REPORT OF CHEMICAL LABORATORY 



211 



Blue Nile water was equal to 45 parts per million. This is less than Schloesing's limit (70) ; Absence of 

 nevertheless, by reason of the long distance over which the river passes, the, at this season, ^" ^ ^'" ^^ 

 more moderate speed of the current, and the fact that no additional clay is brought into it, water 

 the river is able to cdear itself almost completely of its suspended matter, and the water 

 appears blue. In the same month tlie White Nile water contained but little less lime and 

 magnesia (40 parts per million), but the proportion of alkali and bicarbonates was so 

 high (equivalent in alkalinity to 90 parts of sodium carbonate) that the clay remained 

 obstinately diffused in the water, which thus continued turbid (',' white ") throughout the 

 entire vear. 



Absence of Sulphates from White Nile Water 



Blue Nile water was found to contain a small proportion of sulphates, ranging from 

 about 5 to 7 parts of 8O4 per million. White Nile water, on the contrary, was found to be 

 quite free from them. From March till June a minute proportion (about 1 part of SO4 per 

 million) was detected, but this was doubtless derived from the subsoil water which had 

 filtered into the river during the period of low water. The explanation of the above 

 exceptional condition was found during the examination of a series of samples of White Nile 

 water collected by the Irrigation Department. These samples were unfortunately too small 

 in bulk to permit of many determinations, and, moreover, the corks used had evidently, in 

 some cases, contaminated the water. The results, so far as they went were, however, 

 instructive, especially as regards the question of the sulphates. 



It will be seen that the White Nile water, before it reached the sudd region, contained 

 about the same proportion of sulphates as the Blue Nile water at Khartoum. By the time 

 it had reached Lake Powendael, after having passed through a long stretch of grassy 

 swamps, the sulphates were reduced to mere traces ; and after having traversed the sudd 

 region as far as Ghaba Shambe, they were removed altogether and failed to reappear even as 

 far north as Khartoum. 



