Studying the problem, [Chevallier-Appert] decided that higher degrees of heat were needed in cooking. The apparatus called the autoclave, a closed vessel in which steam under pressure gave heat much greater than boiling water, had never been used for cooking food, however, and there was danger of over-cooking, because it lacked apparatus to measure and regulate the heat. Chevallier-Appert equipped the crude autoclave with another crude device, a manometer, which had been used for measuring heat in boilers. It would measure differences of only twenty degrees. He made it an instrument of precision, capable of measuring half a degree, and patented the invention in 1852. With greater heat, and an instrument to measure and control it, the difficulties of canning were overcome to such a degree that in June, 1852, Chevallier-Appert exhibited to scientists a whole sheep that had been cooked and sealed in a huge can in his autoclave four months before.