84 
Journal of the Mitchell Society 
[ November 
A short, description of the method of manufacture of these man- 
tles may be of interest . The first part of the process is the selec- 
tion of the thread fibre from which the mantle fabric is knitted. 
The fibre mostly used is cotton, either the upland, river bottom, 
Peeler, Allen seed, Sea Island or Egyptian variety, the market 
prices varying from about 10c for the upland to 30c per pound 
for the Egyptian. The cheaper cottons are used in the lower grade 
mantles, the highest grade mantle requiring the best quality of 
cotton. The thread is purified, so as to remove every possible 
trace of mineral matter. If the thread used shows a mineral im- 
purity above .015 per cent, it will introduce factors that will affect 
the physical and lighting life of the mantle. Cylindrical networks 
of varying diameters are knitted out of the thread and then wash- 
ed in ammonia and distilled water and wrung out in mechanical 
clothes wringers. After it is dry it is cut into pieces sufficiently 
long to make two good mantles. 
These knitted fabrics are then placed in a suitable vessel and 
covered with the ‘lighting fluid.” They remain in this until 
thorougly saturated. The excess of fluid is drawn off amd the 
fabric put through an equalizing machine piece by piece. The 
“lighting fluid” is composed of a solution of approximately 99 
per cent thorium nitrate and 1 per cent cerium nitrate in distilled 
water, in the ratio of 3 parts of water to 1 part of mixed nitrates. 
The fabric is dried and then cut to the proper length required for 
a hood. They are then shaped over a wooden form and the upper 
end drawn together by means of an asbestos cord (occasionally of 
platinum). After the mantle has been modelled the cotton fibre 
is eliminated by heating them over a hot Bunsen burner flame, 
leaving the mantle composed of the ash of thorium and cerium. 
The peculiarity of these oxides is that they have sufficient cohesion 
to hold together during the balance of the process of manufacture, 
after every bit of the supporting cotton thread has been burned 
aw’ay. They are then subjected to a series of tempering and test- 
ing heats during which the mantle is carefully shaped to its per- 
manent form. In order to protect the ash of the mantle during 
its inspection, packing, transportation, and installation, it is dip- 
ped in collodion. Just before using a mantle this collodion cover- 
