18 the underground waters of north-west yorkshire. 
Fluorescein. 
On the 22nd June an aqueous potassium carbonate solution of 
fluorescein was put into the Tranlands Beck, S.S.W. of Malham, 
and it showed itself early on the following morning half a mile 
away at Scale Gill Spring. It was also evident in the samples 
of water collected at Hanlith Bridge on this date, the river Aire 
being coloured to a point three miles away. It was, therefore, 
with considerable confidence that fluorescein was put into the 
Smelt Mill Water Sink on the 24th June. Having failed to 
make its appearance at any of the outlets, a further solution of 
1 lb. of fluorescein was emptied into this Water Sink on the 
27th, and 2 lbs. more on the 28th, but not until the evening 
of July -ith (the date of the chlorine maximum) did the fluor- 
escein show itself at the Cove. It had become less marked on 
the 8th, and was somewhat uncertain in samples obtained on 
the 10th. Mr. Swann, who saw the waters of the Cove on the 
6th, describes the fluorescence as "most profound and intense." 
The samples received by the analysts also gave results in the 
search for fluorescein which accorded with Mr. Swann's observa- 
tions, that is : the presence of the compound at Malham Cove 
on the dates mentioned, and its absence at Aire Head. It 
may be added that the Sub-Committee find that one part of 
fluorescein in 40 million parts of water may be readily detected. 
On August 26th a new set of experiments was commenced 
on the same lines as before, viz., the simultaneous use of 
ammonium sulphate, salt, and fluorescein. A solution of 1| lb. 
fluorescein was emptied into the bottom of Grey Gill Cave and 
washed down by a copious supply of water. This operation was 
a work of some difficulty and danger : a water barrel had to be 
placed in the middle of a slippery hill side, whence the water was 
piped over the rock into the cave, and this barrel was supplied 
by piping from the hill top. Seven hundredweight of ammonium 
sulphate was emptied into Upper Gordale Beck by the foot- 
bridge, and 18 cwt. of salt was subsequently emptied into the 
"burst" on the side of Cawden. From the 26th of August to 
