192 . Mr. E. Solly on a Chemical Lamp-Imrnace. 



the greatest heat. The mixture of coal-gas and air burnt in 

 this lamp, is made by injecting a sufficient quantity of air into 

 the pipe which supplies the coal-gas. To the end of a com- 

 mon gas- cock connected with the street main, a piece of cop- 

 per pipe about four inches long is attached, having a diameter 

 of about a quarter of an inch ; outside this is another piece 

 of copper tube, of considerably larger diameter, and six 

 inches longer than the internal tube. The air which is to 

 mix with the coal-gas is admitted into this longer external 

 tube, the quantity being regulated by cocks. The object of 

 this is to effect the mixture of the air and coal-gas under the 

 most favourable circumstances ; if mixed otherwise than as 

 two currents flowing in the same direction, a diminution of 

 pressure is caused; whilst by causing them to mix in the man- 

 ner just described, the pressure of the whole current is rather 

 augmented. 



The pressure of the ordinary street gas does not, I believe, 

 generally exceed two inches; if the air was introduced by a 

 pipe entering the gas-pipe at right angles, and if the pressure 

 of the air at all exceeded that of the gas, it was very apt to 

 stop the current of gas altogether, the air forcing the gas back 

 into the pipe; by using the above double pipe this was ob- 

 viated, and it was found possible slightly to increase the press- 

 ure of the air over that of the gas without at all diminishing 

 its force. At first a gasometer was employed as a source of 

 air, but after a few trials it was found that a common double 

 bellows was more convenient; when the lamp is used, the 

 crucible to be heated is supported on the top of the horizontal 

 circle of jets by a triangle of platinum wire, so as to place it 

 in the centre of greatest heat. If only the gas is lighted, 

 it of course burns with a large and very smoky flame, depo- 

 siting abundance of solid carbon ; but the moment the air is 

 admitted, the flame begins to diminish in size and also in bril- 

 liancy, burning, when a sufficient proportion of air is allowed 

 to enter, with a pale blue colour, and perfectly free from solid 

 carbon. The crucible is, in fact, heated by eighteen little blow- 

 pipes, and of course becomes brightly ignited in a few seconds, 

 the heatcontinuing to increase as the ignited platinum facilitates 

 the more complete combustion of the gas and air, causing the 

 blue flame of each jet to be edged with pale yellow, and con- 

 siderably increasing them in size; lastly, the furnace is ren- 

 dered complete by a thin cylinder of sheet iron, three inches 

 in diameter and two high, which is placed above the horizontal 

 circle to prevent the flames being blown about by draugtit of 

 air, and a circular disc of the same metal, having a hole in its 

 centre of an inch across, to place at the top of the cylinder: 



