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POPULAR SCIENCE REVIEW. 
account of their researches on the structure of rubies, sapphires, 
diamonds, and other minerals. The rate of expansion of the 
liquid contents of an unusually large cavity in a sapphire 
between the temperatures of 0° and 30° C. (or 32° and 86° F.) 
was measured and compared with that of liquid carbonic acid 
as determined by Thilorier, between these two temperatures. 
It was found to agree so closely with the surprising dilata- 
bilityof carbonic acid, that they had no hesitation in concluding 
that any difference might be due to an error in one of the t ther- 
mometers. 
Mr. Sorby found that 100 volumes of the liquid in the sap- 
phire expanded to 150 volumes at 30° C. (86°\F.), to 174 
volumes at 31° C. (87°*8 F.), and to 217 volumes at 32° C. 
(89°*6 F.), something quite unapproachable by any other sub- 
stance, even a gas. 
In the same year, 1869, Vogelsang and Greissler, of Bonn, 
published an account of experiments made on rock crystal, in 
which the former observer had noticed a liquid floating upon 
water enclosed in cavities. They crushed the quartz under 
baryta-water and found that the latter became turbid, owing to 
the formation of carbonate of baryta, and they measured the 
rate of expansion of the liquid as nearly as the shape of the 
cavities admitted of this being done. Their most remark- 
able experiments, however, were performed in the following 
manner : — Taking a small retort containing a mineral in 
fragments, it was attached to a tube commonly known as a 
Greissler vacuum-tube. There were platinum wires sealed in at 
each end of the tube, and to one end was affixed an ordinary 
Sprengel pump. After a vacuum had been produced so that an 
electric spark would no longer pass across from wire to wire, 
the fragments of the mineral were heated, the mineral decrepi- 
tated, because the cavities exploded, and the spark passed 
through, because the previously vacuous space then contained 
a gas. This gas, when examined by the spectroscope, declared 
itself to be carbonic acid. 
To Professor Andrews, of Belfast, we are indebted for extra- 
ordinary additions to our knowledge of the gaseous and liquid 
states of matter. He has established the fact that there is no 
gap between these two conditions ; a liquid may pass by a gradual 
change of properties into a gas. It expands and becomes ex- 
cessively mobile ; the boundary between gas and liquid is less 
and less easily recognized, until it finally disappears. When the 
reverse change occurs, the gas becomes more and more com- 
pressible, a wavering and flickering movement is visible, a line 
of demarcation appears, and this, as the liquid contracts, becomes 
more and more distinct. These changes were observed in very 
strong glass tubes of small bore, which being filled with carbonic 
