 The weight of the Qianlong Tongbao was changed several times and tin was added to their alloy to both reduce costs and to prevent people from melting down the coins to make utensils.As the intrinsic value of these coins was higher than their nominal value many provincial mints started reporting annual losses and were forced to close down, meanwhile the copper content of the coinage continued to be lowered while the copper mines of China were depleting.The Qianlong era also saw the conquest of Xinjiang and the introduction of cash coins to this new region of the Qing Empire.