()8 ALUMINOUS CHALYBEATE SPRING IN I. OF WIGHT. 



quired a considerable quantity of water) there always re- 

 mained a small proportion of earthy matter, which resisted 

 all solvents, caustic potash excepted. This insoluble matter, 

 I had thought from some of the first trials, amounted to 

 about 1 gr. in 100 of the residue; but from some subsequent 

 experiments in which the silica was separated by caustic 

 potash, there appeared to be reason to suppose, that this 

 estimate was rather overrated. I shall relate the process, 

 to which, after various trials, I gave the preference. 

 S ilex dissolved 2. 50 grains of residue being boiled with very dilute 

 by caustic pot- mur j a ti c acid, a white flocculent substance remained un» 



ash, and pre- 

 cipitated by -dissolved, upon which neither acid nor water could make 

 muriate of am- an y i mpressiori. This substance, being separated and boiled 

 in a solution of caustic potash, readily redissolved with the 

 exception of a few particles of highly oxidated iron, which 

 subsided. Muriate of ammonia * being added to the clear 

 alkaline solution in sufficient quantity to saturate the whole 

 of the potash with muriatic acid, the white flocculent sub- 

 stance reappeared, which after being well washed, and heated 

 to redness, weighed between 0*3 and 0*4 of a gr. This sub- 

 stance when heated with alkali ran into a vitreous globule, 

 and muriatic acid being poured upon this, the alkali was 

 dissolved, and the earthy matter remained untouched. It 

 was therefore silica, the quantity of which may be estimated 

 at 0'7 of a gr. in a pint of water*. 



On 



* This precipitant, which was, I hclicve, first proposed hy Mr. 

 Cheuevix, is much more appropriate than acids, because if an excess 

 of acid be incautiously added, the precipitate is redissolved: while 

 with muriate of ammonia an excess of the test is attended with no in- 

 convenience. 

 Another exa- t The presence of silica was also shown, and its quantity attempted 

 to be ascertained by the following process. A portion of residue was 

 boiled in caustic potash : this dissolved iiot only the silica, but also 

 the alumine ; both these earths were precipitated from the alkaline 

 solutions by muriate of ammonia, r.nd separated ; muriatic acid being 

 now added, both the silica and alumine were reJissolved (for silica, 

 just precipitated from its solution, and not (.iesiccated, is soluble in • 

 acid)*, and this solution being evaporated to dryness on a water-bath, 

 hy which means the silica parts with its acid and becomes insoluble, 

 the muriate of alumiue was washed off by distilled water, and the 

 silica remained undissolved. This method, though affording a very 



useful 



inmaUun tor 

 3il ex. 



