About the same time three other processes based on somewhat better
chemical knowledge were put forward. Pictet proposed leading the gas
through a strong solution of calcium chloride and then through strong
sulphuric acid, both maintained at a temperature of -20 deg. to -40 deg. C.,
finally washing the gas in a solution of some lead salt. Proof that such
treatment would remove phosphorus to a sufficient degree is not
altogether satisfactory; but apart from this the necessity of maintaining
such low temperatures, far below that of the coldest winter's night,
renders the idea wholly inadmissible for all domestic installations.
Willgerodt suggested removing sulphuretted hydrogen by means of potassium
hydroxide (caustic potash), then absorbing the phosphine in bromine
water. For many reasons this process is only practicable in the
laboratory. Berge and Reychler proposed extracting both sulphuretted
hydrogen and phosphine in an acid solution of mercuric chloride
(corrosive sublimate). The poisonousness of this latter salt, apart from
all other objections, rules such a method out.
BLEACHING POWDER.--The next idea, first patented by Smith of Aberdeen,
but fully elaborated by Lunge and Cedercreutz, was to employ bleaching-
powder [Footnote: Bleaching-powder is very usually called chloride of
lime; but owing to the confusion which is constantly arising in the minds
of persons imperfectly acquainted with chemistry between chloride of lime
and chloride of calcium--two perfectly distinct bodies--the less
ambiguous expression "bleaching-powder" will be adopted here.
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