Page:Text-book of Electrochemistry.djvu/25

8 INTRODUCTION. CHAP

Setting the equivalent of oxygen equal to 8, the following numbers are obtained for other elements: —

Aluminium, $Al$, ${\frac {27.1}{3}}$ $9.03$

Barium, $Ba$, ${\frac {137.4}{2}}$ $68.7$

Bromine, $Br$, $79.96$ $79.96$

Cadmium, $Cd$, ${\frac {112.4}{2}}$ $56.2$

Calcium, $Ca$, ${\frac {40.1}{2}}$ $20.05$

Chlorine, $Cl$, $35.45$ $35.45$

Chromium, $Cr$, ${\frac {52.1}{2}}$ $26.05$

Copper, $Cu^{+}$, $63.6$ $63.6$

Copper, $Cu^{++}$, ${\frac {63.6}{2}}$ $31.8$

Fluorine, $F$, $19.0$ $19.0$

Gold, $Au$, ${\frac {197.2}{3}}$ $65.73$

Hydrogen, $H$, $1.008$ $1.008$

Iodine, $I$, $126.85$ $126.85$

Iron, $Fe^{++}$, ${\frac {55.9}{2}}$ $27.95$

Iron, $Fe^{+++}$, ${\frac {55.9}{3}}$ $18.63$

Lead, $Pb$, ${\frac {206.9}{2}}$ $103.45$

Lithium, $Li$, $7.03$ $7.03$

Magnesium, $Mg$, ${\frac {24.36}{2}}$ $12.18$

Manganese, $Mn^{++}$, ${\frac {55}{2}}$ $27.5$

Mercury, $Hg^{+}$, $200.3$ $200.3$

Mercury, $Hg^{++}$, ${\frac {200.3}{2}}$ $100.15$

Nickel, $Ni$, ${\frac {58.7}{2}}$ $29.35$

Oxygen, $O$, ${\frac {16}{2}}$ $8.00$

Potassium, $K$, $39.15$ $39.15$

Silver, $Ag$, $107.93$ $107.39$

Sodium, $Na$, $23.05$ $23.05$

Strontium, $Sr$, ${\frac {87.6}{2}}$ $43.8$

Zinc, $Zn$, ${\frac {65.4}{2}}$ $32.7$

Atomic Weight. — The atomic weights of the elements are whole multiples of the equivalent weights. The simplest relationship exists in the ease of the so-called monovalent elements, like hydrogen, potassium, chlorine, etc., for which the atomic and equivalent weights are the same. The atomic weight of divalent elements, such as zinc, magnesium, calcium, iron (in ferrous compounds), mercury (in mercuric compounds), is double the equivalent weight; whilst in the case of trivalent elements like aluminium and iron (in ferric compounds), the atomic weight is three times the equivalent weight. In the above table the equivalent weights are given as fractions of the corresponding atomic weights.