APPLICATION OF EQUILIBRIUM LAW TO SEPARATION OF CRYSTALS. 273 



whilst points lying on edges other than those at the margin represent 

 solutions saturated with two, and the angular points solutions saturated 

 with three equilibrators. On account, however, of the number of marginal 

 points to each field — in no case fewer than four — the upper surfaces 



Fig. 4. 



Jlodel of Solutions derived from the liecipiocal Sf.lt Pair ilgCl ,+ R .so.,. 



cannot be represented by single planes, and the information at present 

 available is not sufficient to determine their character ; they are therefore 

 not introduced into the model.' 



' To construct the model, the lengths of the edges terminating at are calcu 

 lat ed fr om^he co-ordinates of the marginal angular points— each length being 

 '^x' + y^ + z^, where x, ?/, and z are the co-ordinates of the points considered — whilst 

 the lengths of the other edges are best found by graphical construction. The 

 triangles forming the hollow base are then drawn and cut out in one piece from 

 a sheet of stiff cardboard which is then bent round and fastened in position by a 

 strip of tough paper gummed along the edge. The edges of the upper surfaces are 

 1901, •J 



