REPORT ON THE COMPOSITION OF OCEAN-WATER. 
221 
Similar results were arrived at by Reiset after a most elaborate series of analyses, which 
comprised 193 samples. Reiset worked in each case on 600 litres of air, and used that 
admirable (baryta-water) method which had been worked out by Pettenkofer in connection 
with his great research on respiration. He found the volume of carbonic acid per 10,000 
to vary only within the narrow limits of 2*94 to 3 ’1. But his experiments (like Schulzes) 
were all carried out at pretty much the same latitude, and, as Dumas points out, since 
each of Reiset’s analyses involved the continued aspirating of air for some twelve hours, 
when there was a moderate wind, so that he may have started with the air of the place, 
and wound up practically with air from some place hundreds of miles away.* 
It is clear that the analyses of air at present at our disposal show only that 
whatever the role of the ocean may be, its local influence on the air is too quickly 
obliterated by the constant commotion in the atmosphere to fall within the grasp of our 
present analytical methods. ’ 
There is one point in Dumas’s memoir with which I cannot agree. Speaking of the 
absorption of atmospheric carbonic acid by the sea, he says : — “ Quand la dose d’acide 
carbonique” (in the water of the sea) “ diminue, le bicarbonate cle chaux marine se 
dissocie et le carbonate neutre de chaux se precipite .” 
The evidence seems to me to point the other way. I have had hundreds of bottles 
of samples of Challenger sea- water standing in my laboratory throughout the last three 
or four years. Many are more than half or three-fourths empty, and having passed 
through three summers must have lost a deal of their loose carbonic acid. And yet, 
apart from the two or three exceptional samples mentioned in the discussion on 
alkalinity, none of them shows any deposit of carbonate of lime. I have just engaged in 
experiments to ascertain the proportion of carbonate of lime which sea-water for a given 
degree of saturation in its carbonates is capable of dissolving. In the meantime, and as 
a general result of my experience, I presume that the water of the ocean in its present 
condition, and even where it contains its minimum of carbonic acid, is not yet saturated 
with carbonate of lime, ‘but is ready to dissolve whatever of this compound the rivers 
send into it. 
Mr. Murray tells me that extensive deposits of pelagic Foraminiferal and Molluscan 
shells are found in the ocean bed only at depths not exceeding a certain limit for each 
latitude with similar surface temperature conditions. For instance, in the tropics 
Pteropod shells are abundant at the bottom in depths of 1200 or 1400 fathoms, but in 
latitudes higher than 45° they are not met with in the deposits. The same remark 
applies to the more delicate Foraminiferal shells. At the greatest depths of the ocean all 
these calcareous shells disappear from the deposits in all latitudes. The cause of this, in 
* This objection possibly applies to Schulze’s analyses as well ; but I have not his memoir at my disposal. 
Thorpe’s analyses were made by Pettenkofer’s method, in which the air to be analysed is collected within a few 
minutes. 
