388 T. Carnelley— Existence of Ice and other 
applied had been very strong indeed and the ice attached to the 
sides of the tube fused completely. On removing the lamp, 
however, for a few seconds the water froze again, notwithstand- 
ing that the portion of the glass in contact with it was so hot 
that it could not be touched without burning the hand. 
The chief conditions necessary for success appear to be—(1) 
That the condenser (A, fig. 1) is sufficiently large to mazniain a 
good vacuum. In the present case the capacity was about 
three-quarters of a liter; (2) That the ice is not in too great 
mass, but arranged in thin layers. Further, in the case where 
the heat is applied to the under surface of the layers of ice, the 
latter must be sufficiently thin to allow of a vent-hole being 
formed for the escape of the steam coming from below, other- 
wise fusion occurs. When the heat is applied to the free sur- 
face of the ice, the layers may be much thicker. 
Mercuric Chloride, 
; m. p.=288°, re-solidifies at 270-275°, b. p.=303°. 
About 40 grs. of pure mercuric chloride were placed in the 
tube (A, fig. 3), and a thermometer arranged with its bulb im- 
bedded in the salt. The drawn-out end of the tube was con- 
nected by a stout india-rubber tubing with one branch of the 
three-wayed tube B, while the other was attached to the 
manometer C. B was connected with a Sprengel pump, fitted 
with an arrangement for regulating the pressure. 
hen the pressure had been reduced by means of the pump 
to below 420™", 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, while 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 mer- 
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. 8, as before, and heated by the full flame of a Bunsen’s 
burner. The lamp was applied during the whole of this exper!- 
ment, and the size of the flame kept constant throughout. The 
mercuric chloride first liquefied and then boiled at 303° under 
ordinary pressure, and while the salt was still boiling the pres- 
ure was gradually reduced to 420™, when the boiling point 
8 a 
slowly fell to 275°, at which point the mercuric chloride suddenly 
