be irrespirable; but in a place
where the gas is present in undue quantity, the fragments of lime
would materially mitigate its action.

In a small cellar-like chamber with a stone flooring and stone walls,
the first experiments were made. We Placed there furnaces containing
resinous pine-wood, lighted the wood, and, placing over it a lid which
prevented too brisk a circulation of the air, generated dense volumes
of smoke. With our eyes protected by suitable glasses, my assistant
and I have remained for half an hour and more in smoke so dense and
pungent that a single inhalation, through the undefended mouth, would
be perfectly unendurable. We might have prolonged our stay for hours.

FIG. 5.

Having thus far perfected the instrument, I wrote to the chief officer
of the Metropolitan Fire Brigade, asking him whether such a respirator
would be of use to him. His reply was prompt; it would be most
valuable. He had, however, made himself acquainted with every
contrivance of the kind in this and other countries, and had found
none of them of any practical use. He offered to come and test it
here, or to place a room at my disposal in the City. At my request he
came here, accompanied by three of his men. Our small room was filled
with smoke to their entire satisfaction. The three men went
successively into it, and remained there as long as Captain Shaw
wished them. On coming out they said that they had not suffered the
slightest inconvenience; that they could have remained all day in the
smoke. Captain Shaw then tested the respirator with the same result,
and he afterwards took great interest in the perfecting of the
instrument.

*****

Various ameliorations and improvements have recently been introduced
into the smoke respirator. The hood of Captain Shaw has been improved
upon by the simple and less expensive mouthpiece of Mr. Sinclair; and
this, in its turn, has been simplified and improved by my assistant
Mr. John Cottrell. The respirator is now in considerable demand, and
it has already done good practical service. Care is, however,
necessary, in moistening the wool with glycerine. It must be
carefully teazed, so that the individual fibres may be moistened, and
_clots_ must be avoided. I cannot recommend the layers of moistened
flannel which, in some cases, have been used instead of cotton-wool:
nothing equals the wool, when carefully treated.

An experiment made last year brought out very conspicu