Buddington — Natural and Synthetic Melilites. 39 



Methods. 



Six constituents, CaO, Na 2 0, MgO, A1 2 3 , Fe 2 3 , and 

 Si0 2 , enter into the composition of the solutions dealt 

 with. Chemically pure calcium carbonate, anhydrous 

 sodium carbonate, silica, and ferric oxide were used 

 in making up charges. Pure magnesium oxide was 

 obtained by heating basic magnesium carbonate in a 

 Fletcher gas furnace, leaching to separate alkalic impuri- 

 ties, and reheating. The aluminum oxide was purified by 

 boiling with a solution of ammonium chloride followed 

 by heating in the Fletcher furnace. 



Charges of a definite composition were made up by 

 mixing together the constituent oxides or their equiva- 

 lents in proper weights to give a ten gram portion. 

 These were then ground for one hour in a mechanical 

 grinder. 



All charges containing ferric oxide were melted in a 

 platinum crucible suspended in a platinum resistance fur- 

 nace at temperatures of from 1400° to 1450° and were then 

 quenched to form glasses. Charges were melted three 

 times with intervening, grindings to a fineness sufficient 

 to pass a sixty-five mesh sieve. 



Charges free from ferric oxide were made up by using 

 the Fletcher blast furnace in place of the electric furnace. 

 This treatment gave homogeneous glasses that were used 

 in subsequent experiments. 



In their work on the system lime-ferric oxide, Sosman 

 and Merwin 7 found that a certain amount of ferrous iron 

 is formed in all melted mixtures, of CaO and Fe 2 3 . 

 When the molecular percentage of Fe 2 3 was less than 50 

 percent in mixtures heated to 1400°-1500°, they found 

 the percentage of ferrous oxide was small. In order to 

 ascertain the possible extent of dissociation in the ferric 

 oxide mixtures used in the course of this work, two 

 charges of prepared glasses were analyzed for ferrous 

 iron by Dr. H. S. Washington. One preparation contained 

 3.14 percent of Fe 2 3 and showed 0.36 percent of FeO ; 

 the other contained 14.1 percent of Fe 2 3 and 1.19 percent 

 of FeO. The optical and thermal data for mixtures rich 

 in ferric iron, therefore, need a slight correction for 

 dissociation. 



7 R. B. Sosman and H. E. Merwin, J. Wash. Acad. Sci., 6, 532-7, 1916. 



