Chemical Composition of the Calcareous Corals. 251 



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 (F), 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 preci- 

 pitated by alcohol. The magnesia was estimated as phosphate. 



H. The crystalline precipitate from (F), which was col- 

 lected on the filter, contained the alumina and iron, previously 

 in combination with phosphoric acid or fluorine. This pre- 

 cipitate is boiled in a capsule with a strong solution of car- 

 bonate of soda, to decompose the sulphate of lime ; it is then 

 filtered, the insoluble residue washed thoroughly 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 afterwards separated in 

 the usual way ; but this was generally not deemed requisite, 

 the quantity of iron being very small in most cases. 



I. The filtrate from (H) is treated for lime by oxalate of 

 ammonia, and the oxalate converted into sulphate and 

 weighed : this dose of lime had been previously united to 

 phosphoric 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 separated in like manner as the am- 

 monio-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 attempted only on those specimens of 

 which we had a large quantity at command ; for a solution 

 of half a pound or more of the coral in nitric or chlorohydric 

 acid, was necessary to afford sufficient precipitate for analysis. 

 The carbonate of lime, by far the most abundant constituent, 

 was separately determined on one gramme, as sulphate of 

 lime, and from this the carbonate was calculated. The ratio 



