done on board H.M.S. ( Challenger. 9 603 



quantity of water used has been almost invariably 225 cub. centims., 

 and the property possessed by sea-water of retaining its carbonic 

 acid with great vigour makes it possible to perform the determina- 

 tion of it even a couple of days after its collection. As a proof 

 of this, on the 10th July, 1875, the surface-water was found when 

 freshly drawn to contain 0*0291 gramme carbonic acid per litre. 

 A quantity likewise of the freshly drawn water was boiled in vacuo 

 for an hour and fifty minutes in order to collect the oxygen and 

 nitrogen, and then allowed to cool protected from the air. One 

 portion of this water was exposed to the air in a flat dish outside 

 the port for three hours, and in another portion the carbonic acid was 

 at once determined. It contained 0*274 gramme per litre, whilst the 

 water exposed to the air contained 0*6273 gramme. The effect, then, of 

 boiling in vacuo was only to remove about 5 per cent, of the whole 

 amount, whilst free exposure to the air had no effect whatever. As the 

 determination of the carbonic acid takes a considerable time, it is only 

 by taking advantage of this property that I have been able to determine 

 it in samples from depths in the same locality ; for where boiling in 

 vacuo has so little effect, there is no danger of losing carbonic acid 

 when the water is carefully decanted. 



As in the great majority of cases, where the carbonic acid has been 

 determined, the oxygen and nitrogen have also been collecte d, and are 

 being preserved until our return home, when they will be analyzed : it 

 would be useless to attempt to discuss the results of the carbonic-acid 

 determinations at present, and before these analyses have been made, 

 especially as there is likely to be some relation between the amounts of 

 oxygen and of carbonic acid. Independently, however, of the relations 

 which may subsist between the two bodies, it may be gathered from the 

 inspection of the accompanying Table that, taking surface-waters alone, 

 the amount of carbonic acid present is many times greater than would 

 be contained in the same volume of distilled water under the same cir- 

 cumstances. I have again and again exposed distilled water, surcharged 

 with carbonic acid, to the air, and after even a very few minutes the 

 carbonic acid was completely gone; on adding to 225 cub. centims. of it 

 5 cub. centims. baryta-water, the mixture remained perfectly clear ; and 

 on titrating with hydrochloric acid there was no diminution of alkalinity. 



The temperature of the water on this occasion was 18°*3 C. On that 

 particular day, namely the 8th July, 1875, when in the middle of the 

 North Pacific, there was no determination made of the carbonic acid in 

 the surface-water; but two days later,when the temperature of the surface- 

 water was 18°*9 C, 225 cub. centims. of it contained 0*0066 gramme carbonic 

 acid. Had there been 0*002 gramme C0 2 in the 225 cub. centims. distilled 

 water, it must have been detected and determined. Hence, under the same 

 circumstances, this particular sea- water, whose specific gravity was 1*02528 

 (at 15°*56 0., water at 4° = 1), contained at least thirty times as much 



