COSMETIC KNOWLEDGE THROUGH INSTRUMENTAL TECHNIQUES 129 field of chemistry. For example, it can be used to demonstrate how a variety of common writing inks consist of a number of colors. The inks are spotted onto ordinary filter paper and allowed to dry. The paper is sus- pended from a trough containing an organic solvent which flows by cap- illary action down the paper. The dyes in the writing inks have different solubilities in the solvent flowing past them and different affinities for the filter paper. As a result, they migrate from the starting point at different rates so that after a few hours the mixture is resolved into its components. These can usually be identified chemically or spectrophotometrically or by the rate they have moved down the filter paper. The entire apparatus is kept in a sealed glass cylinder to prevent evaporation of the solvent from the paper. From dyes in writing inks it is a short step to dyes in hair coloring com- positions. Chromatograms of a commercial brown hair dye are shown in Fig. 1. To ensure complete resolution, a number of solvents were used to examine the dye mixture. These different 'solvents caused the dyes to migrate at different rates. This is very useful for identifying unknown constituents, as it is a very characteristic property. Dyes are fairly easy to separate because they are often quite similar in chemical composition. Oddly enough, it is the mixtures containing unre- lated substances that often give the most trouble in paper chromatography. A good example of such a mixture is a waving lotion which might contain a 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0,7 0.8 0.9 1.0 14 Ninhydrin 13 Alkaline KMn04 + NolO,, 12 AgNO3 + K2Cr207 11 NctN s + 12 10 Dichlorophenolindophenol 9 AgNOs+ NH40H 8 AgNOs + ultra violet 7 KOH + sodium nitroprusslde 6 Platinic Iodide 5 Nesslers 3 B•'omophenol blue+AgNOs 2 HIO4+benzidine 1 Ninhydrin + aseorbie acid NH4•I • Mo•oethnnolnmine ? Thiogl•olic •::id Monoethanoldmine hydrochloride Thioglycerol Figure 2.--Copy of a typical paper chromatogram of a waving lotion. Rs = rate of flow value, •/b = absorption and B = bleach.

130 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS mixture of mercaptans and bases. Figure 2 shows a diagram of a paper chromatogram of such a mixture. Since the components have no color of their own, they have to be visualized by using chromogenic reagents. These are usually sprayed onto the paper to locate the separated constit- . uents of the lotion. A large variety of visualizing agents (up to 19) are : used to make sure that all the substances in the mixture are detected. The .. paper is cut into strips, visualized and then reassembled to give the pic- . ture shown in Fig. 2. The positive and negative reactions of each sub- . stance are very useful in identifying the components. Space does not per- . mat giving all the experimental details here, but it is hoped to publish this i work separately. GAs CHROMATOGRAPHY The principle of gas chromatography is identical with that of paper' chromatography. A mixture of substances is made to move as vapors through a column containing an inert powder, such as crushed fire-brick, which is coated with a high boiling liquid. The vapors are carried through the column by a carrier gas, usually helium. They move at different rates depending on the temperature of the column and the solubility of each vapor in the high boiling liquid coating and take different times to pass through the column. A sensing device continuously compares helium, the gas entering the column, with the gas leaving the column. If any sub- stance besides helium comes off the column, the difference is noticed, and an electrical signal is sent to a strip-chart recorder. The resulting peaks each represent at least one compound. When analyzing complex mixtures, one peak may often represent more than one compound. Thus, rechromato- raphang material, especially that represented by an early eluted peak, on a column bearing a different type of high boiling liquid often will reveal it to gcontain many substances. Gas chromatography has a very important variable not possessed by other forms of chromatography, namely temperature, and, by using high temperature apparatus, oils boiling even in the 250-300øC. range can be separated. Gas chromatography has been used for the separation of perfume con- stituents and flavoring substances. The tremendous power of this method was illustrated by the work of Dimick and Corse (3) on strawberry flavor, which they were able to resolve into over 30 components even though l they found it only occurred to the extent of about eight p.p.m. in the straw-. berry. As in any new method, precautions must always be taken. Figure 31 shows the results of using gas chromatography to examine an oil. The Gill was in toluene solution so it seemed logical to assume that the big peak was• toluene and that the smaller ones were constituents of the oil. However, I