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air-tight. ‘Three glass tubes (£, F, G) form part of the glass 
dome aA, being blown in one piece with it. ‘To these 
caoutchouc tubes are attached, and the desired gases drawn 
into the chamber by their means. When the third tube is 
not in use it is simply closed by a pinch-cock. ‘The tube 
coming from £ is placed in the mouth or attached to an 
aspirator, whilst that from F is connected with the reservoir 
of gas or vapour to be used. Im the case of vapours the 
tube from F is attached to the shorter tube of a Wolff’s 
bottle containing the evaporating liquid, and by suction at 
the tube E a stream of air charged with the vapour can be 
obtained, varying in its intensity at the pleasure of the 
observer. Heat applied to the generating flask will of course 
furnish an increased strength of vapour. In some cases it is 
desirable to pass the stream of vapour through water to 
prevent a too rapid desiccation of the drop of blood under 
observation. This is readily effected by means of a second 
Wolff’s bottle containing water a little warm. Gases which 
are passed from a gas-holder of course do not require the use 
of the suction tube at z. ‘The chief use of the third tube (4), 
which in experimenting with a single gas or vapour is closed, 
is to introduce a second gaseous reagent immediately after, 
or simultaneously with, the introduction of another. It also 
may be used for the insertion of a stout copper wire, which 
is bent round after its introduction into the chamber, the 
other end remaining projecting from the apparatus. The 
projecting portion of the wire being heated as in Stricker’s 
hot plate, a considerable temperature may be obtained 
within the chamber, and vapour may by this means be gene- 
rated from a few drops-of water placed in the chamber in 
contact with the copper wire. In the same way other vapours, 
for the production of which a high temperature is required, 
may be evolved from liquids introduced into the chamber. 
Further, in place of the copper wire, a platinum wire in con- 
nection with the poles of a galvanic battery may be used, and 
a very much higher temperature obtained, if desired. Since 
the cement which fastens the glass plate and dome together 
is easily removed and replaced, the pieces can continually be 
separated for thorough cleaning, and thus any contamination 
of the reagents used prevented. 
As to the reagents which may be used in this way they 
are sufficiently numerous, and though used in combination 
with liquid reagents, still have great advantages. The 
advantage which I claim for gaseous reagents—apart from 
the fact that some bodies are necessarily only to be used in 
the gaseous state—are, firstly, that in this manner the re- 
