372 REPORTS ON THE STATE OF SCIENCE.—1912 
and that isomorphous crystals have a minutely heterogeneous or zonal 
structure,!71 has been recently revived in respect to metallic alloys,’”* 
a department in which the conception of crystalline solid solutions has 
proved most fruitful. A decision as to the conditions under which 
diffusion occurs in solids is of the highest importance in relation to 
this question. A review of the evidence leads to the conclusion that 
the occurrence of diffusion in metals is established beyond any doubt, 
but that experiments are still lacking to prove its occurrence in trans- 
parent crystals of minerals, salts, or organic substances, even under 
favourable conditions, although even here indirect evidence points to 
its possibility. The subject is complicated. by the occurrence of. adsorp- 
tion, and it is sometimes difficult to separate the effects of adsorption 
from those of diffusion, but it*seems an exaggeration to suggest 17* that 
the passage of metals into one another, forming easily recognisable 
intermetallic compounds, should be ascribed to adsorption, although 
such an explanation may possibly suffice in such cases as the passage 
of gases through heated metals, and the staining of transparent crystals. 
‘ 
: 171 See the reviews of the subject by O. Lehmann, ‘ Molekularphysik ’ (1888), and, 
from an altered standpoint, ‘ Fliissige Krystalle ’ (1904). a) inet 
12 (, A. Edwards, Jour. Inst. Metals, 1911, 5,150; 6, 259; P. P. von Weimarn, 
Zeitsch. Chem. Ind. Kolloide, 1911, 9, bes 
173 G, Bodlinder, NV. Jahrb. Min. Beil. Bd., 1899 12 53. 
