186 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS tion of lime, which Winkel's patent mentions as a suitable example of exothermic'reaction. Among the many reactions studied, the oxidation-reduction type of reaction involving the oxi- dation of a metal like aluminum with an oxidizer like a chlorate offered the most possibilities. The explosive violence with which alumi- num combined with an oxidizer to generate a very intense heat and high temperature had been put to use in the metal thermit welding units of Goldschmidt. ' A1 -{- Fe20• --• A120• -{- Fe -{- A How to control this type of reaction became the subject of a research program, giving rise to the invention specified in the Evans and McDon- ough patent U.S. No. Re 22,660. In this research .program it was found that the reaction must involve an electron transfer through a solu- tion means rather than a direct combination of materials. Even with this type of reaction the re- action can either be so slow as to generate no perceptible heat or so violent that the steam development will drive out all the water and will generate temperatures giving rise to direct combination which, of course, results in heat of the intensity of bombs. Means for smoothing out the electron transfers therefore became a problem which was solved through (1) the use of materials to control the hydrogen ion, particularly at the start of the reaction, and (2) the inclusion of materials which would give rise in the reaction mixture to catalysts for example, a nascent metallic element like copper, which would assist the aluminum metal in the loss of electron and a metallic ion like the cuptic ion which would assist the chlorate ion in the accept- ance of the electron. The inclusion of an absorbent material within the mixture is a necessity not only to give body to the water solution but also to pre- vent spontaneous combustion which might result from direct combina- tion of the reducing a•ent and oxidizing agent if only they were mixed together and subjected to high storage temperatures on mechanical attrition. Compositions utilizing the oxida- tion of a metal like aluminum to generate heat for the permanent waving of hair have been disclosed in the Racen U.S. Patent 2,183,587 and Reed's U.S. Patent 2,208,815. The impervious perforable en- velope of Winkel was made of aluminum foil, and so far no better substitute material has been found, even though during the war numer- ous substitutes had to be resorted to. The element carrying the water in Winkel's original pad was flannel, and .while he specified that it must be adapted to be wet with a liquid and that it must give up through the perforation a part of the liquid to the exothermic mixture, never- theless, the flannels were a source of trouble. This was due to the fact that it was hard to get flannel having the standard properties for speedy

DEVELOPMENT OF MACHINELESS PERMANENT WAVING 187 wetting, a capacity for absorbing a uniform weight of water per area and giving up a uniform amount to the exothermic chemical. Investigation of this problem re- sulted in the study of many mate- rials, none of which solved the prob- lem. In the study of papers as an absorbent, Evans and McDonough finally developed a special element primarily composed of multiple layers of crepe paper. This absorb- ent had the water absorptive, wet strength, and water-releasing char- acteristics desired. This invention was the subject of U.S. Patent No. 2,151,692. While the reaction within a machineless pad proceeds automat- ically, nevertheless, we felt that if the operator had visual evidence that the pad was functioning prop- erly, it would not only be an assur- ance and an aid to the operator in checking that she has performed her task properly, but it would also serve to show when the wave was finished. To accomplish this it became necessary to create a pad which contained this signaling unit. By using a combination of mercuric iodide and cuprous iodide, we were ' able to arrive at a pigment which exactly changed colors at hair wav- ing temperatures and reverted to its original color to show as it cooled down that the pad could be removed without affecting the curl. This invention is described in Evans and McDonough U. S. Patent No. 2,196,201. Other improvement modifications of the original Winkel patent which deserve mentioning here are the following inventions. As a means of briefly indicating the scope of the invention one or more claims will be given. The patents are divided into related types of improvements. The first of the following group are directed toward a pad construction which has become increasingly pop- ular since the war, the pad con- struction being adopted by the so- called "oil-fired" m•chineless wav- ing discussed in the second group of patents below and also by the built- in absorbent of the unitary pad- so-called "water-dipped" pads. U.S. Patent No. 2,051,667 to ¾. Worth is the most basic of this group of pads as can be seen from the following two claims: C1.1--a hair waving pad comprising an outer layer of non-absorbent material and an inner layer of absorbent material containing an exothermic material CI. 13--a hair waving pad including a flexible pervious envelope and a backing of flexible material. U.S. Patent No. 2,349,285 to F. Korf and W. Zentler is next most basic as can be seen from C1.28: A hair waving pad comprising a layer of impervious non-soluble material, a layer of porous, absorbent mate- rial, chemical means disposed be- tween said porous and non-porous materials, and means for holding said layers together and confining the chemical means therebetween, thus forming a unitary pad which requires only the application of a liquid to be ready for use. U.S. Patent No. 2,110,667 to F. Racen is a specific type of con-