The spirit level (Fig. 64) is simply a curved glass tube filled with alcohol except for the bubble and closed at both ends. The curve of the tube is part of a circle.
Make a spirit level as follows: Take a piece of No. 4 tube about 7 inches long, heat a space about 3 inches long in the lamp flame, turn constantly, and when soft remove from the flame, hold both ends and allow the center to sink into a slight curve (1, Fig. 65).
Let the tube cool, mark the center of the curve with ink, and make marks 2 inches from the center on each side.
Hold the tube crosswise in the lamp flame, heat at one mark, draw down the tube and close it (2).
In a similar manner draw down the tube at the other mark but do not close it (3).
Let the tube cool and fill it with alcohol to the level shown in 4. To do this easily make the pipette (5), suck alcohol into it within about 1 inch of the top, put your finger over the top, insert the lower end of the pipette to the bottom of 4, and remove your finger.
Fig. 65. Making A Spirit Level
Fig. 66. Mounting the spirit level
Heat the small part of 4, without heating the alcohol, and close the tube (6). Now attach the level to a smooth board as 2 or 3, Fig. 66, mark the center of the bubble, and your spirit level is ready for use.