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Dextrin: Starch Moistened with Dilute Nitric Acid and Heated at 110-120 °C (Payen, in Thorpe 1912)
Dextrin, also called British gum, is starch broken down by heat into a powder that dissolves in water to a sticky gum. A trace of nitric acid lets it form at a lower heat, 110 to 120 °C, so it comes out paler. The lower the heat and the drier the starch, the whiter the dextrin.
Source: Thorpe, Dictionary of Applied Chemistry, vol. 2 (1912), Dextrins, giving Payen's recipe. Ours: potato starch (Payen names no starch) and the scaling to 1 kg. Not given: how long to dry and to heat. Picture drawn by Youblob.
Beginner
2 days
Instructions
1
1
Mix 2 g nitric acid into 300 mL water
Mix 2 g nitric acid into 300 mL water
Payen: 30 gallons of water holding 2 lb nitric acid (sp. gr. 1.38) for 1000 lb starch. Ours, scaled to 1 kg of starch: weigh 2 g of the acid into about 300 mL water. Add acid to water, not water to acid. Goggles and gloves for the strong acid.
Materials for this step:
Nitric Acid2 g
Water300 mlTools needed:
Balance Scale
Measuring Jug
Chemical Splash Goggles
Nitrile Gloves2
2
Knead 1 kg starch with the acid water into balls
Knead 1 kg starch with the acid water into balls
Moisten 1 kg of starch with the acid water, knead it well and make it up into balls. Payen names no starch; ours: potato starch.
Materials for this step:
Potato Starch1 kgTools needed:
Glass BowlNitrile Gloves3
3
Dry the balls in hot air, then powder them
Dry the balls in hot air, then powder them
Dry the balls in a hot-air chamber, then powder them. Time and heat for this drying are not given. Ours: a drying oven, and a mortar to powder.
Tools needed:
Drying Oven
Mortar and Pestle4
4
Heat 4-5 cm deep on trays at 110-120 °C
Heat 4-5 cm deep on trays at 110-120 °C
Spread the powder 1 1/2 to 2 inches (4 to 5 cm) deep on trays (Payen: brass trays) and heat in a hot-air oven at 110 to 120 °C. Time not given.
Tools needed:
Flat Drying TrayDrying Oven
Oven Thermometer5
5
Stop as soon as iodine turns a sample brown
Stop as soon as iodine turns a sample brown
Test small samples with iodine. Starch turns iodine blue; commercial dextrin, mostly erythrodextrin, gives a brown colour. When the change is complete, stop the heating at once. Ours: a few iodine crystals shaken in water as the test liquid.
Tools needed:
Iodine CrystalsWaterDrying Oven6
6
Crush, sift and store dry
Crush, sift and store dry
Crush the roasted dextrin and sift it (in works: crushing pans or rollers, then a rotating silk screen as in flour mills). Ours: mortar and a fine sieve. Keep it dry in a closed jar.
Tools needed:
Mortar and Pestle
Fine Wire Mesh Sieve
Glass JarMaterials
3- 2 gPlaceholder
- 300 mlPlaceholder
- 1 kgPlaceholder
Tools Required
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