PREPARATION OF GASES 81 



quantity of mixture, and keep it in some metal vessel ; a 

 circular tin with hinged cover, such as is sold for biscuits, 

 answers admirably. It is also convenient to keep in the tin 

 an iron gardener's trowel to shovel up the mixture, an old 

 tin canister cut to such a size as will exactly hold the charge 

 found sufficient to fill the bag, and a tin funnel with a large 

 spout. Starting with a retort both clean and dry, it takes 

 but a moment to shovel up enough mixture to fill the canister, 

 unscrew the head of the retort, funnel in the charge, roughly 

 level it by giving the retort a shake, replace the top, and 

 screw it home; a properly-made retort needs no washer or 

 other packing. The retort is then placed on the ring-burner, 

 which itself is controlled by a tap, the delivery-tube connected 

 with the entry-pipe of the first purifier by half a yard or 

 more of vulcanised tubing, all the purifiers properly connected 

 as described, and another length of vulcanised tubing attached 

 to the final delivery-nozzle of the last piece of purifying 

 apparatus, the other end being placed loose where it can be 

 instantly slipped on the nozzle of the gas-bag. The Win- 

 chester quarts should be full nearly to the shoulder, unless 

 the second is left half full as before indicated, for lack of a 

 drier. Then light the burner. Meantime, the bag has been 

 flattened and rolled, so as to expel the contained air, and the 

 tap then closed. In a minute or two bubbles will begin to 

 ascend in the purifiers, but these at first are merely heated 

 air, driven over by expansion. Soon they come more steadily, 

 and then a match should be held ready near the mouth of 

 the last rubber tube. When the operator tninks about as 

 much air is driven over as filled the vessels, he should strike 

 a match, and when well caught blow it out, holding the red 

 coal in the stream of gas from the end of the tube. 1 If 

 oxygen is beginning to come over, the coal will brighten 



1 Care should be taken to hold the tube horizontally, and the match in 

 front and not over it. A case has been reported in which the burning end of 

 Ihe match fell in and ignited the robber, resulting in a fierce combustion. 



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