The sun was getting low in the west, and we therefore postponed the
exploration of our island until the following day. We had been up since
four o'clock that morning and had done some pretty hard work; so,
immediately after supper, we turned in and, lulled by the murmuring of the
river, were soon fast asleep.

[Illustration: Fig. 68. The Small Filter.]


The Barrel Filter.

Immediately after breakfast the next day we started out in two parties to
search the island. The only discovery of any moment was that made by
Dutchy's party, which found a small island separated from ours by a narrow
channel, through which the water ran like a mill-race. No spring was
discovered, so Uncle Ed had to construct his large filter. Bill and I went
over to Lumberville in search of a couple of cider barrels and a pailful
of charcoal. The barrels were placed one on top of the other after cutting
a large hole in the top of the lower barrel, and a smaller one in the
bottom of the upper one. The latter opening was covered by an inverted
saucer. Over this we spread a 3-inch layer of coarse sand, then a 2-inch
layer of charcoal, a 4-inch layer of clear, sharp sand, and a 2-inch top
layer of gravel. The lower barrel was provided with a faucet, through
which we could draw off the filtered water as desired. In order to keep
the water cool we placed the filters in a shady place near the river, and
piled up earth around the lower barrel.

"Now, boys," said Uncle Ed, "form in line there, and we will go through a
fire drill."