12 
BULLETIN OF THE LABORATORIES 
The shelf is braced to a small piece of wood one inch thick and 
two inches wide ; to the lower end is attached a small metal band 
which clasps the standard; while the upper end is secured by a stiff 
wire bent as shown at E, {a, front view, b, side view), with the points 
of the wire inserted in the sides of the slide piece near its upper end 
and the wire passing around the standard. 
Upon this bracket rests a gallon flask ; a glass tube passes through 
the stopper (which is of rubber) to the bottom of ’the flask. On the 
lower end of the tube is arranged a small valve (B) which is made by 
placing a short section of rubber tube which just fits the glass tube 
over the end of the tube and a little longer section of a little larger 
rubber tube over the first rubber section, a small glass cone is then 
made by drawing down a glass rod or tube. This small cone fits in 
the end of the glass tube and is kept from falling out by a small pin 
passed through the diameter of the rubber tube below it. This allows 
the free passage of the air into the flask, but stops the water from pass- 
ing up the tube in case there should be any back pressure. The end 
of the tube should be ground and smooth and greased a little so as to 
make a water tight valve. At the lower edge of the flask a small hole 
is made with a round file and in this is inserted a rubber tube- about 
eight feet long, which opens into the pressure bottle. 
Another flask of the same capacity as the first is used as a press- 
ure bottle. 
The rubber stopper is perforated by three tubes which pass just 
through the stopper. The tube to which the long rubber tube is at- 
tached must not have an orifice more than a quarter of an inch in di- 
ameter, else air bubbles will pass back up the tube when the pressure 
reaches its maximum. 
Another tube is bent, as shown in the diagram, so as to come 
along the side of the flask. This tube is filled half full of mercury 
and is graduated up and down from the zero point in half inch divis- 
ions ; then a half inch reading on either scale records an inch mercury 
column, equal to one half pound of air pressure in the pressure bot- 
tle. At the open end the diameter of the tube is diminished and 
it is curved a little to exclude dust. 
The third tube bears a rubber tube, to which is attached a glass 
cross or metal piece, giving three outlets. To these are attached rub- 
ber tubes leading to the injection bottles. Three injection bottles are 
used, one for normal salt solution, one for red and one for blue gela- 
