380 THE CHEMICAL TIARMONICOX. 





The jet of. hydrogen should under no circumstances be ignite> 

 until the purity of the gas has been ascertained, for a mixture of ai 

 and hydrogen explodes when lighted, and the apparatus may 1) 

 shattered to pieces. A sufficient quantity of the gas should then 

 fore be allowed to escape, and then a glass tube about 10 cm long i 

 attached to the indiarubber tube, which serves for connecting tb 

 jet with the apparatus for generating the gas. A quantity of gas 

 now permitted to enter a test tube in the manner described on pa 

 317. The tube filled with the gas is closed with the thumb and liftc 

 from the water; the thumb is then withdrawn, and a burnin 

 match is held close to the mouth. A faint explosion will be hean 

 because some air mixes with the hydrogen at the mouth of tl 

 tube, but the greater portion of the gas should burn slowly and quiet 

 with a bluish flame which is scarcely visible : if the gas is mixed wii 

 atmospheric air, it burns with a whistling sound or with a soui 

 like a short bark or pop. The gas should never be lighted unle 

 the above test has been applied ; even if the apparatus has stood f 

 some time filled with the gas, and the gas has been tested on 

 before, it should be tested again before using it. 



When the gas is free from air, the indiarnbber tube is attached 

 the jet tube, the gas ignited and the glass tube placed over it. , 

 soon as it has the proper position, the tube emits a loud note. 



The vibration of the air in the tube causes, as has been t 

 plained, a rapid increase and decrease of the density and con; 

 quently of the pressure. These variations of the pressure interft 

 with the steady efflux of the gas from the jet ; it issues in ma 

 successive jerks, and instead of a quietly burning flame we have 

 series of separate combustions, each of which causes the air to 

 heated, and consequently to be expanded: each, therefore, adds 

 new impulse for the continuation of the movement. The sin: 

 combustions succeed one another so rapidly that the second is si 

 before the impression produced upon the eye by the first has d 

 appeared, and consequently the flame appears to be continuoi 

 but in reality it is a series of successively ignited jets, as will 

 shown hereafter. The continuance of* the vibrations, after tli 

 have been once produced, is thus easily explained by the altern 

 expansion and condensation of the air produced by the intermitt 

 combustion of the gas. But the first production of these vibrati i 

 must have some other cause, and the whole phenomenon is ; 

 yet sufficiently accounted for. It is possible that the draught ] - 

 duced by the flame has a share in the production of the sound. 



When the tube is removed, after the most suitable position 

 the production of the note has been determined, and the appar: 



