XI-Ray Diffraction Study of Fractionated Paraffin Waxes' George L. Clark and Howard A. Smith 1'SLraxsiru
OP ILLINOIS, U W S A N A ,
ILL.
A n x-ray diffraction study of fractionated paraffin I K W 1888 mucli interportantfuiictiou is to give the wax samples, previously studied by other methods, est has been showii conlength of the molecules, was proves that no fraction can he a pure compound and cerning the composition obtained by placing a speverifies the conclusion that paraffin wax is composed of paraffin was. The history cially prepared sampIe of the only of normal and isoparaffinic hydrocarbons. of the devplopment and ihe wax in an oscillating speetrnDiffraction patterns are unusually interesting in classification of the ideas congraph such as that shown in showing that the higher the melting point the greater cerning its constitution have Fignre 1. The type of photothe number of orders for the identity period correbeen briefly outlined by Fergraphs given by this method sponding to molecular length indicating more perfect ris,Co&s, and Henderson(4) is strikingly i l l u s t r a t e d in orientation. Only five different hydrocarbons---viz., and ltuchlcr and Gravps ( I ) . IN'igure 3. F i g u r e 2 illusthose with 29, 31, 34, 38, and 42 carbon atoms--impress Within the last decade the trates the method of taking their own spacings on the sixteen fractions. Two new widespread use of x-rays for these photographs except that constituents, GaHv8 and CnHsa,are recognized for the the examination of all sorts of the plate is lield stationary first time. materials has included within perpendicular to the central It is shown that the x-ray diffraction method can be its scope tliis question of the beam. of considerable aid in evaluating crude waxes as to the composition of paraffinwaxes. The sainplcs required for amounts of normal and isoparaffin molecules present. Although there has k e n eonthis method must be carefullv siderable x-rav work done on and identically prepared (3, long chain organic compounds (14, lti, 19) which help much 16) if the results arc to be a t all comparable. The sample in interpreting x-ray data, inention tias liecn made of only was melted on a elcan, dry micromope slide immediately after two studies of ihis complex roixture of hydrocarbons, one the slide had been removed from a coilstarit-~mperatureoven by Piper, Xrown, and Dynicnt (15) and one by Clark ( 3 ) . maintained at 150" C. Rapid cooling was allowed to take place until solidification occorred. The film of wax thus formed prevented the slide from adsorbing a film of moktnre. The slide was then heated on a special electric hot plate until fusion of the was occurred. The current input to the hot plate was t.lien controlled so that the sainpie solidified from just above to just below tlie melting point, in 15 minutes. The hot p1at.e and the sample were then allowed to cool to room temperatore. This time of solidifieat.ionis an intermediate value as compared with thetimesused by Clark (3). The essential feature of this type of sample is a very thiu film,all the molecules of which are oriented as completely as possible in a direction perpendicular to the glass hacking. The one variable, difficult of control, which entered into the preparation of these semples was the thickness of this film., However, the only effect of this variable, if kept within reasonable limits, is to require a lit,tie longer time of exposure. Eieure 1 Oscitla
