lugust, 1932
I N D U S T R I A L A N D E N G I N E E R I N G C H E M IS T R Y
that the synthetic lignin made from hardwood cellulose, and evidently formed largely by the decomposition of pentosan units, has a n absorption spectrum and a reducing value that correspond closely to a typical hardwood lignin, while the synthetic lignin made from a softwood cellulose, and evidently formed largely from hexosan units, has a reducing value corresponding closely t o a typical softwood lignin. (The authors have not yet had opportunity to measure the absorption spectrum of such a sample.) This information leads directly to the hypothesis that the differences between natural hardwood and softwood lignins are due to the relative proportions of hexose and pentose units that have entered into their formation. This hypothesis will be developed further as the next step in the research on synthetic lignins. It should be readily possible t o prepare lignins from
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pure pentosans, pure hexosans, and known varying proportions of the two, and thus to establish the relation between the source and the characteristics of the product. LITERATURE CITED (1) Hawley and Wiertelak, IXD.ESG.CHEV.,23, 184 (1931). (2) Ritter, Mitchell, and Seborg, paper presented before the Division of Cellulose Chemistry at the Sard LMeeting of the American Chemical Society, New Orleans, La., March 28 to April 1, 1932. (3) Ritter, Seborg, and Mitchell, IND.ESG.CHEW.,Bnal. Ed., 4, 202 (1932). (4) Schrauth, Z.angew. Chem., 36, 149 (1923). ( 5 ) Sherrard and Harris, IND. EXQ.CHEM., 24,103 (1932). (6) Stamm, Semb, and Harris, J. Phus. Chem., 36, 1574 (1932). RECEIVED March 28, 1932.
Light-Reflecting Characteristics of Paints D. L. GAXBLE,Research Division, The New Jersey Zinc Company, Palmerton, Pa.
N INDUSTRIAL lighting we are interested p r i m a r i l y in maintaining the proper level or intensity of illumination a t the lowest possible cost. To accomplish this, we must conserve as much of the light energy radiated into the room as possible and also distribute this energy over the working planelso as to useitmost effectively. Both the amount of light a wall coating is capable of reflecting and the manner in which the incident r a d i a t i o n is reflected are factors which determine, to a certain degree in any given case, just how successful we may be in obtaining the desired conditions of illumination.
“milk” glass. Most surfaces exhibit
a c o m b i n a t i o n of both imperfect
specular and diffused reflection. This condition is illustrated in diagrams D and E.
Paints fall into this class of surfaces. The amount of specular reflection given by paint films pigmented with the usual crystalline type pigments depends upon the degree of surface perfection or freec dom from irregularities exhibited by the overlying oil film. Specular reflection from a clear oil film, bePLRTCCT SPECULAR KCILCCT’DY S.FERMPOSED ON PEWEC? DICTUSE W U C T C U cause of the relatively low lightabsorption coefficient of the clear I oil, is of the so-called vitreous type, and, t h e ref o r e , at intermediate a n g l e s of incidence the specular reflecting power of even a perfect oil surface w o u l d p r o b a b l y not REFLECTION CHARACTERISTICS O F greatly exceed 5 per cent as comrlETALLIC PAINT O r LEAFIUG TIPI WHITE W L L PAIN? PAISTS pared t o 90 per cent or more for the FIGURE 1. TYPESOF REFLECTION metallic reflection exhibited There are two distinct types of by polished metal surfaces. The reflection-namelv, diffused reflection, and specular or regular reflection. These two types specular component of even high-gloss films is, therefore, are graphically illustrated in Figure 1. relatively small as compared with the diffused body reflecA perfect specular reflecting surface is illustrated in diagram A . tion arising from the pigment. Thus, films pigmented with In this case the reflected light passes off in a single direction so crystalline-powder pigments are essentially diffusers, and, that the angle of reflection, R, is equal to the angle of incidence, in order t o obtain finishes of relatively high specular reflectI . This type of reflection gives rise to mirror images. A polished ing power, i t is necessary to use special pigments such as mesilver surface reflects in this manner. Diagram B illustrates a tallic powders of the leafing type. perfectly diffusing surface. In this case the surface acts essentially as a new source of light, and the incident energy is hIEASUREMENT O F REFLECTION FACTOR reflected in all possible directions. The intensity of reflected light in any given direction is proportional t o the cosine of the It is obvious from the diagrams of Figure 1 that, if only angle of reflection measured from the normal to the surface, and is independent of the direction or manner of illumination. the light reflected in a single direction is measured in deterFumed ma nesium oxide approaches very closely a perfect diffuse mining the reflection factor, the value thus obtained may vary reflector. I n these diagrams the vectors indicate the relative considerably with the direction of viewing. The apparent amounts of light reflected in the various directions. Only in reflection factor would also depend upon the manner of the case of specular reflection do they necessarily lie in the lane illuminating the surface. Reflection factors; therefore, have of the paper. Diagram C represents a surface which exfibits perfect specular reflection superimposed upon erfect diffused little significance unless the conditions of measurement are reflection. This condition is approached by a Righly polished definitely specified. To avoid as much confusion as possible, the Illuminating Engineering Society has defined the re1 T h e t e r m “working plane” refers t o t h e horizontal plane across t h e room flection factor of a surface as the ratio of the total light flux in which t h e worker observes objects-for example, t h e plane of a desk t o p or work bench. reflected by the surface to the total light flux incident on
the suriwc:i:. Tliis v d i i e way lie dehermined by iiirasuririg the airparent rr4rctioii fact.ors at vwiIKIS ariglcs of vicwing, a r i d illt,egratiiig t i i t * nisolts ti> rr1)tain t,lie t
