THE BOOK OP THE LANTERN. 65 



to know how quickly this exchange takes place in the case 

 of a bag of oxygen; but, as an experienced worker, I 

 have no hesitation in saying that there is a marked 

 deterioration in the quality of the lime-light, if the oxygen 

 gas used has been kept for only 24 hours in a bag 

 instead of being freshly made. The same rule will 

 apply to the hydrogen gas in a greater degree, for the 

 hydrogen passes through a porous diaphragm far more 

 rapidly than can oxygen. But, in practice, the H bag is 

 filled from the nearest gas-tap immediately before it is 

 wanted. (Mr. Fletcher, of Warrington, has patented a 

 method of preventing the smell of gas-tubes, by inserting 

 a partition of tinfoil between the two layers of india-rubber 

 which compose the tube. This foil stops the smell, by 

 stopping endosinose. The same principle might, of course,, 

 be applied to gas-bags. Here is a hint for manufacturers.) 

 Other objections to the use of gas-bags are found in their 

 initial expense, and the necessity for constant renewal, 

 their bulk, and their liability to mechanical injury. In 

 spite of these defects, I have always preferred to use gas 

 in bags, rather than gas compressed in cylinders. My 

 reasons for this choice I will now give. 



If the gases are compressed in cylinders, there is a 

 great saving in trouble, as well as in bulk of apparatus ; 

 but I have hitherto set my face against them for the 

 following reasons: 1. The pressure is so great, that the 

 india-rubber tubes are apt to blow off ; and, if tied on, may 

 burst. 2. The light cannot be regulated at the jets and 

 by the taps provided for that purpose, but the taps must 

 be turned fully on, and the outrush of gas roughly 



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