15 
magnetizing force, it was found that the value of fit gradually 
diminished if the current in the ring was not alternated 
between each observation. Variation of temperature will, 
no doubt, have a great influence on the magnetic induction 
and permeability of iron ; also, the mechanical vibration of 
the iron certainly affect the results. These various disturbing 
causes require to be studied and eliminated before the 
variation of the permeability with the magnetizing force 
can be accurately known. 
Experiments are now being made in the Physical 
Laboratory of the Owens College whereby it is sought to 
electrolytically deposit rings of iron and nickel of sufficient 
thickness to enable their induction and permeability 
coefficients to be examined. 
'‘The Action of Hydrochloric Acid Gas upon certain 
Metals,” by J, B. Cohen, Ph.D., F.C.S., communicated by 
Dr. A. Shuster, F.R.S. 
From certain considerations, I was led to believe that 
hydrochloric acid gas, freed from all traces of water, would 
not act upon certain of the metals. This idea was further 
supported by the observations of Gore with liquefied hydro- 
chloric acid (Proc. Boy. Soc., XIY., p. 204) who found that 
zinc, iron, &c,, were scarcely acted upon, and that out of 
fifteen metals only one, viz., aluminium, was dissolved by 
the pure liquefied acid. 
Preparation of Dry Hydrochloric Acid Gas . — The gas 
was prepared by the action of ordinary concentrated sul- 
phuric acid, previously well boiled, upon lumps of fused 
sodium chloride. The gas passed through two wash-bottles 
containing concentrated sulphuric acid (previously boiled), 
then through a series of eleven bulbs blown on one stem, 
and placed at an angle of about 45 degrees, also containing 
concentrated sulphuric acid; and, finally, through a tube 
