PROFESSOR ROSCOE’S RESEARCHES ON VANADIUM. 
689 
It consists of a hydrogen generator (A) yielding a stream of hydrogen which can be 
kept constantly passing through the wash-bottles day and night for a week at a time, 
Fig. 2. 
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by occasionally adding fresh acid to the upper bottle and drawing off the zinc-sulphate 
solution from the lower bottle by the caoutchouc tube. The first wash-bottle contains 
a solution of lead acetate, the second silver nitrate, and the other three boiled sulphuric 
acid. In order to remove any trace of oxygen which may have accompanied the hydro- 
gen arising either from diffusion or from air absorbed in the dilute acid used, a tube 
(C D) is attached to the end of the last washing bottle ; the first portion of this tube 
contains a quantity of platinum sponge (C), which is heated to redness during the whole 
time the hydrogen is passing through the apparatus, whilst the further portion of the 
tube D is filled with phosphorus pentoxide and plugs of cotton- wool. The greatest 
care was taken to have all caoutchouc stoppers and joints made as tight as possible with 
copper wire and paraffin. At right angles to the drying-tube (CD) is placed the re- 
ducing arrangement shown in the lowest part of the drawing. This consists of a por- 
