[Footnote: Lewes suggests that ammonia in the gas burnt may assist in the
production of this haze, owing to the formation of solid ammonium salts
in the state of line dust.] Immediately it comes in contact with
atmospheric moisture phosphoric anhydride is converted into phosphoric
acid, but this also occurs at first as a solid substance. The solidity
and visibility of the phosphoric anhydride and acid are beneficial in
preventing highly impure acetylene being unwittingly burnt in a room;
but, on the other hand, being merely solids in suspension in the air, the
combustion products of phosphorus are not so easily carried away from the
room by the means provided for ventilation as are the products of the
combustion of sulphur. Phosphoric anhydride is also partly deposited in
the solid state at the burner orifices, perhaps actually corroding the
steatite jets, and always assisting in the deposition of carbon from any
polymerised hydrocarbons in the acetylene; thus helping the carbon to
block up or distort those orifices. Whenever the acetylene is to be burnt
on the incandescent system under a mantle of the Welsbach or other type,
phosphorus, and possibly sulphur, become additionally objectionable, and
rigorous extraction is necessary.
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