174 University of California Publications in Zoology \Vor.9 
the hydrographic side being much less common, especially in the 
United States, than are those on the biological side, may be 
spoken of in somewhat more detail. The apparatus in use 
comprises : 
1. One Ainsworth balance accurate to a tenth of a milli- 
gram, primarily for weighing water samples; 
2. Three Knudsen burettes and three Knudsen pipettes for 
chlorine determination by titration ; 
3. One set of fourteen Ariometers, from R. Kiichler, 
Fimenau, graded readings from 1000-1007 to 1024— 
1031, for specific gravity determinations ; 
4. One set of weighing bottles, Guy-Lussae model, for 
weighing water samples; 
5. One Fox gas analysis apparatus for extracting the gases 
from sea water. 
It will be seen by this list of apparatus that the laboratory is 
prepared to determine the density of the water by three methods. 
All of these are used more or less, partly for checking one 
another as to accuracy and partly for facilitating labor. Where 
thousands of determinations are made, as in this case, rapidity 
and inexpensiveness are important as well as is reliability. After 
much comparing the weighing method has come to be most used, 
it being undoubtedly the most trustworthy. The original cost 
of the apparatus aside, it is less expensive and almost as rapid 
as the titration method. The hydrometer method, though most 
rapid and least expensive of the three, is also least reliable. 
Reports have come to us from some of the European laboratories 
of twenty-five determinations an hour by the chlorine method. 
We have not been able to reach such a speed. The best we have 
attained is about fifteen per hour, and this rate can be reached 
in weighing quite as well as in titrating. 
The problem of the gaseous content of sea water is undoubt- 
edly very complex both actually and manipulatively. In the 
opinion of competent chemists the Fox method of extracting and 
measuring the several gases is probably the most effective so far 
devised. The apparatus used is however rather complieated. 
and although Mr. Burbridge, who alone has thus far manipulated 
