268 Day and Shepherd — Lime-Silica Series of Minerals. 



(see also fig. 3, curve DE). The amount of eutectic in concen- 

 trations X and Y will be so great as to soften the cone long be- 

 fore the melting-points Z and W are reached. If, on the other 

 hand, the liquidus slopes gently (AC), the amount of liquid 

 eutectic as compared with the solid phase is smaller and the tem- 

 perature of softening of the cone will approximate more closely 

 to the change in melting-point. 



Furthermore, if the cones are made up from the initial com- 

 ponents (CaC0 3 and Si0 2 , for example), the heat of combina- 

 ation is liberated as the cone approaches the melting temperature 

 and raises the temperature of the cone above that of the furnace, 

 producing sudden fusion of which the neighboring Seger cone 

 can receive no record. 



Incidentally, one finds here the explanation of Hoffman's ex- 

 periments* on the temperature of formation of slags. Contrary 

 to the statement that the " temperature of formation is above the 



temperature of fusion," just the reverse is true. Under nor- 

 mal conditions these mineral combinations occur at tempera- 

 tures lower than the melting point, the exceptions occurring 

 only when the materials are so coarsely ground or poorly mixed 

 that combination is retarded until the melting point of the slag 

 is passed. The orthosilicate of calcium is a very good instance 

 of the formation of a compound below its melting temperature. 

 We shall show later that while this compound melts at about 

 2080° C, it is possible to prepare it below the melting point 

 of platinum, in fact in platinum vessels, by heating the finely 

 ground material in the Fletcher furnace, regrinding, mixing 

 and reheating. By this process it is possible to obtain a com- 

 pound which gives the optical tests for the orthosilicate and is 

 entirely without free lime or silica. 



Apart from the criticism which this particular application of 

 cones appears to us to deserve, it is also well known that the 



*H. O. Hoffman, Trans. Amer. Inst. Min. Eng., xxix, 682, 1899. 



