218 
TIIE VOYAGE OF II.M.S. CHALLENGER. 
The Four Waters from depths not exceeding 100 fathoms. 
No. 
When 
Collected. 
Tompera- 
ture of 
Water. 
Free Car- 
bonic Acids. 
Milligrams. 
Depth. 
1873. 
355 
December 30 
3°0 
o 
100 fathoms. 
Indian Ocean, lat. 47° S. 
1874. 
397 
February 21 
not found. 
16 
50 „ 
Do. lat. 65° S. 
419 
March 7 
6° -9 
13 
50 „ 
Do. lat. 50° S. 
*1356 
1875. 
December 17 
12°-0* 
none. 
50 „ 
/ South Pacific, lat. 33° 42' S. ; about 
} 8° west of Valparaiso. 
Six of our 10 waters are from a cold region in the Southern Indian Ocean; hence 
thOr richness in carbonic acid needs not surprise us. It is more difficult to account for 
the richness in carbonic acid of the other four, and more especially of No. 532. The 
extraordinary amount of carbonic acid in this water (which, as I am assured by Mr. 
Buchanan, is not a clerical or observational error) seems to point to the existence of a 
carbonic acid spring in the neighbourhood, — lat. 17° 25' S., long. 169° 5' W. 
After having thus completed my review of the samples rich in carbonic acid, I turned 
my attention to those cases where the proportion of carbonic acid assumes low values, 
but. in dfing confinrd myself to surface waters. I divided them into four categories 
as follows : — 
The Carl>onic Acid in Milligrams per Litre ranges 
Number of Cases. 
From less than 55 to 50 exclusivo, .... 
8 
From 50 to 45 exclusive, ..... 
13 
From 45 to 40 exclusive, ..... 
12 
From 40 to 19 - 3, the least value, .... 
36 
Of this hist category of waters, twenty-five had temperatures ranging from 20° to 
-9 ( fourteen came from latitudes of 20° or less ; nineteen from latitudes of 22° to 37°; 
three from latitudes of 42° ^ S., 51 S., 50 S., respectively. 
I - mjrt-r.it ure* less than 20°, and value* of carbonic acid less than 40 milligrams per 
litre, were found combined in the following cases : — 
* Calculated from ascertained alkalinity. 
