AuG. 19, 1923 MOREY: MELTING-POINT DETERMINATIONS 329 
of the melting-point from these curves is, however, arbitrary, and 
comparison with the quenching experiments shows that in most cases 
the tendency is to put the melting-point too low. This is the effect 
to be expected from the discussion given by White of the factors 
affecting the melting-point determination. For example, in the 
discussion of the effect of variable rate of heat supply,* he says: 
“The result is to hurry up the latter end of the melting, apparently 
increasing its obliquity.’’ Again, in the discussion of the heat dis- 
tribution within the charge,’ “. . . the resulting distortion . 
is a rapidly accelerated increase, changing the form of the curve in 
that region. In large crucibles it often masks the break at the end 
of the melting, substituting for it a premature break a degree or two 
lower down, due to the rapid increase in heat supply before the melted 
layer has touched the thermoelement at all.”’ 
This latter consideration appears to me to be of the greatest impor- 
tance in silicate melts; together with a consideration of the data 
given above, it justifies the conclusion that whenever possible the 
results of melting-point data should be checked by the more accurate, 
as well as more convenient, quenching method; where the quenching 
method is not applicable, confirmation by some other static method, 
such as the change in volume, is desirable. 
SUMMARY 
The heating-curve method, which is the method followed almost 
exclusively in the study of metals and of salts which crystallize readily, . 
is compared with the quenching method, used chiefly in the study of 
substances which are difficult to crystallize, such as most silicates. 
It is well recognized both in theory and practise that the melting- 
point of a substance of the latter class is more accurately determinable 
by the quenching method. Taking the melting-point determination 
by this method as the standard, it is shown that the true melting-point 
lies on the more rapidly rising end portion of the heating curve. As 
usually interpreted, therefore, the heating-curve method tends to 
give a melting-point which is too low. The difference in the present 
case (sodium metasilicate) is of the order of magnitude of 2° or less 
at about 1100°. 
4 Op. cit., p. 461. 
5 Op. cit., p. 464. 
