$0 4LCMINOUS CHALYBEATE SPRING IN I. OF WIGHT. 



Sect. XII. Sulphate of Magnesia. 



Examination ]. The presence of magnesia * was acertained beyond all 

 f«r raagncs.*. doubt> m ih& folIowing manner . 



50 grains of residue minutely pulverized were boiled in 

 a solution of neutral carbonate of ammonia, so as to de- 

 compose all the sulphate of iron and earthy salts, and 

 dissolve all the magnesia which might be presentf. This 

 process was, of course, attended with considerable effer- 

 vescence, and when this had subsided, the liquor was 

 filtered. The clear solution deposited on standing a 

 brownish sediment, which was separated, and proved to be 

 oxide of iron. The residue left in the filter had passed 

 from a greenish-yellow to a pale brown colour. 

 IiKiicatimi of 2 « Phosphate of ammonia being added to the clear 

 ammoniaco- solution, a precipitate appeared, having all the characters 

 phosphate. of the am moniaco-magnesian phosphate; and in particular, 

 • that of forming white stripes on the inside of the vessel 

 when scratched with a pointed instrument. This preci- 

 pitate, dried at a temperature of about 120°, weighed 1*9 

 grain}}, a »d being made red hot in a platina crucible, was 

 Proportion of reduced to exactly I gr. — 0*385 of a grain of pure magnesia 

 rtlphate of — 2'26 grains of crystallized sulphate of magnesia in 50 

 pains of residue, or 3'63 grains in a pint of waterj. The 



magnesian 



magnesia, 



* The presence of this earth in the form of sulphate bad already 

 been proved by the application of alcohol, (sect. Xf, l). 



f Jt is scarcely necessary again to state here the well known fact, 

 that carbonate of ammonia, when fully saturated with carbonic acid, 

 has the pewer of dissolving magnesia. 



[) In a subsequent experiment, in which the water itself, instead af 

 the residue, was treated in the same manner with neutral carbonate 

 of ammonia, the quantity of magnesia appeared somewhat greater; 

 bat the difference ^ 1 not amount to more than one tenth of a grain. 



_ _. , t It will be necessary here to state the grounds of this compu- 

 Proportion m + J ft r 



-which magne- tation, which will afford me an opportunity of relating some general 

 sia and phos- results concerning the proportions in which magnesia and phosphoric 

 pfeotie acid aci< j com bine. 



eio*a me. By (dissolving 11*82 grains of the purest magnesia (perfectly free 



from carbonic acid and water) in muriatic acid, and precipitating it 

 by a mixture of phosphate of ammonia, and neutral carbonate of 

 ammonia, I obtained G~. 3 grains of the triple phosphate dried by 

 GKPQSUre fer near forty-eight hours to a temperature which never ex* 



ceed«d) 



