The weight so found multiplied
by 0.278 gives the weight of phosphorus in the form of phosphine in the
volume of gas passed through the absorbent liquid.
Objection may rightly be raised to the Lunge and Cedercreutz method of
estimating the phosphine in crude acetylene on the ground that explosions
are apt to occur when the gas is being passed into the hypochlorite
solution. Also it must be borne in mind that it aims at estimating only
the phosphorus which is contained in the gas in the form of phosphine,
and that there may also be present in the gas organic compounds of
phosphorus which are not decomposed by the hypochlorite. But when the
acetylene is evolved from the carbide in proper conditions for the
avoidance of appreciable heating it appears fairly well established that
phosphorus compounds other than phosphine exist in the gas only in
practically negligible amount, unless the carbide decomposed is of an
abnormal character. Various methods of burning the acetylene and
estimating the phosphorus in the products of combustion have, however
been proposed for the purpose of determining the total amount of
phosphorus in acetylene. Some of them are applicable to the simultaneous
determination of the total sulphur in the acetylene, and in this respect
become akin to the Gas Referees' method for the determination of the
sulphur compounds in coal-gas.
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