168 TREUBIA VOL. Il, 2—4. 
Portion I Portion II Portion III 
Salinity 
Sp: Cte a 2 Salinity | Sp. Gr. 
| i | 
Pycnometer | 1.02602 |34.07°/,,| 1.02603 |34.080/,, 1.02604 | 34.099/,, 
KiiCHLER- 1.02620 [34.31 0/1 1.02610 | 34170/,1 1.02010 |34.17 0 
areometer. 
Seeing that, in what follows below, no conclusions are ever drawn on 
the ground of differences in salinity of less than several units pro mille, it is 
conclusively shown that for my purposes the areometer-method was suf- 
ficiently accurate. 
There would even be very little use in trying to determine the salinity 
of the fish-pond water with greater precision than was observed by me. 
For the salinity of water-samples drawn at the same time from the same 
pond, but at different points a few hundred metres apart, displays, as we 
shall see in what follows, differences of several units pro mille; whilst also, 
in connection with various factors, to which I will refer again later on (such 
as the circulation of the water within the pond-system, the admission of 
salt water or fresh water, rainfall etc.), the salinity of samples collected at 
the same spot but with a few hours’ interval can likewise display creat 
differences. 
The salinity of fish-pond water cannot be determined according to the 
customary simple methods (such as areometer-readings or chlorine titration), 
with the same accuracy as the salinity of sea-water. In determining 
the salinity of fish-pond water by means of the areometer method, the areo- 
meter-readings will probably be influenced by the large quantities of 
organic matter dissolved in it, and sometimes also by the presence of 
suspended detritus and oozy matter '), On the other hand when we deter- 
mine the amount of chlorine and deduce the salinity from this by means 
of the KNUDSEN tables (16), the influence of dissolved organic matter 
and of particles in suspension will be practically nil. 
_ Furthermore when the water in the fish-pond, whose salinity is being 
determined, is a mixture of sea-water and of fresh water, admitted from 
the land-side, such as for instance river-water, the salts dissolved in this 
fresh water will make their influence felt on the areometer-observations 
and consequently on the degree of salinity derived from the KNUDSEN 
tables (1°), 
1) Whenever a sample of pond-water contained so many detritus and/or oozy 
particles that it began to look cloudy, it was strained before proceeding to the areometer- 
reading. 
