o2 PRESIDENTIAL ADDRESS SECTION A. 



No. I. — The suspended matter consists of clay and sand. On 

 addition of alum the suspended matter deposits well. The 

 sample is remarkably free from water organisms (apart from 

 bacteria). 



No. 2. — The turbidity is due to light sand and clay. On standing, 

 the sand deposits, but the clay remains in suspension. 

 Addition of alum causes a ready deposition of the clay. 



Bacteriological Examinations. 



The water has been examined by Dr. W. Watkins-Pitch- 

 ford, the Government Bacteriologist, with the following results: 



The samples of water in this case were taken on June 27th, 

 1913, and sample " A" is similar to the chemical sample (No. 2) 

 taken on the same date. 



B2020/13. A. At Vereeniging Weir. 



53 organisms per c.c. growing at 2i7°^- 



B. coli present in i c.c, not isolated from o.i c.c. 



B2021/13. B. Above Vaal River Bridge. 



30 organisms per c.c, growing at 37° C 



B. coli present in i c.c, not isolated from o.i c.c. 



Silt and Solid Matter carried by the Vaal River. 



The silt contents of any river varies with the discharge, but 

 is also affected by the incidence of the rainfall and the amount 

 of rain which previously fell on the catchment area. For 

 instance, the greatest amount of silt is usually found in a river 

 v/hen there is a heavy fall of rain following immediately after 

 a dry period at the commencement of the rainy season. It is 

 also usual for the water in a rising flood to have a greater silt 

 content than in a falling one. In the Vaal River the silt con- 

 rent varies considerably, and the greatest quantity up to the pre- 

 sent at Vereeniging has been 1,050 parts per million parts of 

 water by weight as compared with 1,500 parts per million in 

 the River Nile (Egypt). Sir W. Wilcocks estimate^ that the 

 River Nile discharges 13,000,000 million gallons of water into 

 the Mediterranean during an average year, and that the total 

 solid matter contained in that quantity is no less than 36,600,000 

 1 ons. 



Some impression of the silt contents of the Vaal River can 

 be obtained by perusing the following figures. The average flow 

 of the Vaal at Kimberley over a period of 30 years is 4,587 

 cusecs, and this is equal to an average annual discharge of 

 904,000 million gallons. 



Taking the average amount of silt at 700 parts per million, 

 the total weight will be 3,164,342 short tons, or 42,191,226 cubic 

 feet, and this will cover 1,935 acres to a depth of 6 inches. 



