ter may be made to yield a perfect skeleton of the fibre after
burning off the organic matter. It is by such means that the mantles
used in the Welsbach system of incandescent lighting are prepared. A
purified cotton fabric--or yarn--is treated with a concentrated solution
of the mixed nitrates of thorium and cerium, and, after drying, the
cellulose is burned away. A perfect and coherent skeleton of the fabric
is obtained, composed of the mixed oxides. Such mantles have fulfilled
the requirements of the industry up to the present time, but later
experiments forecast a notable improvement. It has been found that
artificial cellulose fibres can be spun with solutions containing
considerable proportions of soluble compounds of these oxides. Such
fibres, when knitted into mantles and ignited, yield an inorganic
skeleton of the oxides of homogeneous structure and smooth contour. De
Mare in 1894, and Knofler in 1895, patented methods of preparing such
cellulose threads containing the salts of thorium and cerium, by
spinning a collodion containing the latter in solution. When finally
ignited, after being brought into the suitable mantle form, there
results a structure which proves vastly more durable than the original
Welsbach mantle. The cause of the superiority is thus set forth by V.
H. Lewes in a recent publication (J. Soc. of Arts, 1900, p. 858): 'The
alteration in physical structure has a most extraordinary effect upon
the light-giving life of the mantle, and also on its strength, as after
burning for a few hundred hours the constant bombardment of the mantle
by dust particles drawn up by the rush of air in the chimney causes the
formation of silicates on the surface of the mantle owing to silica
being present in the air, and this seems to affect the Welsbach
structure far more than it does the "Clamond" type, with the result that
when burned continuously the Welsbach mantle falls to so low a pitch of
light emissivity after 500 to 600 hours, as to be a mere shadow of its
former self, giving not more than one-third of its original light,
whilst the Knofler mantle keeps up its light-emitting power to a much
greater extent, and the Lehner fabric is the most remarkable of all. Two
Lehner mantles which have now been burning continuously in my laboratory
for over 3,000 hours give at this moment a brighter light emissivity
than most of the Welsbachs do in their prime.' ...'The new developments
of the Clamond process form as impor