CHAPTER XIX
Water
748. Why is water regarded as a food? 749. Does it enter chemically into the composition of plants? Of animals? 750. In addition to serving as a food, why is water necessary for life processes? 751. In what ways may water be improved? 752. What are the most common forms of impurities? 753. What are the mineral impurities of water? 754. What is their source? 755. What effect do some of these minerals have upon the value of the water? 756. What causes some waters to dissolve limestone? 757. What are permanently hard waters? 758. To what is temporary hardness in water due? 759. What is the best way to remove mineral matter from water? 760. What are the organic impurities of water? 761. What are the sources of the organic impurities? 762. What change does the organic matter of water undergo? 763. What becomes of the nitrogen of the organic matter? 764. What does the presence of nitrates in water indicate? Nitrites? 765. What is the total solid matter of a water, and how is it obtained? 766. Define the terms free ammonia; albuminoid ammonia. 767. What does the presence of chlorine in a surface well water indicate? 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?