COMPRESSED GASES 89 



to BaO, and the oxygen given off. The process thus uses 

 up no chemicals whatever, and becomes simply mechanical. 

 The immediate effect was to reduce the retail price of oxygen 

 to 4:d. per cubic foot, and in large quantities to much less. 



Erin's gas is always perfectly dry, and free from chlorine ; 

 and when also free from nitrogen, appears to me superior to 

 average chlorate gas, though not to gas properly washed and 

 dried (see p. 78). At first, however, the quantity of nitrogen 

 left in it varied materially, and on several occasions I have 

 been greatly disappointed with the light when employing this 

 gas for microscopic or physical experiments. So much was 

 this the case, that some London opticians have turned again 

 to chlorate gas, and gone to the extra expense of pumping 

 that at the lowered rate. I believe, however, that all the 

 practical difficulties have now been overcome by the Brin 

 Company, and the more recent cylinders I have had of their 

 gas have been all that could be desired. 



48. Using Condensed Gases. With a good regulator 

 screwed upon the cylinder, this is used precisely as a gas-bag. 

 The regulator may be set at any given pressure in reason : I 

 recommend 9 inches for ordinary lantern work, and 14 inches 

 for high-power work. It has already been remarked that 

 with blow- through jets no regulator is absolutely required, 

 provided no taps are ever turned off, and all the regulation be 

 done at the cylinder valve. But with the regulator the 

 cylinder may be turned on, and the jet regulated by its 

 taps as usual : also the jet may be turned completely off if 

 needed. At the same time it is not wise to subject the 

 mechanism to the immense pressure for longer than neces- 

 sary ; therefore if the light is wanted off for more than ten 

 minutes the cylinder-valve should be turned off, and it is well 

 not to turn it on till just before the jet can be attended to. 

 As a rule no further attention will be required, the pressure 

 being maintained much more uniform than from bags ; and 

 it will be kept up till the gas left in the cylinder is no longer 



