SKEATS: CHEMICAL COMPOSITION OF LIMESTONES. 63 
ammonium molybdate at 40°, dissolving the precipitate in the minimum 
quantity of ammonia and precipitating as magnesium phosphate, by 
magnesia mixture, and weighing as magnesium pyrophosphate. 
Owing to the slight solubility of magnesium phosphate in water, care 
was taken to keep the bulk of the solution as small as possible. 
About fifteen of the specimens from various islands were analyzed 
gravimetrically as above, but it was felt to be unnecessary to deal with 
all the limestones — nearly two hundred in number — in the same way, 
if some volumetric determination could be employed which would be 
at once more rapid than the gravimetric method, and yet give fairly 
accurate results. ; 
Such a method has been much used in connectiou with the Funafuti 
boring, and was agreed upon by a Chemicai Committee of the Royal 
Society. The details were devised by Professor Tilden, and were first 
worked out by Mr. J. Hart-Smith, under Dr. Tilden’s supervision. 
In this volumetric analysis only the calcium is determined. The 
principle on which the method is based is as follows: — 
The addition of a solution of ammonium oxalate to a sufficiently dilute 
solution containing calcium and magnesium salts, to which a solution of 
ammonium chloride and ammonia has been added, will precipitate cal- 
cium oxalate practically free from magnesium oxalate. 
If a known amount of ammonium oxalate is added, — more than is 
necessary to precipitate all the calcium, — the excess of ammonium oxa- 
late may be determined by titration with potassium permanganate solu- 
tion. The details of the method may be stated thus : — 
Large quantities of the following solutions were made up: — 
1. Potassium permanganate, decinormal solution. 
2. Ammonium oxalate, one gram in 50 cubic centimeters. 
3. Ammonium chloride and ammonia, one gram of each in 25 cubic 
centimeters. 
4. Hydrochloric acid, one gram in 25 cubic centimeters. 
5. Sulphuric acid, one gram in 10 cubic centimeters. 
About .3 gram of the powdered limestone was dissolved in 25 cubic 
centimeters of hydrochloric acid solution, and any insoluble residue, if 
present, was filtered off. 
To the solution were now added 150 cubic centimeters of distilled 
water, and then, from a pipette, 25 cubic centimeters of ammonium 
chloride and ammonia. 
If any appreciable quantity of phosphate were present, a white precipi- 
