1900-1901.] Prof. Letts and Mr Hawthorne on Ulva latissima. 28$ 
Experiment 2 . — Assimilation of Ammonia . — This experiment 
was made with the view of getting some idea of the rapidity with 
which the ulva can absorb free ammonia from sea water, and also 
to ascertain whether it can thrive in a very highly polluted water. 
The frond of ulva had remained in the sea water of the last experi- 
ment an additional four days, making eighteen days in all, and 
appeared to be quite healthy. 
A sample of sea water was collected from the same locality as 
before, and to it 1 per cent, of sewage was added (obtained from 
the pumping station at the Belfast Main Drainage Outfall). This 
mixture gave, on analysis, the following results : — 
Parts per 100,000. 
Tree Albuminoid 
Ammonia. Ammonia. 
Sea water plus 1 per cent, sewage, 0*030 0*024 
But as it contained less free ammonia than was expected, a standard 
solution of ammonium chloride was added, sufficient to bring up 
the free ammonia to 0*050 parts per 100,000. 
The frond of ulva was drained from the first sample of sea water 
and rinsed with this mixture, again drained, and the dish then 
filled with the same mixture. 
It was intended to make a series of analyses of the contents 
of the dish at intervals of about twenty-four hours, but to our 
astonishment we found that practically the whole of the free 
ammonia had been absorbed after a period of only seventeen hours, 
as the following determination shows : — 
In 100,000. 
Free Ammonia. 
Sea water, plus sewage and ammonium chloride, 
after contact with the ulva for 17 hours, . 0*001 
With the object of tracing the fate of the albuminoid matters, 
the weed was allowed to remain for about five weeks in contact 
with the mixture, while a flask containing the same mixture was 
also kept during the same interval. Both samples were then 
analysed, with the following results : — 
YOL. XXIII. 
T 
