6. Page 364

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364

AN INTRODUCTION TO METALLURGY.

Roasting—continued.
Ag₂S + O₂ = 2Ag + SO₂
3                                  71 =  + 68
Ag₂S + H₂O = Ag₂O + SH₂
3           58.2          7          4-6 =  – 49.6
Fe₂(SO₄)₃ + 2Ag = 2FeSO₄ + Ag₂SO₄
618.4                     2  x 235.6     167.3 =  + 20.1
3Ag₂O + Pe₂(SO₄)₃ = 3Ag₂SO₄ + Fe₂O₃
3×7         618.4        3 x   167.3      199-4 =  + 61.9
Ag₂O + CuSO₄ = CuO + Ag₂SO₄
7           182.6        37.2        167.3 =  + 14.9
Ag₂O + SO₃ = Ag₂SO₄
7          91.8        167.3 =  + 68.5
Ag₂SO₄ + 4Fe?O₄ = 2Ag + 6Fe₂O₃ + SO₂
167.3     4 x  265.8              6 x  199.4    71 =   + 36.9
Ag₂S + 4SO₃ = Ag₂SO₄ + 4SO₂
3      4 x  91.8    167.3      4 x 71 =   +.81.1
Ag₂SO₄ + Cu₂O = Ag₂O + 2CuO + SO₂
167.3          42            7        2 x 37.2    71 =  – 46.9

XI

Precipitation (by a cheaper metal).
AgSO₄ + Cu = CuSO₄ + Ag
167.3                   182.6              = + 15.3
CuSO₄ + Fe = FeSO₄ + Cu
182.6                    235.6            =  + 53.0
See also III and IV for cases of precipitation in the dry way
of lead and antimony, from their sulphides, by iron.
The table given on the folding plate will enable the student
to form other thermal equations for himself.
In calculating the heats of formation of the basic ferric sulphates,
it has been necessary to assume that the heat evolved is propor-
tional to the ratio of acid to base. It must be remembered that
in the case of the combination of carbon and oxygen such a
relationship does not exist.