2 8 ▁tons ▁of ▁coal . ▁There ▁were ▁eleven ▁min ers ▁and ▁ 3 4 1 0 ▁tons ▁of ▁coal ▁extracted ▁in ▁ 1 9 2 9 , ▁this ▁was ▁simultaneously ▁the ▁maximum ▁allow ance ▁of ▁the ▁mines . ▁In ▁ 1 9 3 0 , ▁there ▁were ▁five ▁min ers ▁who ▁extra ction ▁ 9 4 4 ▁tons ▁of ▁coal . ▁The ▁last ▁known ▁fund ing ▁and ▁survey ▁of ▁the ▁mine ▁was ▁in ▁ 1 9 3 4 , ▁with ▁four ▁min ers ▁and ▁fund ing ▁for ▁the ▁extra ction ▁of ▁ 9 4 5 ▁tons ▁of ▁coal . ▁ ▁References ▁ ▁Rem arks ▁ ▁Category : Co al ▁mines ▁in ▁Germany ▁Category : Ge ography ▁of ▁North ▁Rh ine - West phal ia <0x0A> </s> ▁Mon oh ydro gen ▁ph osph ate ▁is ▁the ▁in organ ic ▁ion ▁with ▁the ▁formula ▁[ HP O 4 ] 2 -. ▁Its ▁formula ▁can ▁also ▁be ▁written ▁as ▁[ PO 3 ( OH )] 2 -, ▁which ▁shows ▁the ▁presence ▁of ▁a ▁O - H ▁bond . ▁ ▁T ogether ▁with ▁di h ydro gen ▁ph osph ate , ▁mon oh ydro gen ▁ph osph ate ▁occurs ▁widely ▁in ▁natural ▁systems . ▁ ▁Their ▁sal ts ▁are ▁used ▁in ▁fert il izers ▁and ▁in ▁cook ing . ▁ ▁Most ▁mon oh ydro gen ph osph ate ▁sal ts ▁are ▁color less , ▁water ▁sol ub le , ▁and ▁non to xic . ▁ ▁Ac id - base ▁equilib ria ▁Mon oh ydro gen ph