KHARTOUM WATER-SUPPLY 



31 



pipes with that taken from the tap in the Laboratories, i.e. after it lias heen allowed 

 to stand in the reservoir for 48 hours or ovei\ 



The water at the time was the product of Wells Nos. 6 and 7. 



The following determinations of iron and manganese in the tap water were made 

 at various times. 



The iron present in the tap water is largely in suspension. It is apparently due to 

 a slight corrosion of the pipes, since the surface water of the reservoir, after only eight 

 hours settling, contains as a rule a smaller amount. There is also the fact that if it 

 were that originally present, it would be associated with a more appreciable proportion 

 of manganese. (iSV« helow, the analysis of sediment from the reservoir.) 



The cause of the corrosion is doubtless, in part at least, galvanic action, the result of Corrosion 

 the deposition of a small amount of manganese and iron oxide in the pipes. The absence of 

 manganese and presence of iron in the tap water was at first thought to be the result 

 of a slight growth of cmnothrix in the pipes, but no growth of this kind has been detected 

 since the deepening of the wells and the cutting off of the contaiiiiiiated water of the 

 surface strata. 



An analysis, by Dr. Thompson, of the sediment deposited in tlic storage reservoir gave 

 results as follows : — 



