[ ] 
XI. An Enquiry into the ^''al■latlon of A ay lea observed in Crystals; especially 
Eotassiiim-alum and Ainnioniuni-alum. 
By Henry A. Miers, D.Sc., MA., F.B.S., V.P.G.S., V.P.C.E, Waynylcte Pvofossov 
of Mineralogy in the University of Oxford. 
Received M;uch 10,—Eecid March 2G, 1903. 
[Plate 13.] 
1 . 
o 
o 
O. 
i. 
0 . 
G. 
7 . 
8 . 
9. 
A. 
11 . 
C. 
Contents. 
Paut L—The Octahedron- Angle of Aluji and its Vicinal Planes. 
The variations of angle previously observed. 
Object of the present investigation. 
The goniometer. 
Purposes for which the goniometer can be used. 
(a.) Etching of calcite with HCl. 
(B.) Parallel growth of NaXOs "’ith calcite. 
The octahedron angle of potash-alum. 
The nature of the vicinal faces on potash-alum and ammonia-alum. 
The \ icinal faces on sodium chlorate, zinc sulphate, and magnesium sulphate . 
The effect on alum of diluting the solution. 
Some possilile causes of the variations. 
Page 
4G0 
4G3 
4G4 
4G6 
467 
468 
469 
475 
483 
487 
489 
Part II.—The Concentration of the Solution in Contact with a 
Growing Crystal. 
I’reliminary experiments. 
The refractive indices of supersaturated solutions. 
(1.) Potash-alum. 
(2.) Tai'taric acid. 
(3.) Sochum chlorate.. 
(4.) Sodium niti’ate. 
The lefractive index and concentration of the solution in contact with a growing 
crystal. 
(1.) Potash-alum. 
Specific gravity of solution in contact with a growing crystal of potash-alum , 
(2.) Sodium chlorate . . ’. 
(3.) Sodium nitrate. 
492 
496 
497 
501 
504 
507 
510 
511 
513 
513 
515 
Part III.—The Action of the Concentration Streams (Crystallisatton 
iN Motion). 
Intelpretation of the foregoing results. A jiossible cause for the variation of angle in alum 
and other crystals. 
Experiments ujion potassium-alum crystallising in an agitated solution. 
516 
518 
VOL. CCII.—A 356. 
3 N 
15.12.03 
