ON A NATURAL FORMATION OF CARBONATE OF SODA. 
27 
50 cubic centimetres of the same filtrate, treated in a carbonic acid apparatus 
with sulphuric acid, lost '915 grammes of carbonic acid. The carbonate is there¬ 
fore a neutral salt. 4-963 grammes, gently ignited to incipient fusion, lost -976 
grammes, equal to 19-66 per cent. 
From these data the following composition is deduced :— 
Neutral carbonate of soda. 51-05 
Common salt, with traces of sulphate of soda and chloride of magnesium ... 2T94 
Water and organic matter. 19-66 
Sand. 4-35 
100-00 
Subsequent information, obtained through the kindness of Captain Playfair, 
the Assistant Political Resident at Aden, was to the following effect:—“ The 
substance is found all along the coast to the east of Aden, to an extent of per¬ 
haps ten miles, and its quantity is practically unlimited. It is usually found in 
hollows behind (or beyond) high-water mark, to which the sea-water has access 
by percolation. There is no demand for it at present, but some months ago 
sixty to seventy camel-loads a day were brought into Aden, and it met with a 
ready sale at 2} rupees, per ten maunds (equal to two shillings a hundredweight). 
The only use made of it is to mix with snuff, to increase the pungency; rarely, 
too, it is used for washing clothes. It is variously called by the Arabs Dukduka , 
Hurka , and Kara." 
From the valuable paper published by Mr. H. J. Carter in the Transactions 
of the Bombay Branch of the Royal Asiatic Society, on the Geology of Arabia, 
it appears that the whole of the south-east coast of Arabia, from Ras-ul-Had to 
Bab-ul-Mandib, is capped with nummulitic limestone, pierced at frequent inter¬ 
vals with basaltic effusions, and in many places elevated so as to form lofty and 
abrupt cliffs, in which, beneath the limestone, other formations are visible. As 
a result of this formation, the shingle on the coast consists mainly of limestone; 
and although no specific description of the coast immediately to the east of Aden 
has been given, there is no reason to doubt that the same peculiarities prevail 
there. It is then to the percolation of sea-water through a stratum of fragments 
of limestone that we must attribute the production of the carbonate of soda, by 
which percolation, probably, a partial interchange of elements has been effected 
between the chloride of sodium and the carbonate of lime, giving rise to the for¬ 
mation of chloride of calcium and carbonate of soda. It has been long suspected 
that the natural production of carbonate of soda was dependent on the presence 
of carbonate of lime, and was brought about somewhat in this way; but what 
the conditions are uuder which the separation of the carbonate of soda from the 
chloride of calcium is effected, without allowing the former to exert its ordinary 
converse action upon the lime-salt and reproducing carbonate of lime, is a ques¬ 
tion that would form a very interesting subject of scientific inquiry. This is, I 
believe, the first time that the natural production of alkali from sea-water itself, 
without organic agency, has been observed. 
It is hardly probable that the production of carbonate of soda in this way is 
limited to a few miles’ distance from Aden. As the shore is so very similar along 
the whole 1125 miles which form the south-east coast of Arabia, there is a rea¬ 
sonable expectation of finding it at many places elsewhere; and an article so 
much in request, so easily procured, and with water-carriage close at hand, 
might yield a fair amount of profit to an enterprising shipper who should collect 
or purchase it upon the spot. 
Bombay. 
