... the test-tube A, make sure that all con-nectionsaregas-tight, and tap the tube lightly,sothat a dearchannelis left above the coal-dust for the escape ofgasesandvapours.Now gently heat the tube along ... cokeproduced.(c)Take the flaskB,which containsammonia liquorandcoal tar.Pour off the upper ammonialayer ascompletelyaspossible, into a beaker, and then pour into the flask a fewc.cms.of water;shake ... evolved,and bubbles of gas willpass through the twowashing-bottles, BandC.Regulate the heat sothat the gasbubblesare not too rapid, otherwisesomeof the tarandammoniamay becarried on andescape....