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XL. On anew form of Voltameter and Voltastat. By Frede- 

 rick Guthrie, Ph.D., F.R.S.E., Professor of Physics and 

 Chemistry, Royal College, Mauritius*. 



THE instrument described below may be advantageously used 

 when a galvanic current of great 

 constancy is required for a considerable 

 time. When interposed in a circuit it 

 allows a certain quantity of the cur- 

 rent to pass, and it measures the amount 

 which passes. Its construction and use 

 are the following : — 



A is a wide test-tube on a foot. 



B is mercury. 



C is dilute sulphuric acid. 



D is a long tube, open at both ends, 

 passing through the cork M and dip- 

 ping under the mercury. 



E is a tube passing through the cork 

 and open below ; it carries a bulb, N, 

 containing fragments of linen. The 

 upper end is closed, with the exception 

 of a microscopic opening, F. 



H and I are the electrode wires, pro- 

 tected by glass tubes where they pass 

 through the cork. 



K and L are platinum electrodes, in 

 the shape of narrow strips of foil con- 

 verging towards the top, and kept apart 

 at top and bottom by strips of glass 

 fused on to the platinum. 



G is a little test-tube which serves to 

 protect the end of the tube E from dust. 

 It is separated from E by fragments of 

 linen. 



The only point requiring particular 

 attention is the formation of the capil- 

 lary opening F. This opening is best 

 made by blowing a little bulb at the end 

 of the tube, bursting a little hole in this 

 before the blowpipe, and allowing the 

 whole to collapse while the air is conti- 

 nually injected. Several such tubes 

 should be prepared. It is not difficult 

 in this way to get an opening in D so 



* Communicated by the Author. 



