228 Intelligence and Miscellaneous Articles. 



To obtain the deposit of silicium, I dissolved monosilicate of pot- 

 ash (formed by fusing together 1 part of silica with 2^ parts of car- 

 bonate of potash) in water, in the proportion of 40 grs. to 1 oz. 

 measure of water, proceeding in like manner as with the alumina 

 solutions, the process being hastened by interposing onepair of small 

 Smee's battery in tlie circuit. With a yeiy slow and feeble action 

 of the battery, the colour of the deposited metal was much whiter 

 than that of the aluminium, closely approximating to that of silver ; 

 its other properties I have not yet had time to examine. 



I remain. 



Yours very truly, 



George Gore. 



EXPERIMENTS ON THE ARTIFICIAL PRODUCTION OF POLYCHROISM 

 IN CRYSTALLIZED SUBSTANCES. BY M. DE sfixARMONT. 



In some researches upon crystallization which the author has 

 pursued for several years, he has been led to study the absorption 

 of light which takes place in coloured crystals, and the polychrojsm 

 which accompanies it. 



This singular property, which is possessed by many minerals and 

 artificial products, consists essentially in the circumstance that the 

 two luminous rays resulting from double refraction undergo in 

 the interior of the crystal an unequal extinction in their colorific 

 elements, so that a pencil of white natural light is separated on its 

 emergence from the crystal into two pencils of different colours at 

 the same time that they are polarized at a right angle. 



It may be inquired whether such a phsenomenon must be neces- 

 sarily and exclusively caused by the coloration, either of the crystal 

 itself, or of some other substance chemically combined with it; and 

 whether it may not sometimes be the effect of two different and 

 coexistent causes, as a birefractlve power exerted by the crystalline 

 matter itself, and an absorbent power exercised by some foreign 

 colouring matter accidentally distributed in the interstices of the 

 crystal, like the impurities which crystals derive from their mother- 

 liquors. This question can only be decided by synthesis ; it would 

 be solved if we could succeed in introducing into crystalline salts all 

 sorts of colouring matters, incapable of forming a chemical union 

 with them, but capable of incorporating themselves by a sort of 

 impregnation. 



The problem, put in these terms, appears more simple than it 

 really is. For dichroism, selecting different colours for suppression 

 in each of the refracted rays, it is impossible that its cause can be 

 quite independent of that which thus splits the luminous i-ays in 

 crystalline refraction. The absorbent agent, whatever it may be, 

 must, on the contrary, be connected and in some degree subordi- 

 nated to the crystallization ; and if it may reside in coloured non- 

 crystalline particles, it is at least necessary that their arrangements 

 should be continuous to a certain point with the crystalline medium. 



