Synthetic Inorganic Chemistry

HYDROCHLORIC ACID 143

thistle tube.
2-hole rubber stopper to fit flask and bottles.
three 1-hole rubber stoppers to fit Woulff bottle.
one 1-hole rubber stopper to fit drying tube.
glass delivery tube fitted as in diagram.
drying tube packed with glass wool.
pan of cold water.
8-ounce glass-stoppered tincture bottle.
burette clamp. Bunsen burner.
iron ring and ring stand.

Procedure. Set up the apparatus as in Fig. 18

with the rock salt in the large flask and 150 cc. of

water in each absorption bottle. Pour enough

of the sulphuric acid through the thistle tube to

seal the lower end of the tube. Watch the ac-

tion carefully to see that the foam does not rise

into the neck of the flask. As rapidly as seems

safe add the rest of the sulphuric acid. When

the action slackens apply heat very cautiously

to the flask and finally heat it strongly until

all the salt has dissolved and effervescence has

ceased. When the reaction is finished remove

100

CO

FIG. 19

FIGURE 19

The scale at the back is marked off in divisions of 0.1 inch. The acid

is placed in the shallow dish at the left and water in the dish at the right,

both being at the same temperature. The level is adjusted in both

dishes so that the surface of each liquid is exactly at the zero point of the

scale. Suction is applied at the top until the acid rises exactly to the

100 mark when the pinch cock is closed. The reading of the scale at

the top of the water column divided by 100 gives the specific gravity

of the acid.

the burner. Apply a gentle suction to the exit tube in the second

absorption bottle and draw all the hydrogen chloride from the large

flask into the absorption bottle.

Allow the contents of the flask to cool until crystals of NaHSC>4

begin to form. Wrap a towel around the neck of the flask.

Cautiously pour the contents of the flask into running water under

the hood. If allowed to cool completely the by-product of the