OF lEOX STONE. A'TCKERY. 213 



molecules present. Hence the ionization of the magnesium is 

 favoured in every way possible. 



In detail the procedure consists in diluting the filtrate 

 from the iron and aluminium to about 500" and adding 

 ammonium choride in some Cjuantity, and to precipitate the 

 calcium a boiling solution of oxalic acid is added, which 

 contains three or four equiA'alents of mineral acid. A few 

 drops of methyl orange are added and the solution neutralized 

 very slowly (at least half an hour for complete neutralization). 

 Considerable excess of hot ammonium oxalate is added and 

 the solution allowed to stand some hours and the calcium 

 oxalate filtered off and washed chloride free with a one per 

 cent, solution of ammonium oxalate. The precipitate on 

 careful ignition yielded decimal 67% of calcium oxide. 



The magnesium was determined by evaporating the 

 filtrate until salts began to crystalize out and then diluting 

 until these just dissolved. Then exactly one-third volume 

 of strong ammonia was added and an excess of sodium hydrogen 

 phosphate. The precipitate formed is magnesium ammonium 

 phosphate and this on ignition yields magnesium pyro- 

 phosphate from which the magnesium oxide content was 

 calculated, proving to.be 1.18%. 



Sulphur was determined bj" taking fresh samples of 

 iron-stone and fusing "^dth ten parts of a mixture of four 

 parts sodium carbonate with one of potassium nitrate. The 

 samples were very carefully mixed and fused by heating the 

 crucible placed in a hole in an asbestos board to deflect any 

 gases from the flame which might contain sulphur. When all 

 action had apparently ceased the residue was cooled and re- 

 peatedly extracted with boiling water and finally with boiling 

 dilute sodium carbonate solution. The solution thus obtained 

 was made acid, evaporated and the silica dehydrated and the 

 nitric acid expelled by moistening T\dth hydrochloric acid, 

 and again evaporating. The silica was then filtered off and 



