552 
description, for it will be seen at a glance that the circuit 
is completed by the rising of the mercury to the wire 
within the precincts of the closed chamber formed by 
the neck of the funnel, and is adjusted for use by turning 
the base on which it stands, when a cork rises against a 
leather bag, and presses the mercury up to the required 
height. Whether marble will stand long without disintegra- 
tion by carbonic acid has to be determined ; if not, it can be 
replaced by another septum. This instrument is proposed 
for use in those mines where carbonic acid becomes a danger- 
ous substance for the miner. It has been sought by the 
French wine growers as a means of telling the time of the 
commencement of fermentation, and it seems probable that 
the English brewers will use it for a similar purpose. In 
the event of fire-damp being known to exist, either when 
found by the fixed indicators or by the safety lamps, Mr. 
Ansell proposes for the use of the miner, the manager, 
or his deputy, an aneroid indicator, described in detail at 
page 280, vol. xii., of the Chemical News. This is not used 
for the detection of gas in the pit. The intention of this 
particular instrument is that it shall be used to determine 
the amount per cent, of fire-damp or carbonic acid gas where 
they are known or suspected to exist ; and for these purposes 
it must be used rigidly according to the instructions given 
with it, not according to the fancy of the user or as he thinks 
it should be used. It must be taken, with its brass cap still 
on, into the neighbourhood of the suspected atmosphere, and 
allowed to remain there till it has acquired the temperature 
of that place; this usually requires a few minutes (say five). 
The valve must then be opened to allow it to find the true 
zero of that altitude. Then the valve must be closed, and 
the index watched for a few seconds to see if it be stationary, 
and if it be so, then the brass cap must be removed, and the 
indicator held by its handle in the suspected place for the 
time specified on the instrument — about one minute." 
