430 Andersen — System Anorthite-Forsterite-Silica. 



Type 2. The system, with one binary compound which is stable 

 at its melting point. 



The simplest type of systems in which two of the compo- 

 nents join to form a compound is represented in fig. 5. In 

 this system the compound is stable at its melting point as well 

 as below the melting point in all the mixtures where it appears. 

 In the diagram (fig. 5) the compound between the components 

 A and B is represented by the point D. The line D C between 

 the compound and the third component is called the conjuga- 

 tion line. All mixtures along the conjugation line belong to a 

 true binary system C-D with a eutectic at n, which point forms 

 a maximum on the boundary curve, o m, between the fields of 

 O and D. The binary system A-B contains two simple binary 

 systems, A-D and B-D, with the eutectic points h and^'. It 

 is easily seen that the conjugation line, D C, divides the 

 whole ternary system into two independent ternary systems, 

 namely, A-C-D and B-C-D. Each of these systems contains 

 three quadruple points (binary eutectics) and one quintuple 

 point (ternary eutectic). The diagram shows that the type of 

 these systems is identical with the one already described as 

 Type 1. A further explanation of the diagram fig. 5 is there- 

 fore unnecessary. 



With Type 2 as a base a number of other types can be 

 inferred by varying the location of the points m, o and A,^' 

 and also the shape of the boundary curves o j or m h. A few 

 of these types will be considered below. 



Type S. The quintuple points o and m lie on the same side of 

 the conjugation line, whereas the quadruple points h andj lie 

 on opposite sides. 



When the pure compound, D, is stable at its melting point, 

 but unstable in certain mixtures in which it breaks up at tem- 

 peratures below the melting point, we have the Type 3 repre- 

 sented in fig. 6. 



General qualities of curves and points. — In the case now to 

 be considered the boundary curve j o has such a shape that 

 none of its tangents go through the point D. The most char- 

 acteristic feature of this system (and also of the following sys- 

 tems) is the extension of the field of A across the conjugation 

 line, whence it follows that the relations of the mixtures of C 

 and D can not be expressed in terms of the two-component 

 system C-D. Two of the boundary curves now intersect the 

 conjugation line in the two points n and q. The boundary 

 curve, m o, between the fields of C and D, has no longer any 

 maximum but slopes gradually down from o towards the ter- 

 nary eutectic m. The quintuple point o is not a ternary eutec- 



