1865.] Liquefied Hydrochloric Acid Gas. 209 



line throughout, and exhibited a slight change of colour, extending from 

 its surface to the centre, as if the gas or liquid had been forced into its 

 pores. In a second experiment of three days' intermittent immersion, 

 precisely similar effects were obtained. Several minute fragments of very 

 soft marble were immersed in the liquid acid at intervals during seven 

 days. No gas was evolved when the liquid touched them. On removal 

 from the acid, their physical characters appeared unaltered ; they were 

 insoluble in water, but quickly dissolved in dilute hydrochloric acid, with 

 copious evolution of gas. A fragment of bone-earth did not dissolve or 

 alter in appearance during seven days. 



Bright magnesium ribbon slowly became dull in the liquid acid, without 

 visible evolution of gas ; after seven days' intermittent immersion it was 

 still (with the exception of a thin film) in the metallic state. In a second 

 experiment of three days' constant immersion, similar effects occurred ; 

 the residue dissolved and floated in dilute sulphuric acid, with copious 

 evolution of gas. A wire of magnesium and one of platinum immersed in 

 the liquid acid, and connected with a sensitive galvanometer, evolved no 

 perceptible electric current, and only a barely perceptible current after two 

 days of constant immersion. Calcined magnesia in powder did not dis- 

 solve or alter in appearance during four days' nearly constant immersion. 

 Oxide of cerium (containing some oxide of didymium and lanthanum) 

 remained undissolved and unchanged in colour during nine days ; the 

 residue was insoluble in water. Metallic aluminium became dull in the 

 gas, and quickly dissolved, with evolution of gas, when the liquid acid 

 came into contact with it, and formed a colourless solution. A wire of 

 aluminium and one of platinum, immersed ^th of an inch apart in the 

 liquefied acid, and connected with a sensitive galvanometer, produced a 

 steady deflectipn of 1 2g degrees, the aluminium being positive ; the 

 deflection gradually increased to 1 7 degrees in one hour, and two layers 

 of liquid formed, the lower one brown in colour, and the upper one nearly 

 colourless. The conductivity of the liquid acid was probably increased 

 by the metallic aluminium dissolved in it. Precipitated alumina did not 

 visibly alter or dissolve during six days ; the residue deliquesced in damp 

 air. Precipitated silica in powder did not dissolve or visibly alter during 

 four days. Precipitated titanic acid in powder (pale flesh-colour) slightly 

 dissolved in seven days. 



A fragment of fused tungstate of soda did not alter in bulk during ten 

 days ; it had then acquired a superficial green colour. Molybdic acid in 

 powder turned dark green, but remained undissolved at the end of nine 

 days. Native sulphide of molybdenum remained undissolved and appa-r 

 rently unchanged during two days. Molybdate of ammonia in powder 

 became yellowish green in the gas ; it became grass-green in colour in the 

 liquefied acid, but did not dissolve in four days. Sesquioxide of chro- 

 mium in powder did not dissolve in six days, but became of a dull blackish- 

 brown colour. A fragment of anhydrous yellow chromate of potash became 



