i»^ 



Intelligence and Miscellaneous Articles. 



render the attainment of the object in view one of considerable 

 difficulty. 



It will be evident, from what I have just stated, that any instru- 

 ment intended to supply the desideratum must be self-acting, and 



must supply the gas to be consumed 

 exactly as it is required. The in- 

 strument I have been in the habit 

 of using for some time back con- 

 sists of an air-thermometer, AB, 

 containing mercury in the lower part 

 of the bulb B and part of the stem 

 A. A tube of smaller diameter, 

 marked C, passes down the axis of 

 the tube A, the annular space being 

 made air-tight by a small brass 

 stuffing-box, D, by means of which 

 it may be retained at any required 

 elevation. In using the instrument, 

 the bulb B is placed in the same 

 situation as the body to be exposed 

 to the heat of the gas-flame ; for 

 instance, if it is a water-bath con- 

 taining vessels or other objects, it is 

 immersed in the water ; or if an air- 

 chamber or hot-press, it is placed 

 as near the object as possible, so 

 that the air in the bulb may attain 

 the same temperature as the sur- 

 rounding medium. 

 A tube of vulcanized India rubber is now to be connected with a 

 stop-cock attached to the service-pipe, and its other extremity drawn 

 over the end of the pipe C, which will make it sufficiently air-tight. 

 A second India rubber tube is in like manner to be attached at E, 

 to convey the gas to the burner employed as a source of heat in the 

 operation. 



Let us now suppose that it is required to keep an object at a tem- 

 perature of 100° F., the bulb of the instrument being placed con- 

 tiguous to the object ; the stop-cock is to be opened so as to allow 

 a free supply of gas to the burner, which is now to be kindled; the 

 heat now begins to act on the air contained in the ball of the in- 

 strument, causing it to expand and force the mercury up the stem 

 A; when it is found, by the use of a common thermometer, that the 

 heat has risen to 100°, the tube C is to be pushed down till its 

 lower extremity is immersed in the mercury. This would, of course, 

 cause the flame to be extinguished ; but, to prevent this occurring, 

 a small hole is bored through the inner tube opposite F, which per- 

 mits a small quantity of gas to pass to the burner. As the passage 

 of the gas is now interrupted, the source of heat is withdrawn, and 

 the cooling influence of the surrounding air comes into play, which 

 will cause the air contained in B to contract and the mercury to 

 sink in A, leaving the end of C uncovered, and thus open a free 

 passage to the gas, which by its combustion would again raise the 



