the strength of Conservative siam lay in its members ' involvement in trade and taxation with their ministry portfolios the bunnag exercised control over major tax farms as opium and import and export tariffs Land tax also brought in considerable revenue In their official capacity and in accordance with practice known as sib lod (taking a tenth) they earned 10 per cent from these texes As we saw in the previous chapter they used their politically positions in the reign of King Mongkut to hand over to the Treasury a constant revenue irrespective of the expansion of the tax base and reserve the excess for their own purposes