done on board H.M.S. c Challenger. r 605 



platinum surface. In this way I have examined a number of waters 

 between Tahiti and Valparaiso, and with the general result that in ocean- 

 water carbonates are never present except in small quantities, and in 

 many samples they have been absent altogether. They are generally 

 present in waters at or near the surface, disappearing, however, as the 

 depth from which the water has been taken increases. They are generally, 

 though not invariably, absent in waters from greater depths than 400 

 fathoms. They are present or absent in bottom- water according to their 

 occurrence in the bottom ; although here also there appears to be excep- 

 tions, as I have observed water taken from a " Glohigerina-ooze " bottom 

 which contained no carbonate. 



In connexion with carbonic acid I may mention that I have frequently 

 tested waters, and especially bottom-waters, for organic matter. None 

 of the methods in use for determining this substance in drinking-water 

 giving satisfaction when applied to sea-water, I had to content myself 

 with endeavouring to detect its presence. If the jelly-like organism 

 which had been seen by some eminent naturalists in specimens of ocean 

 bottom and called Bathybius really formed, as was believed, an all-per- 

 vading organic covering of the sea-bottom, it could hardly fail to show 

 itself when the bottom-water was evaporated to dryness and the residue 

 heated. In the numerous samples of bottom-water which I have so 

 examined, there never was sufficient organic matter to give more than a 

 just perceptible greyish tinge to the residue, without any other signs of 

 carbonization or burning. Meantime my colleague, Mr. Murray, who 

 had been working according to the directions given by the discoverers 

 of Bathybius, had actually observed a substance like " coagulated mucus," 

 which answered in every particular, except the want of motion, to the 

 description of the organism ; and he found it in such quantity that, if it 

 were really of the supposed organic nature, it must necessarily render 

 the bottom-water so rich in organic matter that its presence would be 

 abundantly evident when the water was treated as above described. There 

 remained, then, but one conclusion, namely, that the body which Mr. 

 Murray had observed was not an organic body at all ; and on examining 

 it and its mode of preparation I determined it to be sulphate of lime, 

 which had been eliminated from the sea-water, always present in the mud, 

 as an amorphous precipitate on the addition of spirit of wine. The 

 substance when analyzed consisted of sulphuric acid and lime ; and when 

 dissolved in water and the solution allowed to evaporate, it crystallized in 

 the well-known form of gypsum, the crystals being all alike, and there 

 being no amorphous matter amongst them. 



These observations were made chiefly on the voyage from Hong Kong to 

 Yokohama in the first quarter of the year 1875 ; and it subsequently 

 occurred to me that an approximate determination of the organic sub- 

 stance in sea-water might be effected in the following way :— Supposing 

 the amount of carbonic acid in the water to be known, let a little per- 



