 Nickel tetracarbonyl is considered carcinogenic, but it can take 20 to 30 years from the start of exposure to the clinical manifestation of cancer.Initial experiments on the reaction of carbon monoxide with metals were carried out by Justus von Liebig in 1834.By passing carbon monoxide over molten potassium he prepared a substance having the empirical formula KCO, which he called "Kohlenoxidkalium".