95 



it is contaminating- the other gas, till the mixture arrives at tlie 

 exploding point, and destroys, if not the operator, at least the ap- 

 paratus. This apprehension was increased in me by the recollec- 

 tion of an explosion which endangered one of our most accom- 

 plished members : an instrument invented by Cuthbertson, to shew 

 the formation of water during the combustion of hydrogen, in 

 which the flame was fed nearly as in the American blow-pipe, 

 from some event of this kind was shattered with a frightful deto- 

 nation. Such considerations long restrained me from gratifying 

 the curiosity which Mr. Hare's account excited, till the news-pa- 

 per accounts of the new blow-pipes added a fresh stimulus. How- 

 ever, I tiled the instrument which I constructed after his plan, 

 with air instead of oxygen, and it appeared that my caution was 

 not unnecessary, for an explosion took place in a few minutes, 

 and blew to pieces tlie connecting tube of the air gasometer, which 

 was in this trial of glass cemented to the stopcock. It soon oc- 

 curred to mc that the possibility of such an event might be pre- 

 vented by a simple contrivance, of which I lay a drawing before 

 the Academy, and I have not had any reason to distrust its ef- 

 ficacy, though I have, in some instances, maintained the flame 

 for 28 and 30 minutes without intermission. In Fig. 1, the tube 

 A, connected with the oxygen gasometer, is an inverted syphon, its 

 ascending leg rises through the neck of the small glass bell B, into 

 which it is cemented ; the shaded part represents mercury, through 

 which the tube passes, being protected from it by cement. C- 

 is a smaller bell, from whose sununit the tube D conveys the gas 

 to the blow-pipe ; In using this, the bend of A, (which is -', of an 

 inch wide) is [hiled with water to the height of 4 inches, 

 it is then screwed to its gasometer, the bell C is pressed down 



