504 



THE DEPTHS OF THE SEA. 



[chap. X. 



carbonic acid was first absorbed by a strong solution of caustic 

 potash; and subsequently the oxygen was absorbed by the 

 addition of pyrogallic acid, the remaining gas being assumed to 

 be nitrogen. 



The results of the analyses were always corrected to the 

 standard temperature of 0° Cent., and to 760 millimetres' baro- 

 metric pressure, for comparison among themselves and with 

 others. In nearly every case the duplicate analyses from the 

 same gaseous mixture agreed closely, if they were not identical. 



(3) The examination of the sea-water for organic matter was 

 made according to the method detailed by Prof. Miller in the 

 Journal of the Chemical Society for May 1865, with an addition 

 suggested by Dr. Angus Smith. Each sample of water was 

 divided into two; to one of these a little free acid was added, 

 and to both an excess of a standard solution of permanganate 

 of potash. At the end of three hours the reaction was stopped 

 by the addition of iodide of potassium and starch, and the 

 excess of permanganate estimated by a standard solution of 

 hyposulphide of soda. The portion to which free acid was added 

 gave the oxygen required to oxidize the decomposed and easily 

 decomposable organic matter ; the second portion gave the 

 oxygen required by the decomposed organic matter alone, which 

 was usually from about one-half to one-third of the whole. 



The following is a summary of the total number of obser- 

 vations, analyses, &c., made during the three cruises respec- 

 tively: — 



Specific Gravity. — The specific gravity of surface-water was 

 found to diminish slightly as land was approached; but the 



