Day and Shepherd — Lime-Silica Series of Minerals. 279 



under constant tension. Immediately beneath the ribbon and 

 supporting its weight was a slender block of selected magnesite. 

 The ribbon and its supports were then enclosed within con- 

 centric glass tubes between which cold water was kept flowing. 

 The atmosphere immediately surrounding the ribbon was nitro- 

 gen. 44- "With this ribbon we proceeded as before, laying out a 

 whole series of compositions from 60 per cent CaO on. With 



this little apparatus, of which fig. 2 will convey a fairly clear 

 idea, we promptly discovered a third and very sharp eutectic 

 with the composition 67 1/2 per cent CaO, 32 1/2 per cent 

 Si0 2 , and a maximum indicating a probable compound at 65 

 per cent CaO, 35 Si0 2 , which corresponds to the anticipated 

 orthosilicate. No other points were obtained up to 2100° C. 



Thus in a very short time and in this simple and expeditious 

 way we were able to locate three eutectics (37, 54 and 67 1/2 

 per cent CaO) and two compounds (48 and 65 per cent CaO) 

 between lime and silica, canvassing for the purpose practi- 

 cally all the compositions from pure lime to pure silica at 

 intervals of 1 or 2 1/2 per cent, and all temperatures from 

 500° to 2100° C. Beyond 75 per cent lime and below 32'5 

 per cent the method yields no information, for reasons which 

 have been elaborated elsewhere. All the important deter- 

 minations were verified by numerous repetitions. 



If we now compare the compounds obtained by this prelim- 

 inary investigation with those which we were led to anticipate 

 from Boudouard's observations, as well as from the hypothetical 



* Even with this precaution, the iridium volatilized so rapidly that the 

 magnesite was black after thirty minutes heating. 



