ALKALI CONDITIONS AT CHEGGA. 



8.5 



TABLE 18. Composition (in percentage by weight) of artesian water at Chegga and of the 

 well at Bir Djefa'ir, Algeria. 



1 Mr. Seidell's original analyses of artesian water of Chegga are as follows : 



2 Holland, Hydrologie du Sahara. 



The preponderance of sulphates is marked in the water of the well used to irrigate 

 the date plantation. They constitute 66. 28 per cent of the total soluble salts, whereas 

 the chlorids make up only 32.529 per cent.# 



The contrast with Fougala is most striking. There the artesian water was very 

 pure, containing only about 0.085 per cent of dissolved salts, whereas at Chegga the 

 water contained 0.6401 per cent, or nearly eight times as much alkali. This water 



The analyses made by Lahache (Archives de medicine milit., vol. 14 (1889), p. 50) 

 have shown the existence of soluble nitrates in the artesian water of all regions of the 

 Algerian Sahara. At Chegga 22.5 grams per cubic meter were found, or 0.00023 per 

 cent, corresponding closely to the 0.00030 per cent of nitrates and dissolved organic 

 matter reported by Carnot in the analysis of the water of the well at Bir Djefair. 

 No nitrates were found by Mr. Seidell, though tests were made. Possibly the small 

 amounts present had been consumed by micro-organisms before the water was 

 analyzed. The nitrates present in the artesian water are considered by Marcassin 

 (Annal. Inst. Nat. Agron., 1895) to be of considerable importance in supporting the 

 date palm and other vegetation grown by irrigation in the Algerian Sahara. 



