It is attacked by nitric acid, yielding a white powder of stannic
phosphate; this is not easily decomposed by ammonium sulphide or readily
soluble in hydrochloric acid.
"Phosphor-tin" is made up only of tin and phosphorus. For the estimation
weigh up 1 gram. Place in a weighed Berlin dish; and cover with 10 c.c.
of nitric acid and 3 or 4 c.c. of water. Let the reaction proceed (under
a clock-glass) on the water-bath till complete. Remove the glass;
evaporate to dryness, and ignite, at first gently over a Bunsen burner,
and afterwards in the muffle at a red heat. Cool in the desiccator, and
weigh as quickly as possible when cold. The substance contains the tin
as stannic oxide, SnO_{2}, and the phosphorus as phosphoric oxide,
P_{2}O_{5}. The increase in weight on the gram of substance taken gives
the weight of the oxygen taken up by the phosphorus and tin, and since 1
gram of tin takes up only 0.271 gram of oxygen, and 1 gram of phosphorus
takes up 1.29 gram, the proportion of tin to phosphorus can be
calculated from the increase in weight. For example, 1 gram of a sample
gave 1.3410 gram of mixed oxides, which is 0.070 gram in excess of that
which would be got with pure tin. If the substance was all phosphorus
the excess would be 1.0190 gram; consequently the proportion of
phosphorus in the substance is 0.
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