- quired to adjust the plate in a truly horisontal position ; such is the form of apparatus employed in the experiments I have made, and the precautions necessary to be observed in conducting them.

10. A solution of nitrate of silver being placed on a glass plate on the magnet, a piece of copper wire, bent into a U was suspended so that its ends, dipping into the silver solution, were exactly over the centre of the poles. The electro-magnet being connected with a constant battery of Daniell's principle, the whole was left at rest for sixteen hours. By the action of the copper, metallic silver was slowly precipitated, copper becoming dissolved proportionally to the quantity of silver which was deposited. The silver arranged itself, in a series of concentric circles around the wire, each circle being made up of very minute crystals, and diidded from each other by fine bands of the oxide of silver. This arrange- ment was much more strikingly exhibited around the north than about the south pole ; the silver formed round the latter being in much finer particles, and acciunulated in mass, whereas the crystals disposed on the former, although consolidated, were found to radiate in all directions towards the circumference of the iron of the magnet Thus were pro- duced around the copper wire two nuclei which formed the centres, from which started off a more dispersed system of crystals. The consolidated group of crystals formed around the north pole, weighed 8*4 grains; whilst that from the south pole weighed but 6. 6 grains. The crystalli- zation which went on beyond the circle corresponding with the iron of the magnet was arranged around the north pole, in a series of the most beautiful diamagnetic curves, those springing off from the south pole being of precisely the same order but more dispersed and irregular.

11. Around tiie south pole, a deposit of a green colour had taken place. This may have be^ either an oxide of copper, or a sub-salt of that metal (the quantity was so small and so much mixed up with the silver that its exact character could not be determined). It is, bow- ever, curious to observe something like a determination of chemical action to a definite pole. This experiment has been several times repeated, and always with the same result

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