29-i Read and Knight — Re-formation of Soda-Leucite. 



Akt. XXI V. — The Reformation of Soda-Leucite • by T. T. 

 Read and C. W. Knight. 



In the case of a steel containing *5 per cent carbon the 

 molten mass on cooling first solidifies at 1225° C. as austenite, 

 a solid solution of carbon in iron. This may for our purpose 

 be regarded as a mineral, since it has a definite crystalliue 

 form and distinctive properties. If cooled slowly the austenite 

 becomes metastable at a somewhat lower temperature and 

 breaks down into two components, ferrite (Fe) and cementite 

 (Fe 3 C), using the former term in the metallographic and not 

 the petrographic sense. The temperature at which this takes 

 place is sharply defined (near 750° C.) and the process is 

 marked by an evolution of heat. If, however, the cooling is 

 accomplished rapidly (e. g., by quenching in water) this re- 

 arrangement does not have sufficient time to take place and 

 austenite is preserved at ordinaiy temperatures. This is the 

 familiar process for the hardening of steel. Under these con- 

 ditions the austenite possesses a constant tendency toward 

 rearrangement, which is restrained by the lack of molecular 

 freedom at this temperature. On heating, this restraint is 

 lessened and the austenite begins to effect the rearrangement, 

 finally completing it at about the temperature at which it 

 would have taken place with slow cooling. On raising the 

 temperature slightly above this point austenite is again formed 

 and may be preserved by quenching as before. 



Following the line of thought suggested by these facts, it 

 occurred to one of the authors* that if the crystals of pseudo- 

 leucite could be heated to somewhat above the temperature at 

 which the rearrangement to orthoclase and nephelite had taken 

 place, soda-leucite would be yielded, which might then be pre- 

 served by rapid cooling. The slightest fusion of the crystal 

 must, of course, be avoided. If the rearrangement in the 

 pseudo-leucite is entirely analogous to that in the steel, then 

 this change would be effected by temperature alone. But to 

 make the analogy complete the heating should be effected at 

 the pressure at which the rearrangement originally took place. 

 Since this could not be ascertained, an attempt was made to 

 cause the formation at atmospheric pressure of soda-leucite 

 from the products resulting from the rearrangement. 



In order to gain some idea as to the temperature required to 

 produce this change, a small crystal of the pseudo-leucite, care- 

 fully freed from adhering groundmass, was placed in a plati- 

 num crucible provided with a closely fitting cover and sub- 



* T. T. Bead. 



