Intelligence and Miscellaneous Articles. 251 



A string vibrating in free space produces little or no sound ; but 

 if it be strung over, or in connexion with, an elastic board or box, 

 a great resonance is produced. This arises from two sources ; first, 

 the string when by itself is the centre of two waves excessively 

 close, and the action of which is therefore interfering. But if the 

 string A B vibrate near a plane surface C, 

 the wave — 1 , which passes towards it, is re- 

 flected back, and meeting the wave + 2, 

 which follows, it neutralizes it partly, and 

 enables the wave — 2 to reach the ear with- 

 out diminution. It is probable, however, that 

 the great portion of the sound arises from the 

 board or plate itself vibrating in parts, or as a 

 whole. If in parts, these parts are variously 

 situated, as regards the ear, and hence produce 

 an effect upon it. Or if, as a whole, the plate 

 C is so broad, or bounded, if a box, that one 

 wave is lost by internal reflexion, and only the wave emanating 

 from the outer surface can arrive at the ear. 



When a tuning fork is placed on a table, one wave is lost by in- 

 ternal transmission and reflexions, whilst that directed from the 

 outer surface reaches to the ear. 



In the case of reed instruments, the reed produces two waves, 

 which, if it vibrated freely, should neutralize each other on the ear ; 

 but in practice whilst an open passage is allowed to one by the 

 mouth-piece, the other wave is lost within the cavities of the lips 

 and mouth. In mouth-piece instruments, as bugles and trumpets, 

 the cavity of the mouth serves also for the absorption of the one 

 wave, leaving the other free to act. 



XXXVI. Intelligence' and Miscellaneous Articles. 



ACTION OF SULPHURIC ACID ON NITRATE OF AMMONIA. BY 

 M. PELOUZE. 



WHEN sulphuric acid and nitrate of ammonia are mixed at 

 common temperatures, no phenomena occur which might 

 not be expected, whatever may be the properties employed, that is 

 to say, reagents indicate the presence of ammonia, sulphuric acid 

 and nitric acid. 



If the mixture contain water and be submitted to distillation, 

 nitric acid and the sulphate of ammonia indicated by theory are ob- 

 tained. When, on the contrary, the nitric of ammonia is deprived 

 of water, and it is heated in fifty times its weight of concentrated 

 sulphuric acid, the mixture yields, at about 302° Fahrenheit, a very 

 considerable quantity of nitrous oxide ; water is formed, which com- 

 bines with the sulphuric acid, and neither nitric acid nor ammonia 

 exists in the product of this reaction. The nitrate of ammonia be- 

 haves under these circumstances as it does when merely heated, and 



