236 Dr. Marcet oji an Aluminous Chalybeate Spring 



sulphat of iron and earthy salts, and dissolve all the magnesia which 

 might be present.* This process was, of course, attended with con- 

 siderable effervescence, and when this had subsided, the liquor was 

 filtered. The clear solution deposited on standing a brownish sedi- 

 ment, which was separated and proved to be oxyd of iron. The 

 residue left in the filter had passed from a greenish-yellow to a pale 

 brown colour. 



2. Phosphat of ammonia being added to the clear solution, a 

 precipitate appeared, having all the characters of the ammoniaco- 

 magnesian phosphat, and in particular, that of forming white stripes 

 on the inside of the vessel when scratched with a pointed instrument. 

 This precipitate dried at a temperature of about 120% weighed 

 1,9 grains,t and being made red hot in a platina crucible, was 

 reduced to exactly 1 gr. =:= 0,385 grains of pure magnesia 

 =: 2,26 grains of crystallized sulphat of magnesia in 50 grains of 

 residue, or 3,63 grains in a pint of the w^ater.:]: The magnesian 



* It is scarcely necessary again to state here the mcII known fact, that carbonat of 

 ammonia, when fully saturated with carbonic acid, has the power of dissolving magnesia. 



+ In a subsequent experiment in which the water itself, instead of the residue, was 

 treated in the same manner with neutral carbonat of ammonia, the quantity of magnesia 

 appeared somewhat greater ; but the dificrcnce did not amount to more than one-tcnth 

 of a grain. 



% It will be necessary here to state the grounds of this computation, wliich will afford 

 Txte an opportunity of relating some general results concerning the proportions in which 

 magnesia and phosphoric acid combine. 



By dissolving 11,82 grains of the purest magnesia Cpcrfectly free from carbonic acid 

 and water) in muriatic acid, and precipitating it by a mixture of phosphat of ammonia 

 and neutral carbonat of ammonia, I obtained 65,8 grains of the triple phosphat dried by 

 exposure for near forty-eight hours to a temperature which never exceeded 120°, a degree 

 of heat under which this salt appears to retain the whole of its ammonia. These 65,8 

 grains of triple salt being exposed for half an hour to a strong red heat in a platina cru- 

 cible, were reduced to 30,8 grains. The salt appeared then in the form of a friable cake 

 or loose aggregate, a fragment of which, on being urged by the blow-pipe, ran into a 



I 



