3916] THe GrowrH oF Ercu-FIGuRES 235 
and there the old centres of action remained and the pits grew down- 
wards into the substance of the crystal (Plate I, fig. 6). Alongside of 
these there occurred great numbers of minute pits of a new generation 
and a new quadrilateral form somewhat like the typical pits on the 
clinopinacoid of diopside to be described in a subsequent section (Plate I, 
fig. 7). Some of these, it should be remarked, had rudimentary beaks. 
Subsequent action did little more than slightly increase the size of the. 
pits already formed, and after the seventh test it was finally discon- 
tinued. 
Since Baumhauer, in the article already referred to in these pages, 
had spoken of the occurrence of beaked pits, a phenomenon not ob- 
served in these tests in which dilute hydrochloric acid was the corrosive, 
a new series of experiments was designed to determine whether they 
could be obtained by using solutions of greater concentration. Three 
solutions were accordingly prepared containing respectively 4, 6 and 
8% of the acid, and each was allowed to act upon a cleavage fragment. 
In the first case the comparatively large, four sided pits produced, 
although their general outline was typical for the clinopinacoid, were 
lacking in the full symmetry in having their deepest part asymmetri- 
cally located (Plate XXVI, fig.8). When the strength of the solution was 
increased to 6%, still larger and clearer pits were produced, some of 
which had fine, hair-like beaks (Plate XXVI, fig.9). In an 8% solution 
very clear, straight sided pits were formed but stronger solutions resulted 
in pits of less distinctness. Evidently a corrosive of medium strength 
is the most likely one to produce beaked pits. 
From time to time pits had been observed which were characterized 
by minute extensions somewhat resembling beaks, but growing out 
from one of the angles of the pit and not from the bottom. When a 
10% solution was used this phenomenon was strikingly evident. Ona 
careful examination, the projection was seen to consist of a narrow 
crack running downwards from the surface of the crystal face in such a 
way as to appear like an extension of one of the side faces of the figure. 
Similar pit formations as observed in other crystals will be referred to 
in a subsequent section of this paper. 
One group of these experiments was designed to throw some light 
upon the problems of the point of origin of the pit. It will be remembered 
that Professor Goldschmidt had suggested that each pit indicates the 
place where currents have started in the corrosive, and that the growth 
of the pit is the result of the continuance of these currents. It was 
observed however that characteristic corrosion was obtained in the 
foregoing experiments, even when the test tube was vigorously shaken. 
Further, remembering that in the process of electro-metallurgy, similar 
