te? 768. Explain natural purification of water. 769. Can natural
purification always be relied upon? 770. Why does the character of the
drinking water affect health? 771. What diseases are mainly caused by
impure drinking water? 772. With what materials in water are the
disease-producing organisms associated? 773. Why should a water of
questionable purity be boiled? 774. State how the boiling should be
done, to be effective. 775. Why should boiled water receive further care
in its storage? 776. What effect does improvement of the water supply of
a city have upon the death rate? 777. How may connections between
cesspools and surface well waters be traced? 778. What impurities do
rain waters contain? 779. Explain the workings of the Pasteur and
Berkefeld water filters. 780. Why must special attention be given to
cleaning the water filter? 781. Explain the processes employed for the
removal of mechanical impurities of water by sedimentation and the use
of chemicals. 782. Why should such purification be under the supervision
of a chemist or bacteriologist? 783. What effect does freezing have upon
the purity of water? 784. Why are precautions necessary in the use of
ice for refrigeration? 785. What are mineral waters? 786. How are
artificial mineral waters prepared? 787. What are the more common
materials used in their preparation? 788. Why should mineral waters be
extensively used only by the advice of a physician? 789. What are some
of the materials used for softening water? 790. Which are the least
objectionable of these materials? 791. Which are the most objectionable?
792. What can you say of the use of ammonia and ammonium carbonate for
softening waters? 793. In washing clothing after contagious diseases,
what materials may be used for disinfecting? 794. Why, in softening
waters for household purposes, must caustic soda, potash, and bleaching
powder be used with caution? 795. Why is it necessary to determine by
trial the material most suitable for softening water? 796. What
advantage, from a pecuniary point of view, results from the improvement
of the water supply of a community?

CHAPTER XX

FOOD IN ITS RELATION TO HOUSEHOLD SANITATION AND STORAGE

797. What are the compounds usually determined in a food analysis? 798.
Does such an analysis necessarily indicate the presence of injurious
compounds? 799. What are the sources of the injurious organic compounds
in foods? 800. Why is it necessary to consider sanitary c