470 Galvanic Apparatus. 



are covered witli a variety of brushwood common to other 

 parts of the country, interspersed by a great number of date 

 trees [Phcenix dactyl if era). At this season (April 1819) the 

 river was very low, with scarcely any stream, and in many 

 parts the water had formed large stagnant pools. In the course 

 of a walk along the bed of the river, I observed that on the 

 margin of one of the above pools the ground for a considerable 

 space appeared beautifully white : on examining it closely, I 

 found it covered with a fine pure saline efflorescence, in ge- 

 neral about 2-lOths or 3-lOths of an inch in depth, covering 

 a soft, wet, and shppery mud ; the taste and appearance of this 

 salt induced me to conclude that it was carbonate of soda, 

 which I found to be the case on taking some of it to my tent. 

 I was natux-ally anxious to make some search to discover the 

 extent of this bed, and whether similar beds might not be found 

 in other places of the river ; but an ordei-, soon after received, 

 to march at midnight, called my attention to objects of a dif- 

 ferent kind." 



" From the quantity and apparent purity of the salt on the 

 surface (where I am convinced that with a little care a pound 

 or two might have been collected perfectly clean), there is no 

 doubt of the earth being very richly impregnated with it, and 

 it would only require to be washed and filtered to produce the 

 carbonated alkali in great abundance ; and there is every rea- 

 son to believe that there are numberless places in the bed of 

 the river, beside the one I have discovered, equally productive 

 and of greater extent, which might be worked annually in the 

 dry season. I may state that, from the remarkable whiteness 

 of the bed I have mentioned, it is reasonable to conclude that 

 the alkali is here in its native state uncommonly pure." 



GALVANIC APPARATUS. 



A new and powerful apparatus has been constructed at the 

 London Institution by the ingenious W. H. Pepys, Esq. It 

 consists of a single sheet of copper and one of zinc, each 50 

 feet long and 2 feet broad. They are wound round a wooden 

 centre, and kept apart by pieces of interposed hair-lines. The 

 coil and its counterpoise are suspended by a rope over a tub 

 of dilute acid. When lowered into the tub, its electricity is so 

 low as not to affect ':he electrometer ; even a bit of charcoal 

 serves to insulate it, and it can hardly ignite an inch of pla- 

 tinum wire of J^ of an inch diameter ; but when the poles are 

 comiected by a copper wire J of an inch diameter and 8 inches 

 long, it becomes hot, is most powerfully magnetic, and admi- 

 rably adapted for all electro-magnetic experiments. 



