THREE PRIME FACTORS IN SUCCESSFUL PACKAGING 15 istics. It is white in color, although not as efficient as Vinylire or Pana- seal mo. unted on pulpboard or newsboard. Since the liner repre- sents a very small factor in total package cost, price consideration should have very little influence on the manufacturer's selection of the liner to protect his product. Unless the liner provides maximum pro- tection for the product, it is worth- less at any price. Furthermore, while a liner may satisfactorily seal a product marketed by one manufac- turer, it does not follow that another product of similar nature (but with a slight change in formulation) will be satisfactorily sealed with the same type of liner. To obtain the most dependable liner, laboratory recom- mendations by the cap manufac- turer should be obtained and the cap manufacturer's recommendation should, in turn, be checked by the laboratory of the manufacturer who packages the merchandise. Often it is desirable to run tests for ex- tended periods of time. Screw caps should be applied to containers with a proper tightening force: With too little force, the liner may not be properly seated and leakage may result. With to• great force, the threads or top finish in metal caps may be distorted and. molded caps may be broken. Again, if the caps are too tightly applied, they may be difficult to remove, causing customer dissatisfaction. Studies conducted by the Pitts- burgh Testing Laboratory for one of the cap companies, indicated that the average housewife could exert a force on a 28 min. cap equivalent to 33 lbs. tangential, or 17.95 torque inch pounds to remove a screw finish cap. This force is therefore the maximum that should be applied, and laboratory experience has indi- cated that it is not necessary to reach this limit to produce an effec- tive seal with properly chosen liners and good glass finish. The torque inch pounds, of course, will depend upon the diameter of the cap and the number of threads per inch, and will vary from 4.75 torque inch pounds in a 15 min. cap to 95 lbs. for 120 min. caps. Waxed liners reduce the friction between the liner itself and the glass finish consequently, the caps can be applied furthee than normal, and the application of caps with such liners should be studied carefully to avoid excessive tighten- ing. As has been indicated, the liners can be attacked by various products. This is also true of glass containers. The better glass companies now pro- duce glass which is of good chemical durability. The common container glass several years ago was quite high in soda, and would cause a change in pH in a neutral product. As a matter of fact, some of the glass would show a definite alkaline reac- tion to phenol-phthalein when ar- bon dioxide-free distilled water was placed in the bottle, and the bottle then placed in a water bath and the temperature raised to 90øC. and held for one hour. The glass which showed this reaction would deft- nitely. produce flakes or spicules in water or in 50-50 alcohol and water.

16 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS A product having a pH of approx- imately 6.8 when packaged, after six months or a year or more at room temperature, might change to a pH of 8.5 or 9 and definitely show flakes. The smaller the container, the greater is the relative change, for the change depends on the sur- face-to-volume ratio. A 2 oz. bottle will show more alkali extract than will a 32 oz. container, since there is more surface with respect to the contents in a smaller container. Glass with poor or low chemical durability will "weather" or show crystal growth on the inside surface when exposed to damp or humid conditions of storage before use. This crystalline growth has been considered as a mold growth by some observers, though culture tests and examination under a' microscope definitely indicate that it is a condi- tion on the glass surface due to the glass itself, and not due to mold. A dilute acid rinse has been used in the past to reclaim such containers, though glass of good chemical dura- bility, low in alkaline extract, will not show the weathered condition. Acid products do not show any attack and only a slight change in pH when packaged in glass of poor chemical durability, so it is possible to introduce organic acids such as malic, to lower the hydrogen ion concentration, and thus prevent the formation of flakes or p.recipitates due to the glass. Borosilicate glasses are not alka- line in nature, consequently have good chemical durability. They are about five times more expensive than the better commercial glass containers and their use is indicated only for special biological and pharmaceutical use. The three major factors in pack- aging have been discussed in some detail with special reference to the container and the closure. It is apparent that there is a very close relationship of these three fac- tors and each should be considered in relation to the other two. Best results can be obtained by close cooperation between the technical staffs of the customer and the producer of the closures and con- tainers.