330 Formation of Minerals by Electro-Chemical Action. 



when compressed between two polished plates. It is insoluble in 

 acids, unalterable by heat, and under the microscope it shews that it 

 is composed of very distinct rhomboidal crystals almost cubical, gene- 

 rally perfect, and more rarely modified by truncations on the angles, 

 perfectly transparent, and acting regularly upon polarized light. 



These rhomboidal crystals are often accompanied by other crystals 

 in thin elongated plates. They are, like the corundum^ insoluble in 

 acids, but are decomposed when heated, and then the alumina is dis- 

 solved by sulphuric acid, a singular property, which M. Damcour 

 has recognised in diaspore. In their normal state, they are transpa- 

 rent, act strongly upon polarized light, and their neutral lines are, 

 the one parallel, the other perpendicular, at their greatest length. 



It is worthy of remark, that the natural diaspore, almost always 

 accompanies corundum in its various repositories, and this associa- 

 tion is one of the geological proofs to which every attempt of arti- 

 ficial reproduction which endeavours to imitate the processes of 

 nature should be subjected. 



The oxides of iron, of chrome, of tin, and of titanium, are preci- 

 pitated too rapidly to assume a regular structure. We can retard 

 this separation, by rendering the liquid extremely acid, but then it 

 very much corrodes glass. I am, then, obliged to defer these expe- 

 riments until I have been able to procure tubes which will be more 

 resisting than those generally furnished by commerce. 



t.rfv/ benfleb leWod bm -o edj J*siit bsno?-' 



^^vjOn^UmArUflGidX Formation of Minerals hy Electrb- Chemical 

 '.:-■■ '.1 Action. By M. Becquerel. 



In ordinary chemical operations, when one body is made to act 

 upon another, it is customary to powder them, to dissolve them, or 

 to bring them into a state of igneous fusion. It is then almost im- 

 possible to observe the results of slow action, such as nature presents 

 so often, and the electrical effects resulting from immediate contact, 

 which may in certain cases aid in bringing about the former, or 

 giving them a greater energy. Electro-chemistry, therefore, differs 

 from chemistry in employing electricity as a subsidiary means of 

 exciting affinity, or rendering it more efficacious, and in its requiring 

 the mutual presence of three bodies, of which one at least must be 

 in a solid state and another liquid. Such is the point of view under 

 which I have constantly regarded electro-chemistry, which furnishes 

 means of analysis and synthesis of which advantage might be taken. 

 These researches have moreover the advantage of making known 

 the necessary conditions under which solutions containing one or 

 more combinations can react upon , ineoluble compounds with which 

 they are in contract. . , , , 



The weak actions .which have particularly attracted my atten- 

 tion are those which commence as soon as the rocks, the metallic 



