ANHYDROUS AEROSOL HAIR SPRAY SYSTEMS 303 due to the CClaF only. Furthermore, it was established that not all CClaF showed this characteristic, only certain lots from a particular plant. Since all of these reactions were carried out in glass, it ruled out the partici- pation of tinplate in this reaction. It was therefore decided to study the effect on pH of the addition of very small amounts of hydrochloric acid to anhydrous ethyl alcohol. To effect these minute additions, a glass rod wetted with anhydrous alcohol was passed into the head space of a bottle of concentrated hydrochloric acid and then dipped into the alcohol. The same procedure (glass rod wetted with anhydrous ethanol) was followed with distilled water. Figure 2 shows the procedure that was followed, and Fig. 3 shows the results with one, two, and three passes of the glass rod into the bottle. As can be seen, pH VALUES in DISTILLED WATER and ANHYDROUS ETHYL ALCOHI.)L Contact T•me of p H Glass Rod Over Top Anhydrous of Bottle Ethyl Distilled Concentrated HC1 Alcohol Water , , 0 * 7.8 7,0 1 0.9 4, l 2 0.6 3.9 3 O,5 3.6 Figure 3. the pH has dropped down to 0.9 in the anhydrous ethyl alcohol with one pass of the glass rod, whereas in the water the pH is 4.2. It is apparent from this that pH is a sensitive method of detecting minute amounts of hydrochloric acid formation in anhydrous ethanol. Figure 4 is a graph showing the effect on pH of a strong acid (HC1) and strong base (NaOH) in anhydrous ethanol as compared with water• As can be seen, as little as 0.00005N HC1 drops the pH in the alcohol down to 2. The pH change in the alcohol with sodium hydroxide is also greater than that in water, except that this reverses at concentrations over 0.0001N. Figure 5 is a graph showing the effect on pH of a weak acid (acetic) and a weak base (NH4OH) in anhydrous ethanol as compared to water. As can be seen, the pH change is less in anhydrous ethanol than it is in water, except at the point where the lines cross. Most hair spray concentrates have a pH slightly above 7. Figure 6 shows the pH of 5 different resin base hair sprays. With propellents that have passed the stability test previously mentioned, only shellac base hair sprays have been known to drop in pH on shelf aging with resultant corrosion of the container. Figure 7 shows the pH of samples of an

3O4 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 4.--pH values of a strong base (sodium hydroxide) and a strong acid (hydrochloric) in anhydrous ethanol and water at various esterified shellac base hair spray after four years of shelf testing. The samples that had the low pH were discolored, and the cans were badly corroded. Figure 8 shows the appearance of the can that contained Sample No. 5. The pH was down to 2.5. The perfume had turned sour and the color of the product was dark brown. Analysis of the product showed only 1.5 p.p.m. iron and 23.8 p.p.m. tin. Figure 9 shows another container with the same product in which the pH remained at 5.9. Here the container is clean and unaffected. The product retained its light color and its odor. Invariably a drop of pH to below 3 results in considerable container corrosion and product deterioration. From periodic analyses of shelf life samples, it appears that pH drop occurs first, followed by corrosion and product deterioration. Conductivity Figure 5.--pH of a weak acid (acetic) and a weak base (NH4OH) in anhydrous ethanol and water at various concentrations.