a 36 Intelligence and 31iscellatieous Ar fides. 



the alkaline earth sparingly soluble salts. If concentrated solutions 

 of oxalurate of ammonia, chloride of calcium or barium be mixed 

 with each other, after standing some time, brilliant transparent scales 

 or needles of oxalurate of barj'ta or lime will be deposited ; a solu- 

 tion of the latter in water when treated with an excess of ammonia 

 gives a basic salt in the form of a transparent gelatinous precipitate, 

 which is redissolved by a large quantitj- of water. 



Oxalurate of Silver. — This salt is obtained b}'' mixing boiling so- 

 lutions of oxalurate of ammonia and nitrate of silver, and is depo- 

 sited as the solution cools in long anhydrous needles of a silky 

 lustre ; these are decomposed at a high temperature without ex- 

 plosion. 



Its formula is AgO + CeNM.O-. 



PNEUMATIC TELEGRAPH. 



A pneumatic telegraph has been invented by Mr. S . Crosley, an ope- 

 rative model of which is preparing for exhibition at the Polytechnic 

 Institution. Atmospheric air is the conducting agent employed in its 

 operation. The air is isolated by a tube extending from one station to 

 another ; each extremity of the tube being connected with a vessel con- 

 taining a small volume of air in direct communication with the air in 

 the tube. This vessel is employed as a reservoir to compensate for 

 any increase or diminution which must necessarilj- arise from compres- 

 sion, or from changes in the temperature of the air, and for sup- 

 plying any casual loss b)' leakage ; the vessel must, therefore, be 

 capable of enlargement and contraction in its capacity, after the 

 manner of bellows, or as a gas-holder, by immersion in water, so as 

 to maintain, uniformlj^, any particular degree of compression which 

 may be given to it. 



It will be evident to every one acquainted with the physical pro- 

 perties of atmospheric air, that if any certain degree of compression 

 be produced and maintained in the reservoir, at one station, equili- 

 brium will rapidly succeed, and the same degree of compression will 

 extend to the opposite station, where it will become visible to an 

 observer by means of a pressure Index. 



Thus, with ten weights producing ten different degrees of com- 

 pression, distinguished from each other numerically, and having a 

 pressure index at the opposite station, marked by corresponding 

 figures, any telegraphic numbers may be ti'ansmitted, referring in 

 the usual way to a code of signals, which may be adapted to various 

 purposes and to an)' language. The only manipulation is that of 

 placing a weight of the required figure upon the collapsing vessel at 

 either station, and the same figure will be represented by the index 

 at the opposite station. 



Pre'viously to making a signal, the attention of the person, whose 

 duty it is to observe it, is arrested by means of a preparatory signal. 



The communications between one extremity and the other may 

 be made knosra at intermediate stations, by connecting with the air 

 tube, indexes corresponding with those at the extremities ; but in 



