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SECTION XII. 



THE CHEMICAL EXAMINATION OF THE MATERIALS FROM 



FUNAFUTI. 



By Professor J. W. Judd, C.B., LL.D., F.R.S. 



Contents. 



Page 



1. Method of Analysis 362 



2. Greneral Results of Analyses of the Cores 363 



3. Preparation of Samples for Analysis 366 



4. Proportion of Organic Matter in the Samples 367 



5. Proportion of Insoluble (Inorganic) Matter in Coral-Reef Rocks 368 



6. Proportion of Phosphates in the Materials from Funafuti 371 



7. Proportions of Calcium and Magnesium Carbonates in the Funafuti Rocks as bearing on 



Theories of Dolomitisation 373 



a. Amount of Magnesium Carbonate secreted by Hants and Animals to form their 



Skeletons 375 



b. Changes in the Proportions of the Calcium and Magnesium Carbonates which 



occur after the Death of Calcareous Organisms 376 



c. The Action of Weak Solvents upon Mixtures of the Calcium and Magnesium 



Carbonates 378 



d. Bearing of the Analyses made of the Fiuiafuti Materials, upon the Question of the 



Causes of Dolomitisation in Coral-Reef Rocks 383 



1. Method of Analysis. 



On the arrival in 1897 of the first portions of the core from the Main Boring at 

 Funafuti, which had then been carried down to the depth of 698 feet, I found in the 

 lower portions of the materials brought up unmistakable evidence of an extensive 

 replacement of calcium carbonate by magnesium carbonate. The interest attaching 

 to the chemical changes which undoubtedly go on in coral-reef rocks, as was long 

 ago shown by Dana — an interest which had been revived by the results obtained by 

 Sir John Murray at Christmas Island — suggested the great importance of a thorough 

 chemical examination of the whole of the specimens which were being obtained at 

 Funafuti. 



A series of samples, thirty in number, taken at short intervals from this portion 

 of the bore-hole, were, therefore, entrusted to Dr. C, G. Cullis for analysis by 

 ordinary gravimetric methods. 



The phosphoric acid was precipitated as ammonium phosplio-molybdate, tlie 



