CHAP. X.] CONTINUITY OF THE CHALK. 503 
charged with dissolved gases than surface-waters ; a considerable 
elevation of temperature being in all cases necessary for the 
evolution of any dissolved gas. 
Mode of examining Sanvples—The samples of water thus 
taken were examined with as little delay as possible, with a 
view to determine :— 
(1) The specific gravity of the water. 
(2) The total quantity of dissolved gases contained in them, 
and the relative proportions of oxygen, nitrogen, and 
carbonic acid. 
(3) The quantity of oxygen necessary to oxidize the organic 
matter contained in the water; distinguishing between 
a, the decomposed organic matter, and 
b, the easily decomposable organic matter. 
(1) The specific-gravity determinations were made at a tem- 
perature as near 60° Fahr. as possible, with delicate glass hy- 
drometers, so graduated that the specific gravity could be read 
off directly to the fourth decimal place with ease. 
(2) The apparatus for the analysis of the gases dissolved in 
the sea-water was essentially that described by Prof. Miller 
in the second volume of his ‘Elements of Chemistry.’ It was 
found necessary to make several modifications in it, to adapt it 
to the motion of the vessel. These consisted chiefly in sus- 
pending much of it from the cabin-ceiling, instead of supporting 
it from beneath, and in rendering all the parts less rigid by a 
free use of caoutchouc tubing, &c., the utmost care being taken 
to keep all joints tight. . 
It was found possible to make correct analyses, even when 
the vessel was rolling sufficiently to upset chairs and cabin- 
furniture. 
The method of analysis may be thus summarized :—From 
700 to 800 cubic centimetres of the sample to be examined 
were boiled for about thirty minutes, in such a way that the 
steam and mixed gases evolved were collected over mercury in 
a small graduated Bunsen’s gas-holder, all access of air being 
carefully guarded against. The mixed gases were then trans- 
ferred to two graduated tubes in a mercurial trough, where the 
