236 William E. Ford, 



It will be noted that the agreement between the measured and 

 calculated values is surprisingly close as far as through analysis 

 No. 28. In these twenty-five analyses only six show a difference 

 in these two values greater than .025 and in nine cases this dif- 

 ference is equal to or less than .01. The average difference for 

 the twenty-five analyses is .017 or if the -\- and — signs be 

 considered, -)-.002. It will be noticed that these analyses include 

 approximately those that contain 90 per cent or more of the 

 normal dolomite molecule. Beyond this point, however, the 

 table shows a rapid and progressive rise in the amount of the 

 departure of the calculated from the measured gravities. From 

 this it is evident that with increasing proportions of the isomor- 

 phous molecules the crystal lattice must change, this change 

 being accompanied by an increase in the molecular volume. This 

 is shown clearly in Fig. 4 where the percentage of CaMg( 003)0 

 present in the different analyses are plotted as abscissas and their 

 molecular volumes as ordinates. These molecular volumes were 

 obtained by multiplying the molecular weights of the various 

 molecules by their percentages and dividing the sum of these 

 values by the measured specific gravity multiplied by 100. The 

 molecular volumes of normal dolomite CaMg(C03)o is 64.2. 



