ACKROYD : ON THE CIRCULATION OF SALT. 
421 
the genesis of ammonia and carbonic acid ; next the formation of 
ammonium carbonate, which is changed to ammonium nitrite. 
The nitric organism transforms the nitrite to nitrate, and finally 
common salt yields its sodium in the change of ammonium nitrate 
to sodium nitrate. That the common salt is of marine origin is proved 
by the composition of the caliche of the South American nitrate 
industry, for the mother liquor left after the nitrate crystals have 
been removed contains iodine in the form of iodate, the state of com- 
bination in which it exists in sea-water. Although unaware of this 
chemical fact, geologists have looked to salt of marine origin as the 
source of the sodium in sodium nitrate. There remains now only 
the sodium in the sodium sulphate. This is of too uncertain origin 
for one to say how much or how little is available for the purpose 
under consideration, but sufficient has been said to show that the 
quantities of which the denominator is made up are not definite 
enough for calculating the age of the Earth. Nor does the uncertainty 
end here, for while, as Prof. Sollas mentions, the outflow of the rivers 
yielding the data relied upon forms only some 7J per cent, of the 
total quantity of water being annually delivered into the ocean, there 
is, besides, the fact that in some of the largest of these rivers having 
their origin in the torrid zone, the saline contents, as in the case of 
the Nile, vary some 400 per cent, in the course of the year. 
