ANALYSIS OF MINERAL WATERS. 271 



same effect as phosphoric acid. In applying the phosphoric 

 acid to this purpose under any of these forms, it is necessary 

 to be careful that it be entirely free from any impregnation of 

 lime. 



There is one other advantage which this method lias, that if 

 even a slight excess of phosphoric acid, be added, the error it 

 can introduce must be extremely trivial ; for the effect of it 

 will be only to decompose a small portion of the original mu- 

 riate of soda; and. as the difference is very inconsiderable in 

 the proportion in which phospiioric and muriatic acids com- 

 bine with soda, any difference of weight which may arise from 

 this substitution, to any extent to which it can be supposed to 

 happen, may be neglected as of no importance *.. 



To 



* For the sake of comparison, and to ascertain the accuracy of different me- 

 thods, I submitted a similar solution of muriate of magnesia and muriate of soda 

 to analysis by sub-carbonate of ammonia. To the saline liquor, heated to 100°, 

 a solution prepared by dissolving carbonate of ammonia in water of pure ammo^ 

 nia, was added, until it was in excess. A precipitation rather copious took 

 place ; the precipitate being collected on a filtre, the clear liquor was evaporated 

 to dryness, and the saline matter was exposed to heat, while any vapours ex- 

 haled. Being redissolved, a small portion remained undissolved, and on again 

 adding sub-carbonate of ammonia to the clear liquor, precipitation took place, 

 rather less abundant than at first. This was repeated for a third, and even for 

 a fourth time, after which the liquor was not rendered turbid. Being evapora- 

 ted, the muriate of soda obtained, after exposure to a red heat, weighed 20.5 

 grains. The whole precipitate washed, being heated with sulphuric acid, af- 

 forded of dry sulphate of magnesia 4.8 grains, a quantity inferior to that ob- 

 tained by the other methods, evidently owing to the less perfect action of the 

 ammoniacal carbonate as a precipitant. A similar deficiency in the proportion 

 of magnesia was found in the analysis of sea- water by sub-carbonate of ammo- 

 nia, as has been already stated ; while, on the other hand, in its analysis by 

 phosphate of soda and carbonate of ammonia, a larger quantity of muriate of so- 

 da was obtained than by the other methods, probably from the difficulty of 

 avoiding .an excess of phosphate of soda in precipitating the magnesia. 



