The acid lake inside the volcano Kawah-Idjen is called " green crater ". It's the biggest : (700 m about), the deepest (200 m, 36 millions/ m3), it has lasted over 2 centuries and it's the most acid too (pH minimum 0,18) - so says the sign ! Its température is between 20 and 40 °C depending on the activity of the volcano and the rain.
A limestone rock boils and melts in this mixture of sulfuric and hydrochoric acid. Some globuls of sulphur (1 mm in diameter) float on the surface.
There is a major sulphur deposit on the South side of the lake. The highest temperature measured has been 224 °C (December 1998). It emits a lot of sulphur dioxyde.
A mine was opened there in 1968. A clever system of pipes (10 m long, 50 cm in diameter) allows the sulphur to be carried as an orange liquid (115 °C) and it cristallizes yellow.
Then it is broken in big blocks and carried by men out of the crater. 200 miners, " sulphur slaves ", each carry 70 to 90 kg of sulphur in their baskets balanced on their shoulders.
They walk 4 km on steep slopes. It's a feat of skill and thus 5 to 6 tons of sulphur are extracted each day, mainly to whiten the sugar.
They are paid 150 rupees a kg, about a penny !
