486 



Messrs. Carpenter, Jeffreys, and Thomson [Not. 18, 



In crossing: the wide channel from the N/W. of Ireland towards Rockall, 

 where the water for some distance is over 1 000 fathoms depth, so that the 

 other circumstances varied very little, if at all, the proportion of Carbonic 

 acid appeared to vary with the dredge-results ; so that the analyst Yentured 

 to predict whether the collection would be good or not before the dredge 

 came to the surface — drawing his inference from the results of his analyses 

 of the gases of the Bottom-water. In each case his prediction was justified 

 by the result. 



Station 17. Station 19. Siation 20. Station 21. 

 U25 fms. 1360 nn 3. 1443 6ns. 1476 fms. 



Oxygen 16-14 1792 2134 1668 



Nitrogen 4v7S 45'SS 47'51 4346 



Carbonic acid .. 35 07 3620 31 15 39'86 



100 00 100 00 100-00 100-00 



Good haul. Good haul. Bad haul Good haul. 



In the analyses made of the water in the Cold Area, and generally in 

 the Third cruise, there appears, as might be expected from the various 

 currents &c, a greater variation in the results than in the other series. 

 In the Bottom and Intermediate waters the Nitrogen appears to be rather 

 in excess of the average, and the Carbonic acid has a large range of varia- 

 tion — from 7'5S per cent, at Station 47 (540 fathoms, Temp. 43°'8) to 

 45*79 per cent, at Station 52 (354 fathoms, 3(f'6 Fahr.). The average of 

 the Surface-waters is much the same as in the other parts of the cruise. 



It may be worth notice that in localities where the greatest depth did 

 not exceed 150 fathoms, the results of the gas-analysis of Bottom and 

 Surface-water were frequently so nearly the same, whatever the amount of 

 Animal life on the bottom, as to lead to the supposition that there might 

 be at that limit a sufficient circulation, either of the particles of the water 

 itself or of the gases dissolved in it, to keep the gaseous constitution alike 

 throughout. The coincidence of this depth with the extreme depth at 

 which Fish are usually found to exist in these seas is suggestive. 



Organic matter. — With a view to test the method of analysis by Per- 

 manganate of potash, two or three series of analyses were made where fresh 

 and salt water mixed together, as in Killibegs Harbour, Donegal Bay, &c. ; 

 and the results in all cases justified the expectation formed, that the amount 

 of permanganate was an index of the comparative purity of the water, both 

 as regards the " decomposed" and the " decomposable" organic matter. 



Disregarding the above series, a total of 134 experiments were made 

 upon Sea-water, which may be thus divided : — 

 56 upon Surface-water, 

 18 „ Intermediate water, 

 60 „ Bottom-water, 

 134 



during the First and Third cruises. 



