448 W. Ackroyd — The Circulation of Salt. 



a molecule of common salt or sodium chloride contains two atoms, 

 one of chlorine and one of sodium. 



1. In common salt 



2. In the solids dissolved in sea-water ... 



3. In Pierre's rain 



4. In the solids dissolved in average river-water 



(from Sir J. Murray's data) 1 : 0-345 



6. In the older crust of the earth (from Professor 



F. W. Clarke's data) 1 : 0*0024 



Compare 4 and 5. In the earth's crust there is only one atom 

 of chlorine to 417 atoms of sodium, while in river- water to each 

 atom of chlorine we have three atoms of sodium. Therefore 

 average river-water contains a proportion of over 140 times more 

 chlorine atoms than the earth's crust could supply it with. Where 

 does it get them from if transported sea-salt does not enter into the 

 composition of the so-called average river- water ? This difficulty 

 presented itself in another form to the Eev. Osmond Fisher when he 

 asked : " Whence came the chlorine ? The amount of 0*01 per cent, 

 stated to occur in crystalline rocks seems insufficient " (Geol. Mag.,. 

 March, 1900, p. 129). 



The Age of the Earth. — Now come we to the knotty question of the 

 bearing of the foregoing facts on the rate of solvent denudation used 

 as a measure of time. Here I have to point out the important fact 

 that in estimating the numerator all the sodium of the sea has been 

 calculated from sodium chloride. This involves the tacit assumption 

 that all the sodium going into the sea throughout the ages has either 

 gone there allied with chlorine or has finally taken the form of 

 sodium chloride. In either case the chemist's convention of taking 

 chlorine as a measure of sodium in rain- and river- water is serviceable, 

 and cannot involve more final error in connection with this problem 

 than that indicated by the ratio of these elements in sea-water. 

 Our estimate of 99 per cent, for cyclic sea-salt therefore still 

 stands, and, being applied to Professor Joly's calculation, brings 

 the age of the Earth to over 8,000 millions of years ; and even if 

 we were inclined to be prodigal in this respect and only deduct 

 so little as 80 per cent, for cyclic salt the age of the Earth would 

 still come to over 400 millions of years ! 



I will not go further into this matter here than to point out that 

 Professor Joly's grounds for making an allowance of 10 per cent, 

 for cyclic sea- salt is not convincing reading. We are invited to 

 contrast the chlorine content of average river-watev, put at "3 part 

 per 100,000, with the chlorine content of rainfall at Ootacamund in 

 India, which is given as -04 part per 100,000. It would have been 

 more conducive to progress in this discussion if relevant particulars 

 had been given of the Ootacamund region. Knowing as I do that 

 chlorine content and amount of rainfall bear an inverse relation to 

 each other, and that in some parts of India the rainfall is prodigious 

 in amount, any isolated fact concerning the chlorine content of 

 a sample of rain does not add to our enlightenment, because for 



