PREPARATION OF GASES 79 



the fluid. The tube passing into the purifier should go nearly 

 to the bottom of it, and about two inches from the bottom 

 end should be perforated with six or eight holes about ^ inch 

 diameter, that the gas may enter the water in small streams. 

 Care must be taken to make no mistake about the proper 

 connections, as shown in the figure. 



Many people pass the gas simply once, through water, in 

 this way. This will cool it but not purify it ; and it also 

 carries it damp into the bag, to the latter's rapid destruction. 

 To absorb the chlorine, sodic carbonate (common washing 

 soda) or potassic carbonate (salt of tartar) may be dissolved 

 in the water, and answers fairly well ; but the way to per- 

 fectly neutralise it is to use caustic soda. With this, the same 

 solution may be used several times, if at home ; the quantity 

 is not very material, using, say, a couple of sticks of the caustic 

 to a Winchester quart bottle. One washing is not, howevei\ 

 enough ; two purifiers are necessary to get really pure gas, 

 connecting the delivery-tube from the first with the entering 

 pipe of the second. 



Formerly sheet-metal purifiers were used ; but it ia 

 advisable, if not necessary, to see just how fast the gas is 

 coming over, by which the heat under the retort is to be 

 regulated, and hence glass bottles have long been usual. 

 These are generally made as in fig. 48, with screwed caps, 

 through which the entry and delivery-tubes passed. But 

 there are two far better methods. The first is to employ 

 vulcanised ' Woolff ' caps, through whose nipples the brass 

 pipes are passed, and which simply stretch over the open 

 mouths of wide-necked Winchester quarts. These will 

 also act as safety- vents for too great a rush of gas, allowing 

 either some leakage, or blowing off altogether if it were 

 necessary. But the best and handiest fittings of all are made 

 as in fig. 49. Here B is a brass tube about one inch in 

 diameter, closed in at the top, into which closed top the brass 

 entry-pipe (A) is brazed. Into the side, at (c) the delivery nipple, 



