Calcium cyanamide is the inorganic compound with the formula CaCN2. It is the calcium salt of the cyanamide () anion. This chemical is used as fertilizer and is commercially known as nitrolime. It was first synthesized in 1898 by Adolph Frank and Nikodem Caro (Frank–Caro process). History In their search for a new process for producing cyanides for cyanide leaching of gold, Frank and Caro discovered the ability of alkaline earth carbides to absorb atmospheric nitrogen at high temperatures. Fritz Rothe, a colleague of Frank and Caro, succeeded in 1898 in overcoming problems with the use of calcium carbide and clarified that at around 1,100 °C not calcium cyanide but calcium cyanamide is formed in the reaction. In fact, the initial target product sodium cyanide can also be obtained from calcium cyanamide by melting it with sodium chloride in the presence of carbon: CaCN2 + 2 NaCl + C → 2 NaCN + CaCl2 Frank and Caro developed this reaction for a large-scale, continuous production process. The process was particularly challenging due to the equipment requirements required by the high temperatures during the initial igniter step. This process requires meticulous temperature control since the melting point of calcium cyanamide is only about 120°C lower than the boiling point of sodium chloride. In 1901, Ferdinand Eduard Polzeniusz patented a process that converts calcium carbide to calcium cyanamide in the presence of 10% calcium chloride at 700 °C. The advantage of lowering the reaction temperature by about 400 °C, however, must be weighed against the high amount of calcium chloride required and the discontinuous process control. Nevertheless, both processes (the Rothe–Frank–Caro process and the Polzeniusz-Krauss process) played a role in the first half of the 20th century. In the record year 1945, a total of approx. 1.5 million tonnes were produced worldwide using both processes. Frank and Caro also noted the formation of ammonia from calcium cyanamide. CaCN2 + 3 H2O → 2 NH3 + CaCO3 Albert Frank recognized the fundamental importance of this reaction as a breakthrough in the provision of ammonia from atmospheric nitrogen and in 1901 recommended calcium cyanamide as a nitrogen fertilizer. Between 1908 and 1919, five calcium cyanamide plants with a total capacity of 500,000 tonnes per year were set up in Germany, and one in Switzerland. It was at the time the cheapest nitrogen fertilizer with additional efficacy against weeds and plant pests and had great