Analysis shows the gas to consist almost entirely of nitrogen, only small quantities of oxygen and carbon dioxide being present; and it has been estimated by rough experiment that the volume of gas issuing from Bore No. 1 (internal diameter, 4¼ inches) amounts to half a pint per minute. My own opinion is that this nitrogen represents ordinary air deprived of its oxygen during the underground passage of the water, and this explanation seems confirmed by Mr. Lucas, F.C.S., Chemist to the Egyptian Survey Department, who refers me to several cases in which air is believed to have been depleted of its oxygen by pyrites, etc., during its passage underground. The quality of the artesian water is in all respects excellent, and when taken direct from a cased well forms, after cooling, a palatable water free from all danger of contamination. Analyses by Mr. Garsed of water samples from four bores show the total dissolved solids to range from 43 to 47 parts per 100,000, equivalent to from 30 to 33 grains per gallon. In new bores the water is usually only slightly ferruginous, though, as already mentioned, in some of the ancient wells of certain districts it is so highly charged with ferric oxide that thick deposits of ochre have been formed along the irrigation channels. The chemical composition of the dissolved salts, so far as determined, is shown in the following table: ANALYSES OF TYPICAL ARTESIAN WATER OF KHARGA OASIS (HEADQUARTERS DISTRICT). +-------------------------+------+------+------+------+ | | Bore | Bore | Bore | Bore | | |No. 1.|No. 2.|No. 5.|No. 6.| +-------------------------+------+------+------+------+ |Total solids (grains per | 33 | 30 | 33 | 32 | | gallon) | | | | | +-------------------------+------+------+------+------+ |Composition of dissolved | | | | | |salts, per cent. | | | | | | Silica | 4·2 | 4·5 | 4·6 | 3·4 | | Ferric oxide | 1·7 | 0·8 | 1·2 | 1·3 | | Lime | 6·5 | 7·0 | 5·4 | 5·6 | | Magnesia | 2·9 | 3·1 | 2·7 | 3·8 | | Sulphuric anhydride | 4·5 | 4·9 | 4·4 | 4·4 | +-------------------------+------+------+------+------+ CHAPTER X FLOWING WELLS: SOME EXPERIMENTS AND OBSERVATIONS