Aphlogistic Lamp. 328 
being comparatively a slow conductor of caloric, and not 
easily oxidated at the highest temperatures. 
This is to be drawn into wire of the dinates of 525; 
or ;°°, of an inch, being about equal in size to card, or brass 
wire No. 26. Experience has shewn that this size suc- 
ceeds better than any other. If larger, the heat is carried . 
off too rapidly, and ignition ceases ina few moments. If. 
much finer, it does not retain sufficient heat at the lower 
part of the coil to keep up the evaporation of the alcohol 
from the wick. ‘The coiling of the wire, and the adjustment 
of the wick, are the most difficult parts of the construction. 
The coil A. fig. 1, of the annexed plate,* is made by wind- — 
ing the wire round a piece of wood cut of the proper size 
and shape. The size is determined by the bore of the 
glass tube, allowing for the diameter of the wire. The. 
shape in that part which enters the tube is plain cylindrical, 
but slightly conical where it projects above the tube, as seen 
in the figure. (I believe this is the best shape, though I 
have succeeded equally well when the coil was of the same 
shape throughout.) 
In winding the coil, it is best that the turns of the wire 
should come in contact. Afterwards it is to be gently ex- 
tended, so as to leave the turns as near as possible to each 
other without touching. 
The diameter of the coil is about one sixth part of an 
inch where it enters the tube. Its length half an inch or a_ 
little less, containing from twenty to thirty turnsof the wire. 
The projection above the tube is rather less than one half 
the length. ae 
B. fig. 1, is a glass tube containing a cotton wick which 
by capillary attraction carries the alcohol. up to the platina 
coil. ‘The length of this tube is arbitrary, being from one inch 
to three or four inches. The bore is about one sixth of an 
inch, so as barely to admit the coil. The wick consisting 
of eight or ten threads, is first drawn through the tube, and 
then introduced about half way into the coil, so as to come 
nearly even with the top of the tube. This requires very 
nice adjustment. If the wick is too high, the wire is rapid- 
ly cooled by the alcohol, and ignition soon ceases. If too 
low, the evaporation by the heat of the wire is insufficient. 
If, however, the other parts are well constructed, a few tri- 
als will insure success. 
* See the end of the Vol. 
