XVIII. PUMPS AND THEIR VALUE TO MAN

XIX. THE WATER PROBLEM OF A LARGE CITY

XX. MAN'S CONQUEST OF SUBSTANCES

XXI. FERMENTATION

XXII. BLEACHING

XXIII. DYEING

XXIV. CHEMICALS AS DISINFECTANTS AND PRESERVATIVES

XXV. DRUGS AND PATENT MEDICINES

XXVI. NITROGEN AND ITS RELATION TO PLANTS

XXVII. SOUND

XXVIII. MUSICAL INSTRUMENTS

XXIX. SPEAKING AND HEARING

XXX. ELECTRICITY

XXXI. SOME USES OF ELECTRICITY

XXXII. MODERN ELECTRICAL INVENTIONS