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POPULAR SCIENCE REVIEW. 
otherwise fusion occurs. When the heat is applied to the free 
surface of the ice, the layers may be much thicker. 
Mercuric Chloride, 
m. p. = 288° C., re-solidifies at 270-275°, b. p. = 803°. 
About 40 grs. of pure mercuric chloride were placed in the 
tube (A, fig. 3), and a thermometer arranged with its bulb 
imbedded in the salt. The drawn-out end of the tube was con- 
nected by stout india-rubber tubing with one branch of’ the 
three-wayed tube B, whilst the other was attached to the mano- 
meter C. B was connected with a Sprengel pump, fitted -with 
an arrangement for regulating the pressure. 
When the pressure had been reduced by means of the pump 
to below 420 minim s., the mercuric chloride was strongly 
heated by the flame of a Bunsen’s burner, with the following 
results : — 
Not the slightest fusion occurred, but the salt rapidly sub- 
limed into the cooler parts of the tube, whilst the unvolatilized 
portion of the salt shrank away from the sides of the tube and 
clung tenaciously in the form of a solid mass to the bulb of the 
thermometer, which rose considerably above 300° C., the 
mercury of the thermometer shooting up to . the top of the 
stem. After slight cooling the air was let in, and under the 
increased pressure thus produced the salt attached to the bulb 
of the thermometer at once melted and began to boil, cracking 
the tube at the same time. 
The experiment was next varied as follows 
About the same quantity of chloride was placed in the 
tube A, fig. 3, as before, and heated by the full flame of a 
Bunsen’s burner. The lamp was applied during the whole of 
this experiment, and the size of the flame kept constant 
throughout. The mercuric chloride first liquefied and then 
boiled at 303° under ordinary pressure, and whilst the salt was 
still boiling the pressure was gradually reduced to 420 millims., 
when the boiling point slowly fell to 275°, at which point the 
mercuric chloride suddenly began to solidify, and at 270° was 
completely solid, the pressure then being 376 millims. When 
solidification was complete the pump was stopped working, but 
the heat still continued to the same extent as before. The salt 
then rose rapidly to temperatures above that at w r hich a thermo- 
meter could be used, but not the least sign of fusion was 
observed. From the completion of the solidification to the 
end of the experiment the pressure remained at about 350 
millims. 
The above experiment, which was repeated three times, 
