Although portable chemical chests had existed as early as 1791, they were intended for use by adults, rather than children. Porter Chemical Company’s Chemcraft set, marketed in 1915, was likely the first chemistry set intended for children. By 1950, Porter sold as many as 15 different chemistry sets, ranging widely in price and contents. The A. C. Gilbert Company was another leader, producing toys that promoted a wide variety of science activities. Their first chemistry sets appeared in the 1920s, and were followed by many others. Gilbert's biology toys included microscopes (e.g. the Skil Craft Biology Lab). Other companies produced biological models such as the Visible Frog Anatomy Kit and human anatomical models such as the Visible Man. In 1950, Gilbert even produced a toy targeted at potential physicists, the Gilbert U-238 Atomic Energy Laboratory, including a cloud chamber with a small amount of radioactive material. During the cold war, marketing slogans again reveal social tensions of the time, asserting that “Porter Science Prepares Young America for World Leadership”.