THE YOUNG SCIENTIST. 
35 
common recipe for annealing lamp chim- 
neys is to boil them in water, and allow 
them to cool gradually. This does not 
heat them enough, however. If salt were 
dissolved in the water it would be still 
better, and if th*e chimney were placed in 
an oven which was allowed to cool very 
gradually, it would be better still. It is 
the gradual cooling from a high tempera- 
ture that does the work, as the particles 
of glass then have time to arrange them- 
selves properly. 
An example of glass in a condition the 
very opposite of the balls just described, 
may be seen in the Kupert Drops, shown 
in Fig. 2. These are drops or tears of 
Fig. 2. 
glass which have been allowed to fall 
into water so as to cool them suddenly. 
The outer portion of the glass then con- 
tracts before the inner portion has time 
to cool, and the consequence is that the 
surface is in a state of high tension. If 
we take one of these drops, and break off 
the slender tail, the shock of the fracture 
will be communicated to every part of the 
drop, and it will fall to pieces, as shown 
in Fig. 3. Sometimes the glass arranges 
itself in centres of compression, as shown 
in Figures 4 and 5. 
When the glass is broken in this way, 
its volume suddenly enlarges and the 
pieces fly from each other with consider- 
able force. It is best, therefore, to wrap 
the drop in paper before breaking off the 
end. That which a moment before was a 
solid, clear piece of glass will now be 
found to be a fine powder. 
The effect of the expansion, etc., may 
be curiously shown by breaking the drop 
in a thin glass bottle filled with water. 
The force of the blow will be transmitted 
Fig. 3. Fig. 4. Fig. 5. 
\ through the comparatively incompressi- 
ble water, and the glass vessel will be 
broken. This is a very curious and start- 
ling experiment. 
Another form of annealed glass is seen 
in the so-called Bologna phial, of which 
we Bhall give a description in our next 
article. It forms a most curious and 
useful study, teaching us a great deal that 
is very important and useful about the 
care and management of glass vessels. 
Unconscious Effort. 
TAAILY instances of unconscious effort 
^ present themselves to us, and would 
be noted and understood if we only knew 
how to detect them. Amongst those who 
have had no training in the more delicate 
manipulations of science and of refined 
life, we constantly see the unconscious 
exercise of great and unnecessary force. 
Such persons, if asked to wipe a delicate 
glass vessel, will twist it in two and won- 
der why it breaks ! They have probably 
applied a force of several pounds where 
as many ounces would suffice, and a 
fracture is the result. The table tipper 
and spiritualist take advantage of this 
and get them to place their hands on a 
