202 
POPULAR SCIENCE REVIEW. 
rised felspar or artificial mixtures of the chemical constituents, in short 
silicic acid and alumina, fused carbonate of potash and soda, and ignited 
carbonate of lime. The mixture is placed in a platinum crucible and heated 
to a temperature approaching that at which platinum melts in a Scliloesing’s 
furnace. The homogeneous mass thus formed, if suddenly cooled, is isomor- 
phous ; it must be placed without any delay in the flame of a Bunsen 
burner with a blast attached to it, and kept there for forty-eight hours at 
a temperature as little below the point of fusion as possible ; and then, 
without any further precaution, allowed to cool in the crucible. Although 
the mass while fused occupies but little space, when heated with the blast it 
gives off bubbles and presents a porcelain-like appearance. Although the 
pocket-lens fails to detect the presence of crystals in this mass, the micro- 
scope shows the material to be made up of crystalline felspar. By this method 
Fouque and Levy have succeeded in preparing crystals of the three varieties 
of felspar which have the lowest fusing point, oligoclase, labradorite, and 
albite, in the forms in which they occur in eruptive rocks ; and they hope in 
further experiments to prepare, not only the other simple varieties of this 
mineral, but the many combinations of them which are known. — Compt. 
rend., lxxxvii., 700. 
The Liquids Enclosed in the Cavities of Topaz. — T. Erard and A. Stelzner 
have examined the liquids in some cavities of topaz in the following manner. 
The microscope, the preparation, and a thermometer were all placed in a 
water-bath and so kept at an even constant temperature. The water was raised 
to a temperature of 30°, and after, in ten minutes, it had cooled to 28°, it 
was assumed that microscope, preparation, and thermometer had all the same 
temperature. The liquid enclosed in a cavity was now examined through the 
microscope, and warm water was slowly poured in as far removed as possible 
from the microscope, and carefully mixed up with the other water, while the 
other observer noted the temperature of the thermometer. When the liquid 
vanished, the apparatus was allowed to cool, and the return of the liquid ob- 
served. Seven cavities in two topazes from an unknown locality were examined. 
Each cavity contained two fluids ; the individual point of limit of each at the 
lower temperature to which the preparations were exposed remained un- 
changed. The liquids always vanished suddenly, and their return in each of 
the seven cases was accompanied by violent boiling. It was found that for 
one and the same enclosure of the kind referred to the sudden disappearance 
of the liquid and its equally sudden return with the accompanying boiling 
took place at one and the same temperature, the difference in the observations, 
amounting to 0‘03°, being evidently within the error of observation. The 
critical point was found not only to be somewhat different in the case of each 
preparation, but in the case also of the fluids contained in one and the same 
cavity. Although the sudden disappearance and return of the liquid took 
place at temperatures lying between 28°*745 and 29°T8, the fluid in no case 
can be pure carbonic acid, the critical point of which lies, according to 
Andrews, at 30°*92. As, however, Andrews has since shown experimentally 
that an admixture of permanent gases lowers the critical point of carbonic 
acid, it is probable that the so greatly expanding liquid contained in these 
cavities is a somewhat impure carbonic acid . — Mineralogische und Petrogra- 
phische Mittheilungen , i., 450. 
