Measuring the volume

Volume is the space an object takes up. When a carton says 200 mL buttermilk, it's telling you how much space the drink fills, not how heavy it is.

So 1 mL = 1 cm³.

To measure a liquid, use a measuring cylinder: a narrow, clear tube, open at one end, with markings up its side. They come in sizes such as 5, 10, 25, 50, 100, 250 and 500 mL.

How fine can it read? (Activity 9.4) The cylinder in Fig. 9.16 is marked up to 100 mL, the most it can hold. Between the 10 mL and 20 mL marks there are 10 small divisions, so each small division is 10 ÷ 10 = 1 mL. That's the smallest volume it can read.

Bigger cylinders read less finely: usually 0.1 mL for a 10 or 25 mL cylinder, 1 mL for 100 mL, 2 mL for 250 mL and 5 mL for 500 mL. So choose carefully. For 70 mL of water, a 50 mL cylinder means two pourings (50 + 20); a 250 or 500 mL cylinder does it in one go but less accurately. A 100 mL cylinder is best.

Measure 50 mL (Activity 9.5). Stand a clean, dry cylinder on a flat surface and pour water in slowly to the 50 mL mark, using a dropper for the last bit. The water's surface is curved: this curve is the meniscus. For water and other colourless liquids, read the mark at the bottom of the meniscus, with your eye level with it. For coloured liquids, read the top.

For a solid with a regular shape, just calculate (Activity 9.6). Measure a notebook, shoe box or dice with a scale: Volume = length × width × height. A notebook 25 cm by 18 cm by 2 cm has a volume of 25 × 18 × 2 = 900 cm³.