128 ZOOPHYTES. 



of calcium to the filtrate (F), or a portion of perchloride of iron. The object in either 

 case, is to separate the phosphoric acid in combination with a base, from whose weight its 

 quantity may be directly estimated, which is an indispensable step, since the fluorine, 

 according to this plan of analysis, can be estimated only by the amount required to satu- 

 rate the excess of bases. In case the chloride of calcium is employed, we have all the 

 phosphoric acid in the form of phosphate of lime, mixed with a large quantity of sulphate 

 of lime, derived from the sulphuric acid and sulphate of potassa previously employed. 

 This mixture of phosphate and sulphate of lime is collected, washed, and redissolved in 

 chlorohydric acid. Thesulj)hate of lime is separated by alcohol, and the phosphoric acid 

 remains in solution, which, after the excess of alcohol has been expelled, may be 

 thrown down by ammonia, ignited and weighed, or preferably, may be estimated by a 

 magnesian salt. If we employ the method by perchloride of iron, we form in the acid 

 solution containing the phosphoric acid, a basic perphosphate of iron, on supersaturating 

 the solution with ammonia. This compound is mixed with a bulky mass of peroxide of 

 iron, which being thrown on a filter and thoroughly washed, is subsequently decomposed 

 completely by hydrosulphuret of ammonia, into sulphuret of iron and phosphate of am- 

 monia. Care must betaken to use a sufficient quantity of perchloride of iron, otherwise a 

 white precipitate of neutral perphosphate of iron is formed, which is soluble in an excess 

 of ammonia. In either case (the employment of the chloride of calcium, or the per- 

 chloride of iron), the phosphoric acid eliminated may be finally best estimated by a mag- 

 nesian salt and ammonia, as the ammonio-phosphale of magnesia, fi'om whose known 

 constitution the phosphoric acid is easily calculated. We have employed both of these 

 methods ; but on many accounts prefer that by the perchloride of iron. 



" G. The alcoholic filtrate from (H), containing magnesia and lime, is treated by the 

 well-known methods of analysis for the estimation of those substances. The lime in all 

 cases in these researches, was converted into sulphate and precipitated by alcohol. The 

 magnesia was estimated as phosphate. 



" H. The crystalline precipitate from (F), which was collected on the filter, contained 

 the alumina and iron, previously in combination with phosphoric acid or fluorine. This 

 precipitate is boiled in a capsule with a strong solution of carbonate of soda, to decompose 

 the sulphate of lime; it is then filtered, the insoluble residue washed thoroughlv and 

 treated with chlorohydric acid, the precipitate by ammonia from (F) being added, and 

 the whole treated with excess of ammonia. Alumina and iron fall, which may be after- 

 ward separated in the usual way; but this was generally not deemed requisite, the quan- 

 tity of iron being very small in most cases. 



"I. The filtrate from (H) is treated for lime by oxalate of ammonia, and the oxalate con- 

 verted into sulphate and weighed : this dose of lime had been previously united to phos- 

 phoric acid or fluorine. 



"J. Magnesia is next separated from the filtrate of (I), by ammonia and phosphate of 

 soda. 



"K. The alkaline liquor from (H) contains another portion of magnesia, which is sepa- 

 rated in like manner as the ammonio-phosphate. Much labour is saved if we take care 

 to reserve the several portions, from which magnesia has been thrown down, and unite 

 them in one filtration and weighing, instead of treating them as so many separate portions. 



"The minute determination of all the constituents of the lime-water precipitate, was at- 

 tempted only on those specimens of which we had a large quantity lat command ; for a solu- 

 tion of half a pound or more of the coral in nitric or chlorohydric acid was necessary to 



