jS. L. Penfield and G. S. Jamieson — Tychite. 219 



might also be prepared synthetically. Following in general 

 the method of de Schulten, 8 grams of Na 2 C0 3 and 34 grams 

 of Na 2 S0 4 were dissolved in 120 cc of water, and to the solution 

 1*4 grams of MgS0 4 were added, which immediately produced 

 an amorphoid precipitate, presumably of some basic magnesium 

 carbonate. The mixture, contained in a flask, loosely stop- 

 pered to prevent evaporation, was then heated on a steam 

 bath. By using chlorides in the place of sulphates, as 

 described above, de Schulten succeeded in making northupite 

 in a crystallized condition in about seven hours; in our exper- 

 iment, however, we waited five days, the solution being heated 

 without interruption, before any signs of crystallization 

 appeared. In the meantime we had tried heating a similar 

 mixture in a sealed tube at a high temperature, without 

 definite results, and had practically given up hope of obtaining 

 the desired crystals. It was almost a matter of accident, 

 therefore, that the flask containing the mixture was left stand- 

 ing on the steam bath for so long a time. When the crystal- 

 lization had once started, however, it apparently proceeded 

 quite rapidly, and the insoluble material in the flask was 

 almost wholly converted into octahedral crystals, very sym- 

 metrical in development and remarkably uniform in size, about 

 0*15 mm in diameter. Having once produced a crop of crystals, 

 we are now able, by " seeding " or adding some of the product 

 already formed to a new experiment, to produce crystals in 

 fifteen hours, though it still seems to take several days to 

 complete the reaction. When examined under the microscope, 

 it was found that each crystal contained minute inclusions, 

 presumably of basic magnesium carbonate, but the inclusions 

 constituted a very small proportion of the total bulk of the 

 material. The crystals were next suspended in acetylene 

 tetrabromide, diluted with benzol, and it was found that they 

 all floated when the specific gravity was 2*594, and on diluting 

 to 2*583 almost all of the material sank. The mean of the two 

 values, 2*588, may therefore be taken as the specific gravity of 

 the mineral. It was found that the lighter crystals, left float- 

 ing on the heavy solution, were preceptibly richer in inclusions 

 than those which sank at 2*583. The crystals are quite hard 

 and give a gritty sensation when ground in an agate mortar. 

 They scratch calcite and probably, like northupite, have a 

 hardness between 3*5 and 4. The crystals are isotropic when 

 examined in polarized light. Using two surfaces which come 

 together at the apex of an octahedron as a prism, it was pos- 

 sible to determine approximately the index of refraction, but 

 the surfaces of the crystal were not good enough to make the 

 determination accurate beyond the second place of decimals : 

 the value found was 1*510, while n v for northupite was 

 1*514. 



