86 PEACTICAL PHOTO-MICKOGKAPHY 



with right- and left-handed screws, so that only the gas for 

 which the cylinder is made can be put into it. 



The oxygen is always contained in a black cylinder, and the 

 hydrogen in a red one, and these are regarded by the trade as 

 sufficient indication of the contents. 



The regulator made by Mr. E. Beard fulfils every 



FIG. 24. Lime-light Jet on Saddle-stand. 



requirement. It has been in use for many years, and, so far 

 as the writer is aware, without accident of any kind. 



A regulator that has been used on an oxygen cylinder should 

 never be transferred to the hydrogen one ; but if two cylinders 

 are used, a regulator for each must be kept. These are now 

 also made with right- and left-handed screws, so that an oxygen 

 regulator will only go on to an oxygen cylinder, and the same 

 applies to the hydrogen. 



There are a large number of lime-light jets on the market, and 

 it will suffice to refer to two or three typical ones. 



Fig. 23 b is a type of blow- through jet, with a movement to 



