182 GENERAL BIOLOGY OF MICRO-ORGANISMS 



cent of iron (Fe 2 O 3 ) and the iron shall be preferably in the 

 ferrous state. 



Chemical Disinfection. Various methods for the purification 

 of water by means of chemicals have been proposed. The use 

 of copper sulphate to disinfect drinking water was recommended 

 by Moore and Kellerman, 1 and various investigators tested the 

 value of their recommendation. Clark and Gage 2 came to the 

 conclusion from their investigation that the treatment of water 

 with copper sulphate or the storing of water in copper vessels 

 has little practical value. Others also have come to practically 

 the same conclusion. While the addition of copper sulphate is 

 of use in preventing the growth of the algae, which sometimes 

 grow so abundantly as to choke up water pipes, and is of benefit 

 in this direction, the weight of evidence appears to be against 

 its efficacy for purifying water for drinking purposes. More 

 effective chemical disinfection has been obtained by means of 

 ozone generated by electricity. More recently, calcium hy- 

 pochlorite and free chlorine have been employed for this purpose 

 with considerable success. 



Physical Disinfection. The most effective and surest method 

 of disinfecting drinking water is by boiling it or by distillation. 



Bacteriological Examination of Water. For bacteriological 

 examination samples from the water-supply of a city may be 

 drawn from the faucet, but the water should first be allowed to 

 run for half an hour or longer. From other sources the supply 

 should be collected in sterilized tubes or bottles, taking care to 

 avoid contamination. These samples should be examined as 

 promptly as possible, for the water bacteria increase rapidly 

 in number after the samples have been collected. When trans- 

 portation to some distance is unavoidable the samples should 

 be packed in ice, but even this precaution does not preserve the 

 original bacteriological condition of the water at the time of 

 collection; for more or less change probably takes place at all 



1 U. S. Dep. Agriculture, Bu. Plant Ind. Bulletin 64, 1904. 

 8 Journ. Inf. Diseases, Sup. No. 2, Feb., 1906, pp. 175-204. 



