348 PHARMACEUTICAL BACTERIOLOGY 



2. The effects of colloidal copper and copper sulphate in the purifica- 

 tion of drinking water are in a quantitative sense much like those of filtra- 

 tion, only the organisms are completely destroyed. 



3. Pending the introduction of the copper treatment of water on a large 

 scale the householder may avail himself of a method for the purifications 

 of drinking water by the use of strips of copper foil about 3 J inches square 

 to each quart of water, this being allowed to stand over night, or from six 

 to eight hours, at the ordinary temperature, and then the water drawn off 

 or the copper foil removed. 



The alum method of purifying water has met with considerable success, 

 but more recently the alum-sodium hypochlorite combination has proven 

 more satisfactory. The alum coagulates and precipitates the organic im- 

 purities and the sodium hypochlorite, through its electric dissociation, acts 

 as a germ destroyer. The coagulated and precipitated organic material 

 holding most of the bacteria is then removed by filtration. The amount of 

 chemicals used depends somewhat upon the degree of contamination. 

 With highly contaminated waters it is customary to use 3.3 per cent, of 

 alum as the coagulant, subsequently introducing 1.2 per cent, of the hypo- 

 chlorite. The water is then filtered, whereupon it is ready for use. 



Small quantities of drinking water may be purified as follows: Dis- 

 solve a level teaspoonful of powdered chloride of lime in a teacup of water. 

 This solution is diluted with three cupfuls of water, and a teaspoonful of 

 this mixture may be added to each two-gallon pail of drinking water. 

 This will give 0.4 or 0.5 part of free chlorine to a million parts of water and 

 will, in ten minutes, destroy all typhoid and colon bacilli or other dysentery- 

 producing organisms in the water. Moreover, all traces of chlorine will 

 disappear rapidly. 



There are in use a number of methods for dissociating sodium hypo- 

 chlorite by electricity. Some of them are patented and modifications 

 thereof are in use by city water purification works, giving excellent results. 

 Dr. C. P. Hoover, assistant chemist of the Columbus Board of Health, has 

 the following to say regarding the process: 



''There are two general types of electrolyzers for dissociating sodium 

 chloride. In one the cathodic and anodic products are allowed to recom- 

 bine in the main body of the electrolyte and in the other, known as the 

 diaphragm process, the products are removed separately from the cell as 

 produced. 



"For the production of sodium hypochlorite the non-diaphragm process 

 has been considered best because it dispenses with the destructible dia- 

 phragms and the loss of energy that all such diaphragms occasion. 



"When a direct current of , electricity is passed through a solution of 

 sodium chloride, sodium is liberated at one pole and chlorine at the other. 



