Intelligence and Miscellaneous Articles. 539 



water; and these resemble the natural crystals of " fer oligiste" 

 from Elba. So Becquerel has obtained the oxides of copper, lead, 

 zinc. But by far the most valuable and important of such ex- 

 periments appear to be those of M. Becquerel on the sulphurets, 

 iodurets, and broimirets of metals, which he has obtained by arti- 

 ficial chemical action in a perfectly crystalline form. The agency 

 which !ie em|)loys is very weak galvanic tension; and he has suc- 

 ceeded thus in producing sulphuret of silver in small octohedral 

 crystals resembling the native mineral, and sulphuret of copper, 

 also closely resembling the native sulphuret. The sulphurets of 

 zinc and iron require additional precautions, but are also obtained 

 like to the native species ; and iodurets, bromurets, and seleniurets 

 of various metals are procured as crystals by similar processes. 

 {Ann. de Cliim. Oct. 1829.) These important steps in synthesis 

 will probably throw a new light upon known analytical results." 



M. Beudant has made a number of interesting experiments on 

 the subject of another class of causes which modify the forms of 

 crystals, and of which the general laws are, if possible, more un- 

 known and obscure than those which determine different funda- 

 mental forms to different compounds. He has examined the cir- 

 cumstances which determine the various modifications which a 

 given fundamental form undergoes; and has proceeded so far as to 

 be able to produce at will one or other of certain possible modifi- 

 cations. Thus (MJHcVa/ogi'e, i. 190.) common salt crystallizing in 

 pure water affected almost always the cubical form; if it crjstal- 

 lized in a solution of boracic acid, it assumed the form of the cube 

 with truncated angles. Alum in nitric acid had the same form ; in 

 muriatic acid it was a figure of twenty sides, the octohedron and 

 dodecahedron combined; the faces of the former being much the 

 larger. An addition of alumine to the liquor, produced, in addi- 

 tion to the former faces, those of the cube; in pure water this salt 

 is the simple octohedron. Sulphate of iron has commonly a simple 

 form ; by adding a few drops of sulphuric acid, more complex forms 

 are obtained; and this rule respecting the effect of the addition of 

 acid appears to be extensively true. The sulphate of iron mixed 

 with sulphate of copper has its simple form, an oblique rhombic 

 prism ; the mixture of sulphate of nickel produced the same effect, 

 but that of zinc an opposite one, the crystals becoming less simple. 

 It has long been known that common salt mixed with urea, affects 

 the octohedron instead of its usual form, the cube ; and that in 

 similar circumstances, sal ammoniac becomes the cube instead of 

 the octohedron. Alum in a concentrated solution of alumine as- 

 sumes the cubical form ; an octohedral crystal of alum placed in 

 such a solution soon assumes a cubical form; by being placed again 

 in a solution adapted to give octohedral crystals it may be made to 

 assume the octohedron. It is impossible not to be tempted to refer 

 phaenomena similar to these, occurring, as they so often do, in na- 

 tural crystals, to similar circumstances which have prevailed when 

 the crystals have been forming." 



" Several statements of a curious kind have been made concerning 

 the recent crystallization of substances which we cannot cause to 

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