MODERN METHODS OF WATER PURIFICATION. 345 



or rather an arm or canal off the Nile, the Mahmoudieh canal. 

 I was on the banks of this canal and saw the native shipping- 

 and boats which sail between Alexandria and Cairo depositing 

 their refuse and sewage into the canal. Also the villages 

 along the Nile and the canal drain into the river, so it is highly 

 polluted, although a great volume of water. Here the Jewell 

 filter does the following, in the words of the chief engineer of 

 the water works : — 



" The results leave no room^ for doubt as to the efficiency of the method 

 of sedimentation and filtration The percentage removal of bacteria 

 is distinctly high, the daily averages are verj^ uniform, and never 

 since the first month of the filters' working has the removal of 

 bacteria been less than 98 per cent." 



I was given a copy of a record of the results for August, 

 September and October, the worst months for impurity of the 

 Nile water, and the removal of bacteria was 9874, 98*84 and 

 99 51 per cent, for the three months respectively, the number 

 of bacteria present in the filtered water during these three 

 months is given in the report as 10, 44, 44 per c.c. These 

 results from the polluted waters of the Nile in their worst 

 months are an eloquent tribute to the bacterial efficiency of the 

 Jewell. 



Results such as these are comparable with any slow sand 

 filter, and are not a solitary record, but can be matched month 

 after month. I do not desire to prolong the comparison by 

 quoting other names of experts and other places where similar 

 purification is taking place by modern mechanical filters, but 

 it will be evident that it is no longer possible to contrast slow 

 sand filtration as being alone safe, if a little more expensive 

 in initial and upkeep expenses, and refer to the other modern 

 mechanical methods as possessing only the virtues of compact- 

 ness and perhaps cheapness and liandiness, but also to be re- 

 garded with a good deal of suspicion of danger in their use. 

 That that may have been true at first Hazen admits, but it is 

 not true now and will be less true as improvements come, as 

 they are bound to come, and are coming all the time. 



Experiments must be made to so thoroughly test the Modder 

 River water as to be sure that it is suitable for what method 

 may be recommended. 



Bremen has double filtration through sand. But they have 

 had to adopt alum coagulation besides when the water is 

 muddy. Schiedam is also a double sand filtration town, where 

 coagulation has had to be adopted to get the water clear, in 

 spite of double sand filters, and, like many other American 

 ideas, coagulation is extending on the Continent of Europe. 



These two instances, where double filtration through sand 

 fails without coagulation, should serve to demonstrate the 

 cardinal truth above referred to, namely, that four, or on rare 

 occasions, more days sedimentation, if without chemical pre- 

 cipitation, followed by sand filtration, has been " tried and 

 found wanting " to deal with very turbid water, and here that 

 fact is not due to faults in working or errors of officials in 

 charge, but owing to the incapacity of sand filters unaided bv 



