102 
commonly used as terminals for the electric lamp ; these 
poles are of such a length that they pass to the bottom of the 
glass bottle. This is then filled with strong aqueous hydro- 
chloric acid containing about 80 per cent of the anhydrous 
acid ; the stopper in the poles and wash bulbs containing 
a few drops of water is then fixed into its position, and the 
evolution vessel placed in a beaker of cold water whilst con- 
tact is made with the terminals of four ordinary sized Bunsen’s 
cells, the whole apparatus being placed in a dark room. The 
mixed gases at once begin to be given off, and ought to pass 
through the wash bulbs at the rate of about two bubbles per 
second. It is absolutely necessary that the gas be allowed to 
come off at this rate for three hours* before it is collected, as 
up to this time it does not attain a sufficient degree of purity 
and sensitiveness, whilst after the lapse of this time it is 
generally found to be fit for use. In order to absorb the 
excess of chlorine, the waste gas may be led into a condenser 
containing slacked lime and charcoal in alternate layers. 
When the evolution has gone on for the above mentioned 
time a bulb tube, connected by caoutchouc joinings, is placed 
between the evolution vessel and the condenser, and the gas 
allowed to pass through. The bulbs, which are made of 
fusible glass tubing, are blown about the size of a hen’s egg, 
and so thin that they easily break when pressed with the 
finger. At each side of the bulb the tube is drawn out so as 
to be very thin in the glass, and to leave the internal diameter 
not less than 1mm., whilst at the extremities the tube is 
wider so as to fit ordinary joinings. When the gas has 
passed through the tube for about ten minutes, the joinings 
are loosened and each end stopped with a piece of glass rod. 
The bulb tube thus closed is then removed from the evoluting 
vessel, and the thinnest part of the tube brought some little 
distance above a very small Bunsen’s flame ; the glass then 
softens below a red-heat, and the ends may be drawn out and 
* See Bunsen and Roscoe, Photochemical Researches, 1857, p. 855. 
