162 Intelligence and Miscellaneous Articles. 



If a hydrochloric solution of an oxide of the formula R^ O^ or 

 RO* be strongly heated, the acid, even when in excess, becomes free 

 in the solution, and the oxide is separated. The complete precipi- 

 tation moreover corresponds to a temperature which appears to de- 

 pend upon the state of dilution and the excess of acid present. In 

 this manner I have obtained the sesquioxides of iron and chromium 

 and titanic and stannic acids, in a pulverulent, amorphous and an- 

 hydrous state ; the latter alone presenting traces of crystallization. 

 Alumina, on the other hand, crystallizes, under favourable circum- 

 stances, in the anhydrous state in the form of corundum, and in the 

 hydrated state in the form of diaspore. The corundum obtained by 

 heating a dilute solution of hydrochlorate of alumina to a tempera- 

 ture which must exceed 662° F., is a white crystalline sand, which 

 scratches the emerald when pressed between two polished plates. It 

 is insoluble in acids, unalterable by heat, and under the microscope 

 is seen to be uniformly composed of minute, very distinct, almost 

 cubic rhombohedra ; they are usually perfect, and more rarely modi- 

 fied by truncatures tangential to the culminating angles, perfectly 

 transparent, and acting regularly upon polarized light. These rhom- 

 bohedric crystals are often accompanied by others, elongated, and in 

 thin layers, the lateral boundary of which is terminated by two pa- 

 rallel right lines, and towards each extremity by two obtuse symme- 

 trical beveled lines. Like corundum, they are insoluble in acids, 

 but when heated they become changed, and then some of the alu- 

 mina is dissolved by sulphuric acid ; which singular property M. Da- 

 mour detected in diaspore. In the natural state they are transpa- 

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

 one parallel and the other perpendicular to their greatest length. 

 We may convince ourselves, by the aid of the camera lucida, that 

 the plane obtuse angle of the terminal slopes is nearly equal to 115 

 degrees. All these characters are those of diaspore, in layers parallel 

 to the plane of cleavage, and there can be no doubt that the prismatic 

 crystals belong to this species. 



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

 accompanies corundum in its various repositories ; and this associa- 

 tion is also one of the geological proofs which every means of arti- 

 ficial production aiming at imitating the processes of nature must 

 satisfy. 



The oxides of iron, chromium, tin and of titanium, are too rapidly 

 precipitated to assume a regular structure. This separation may be 

 retarded by rendering the liquid very acid ; but then it strongly cor- 

 rodes the glass. — Comptes Rendus, May 19, 1851. 



THE THEORY OF SOUND. 



A further communication on this subject has been addressed to us 

 by Professor Potter, from which we extract the material portions, 

 and with which we shall consider the controversy in this Magazine 

 as closed, all parties having had the fullest latitude in bringing their 

 views fairly before the public. Mr. Potter observes, 



