The mixing tube is 0.24
inch, and the burner head 0.475 inch in internal diameter. The opening in
the cap of the burner is 0.16 inch in diameter. There is a diaphragm of
double gauze in the cap, and this is the only gauze used in the burner.
All the incandescent burners hitherto mentioned ordinarily have the gas
nipple made in brass or other metal, which is liable to corrosion, and
the orifice to distortion by heat or if it becomes necessary to remove
any obstruction from it. The orifice in the nipple is extremely small--
usually less than 0.015 inch--and any slight obstruction or distortion
would alter to a serious extent the rate of flow of gas through it, and
so affect the working of the burner. In order to overcome this defect,
inherent to metal nipples, burners are now constructed for acetylene in
which the nipple is of hard incorrodible material. One of these burners
has been made on behalf of the Office Central de l'Acetylene of Paris,
and is commonly known as the "O.C.A." burner. In it the nipple is of
steatite. On the inner mixing tube of this burner is mounted an elongated
cone of wire wound spirally, which serves both to ensure proper admixture
of the gas and air, and to prevent firing-back.
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