198 
ME. G. GOEE ON HYDEOELUOEIC ACID. 
densation. Various other fluorides besides that of chromium evolve much hydrofluoric 
acid when heated. 
A very weak acid became concentrated to a large extent by desiccation over strong 
sulphuric acid in a closed leaden chamber at 60° Fahr. ; but as the concentration pro- 
ceeded the acid itself began to volatilize along with the water, until finally the vessel 
became empty. The sulphuric acid acquired an acid odour as if it had absorbed some 
of the hydrofluoric acid. 
Pure aqueous hydrofluoric acid of about 40 per cent, in strength did not show any 
signs of solidifying by prolonged immersion in a freezing-mixture at —24° Fahr. ; nor 
did a mixture of two measures of that acid with one of water freeze at that temperature ; 
but with 1^ measure it froze imperfectly, and with 2 measures became nearly solid : no 
vapour of hydrofluoric acid appeared to escape during the solidification. It is evident 
from these experiments that a comparatively small quantity of hydrofluoric acid lowers 
the freezing-point of water very considerably. 
The chemico-electric series of metals &c. in pure dilute hydrofluoric acid at 60° Fahr. 
containing about 10 per cent, of anhydrous acid was determined. The order obtained 
was as follows, the most positive substance being named first : — Aluminium, zinc, mag- 
nesium, thallium, cadmium, tin, lead, silicon, iron, nickel, cobalt, antimony, bismuth, 
copper, silver, gold, gas-carbon, and platinum. The aluminium evolved gas rapidly. 
The following series was obtained with pure hydrofluoric acid containing about 30 per 
cent, of anhydrous acid : — Zinc, magnesium, aluminium, thallium, indium, cadmium, tin, 
lead, silicon, iron, nickel, cobalt, antimony, bismuth, mercury, silver, copper, arsenic, 
osmium, ruthenium, gas-carbon, platinum, fused rhodium, palladium, tellurium, fused 
osmi-iridium, gold, iridium*. Magnesium was remarkably unacted upon by aqueous 
hydrofluoric acid. 
The chemico-electric position of aqueous hydrofluoric acid to that of other acids was 
ascertained as follows : — A diaphragm of parchment-paper was fixed upon the end of a 
short piece of platinum tube, about ^ an inch wide and 1 inch long, by means of a ring 
of gutta percha sealed at its edge with paraffin. The acid to be compared with it was 
put into this porous vessel, and the vessel immersed in aqueous hydrofluoric acid con- 
tained in an outer cup of platinum. With the outer vessel connected with one pole of a 
galvanometer and a sheet of platinum immersed in the inner liquid and connected with 
the other pole, and with acid of 28^ per cent, in the outer vessel, the following electrical 
order of acids was found, the first-named being the most electro-positive: — Strong 
aqueous phosphoric acid, aqueous hydrofluoric acid, concentrated sulphuric acid, strong 
hydrochloric acid, strong nitric acid. The current in each case passed from the positive 
acid through the diaphragm to the other acid. 
According to Faraday (Gmelin’s Handbook, vol. i. p. 455) hydrated hydrofluoric acid 
is not decomposed by electrolysis, only the water in it is decomposed. I electrolyzed 
* I am indebted to the kindness of Messrs. Maithey and Co. for the specimens of osmium, ruthenium, 
rhodium, and iridium. 
