1.4. Solution Equilibria¶
1.4.1. Dissolution of Ionic Compounds¶
1.4.2. Use by Aboriginal and Torres Strait Islander Peoples¶
Cycads are a seed plant that produces a cycad fruit which was eaten by Aboriginal and Torres Strait Islander Peoples. They were farmed as the plant had:
high drought resistance
high yield per unit area (12kg of fruit per 200m^2)
- high in carbohydrates and proteins
similar to that of an energy bar
1300kJ / 100g
5g of protein
However, the cycad fruit contains the toxin cycasin at levels around 1.22g / 100g [Beck, 1989]. Cycasin’s lethal dose (LD50) is 50mg / 100g. In lower levels, it causes long-term nerve damage due to the removal of the myelin sheath, liver disorders, and cancer.
Thus, Aboriginal and Torres Strait Islander Peoples used solubility equillibria in order to reduce the high cycasin concentration.
The use of running water reduces the concentration of the dissolved cycasin, and hence according to Le Chatelier’s Principle the equillibrium will shift to the right to increase the concentration of the dissolved cycasin. This will increase the rate at which the cycasin dissolves.
In areas of lower rainfall, the dissolving was a slow process, and without the running water to shift the equillibrium to the right it would take up to 5 months for all the cycasin to dissolve.
Cycad seeds could be prepared with various leaching methods, such as [Beck, 1989]:
brief leaching
prolonged leaching
ageing
Brief Leaching¶
Cycad seeds would be roasted, then sliced, pounded/ground [increasing surface area and hence rate of reaction]. They would then be leached overnight in running water. This method would store for about a week.
Prolonged Leaching¶
Prolonged leaching involved drying the seed, then it would be crushed and then leached in running water for 3-9 nights, or still water for 1-5 months. It would then be eaten or made into a loaf and roasted. Either of these would store for months at a time.
Ageing¶
Cycad seeds could be collected from the ground, and would be sorted by smell and sound by skilled Aboriginal and Torres Strait Islander Peoples. They would then be buried in the ground for weeks. They could be eaten, or ground into a paste and roasted. These would store for long periods of time.