294 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Oak Ridge without much decay in activity. The radioactive decay is nevertheless fast enough so that it is not likely to become a radiation hazard when it is necessary to give repeated small doses. 2. Radiation Characteristics-- Beta and gamma rays are emitted so that it is possible, and in this case most desirable, to measure the gamma rays which are able to pene- trate intervening tissue to reach the Geiger counter. The beta rays are not counted since they have limited penetrability in matter. 3. Chemical Characteristics-- I TM is chemically identical to ordi- nary iodine, so that the thyroid does not distinguish between the two. Most of us are aware of the use of I TM in the treatment of cancer of the thyroid, Phosphorus •2 in the treatment of certain blood dyscra- sias (4) and the application of col- loidal Gold •ø8 in ovarian tumors, prostate tumors, and metastases (5). Iodine tagged albumin is being used in the determination of plasma volume or total blood volume, and brain tumor localization iodinated globulins for research in antibody formation and diiodothyrosine for studies of thyroid function. The rate at which sodium ex- changes in and out of the eyeball and across blood vessels has been studied with the aid of Sodium% It is difficult to see how one could have discovered the following with- out the tracer method. In 75 seconds after Sodium •4 is injected into one arm it starts being excreted from a sweat gland in the other arm (6). Radioiron has been used to study the effectiveness of whole blood preservatives. The Sulfur •5 and Carbon TM labeled compounds are too numerous to mention. Labeled organic com- pounds of every description are employed every day to delve into the secrets of animal and plant metabolism. A list of these com- pounds and the sources of supply may be obtained from the Atomic Energy Commission (7) and from certain commercial firms. INr)vs•rR•^I• UsEs Let us see what the cosmetic chemist has to learn here. By irradiating piston rings so that part of the natural iron becomes radio- active iron the 1,ubrication value of various oils can be measured in a fraction of time required by older methods and with a much higher degree of accuracy. The transfer of one-millionth of an ounce of metal can be measured in this way. These studies will eventually lead to the design of better Diesel, auto and air engir•es, and lubricating oils (8). In metallurgy Phosphorus a• has been used to study the passage of phosphorus from slag into the mol- ten iron bath and sulfur has been followe.d from the melt into the slag employing Sulfur% Alpha-emitting radioactive sources such as polonium are being used in factories for the dissipation of electrostatic charges where this is a

TRACER CHEMISTRY 295 problem. The highly ionizing alpha particles make the air conducting so that these accumulated changes can leak off. Small sources can be placed inside analytical balances to accomplish the same thing (9). Beta ray gauges, employing Stron- tium øø, are being installed every day in paper mills, rubber factories, and steel mills to measure the weight and thickness of these materials on a continuous basis by a non- contacting method. This type of gauge makes use of the principle of absorption of beta radiation as a function of mass. By tagging sewage with radioiso.- topes it has been possible to explore the extent and course of pollution in our water systems. Labeled sodium has been used to test the enteric coatings of cap- sules. The cleaning abilities of various detergents have been studied by tagging soil (10). TRACERS FOR THE COSMETIC CHEMIST Thus far the literature on this side of the ledger is very small in- deed. I do believe, however, that the little that has been done points the way. The absorption by the skin of mustard gas and lewisite labeled with Sulfur a5 and Arsenic TM, respec- tively, has been studied (11). The tracer method reveals that lewisite is fixed in the epidermis with very small amounts in the dermis. It is also found in hair follicles and some blood vessels. Mustard gas is found fixed in the epidermis and dermis and has been shown to penetrate deeper than lewisite. The absorption of Thorium x in the skin has been studied by the autoradiographic technique to un- cover the route that Thorium x takes after being applied to the skin. This study will eventually attempt to relate the therapeutic effects noted with the radiation effects produced within the complex structure of the skin, (12). ' Cold cream has been labeled and found to penetrate only very slightly in skin. The cancer producing substance methylcholanthrene has been tagged with Carbon TM and found in the cancer produced by it. It is possible to label most of the 2000 ingredients used in cosmetics to study the absorption of these in skin. Radioactive strontium and cal- cium are available to tag these elements in depilatories which base their results on the action of the sulfides of these elements. To what extent does propylene glycol or glycerin function as a percutaneous vehicle? Why not tag these with radioactive carbon and find out? Sulfur a5 labeled thioglycolates can be made readily available to study the action of these on the hair. Does ammoniated mercury pene- trate the skin? A suitable radio- active twin, Mercury 2øa, can be used to resolve this question. The stability of emulsion may be evaluated in a fraction of the time