84 PRACTICAL PHOTO-MICROGKAPHY 



somewhat difficult to observe directly, but any piece of glass 

 or the surface of a condenser that may be in use at the time will 

 act as a reflector if temporarily placed a short distance in front 

 of the lime. 



The blow- through jet is somewhat more simple to use. 

 The tube through which the hydrogen or coal-gas is conducted 

 may be connected up to any tap or tube which is in connection 

 with a house supply of gas. This should be lighted up so that 

 the flame is from an inch to an inch and a half higher than the 

 top of the lime cylinder. The oxygen gas should then be carefully 

 allowed to pass in from the cylinder, and very much the same 

 condition of affairs will be noted as occurs in the mixed jet, 

 excepting that the adjustment of the oxygen gas is the only 

 one that is of importance. The oxygen should be allowed to 

 pass in until it hisses or causes a distinct falling off in the light. 

 If there is then any unnecessary excess of coal-gas it will show 

 itself by the flame extending rather above the top of the lime, 

 and in this case the coal-gas must be gently turned off until only 

 a slight excess is apparent. 



The ' saturator ' method has advantages over either of the 

 two above mentioned. As ether vapour is substituted for the 

 somewhat impure coal-gas, a very much brighter light can be 

 obtained. The writer has himself tried only one type of these, 

 namely, that known as the Pendant Saturator, and made by 

 Messrs. Willway & Sons of Bristol. This saturator is arranged 

 to work with any jet made for mixed gases. Pressure is, of course, 

 obtained only from the oxygen cylinder. It is claimed for this 

 method that it is the most economical means of producing 

 oxyhydrogen light, since not only is the hydrogen substitute 

 less costly than compressed coal-gas, but owing to the free- 

 dom from impurities, less oxygen is required. Where this 

 method of light production is decided upon, it is recom- 

 mended that the makers of this apparatus should be 

 referred to, for they issue a very concise and fully illustrated 

 description of it, together with instructions on its method of 

 working. 



The selection of the limes for either jet is of some importance. 

 For the mixed jet a hard form of lime is necessary, as both gases 

 work under pressure ; and, further, as the temperature is so 

 extremely high, pitting or excavation of the surface of the 



