THE LIME-LIGHT 63 



With most of the jets commonly sold it is fair too thick and 

 clumsy at the tip. Such a thick end positively obstructs the 

 light from the lime, and by preventing the smooth access of 

 air to the outside of the flame, it further diminishes the power 

 of the jet. The nipple should, therefore, be carefully tapered 

 down to a thin edge. Small bores up to -^ inch can be 

 tipped with platinum, though this is not necessary ; but with 

 large bores, unless the platinum is carried over \ an inch 

 down, the brass will be melted away from it. For large bores 

 solid plain brass nipples are therefore best. It is well to have 

 at least two nipples of different sizes, and they should screw 

 on so nicely as to be gas-tight without cement, for interchange 

 when desired. 



After all possible pains, a powerful jet such as above de- 

 scribed, will sometimes ' sing.' In that case it can usually be 

 quieted by dropping a wire ring 

 on the bottom of the chamber, 

 laying on that a disc of perfo- 

 rated zinc cut to fit the chamber, 

 and keeping that down in place 

 by another ring, cut so as to 

 spring tightly. But the best 

 arrangement of all I have found 

 to consist in a few alternations 

 of thin discs pierced as fig. 41, 



separated by rings, as devised by Mr. Lancaster. With a 

 chamber properly tapered at top and bottom, as shown, this is 

 quiet under any reasonable pressure, and gives aperfect mixture 

 and a powerful light, which can sometimes be pushed as high 

 as 1,000 candles. After exhaustive trial of many experimental 

 chambers most carefully made for me by Messrs. Newton, this 

 is the form I have finally adopted as the best. 



It must be clearly understood that the object of this 

 packing is not ' safety,' which is never ensured by such means, 

 but solely a quiet and thorough mixture of gas in the chamber. 



