36 METHOD OF DESTROYING A1.QM IN WATER SUPPLIES. 



suggested in the preceding section in the case of acid and soft waters 

 may bo employed^that is, precipitate the copper by some soluble 

 hydroxide or carbonate. This somewhat complicates the treatment, 

 as it will be necessary to determine from the c-haracter of the water 

 the amount of copper necessary to produce a solution of 1 to 100,000, 

 as well as to estimate how much of the h3^droxide or carbonate should 

 be added. That such work be conducted under the constant and direct 

 supervision of comf)etent authorities is even more important than when 

 treating for algal contamination. 



COMPAillSON OF EFFECT OF OTHER DISINFECTANTS. 



A comparison of the effect of copper sulphate with certain other 

 substances commonl}^ used as disinfectants is instructive, and gives 

 some idea of the great toxicity of this metal. Mercuric chloride (cor- 

 rosive sul)limate) is slightly more fatal to typhoid and cholera than 

 copper sulphate acting at a lower temperature and in a shorter length 

 of time. Carbolic acid, one hundred times as strong as the dilution 

 found to be effective for copper sulphate, and acting eight times as 

 lono-, failed to kill. The same is true of formalhi used between fifteen 

 and twenty times the strength of a 1 to 100,000 solution. Using one 

 thousand times the amount of citric acid that would be used of copper 

 sulphate produces death. Thymol is effective in six hours when used 

 in a solution of 1 to .5,<»<)0, and naphthalene is five times weaker. 



COLIiOIDAL SOLUTIONS. 



The preceding experiments have dealt with copper in solution as the 

 salt of some acid. The effect upon water of metallic copper surfaces, 

 producing the so-called colloidal solution of copper, deserves especial 

 mention. As Niigeli, Galeotti, and Israel and Klingman have abun- 

 dantly demonstrated, the slight amounts of copper thus brought into 

 solution are highly toxic to many forms of algse and l)acteria. 



The experiments carried on in this laboratory show that it is 

 undoubtedly possible to exterminate TJroglena and some forms of 

 Sjyirogyra by suspending in the water copper foil sufficient to give 

 an area of about 1 sq. cm. to each 100 cc. of water. This would not 

 be a practicable method of treating a reservoir, but it suggests the 

 possibility of sheet copper being used as a preventive of pollution. 

 By suspending large sheets of this metal at the intake of a reservoir, 

 it is probable that conditions would be rendered sufficiently antago- 

 nistic to algal growth to maintain the sterilit}^ of a reservoir after 

 it had once been thoroughly cleansed of polluting forms. It w^ould, 

 of course, be necessary to keep such copper sheets clean in order to 

 prevent a reduction of the toxic action due to the formation of an 

 insolul)le or slimy coating on its surface. It is possible that some 



