OXY-ETHER AND HYDRO-CARBON LIGHTS 99 



tap of the jet, and after a few seconds, to let air escape, turn 

 it off again for inflammable vapour to leave the lantern. 

 Turning it on again we apply a light, which burns in place of 

 house-gas. All the * pure ' oxygen taps, from the fork on- 

 wards, are meanwhile turned off. 



It is always to be remembered that full saturation with 

 ether vapour is the condition of silent combustion and safe- 

 guard against explosion ; the explosive mixture with oxygen 

 only being allowed at the jet itself. The test of this is the 

 condition of the flame. While all is safe, this is white or 

 yellowish-white. As oxygen increases, this changes to deep 

 yellow, and finally to a purplish or blue colour. This last 

 shows an explosive condition, and whenever it occurs with what 

 stands for the hydrogen supply alone, proceedings should at 

 once be stopped. This test refers to naked flame only. When 

 the lime is adjusted close to the jet, even a dangerous mixture 

 may appear to burn yellow, and therefore it is best always to 

 light the flame first, at a distance from the lime. If it is a 

 good light colour the lime can be adjusted and warmed, after 

 which the oxygen is gradually turned on and adjusted in the 

 usual manner, till the brightest light is attained. As the 

 work proceeds, however, if it be found that the pure oxygen 

 has to be gradually turned off, it shows that from some cause 

 saturation is becoming more and more defective, and work 

 should be stopped and the light put out. To proceed under 

 such conditions is dangerous. 



At the end of work, the hydrogen tap of the jet may 

 be turned off, so that the surplus oxygen ' snaps ' the jet 

 and puts it out. The condition of safety is to turn off at 

 the jet first, and never at the bag or cylinder till the light is 

 out. 



When two lanterns or a bi-unial are worked with this light, 

 it will often be found that the dissolver (see Chapter VIII.) will 

 not work properly without some alteration. No oxygen bye- 

 pass whatever must be allowed, as is often done with the 



H2 



