13   C. Drawing on the Plate with the Needle. 19.  The Transparent Screen 14 20.  Needles or Points 14 21.  Temperature of the Room 15 22.  The Tracing 16 23.  Reversing the Design 16 24.  Use of the Mirror 17 25.  Precautions to be observed while Drawing 17 26.  Directions for Drawing with the Needle 17   CHAPTER III. BITING.   27.  Bordering the Plate 20 28.  The Tray 20 29.  Strength of the Acid 20 30.  Label your Bottles! 21 31.  The First Biting 21 32.  The Use of the Feather 22 33.  Stopping Out 22 34.  Effect of Temperature on Biting 22 35.  Biting continued 23 36.  Treatment of the Various Distances 23 37.  The Crevé.—Its Advantages and Disadvantages 24 38.  Means of ascertaining the Depth of the Lines 24 39.  The Rules which govern the Biting are subordinated to various Causes 25 40.  Strong Acid and Weak Acid 25 41.  Strength of Acid in relation to certain Kinds of Work 26 42.  Last Stages of Biting 27   CHAPTER IV. FINISHING THE PLATE.   43.  Omissions.—Insufficiency of the Work so far done 29 44.  Transparent Ground for Retouching 29 45.  Ordinary Ground used for Retouching.—Biting the Retouches 30 46.  Revarnishing with the Brush 31