Drinking straw hydrometer
Procure a drinking straw or a stout natural straw about 20 cm long. If it is not 'water-proof' dip it in melted candle wax and permit it to dry. Seal one end with wax, and introduce some lead shot or fine sand unless it floats in a vertical position. Then drop in melted wax to keep the shots or sand in place. Have a thin rubber band or a piece of black cotton tied round the stem so that it can be slid up and down as a marker.