492 
PROrESSOK HENRY A. MIERS: AN ENQUIRY INTO 
From the above observations it is very difficult to draw any definite general 
conclusions, since the difterences between the various angles in the same crysffil are 
o-reater than the difterences between the mean values in difterent crystals. This may 
indicate that the variations are mainly due to local causes. 
On the whole, the angle made by the vicinal forms with the octahedron is perhaps 
slightly greater when the temperature is falling rapidly; and for stationary 
temperatures it is perhaps slightly greater for low than for high temperatures ; but 
the differences are very small, if, indeed, they really exist, and in many cases quite 
difterent vicinal faces are developed at the same temperature, so that in any case 
the ano’le of the vicinal form can hardly be a direct result of the particulai 
temperature at which it was produced. 
Having found, however, that there seemed to be a general relationship between the 
acuteness of the vicinal faces and the depth at which the crystal was growing in the 
solution, I was naturally led next to enquire whether one detei’inining factor is not 
the concentration of the solution ; it is certain that the concentration varies slightly 
with the depth, especially in solutions which contain loose crystals at the hottom of 
the trough, and the concentration seemed to be one of the variable factors capable of 
accounting for the changes of angle. 
PART II. 
The Concentration of the Solution in 
Contact with a Growing Crystal. 
(A.) Fre I in linai ■// Exp e i 'in tents. 
It was pointed out above that in studying the growth ot a crystal ve aie dealing 
with the conditions of equilihrmm lietween the growing crystal and the liquid in 
contact with it, and it is therefore a matter of primary importance to know all that 
can be ascertained about the latter. 
Very little seems to be known at present about the nature ol this licpiid; that it is 
supersaturated is a reasonalile supposition, but to what extent is not ceitain. The 
solution is being constantly impoverished by the growth of the crystal, although it is 
heing constantly enriched liy the influx of more saturated liquid. 
Among the possible factors which determine the difterent vicinal faces succeeding 
each other during the growth of the crystal, it appeared troin the expeiiments 
descrilied above that differences in the degree of concentration ot the liquid may 
conceivably play an important part; lint in order to test this possibility it would be 
necessary to ascertain the composition of the liquid, not merely in the neighhoiirhood 
of the crystal, liut actually in contact with it. Two methods of attacking the 
problem suggest themselves ; although one cannot hope to analyse the layer ot liquid 
