existence, but enters into combination like a single atom; e.g.
(NO3) in the compounds HNO3 or KNO3; (SO4) in H2SO4. In HNO3 the
radical has a valence of 1, to balance that of H, H-NO3). In
H2SO4, what is the valence of (SO4)? Give it in each of these
radicals, noting first that of the first element: K(NO3),
Na2(SO4), Na2(CO3), K(ClO3), H3(PO4), Ca3(PO4)2, Na4(SiO4).

Suppose we wish to know the symbol for calcium phosphate. Ca and
PO4 are the two parts. In H3(PO4) the radical is a triad, to
balance H3. Ca is a dyad, Ca==(P04). The least common multiple of
the bonds (2 and 3) is 6, which, divided by 2 (no. Ca bonds),
gives 3 (no. Ca atoms to be taken). 6 / 3 (no. (PO4) bonds) gives
2 (no. PO4 radicals to be taken). Hence the symbol Ca3(P04)2.
Verify this by writing graphically.

Write symbols for the union of Mg and (SO4), Na and (PO4), Zn and
(NO3), K and (NO3), K and (SO4), Mg and (PO4), Fe and (SO4) (both
valences of Fe), Fe and (NO3), taking the valences of the
radicals from HNO3, H2SO4, H3PO4.

Chapter XII.

ELECTRO-CHEMICAL RELATION OF ELEMENTS.

58. Examine untarnished pieces of iron, silver, nickel, lead,
etc.; also quartz, resin, silk, wood, paper. Notice that from the
first four light is reflected in a different way from that of the
others. This property of reflecting light is known as luster.
Metals have a metallic luster which is peculiar to themselves;
and this, for the present, may be regarded as their chief