THE Perkin Medal of the American Section of the Society of Chemical Industry has this year been awarded to Dr. Thomas Midgley, who has achieved world-wide fame for his discovery of tetra-ethyl lead as an anti-knock agent. This, it should be emphasized, was no chance discovery but the result of systematic trial following a study of the periodic system, the final finding that the lead derivative would solve the problem being predicted beforehand. To-day ‘ethyl’ is added to seventy per cent of all the petrol used in America, and the increased horse-power thereby generated amounts to a very large figure. In a characteristic address given at the time of receiving the medal, Dr. Midgley told the story of his more recent discovery of a compound of carbon, chlorine and fluorine, CHC12F, to be used as a refrigerant, which is non-toxic and non-inflammable. Apparently he was told of the need for a new refrigerant over the telephone, and with the aid of two colleagues, the use of a chemical library and some deductions from the periodic table, arrived at the probability that the above fluorine compound might prove non-toxic and suitable. Small quantities were prepared from various samples of available starting material. The first batch was pure and proved non-toxic; in the others the raw material proved to be contaminated and gave toxic products, which, however, could be purified when this fact was realized, and became non-toxic. Three days' work sufficed to solve the problem and to give the refrigerating industry a new material which is expected will prove of outstanding importance in its development.