210 A TREATISE ON METAMORPHISM. 



99.31, 59.94, and 115.58. Their specific gravities are 2.7135, 2.6535, and 

 2.85, respectively. The volume of the wollastonite is, therefore: 



115.58 . / 99.31 . 59.94 \ 

 ~2785~l 2.7135+ 2.6535 J~ ^ bbb 



That is, the decrease in volume in this case of silication of calcite is 31.5 

 per cent. 



In order to expedite the laborious numerical calculations of the volume 

 relations for the very numerous alterations, Mr. Lincoln completed the table 

 on pp. 195-201 by adding the molecular weights, the logarithms of the 

 molecular weights, the logarithms of the specific gravities, the molecular 

 volumes, and the logarithms of the molecular volumes of each of the min- 

 erals. These determinations have been carefully verified by Mr. Chapman, 

 and may be used to check the volume changes given in the succeeding 

 pages, and also to make additional volume calculations. 



In calculating the volume relations, unless otherwise specified, the 

 compounds on both sides of the equations are regarded as solid except those 

 which by themselves independent of the solvents are liquids or gases, such 

 as H 2 and C0 2 . All such compounds are supposed to be added in the 

 solutions or to be taken away by the solutions, and therefore are not taken 

 into account in the volume calculations. In general these liquid and 

 gaseous compounds do undoubtedly escape in large measure, although in 

 some cases they are confined as inclusions within the minerals formed. 

 (See p. 678.) 



Where +k is added to the equation, this signifies that heat is liberated; 

 where — k appears, this means that heat is absorbed by the reaction. 



No claim is made that the equations which are written in the following 

 pages exactly represent the changes that take place in the alterations of 

 the various minerals into other minerals Indeed, the probability is that 

 not half exactly represent the facts; for the great majority of the reactions 

 are more complicated than written, and in many cases substances in the 

 solutions or as solids not taken into account are concerned. Since these 

 are the facts, the question may be asked why the equations are written. 

 The answer is, first, that at some time the attempt must be made to give 

 a first approximation to quantitative exactness in the alteration of minerals. 

 The equations found on the following pages represent such an attempt- 

 Before the appearance of this treatise scarcely more than a score of mineral 



