AT HANGMAN'S WOOD, GRAYS, 229
fig. 2) was considered to be too much filled with sand, in conse-
quence of heavy falls from the roof, and too generally insecure to
repay the trouble of connecting it with No. 4.
The southerly tunnel admitting to the open shafts Nos. 2 and 4,
in addition to the power it gave us of working in those pits without
a second winding-up apparatus, greatly improved the air in all three
of these open-shafted deneholes, a current of air descending the
cooler shafts and ascending the warmer shaft near which lights were
burning and men at work. This enabled the work to be carried on
with much increased vigour. For though even the closed pits have
always been found perfectly easy to breathe in as soon as they could
be entered, yet the stagnation of the air in such pits made the most
moderate amount of work in them extremely fatiguing. And there
was some approach to stagnation, even in the open-shafted pits,
before the existence of the tunnels connecting them.3
The open-shafted pits having all been visited and described in
previous years (vide papers in Trans. Essex Field Club mentioned
above), little need be said about them till we come to consider the
mounds and their contents. These we removed in Nos. 2, 3 and 5,
leaving that in No. 4 untouched, the presence of large pipes in the
latter pit making it somewhat unsafe to work in. Another pipe had
been the cause of a considerable downfall of sand from the roof of
No. 2, at the end most remote from the tunnel between 2 and 3-
And at the side of the end of No. 2 and close to this downfall, we
found an irregularly shaped hole of considerable size, which is note-
worthy as the only example yet discovered of an excavation distinctly
out of harmony with the original plan. Many inscriptions figure
upon the walls of these open pits, the most ancient of those
apparently genuine being in No. 2, and bearing the date 1750.
We may now leave No. 3 by the easterly tunnel to visit Nos.
7, 8, 12 and 13. We found No. 7 very full of sand and gravel, and
its floor from two to three feet higher than that of No. 3, the apex of
the roof showing apparently the same band of flints in each case.
3 The purity and comparative freshness of the air (even in the closed pits when first entered)
has been before commented upon. There was no indication of the presence of the deadly
"choke-damp," commonly found in the stagnant air of old wells and pits. It is reasonable to
suppose that quantities of carbon dioxide and other gases would be set free during the decom-
position of the vegetable and animal refuse which had fallen into the pits, and it was suggested,
as a possible explanation, that the damp chalk might itself absorb the gas as fast as it was set
free, forming a double carbonate of calcium (Ca H2 (C O3) 2), a salt supposed to be produced
when carbon dioxide gas is passed in excess into lime water. An experiment made in Prof.
Meldola's laboratory, however, seems to show that wet chalk exerts no such absorbent power.
A piece of chalk was kept over mercury in an atmosphere of moist carbon dioxide for a fort-
night, but no absorption could be detected. The cause of the absence of bad air in the pits
has still, therefore, to be discovered.—Ed.