io8 NATURAL SCIENCE. 



August, 



years. " It is diflficult," writes Dr. Murray, " for anyone, except 

 those who actually witnessed the daily work at sea, to form an 

 adequate idea of the labour, skill, and continuous effort required to 

 carry on these observations in all sorts of weather, and to form, and 

 bring home successfully, collections and observations like those which 

 have resulted from Mr. Buchanan's exertions.'' 



After the return of the Expedition to England, Mr. Buchanan 

 proceeded to analyse the gas samples which had been brought home ; 

 but he being unable to proceed with the chemical work of the Expedi- 

 tion, all the material was handed over to the late Professor Dittmar 

 for completion of the work. The resulting volume, published 

 six years after, in 1884, besides being a valuable addition to oceano- 

 graphy, contributed not a little to the art of chemical analysis, in 

 which Professor Dittmar was a recognised master ; and as a piece of 

 scientific work it is a monument of painstaking and unwearied search 

 after accuracy, doubly instructive in its mathematical habit of 

 thought and its simple record of persistent trial and failure until the 

 desired result was accomplished. 



The first really great work on the chemistry of ocean-water was 

 that of Georg Forchhammer, who, in 1864, just twenty years before 

 the appearance of Dittmar's Report, pubhshed his paper, " On the 

 Composition of Sea-water in different parts of the Ocean." Beyond 

 his demonstration of the existence in sea-water of constituents 

 hitherto unsuspected, his great service to science consisted in showing 

 that the proportions of the cardinal constituents of sea-water salts, 

 the chlorine, sulphuric acid, lime, and magnesia, vary very little 

 throughout the great oceans. After Forchhammer's work no analysis 

 of sea-water was of any value unless executed with the highest attain- 

 able precision, and it was in full consciousness of this that the late 

 Professor Dittmar entered upon the complete analysis of his seventy- 

 seven samples of ocean-water, and endeavoured to furnish, as he says, 

 " if nothing more, at least a valuable extension of Forchhammer's 

 great work." 



The small quantity of each sample at his disposal (from one to 

 two litres) rendered impossible the determination of the minor con- 

 stituents (some twenty-two in number) enumerated by Forchhammer, 

 so he restricted himself to the determination with great accuracy of 

 the chief components, sodium, potassium, magnesium, calcium, and 

 sulphuric and hydrochloric acids. This direct determination of the 

 sodium, which had been omitted by Forchhammer for want of an 

 accurate method, was a great advance, and led to a very valuable 

 result, viz., that the equivalents of base were always in excess of the 

 sum of the equivalents of sulphuric and hydrochloric acids, thus 

 establishing beyond doubt the presence of considerable quantities of 

 carbonates in sea-water. 



Combining acids and bases in an arbitrary way, we may state 

 Dittmar's final results as follows : — 



