AND CHLORINE UNDER THE INFLUENCE OF LIGHT. 
79 
kept in the dark and was found to work extremely well. Fig. 1 is a diagram of 
the cell. 
The insolation apparatus (fig. 2) was essentially the same as that 
of Bunsen and PvOSCOE. Considerably larger bulbs were sometimes 
used to make the Draper effect more evident. The gases from the 
generating vessel pass through the washing bulbs (b) to the tube (c) 
leading to the insolation bulb (cl). At (e) a side tube is sealed, so as 
to allow the gases when the tap C is closed to pass through the 
water in (/) and so out through {g) into [h], an earthenware pot filled 
with lime to absorb the chlorine. The clip in (g) serves to close this 
outlet. With (c) open, all the gas evolved passes into the bulb (d), 
which contains some water in its lowest part, thence through the 
capillary tube (^) to the bulb {j), and thence to the absorbing vessel 
(Jc), which is similar to (h). The bulbs (d) used were from 3 to about 
8 centims. in diameter. The capillary tubes (i) were from 50 centims. 
to 200 centims. long. The bulb (j) has water in it to just above 
the level of the capillary tube, so that when (c) is open the gases 
bubble through the water in {j), and when (c) is closed the water- 
runs a few centimetres into the capillary and forms the index 
defining the volume of the gas in the insolation bulb (d). With 
large insolation vessels it is very necessary that the capillary tube (i) 
should be level along its whole length, as it is easy to see that the 
water in the capillary may produce changes of pressure in the bulb (d), causing 
corresponding changes of volume which are greater than the effects to be observed 
unless the tube is horizontal. This tube was usually supported along its whole length 
on a wooden table. The bulb (j) also must be large enough for the alteration of level 
Fig. 1. 
Fig. 2. 
of the water in it, due to motion of the index, to be negligible. When practicable, 
the whole apparatus from the generating vessel to the outlet tube had only glass 
joints, as indiarubber is soon destroyed by chlorine, and, also, with only glass joints 
there is no danger of contamination of the gases. The glass joints at the ends of the 
