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| | Earth | Human World on Jul 24, 2013

This date in science: Johan Georg Forchhammer and ocean salts

The ocean is saltier in some places than others. But the percentages of various salts in seawater is a constant.

July 24, 1794. Today is the birthday of the chemist Johan Georg Forchhammer, born in Sleswig (now a part of Denmark). In 1865, at age 71, he noted that that – although the total amount of dissolved salts in the ocean might vary from place to place – the ratio of major salts in seawater stays constant. In other words, the percentages of various salts in seawater appears to be a constant, no matter how salty the water is. This discovery is now known as Forchhammer’s Principle, or the Principle of Constant Proportions.

Image credit: Wikimedia Commona

Johan Georg Forchhammer. Image credit: Wikimedia Commona

It’s known that the ocean is saltier in some places than others. The North Atlantic is saltier than the Arctic Ocean, for example. But, according to Tom Garrison’s book Oceanography: An Invitation to Marine Sciences, if you could isolate salt solids from both of those oceans (and others around the world), you’d find that 54.04% of those solids would be in the form of chloride ions. That is Forchhammer’s Principle.

Building on Forchhammer’s work, William Dittmar in at the end of the 19th century tested new methods to analyze the salinity and the chemical composition of seawater. He later analyzed 77 samples from around the world, taken during the H.M.S. Challenger Expedition from 1872 to 1876. Dittmar noticed the same constancy of in the composition of salts in seawater observed by Forchhammer. He wrote:

… although the concentration of the waters is very different, the percentage composition of the dissolved material is almost the same in all cases.

So science proceeds, slowly and steadily over many years, with the work of one scientist building on those who came before.

Bottom line: July 24, 1794 is the birthday of the chemist Johan Georg Forchhammer, who noted that the percentages of various salts in seawater appears to be a constant, no matter how salty the water is. This discovery is now known as Forchhammer’s Principle, or the Principle of Constant Proportions.