290 
Proceedings of Royal Society of Edinburgh. [sess. 
Sea-water, plus sewage and am- 
monium chloride, kept for 5 
weeks, ..... 
The same mixture after contact 
with the ulva for 5 weeks, 
Parts per 100,000. 
Free 
Albuminoid 
Ammonia. 
Ammonia. 
0*050 
0*016 
0*004 
0*017 
These results further prove that the ulva cannot absorb albu- 
minoid matters. 
Experiment 3 . — Assimilation of Nitrates . — The result of these 
experiments, as well as other considerations to be mentioned pre- 
sently, induced us to extend our inquiry somewhat further, in 
order to ascertain whether the ulva can absorb nitrogen in the 
form of nitrates, with the same ease and rapidity as it assimilates 
that element as ammonia. 
The same frond of ulva was again used, which had now been 
under observation in the dish for six months. In the interval 
from the last experiment, the water in which it was growing had 
been changed only once. On examination, it was found that, 
owing to the inflation of some of its under surface by evolved 
oxygen, a portion of the frond had become quite dry and almost 
bleached. We thought it highly probable that it was no longer 
in a sufficiently healthy condition for further experiment ; but 
having no other specimen at hand, we decided to test its vigour 
by its power of absorbing ammonia. 
Some fresh sea water was therefore obtained and examined as 
follows : — 200 c.c. were distilled until 100 c.c. had passed over, 
and 50 c.c. of this distillate were Nesslerised for the free ammonia. 
The residue left in the distilling flask was then diluted to the 
original volume (200 c.c.) with ammonia free water, and treated 
with zinc-copper couple for twenty-four hours at ordinary tempera- 
tures, then poured off, again distilled, and the distillate Nesslerised. 
The results of the analysis were as follows : — 
Parts per 100,000 
Nitrogen, as : — 
Free Ammonia. Nitrates. 
The sample of sea water contained, 0*005 0*006 
