126 ILLINOIS STATE ACADEMY OF SCIENCE 



bility products obtained by H. W. Foote 2 . Of course it 

 is also possible that at this high temperature the un- 

 stable aragonite has partly changed to calcite and that 

 the equilibrium is established with the more insoluble 

 form. A specific gravity of the undissolved residue was 

 run, but the results were not conclusive as the sample 

 had not been ground fine enough and a true specific 

 gravity was not obtained. 



Fifty percent mixtures of aragonite and calcite were 

 ground together, covered with water containing carbon 

 dioxide and exposed to various temperatures. These 

 mixtures were allowed to react one week when they were 

 ground and the specific gravity determined. Tempera- 

 tures of 20°, 37°, 65° and 100° were used. The change in 

 specific gravity in every case indicated that the aragon- 

 ite was being changed quite rapidly to calcite and that 

 the reaction was more rapid at 65° than at 25° and 37°. 

 The specific gravity determinations of the material ex- 

 posed to 100° were not very concordant and no very defi- 

 nite conclusions could be drawn. This rapid change is 

 contrary to most of Johnson's 1 findings. 



Certain of the samples which were allowed to react at 

 65 °C cemented firmly together to form a mass which was 

 quite strong and which showed rather large crystals of 

 calcite mixed in a matrix of small crystals. Samples ex- 

 posed to other temperatures, while they became much 

 more granular than the original material, did not cement 

 together. The samples which were finely ground did not 

 form as strong a material as that which was more 

 coarsely ground. The condition of packing seemed also 

 to have some effect upon the strength of the material. 

 An attempt was made to form this. cemented material by 

 the use of ground marble and the aragonite from ground 

 oyster shell. This material recrystallized into a more 

 granular form but did not cement together. 



This formation of a cemented material, using as a 

 binder only a more unstable crystalline modification, 



2 .H. W. Foote, Zeitshr. Physikal, Chemie, 33, 740 (1900) Uberdie Physi- 

 kalish Chem. Beziechungen Zwischen Aragonit and calcit. 



Showed by oxalate reaction and conductivity experiments that the 

 solubility of calcite and aragonite approached each other with increas- 

 ing temperature worked from 8° to 59° also show increase and then 

 decrease. Aragonite- at 50° still considerably higher than calcite. 



