328 LEFEBURE : ABSORPTION OF GASES BY CELLULOID.XXXVL-Absorption of Gases by Celluloid.By VICTOR LEFEBURE.THE discovery of the fact that celluloid films will take up gases wasmade in an indirect manner. It was proposed to use celluloidfilms as a basis on which to deposit plant pigments, in order t oexpose as large a surface as possible of the pigments to the actionof certain gases. Amongst these gases was carbon dioxide, and onattempting a control experiment, using simply celluloid film andcarbon dioxide, the film was found to take up a large quantityof gas.Considerable work has been carried out on the absorption ofgases by membranes. The object of most of it, however, has eitherbeen to demonstrate the specific nature of diffusion through themor to establish a parallel to some physiological process in livingorganisms (compare Hill and H.E. Ridewood, Proc. Physiol. SGC.,Few and more recent exp0riment.s have been concerned with theactual determination of the nature of the phenomenon by quanti-tative methods. Doubt still exists, however, on two essential points.First, the exact nature of the absorption in any particular case isnot clearly established. Secondly, it is not known whether thereis a general mechanism.We cannot experiment on the first point without throwing lighton the second.I n view of these facts, and knowing that celluloid offered certainadvantages for experimental work, the, experiments to be describedwere carried out. Both purely qualitative and actual quantitativeexperiments were commenced.Most of the latter are not yetcomplete.The apparatus and working method were common to all theabove so-called qualitative experiments, and were as follows :The absorbing material was placed in -4 (Fig. l), a tube con-nected by a mercury seal with the rest of the apparatus. T, ledto a mercury pump. All the taps wereopened except T3, leading t o the gas reservoir, and T4, leading tothe atmosphere. The whole apparatus was freed from all gas,using the mercury pump, in the circuit of which was a phosphoricoxide tube. That a vacuum could be obtained over celluloid wasfound by leaving the exhausted apparatus, containing that material,1899, 13-19).G was a mercury gaugeLEFEBURE: ABSORPTION OF GASES BY CELLULOID. 329overnight. After twenty-four hours the apparatus was stillvacuoiis.Gasentered up to 1', and into the tube B, and it was admitted to theactual apparatus by judicious use of T, and previous adjustmentof R until the gauge G indicated atmospheric pressure.The wholeoperation of entry of gas did not occupy more than ten seconds.Any absorpt>ion now occurring would cause a rise in the gaugeT I and T, were now closed, and T, and T, were opened.FIG. 1.R iarm y. This rise, measured at equilibrium, gave, for differentsamples in A , a comparativ'e measure of the absorption. Themeasure might be thought untrustworthy owing to gas being takenup during the few seconds of entry. This correction was foundt o be small, and, further, a small heat evolution accompanyingabsorption must have neutralised this initial error,It should first bO mentioned that all the gas taken up by thecelluloid could be pumped off in a few hours.The following tables give the results of the experiments :VOL.cv. 330 LEFEBURE : ABSORPTION OF GASES BY CELLULOID.Material.Kinema film ......Xylonite ..........Greenberg's Cel-luloid .........Viscose .............ArtXcial silk ....Gelatin ............." Precipitate . ' ...2a. {Refilmed film ....3. { Nitrocellulose ....Camphor ...................Celluloid ............Charcoal ..........Caoutchouc2b. [ ......Weightof film.Grams.1013.710101010106101010101010Pressure differenceTemperature. in cm. of mercury.18 36.723 38.718 37.150 44-518 2.6518 4.218 8.918 6.022.418.0< 1.0Volume Absorbed at N.T.P.40 C.C.approx.100 7 ) 7 )5-10 y y 9 7The conclusions to be drawn from these experiments may besummarised as follows :Series 1.-The effect is common t o all kinds of celluloidexamined.Series 2.-The effect is relatively specific for celluloid in so faras the materials examined were concerned (with the exception ofcaoutchouc and charcoal).Series 3.-The effect is not retained by the precipitated material(made by pouring the acetone solution into water). It is recoveredto a large extent by the refilmed film. A more complete accountof work on this " precipitate " is being prepared.Experiments made by substituting for carbon dioxide the gasesair and hydrogen showed the relative magnitudes of the effects tofollow the same order as that in which the gases are mentioned,hydrogen being the least absorbed.Finally, diffusion of carbon dioxide through celluloid films wasestablished.The quantitative experimenk, the chief object of which was todetermine the mechanism of the effect, were, and are, being carriedout along three distinct lines.The experiments include determinations of :I.Rates of absorption a t varying ( a ) temperature, ( b ) pressure,11. Equilibrium curves under varying conditions.111. Rntes of difficsion under varying conditions.Dispersivity is a term which has been used to express the ratioof tho total surface of a substance to its total volume.I n the aboveexperiments it is used in the sense of the ratio of total measurableexternal surface t o total voluine, unless otherwise stated.( c ) dispersivity (defined below)LEFEBURE : ABSORPTION OF GASES BY CELLULOID. 331Determinations of I and I1 have already been made, andalthough the data obtained are not yet complete enough t o yieldany definite conclu~ions, yet the curves will be given and theirfeatures indicated.I.-Bates of Absorption.The apparatus used will now be described, and a t the same timethe general experimental method given.FIG. 2.The experimental t.ube T, (Fig. 2) rested against a scale S etchedupon glass. I', was connected by means of the four-way piece F to(1) experimental bulb B through C, (2) mercury pump through P,and (3) gas reservoirs through R.From below T, was in connexion with another clean tube T,through a tap A of large bore (to ensure freedom of movementof mercury column).2 332 LEFEBURE : ABSORPTION OF GASES BY CELLULOID.For a determination the level, L, in T, was set a t a convenientheight a t the lower end of the scale.With Rclosed the whole cipparatus was completely exhausted. C and Pwere then closed, and gas was admitted from R at normal pressure.C was then opened, and the time taken. As soon as the desiredpressure was attained (seen by the gas reservoir), R was closed andA opened, and readings of time and absorption were taken withthe two levels adjusted. The gap between the first and second timereadings was usually about thirty seconds, and the amountabsorbed during that time was found by extrapolation.This wasmade possible by the close approximation of the initial part of therate curve t o a straight line.A was turned off.Prelimi?mry Rntc. Rendirigs witlb Vnrying Bispersiuity.Rate, curves were obtained for five samples of celluloid, comingfrom the same source, each weighing 5 grams and varying inthickness.Weight.Sample. Grams.1 52 53 54 55 56 5Thickness. Area.Mm. Sq. cm.1-32 -0.75 155.230.52 159-500.33 235.460.25 309.410.10 807.74The curves indicate that as the films become thinner, and withincreasing dispersivity, the effect becomes more like “ adsorption.”I n fact, curve 6 (Fig. 3) shows clearly the two features of aninitial rapid taking up of gas, followed by a very slow one, corre-sponding with adsorption, and later, solution attending slowdiffusion.Observations on Initial Rates.The actual readings of time and absorption reveal better thanthe curves of the last series that the initial rates are practicallystraight lines (Fig.4).A case of pure solution would yield the relationship: initialrate xi area of external surface, other factors remaining constant.The following figures are obtained, however :Sample. Initial rate. Area x.6 26.7 807.7 5-25 11.3 309.4 2.04 5-4 235.5 1.5159.5 1.0155-2 1.0 213 ‘;:;I- - -They indicate that no simple relationship exists, such as oneThe initial rate increases much would expect for tru0 solutionLEFEBURE: ABSORPTION OF GASES BY CELLULOID.333FIG. 3.0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2Time in hours.Broken Ziii c-No readings over this period, Temp. = 18".&FIG. 4.ITime in minutcs334 LEFEBURE : ABSORPTION OF GASES BY CELLULOID.more rapidly tlhan does the area. The initial rate will depend onSOMB factor which will probably be capable of expression a~ afunction of the surface, but is not directly proportional to thesurface. Such a factor might be variation in surface structureowing to conditions of formation of the film, such as evaporationafter rolling.A more definite view will be given when more comprehensiveevidence is acquired.Tlaria tion of Temperature.Just sufficient readings were taken to indicate the general natureof the influence of temperature change.Sample (4) was thoroughlydeprived of any gas held from the previous experiment. RatesFIG 5 .0 1 2 3 4 5 6 7 8 9 l O i l l 1 2 1 3 1 4Time in hours.were then measured a t the following temperatures: (a) 66O, usinga bath of methyl alcohol vapour; ( b ) room temperature, 18O, usinga cotton-wool covering; and ( c ) temperature of melting ice.The curves (Fig. 5) indicate that with rise of temperature thereoccurs small khange in rate of absorption but a decrease in totaleffect.It will be noticed that the initial rise in the curve, due presum-ably to adsorption on a rapidly attained surface, is not accentuatedin the case of the ice-temperature experiment. This may be takenas another indication of the fact that any truly external surfaceis small compared with internal adsorption and solution. Interest-ing results are expected with curves for the temperature of boilingcarbon dioxideLEFEBURE: ABSORPTION OF GASES BY CELLULOID.335E p ~ i l i b rium Curves.The burette used t o measure gas absorbed a t varying pressureswas similar to that used by Travers and Miss Homfray in theirinvestigations on gas absorption by charcoal. The author isindebted to Miss Homfray for the use of parts of her originalburette.The entire system, including gas generator, point burette, andgas burette, was, however, complete in itself. Carbon dioxide waegenerated in A (Fig. 6) by heating previously dried and pure mag-nesium carbonate. The gas passed through phosphoric oxide in B,and was collected by the pump C, which also served t o exhaust thepoint burette E.The collected gas was carried in gas jars overmercury to the gas burette D, whence a known volume of i twas passed through capillary tubing to E.Two isotherms were obtained for the temperatures Oo and 1 8 Oby using baths of ice and layers of cotton-wool respectively. TheFIG. 6 .A 3 <POINT BUR€TT€ - PUMP cErelationship between concentration in solid phase and concentra-tion in gas was plotted, and in both cases curves were obtainedintermediate in form between the true adsorption curve and thesolution straight line (Fig. 7). They tended, however, towardsthe straight line relationship, and in this connexion it is inter-esting to note the result of Reychler.This investigator, examin-ing the case of the absorption of sulphur dioxide by caoutchouc,drew the conclusion that it was probably a cast3 of solution. Thethree readings on which the conclusion was based, however, occurbetween the pressures 34 cm. and 59 cm. of mercury. Fromthe curves it is seen that three readings between these pressurelimits might have been interpreted in terms of solution in ourcase of celluloid. I f there is any analogy between the cases ofindiarubber and celluloid, one might imagine that a continuationof Reychler's readings would yield curves similar to those obtainedfor celluloid336 LEFEBURE: ABSORPTION OF GASES BY CELLULOID.General Summary.The wholes of the more preliminary work, both qualitative andquantitative, leads to the conclusion that the phenomenon isanother case of adsorption? or a combination of adsorption andsolution.We are then faced with the question as t o what is theadsorbing surface. There are three possibilities, namely, I. Actualexternal surface seen by the naked eye. 11. A surface of a similarnature, between celluloid and gas, presented by a porous structuredeveloped within the celluloid mass, and in view of the observationsbelow, probably near t o the external surface of the celluloid; andFIG. 7.0 10 20 30 40 50 60 70 80 90 100Pressure of c'wbon dioxidc in em. of mercury. Weight of film = 8 grams.111. A surface between two phases which are the remains of thedisperse and continuous phases of the colloidal system whichcelluloid admittedly possessed just previous to solidification byevaporation.These possibilities may be considered in turn, from the pointof view of data already obtained.It should be remembered thatany subsequent explanation is put forward with great reserve,subject t,o change when more data are acquired.I. I f this be the state of affairs, then it can be detected fromthe isotherms f o r equal weights of celluloid with different surfacLEFEBURE : ABSORPTION OF GASES BY CELLULOID. 337development. Considering the small variations of external surfaceexposed in the, rate and equilibrium experiments already made, itis highly improbable that mere external surface is the only factorin the adsorption.11. It should be noted, however, that in the rate experiment withthe thinnest film, where the rate curve indicated a true adsorption,the part of the curvy indicating adsorption accounted for morethan nine-tenths of the total gas taken in, and the time was lesstha.n one hour.Now this large initial effect must be concernedwith some part of the celluloid which can be attained withoutslow diffusion, for in the experiments with the thicker films, wherethe influence of diffusion is greatest, hours passed before one-thirdof the total ,gas had been taken in. We are thus led to concludethat the initial effect, which becomes so large with the thinnestfilm, is Concerned with some easily available surface between gasand celluloid. Such a surface might be caused by a developmentof porous structure within the mass, and near to the externalsurface of the celluloid.The experiments giving initial rates can now be appropriatelyconsidered.They indicated that a factor in absorption was somefunction of the actual external surface, increasing from film (1) tofilm (6) more rapidly than external surface. This factor, it wassaid, might be concerned with conditions of formation of the film,possibly some evaporative process. Porous structure would, nodoubt, be influenced by this process; thus the two lines of evidenceare capable of a similar explanation, that is, one in terms of adevelopment of porosity at the surface.111 The surface between disperse and continuous phases will,no doubt, play an important part in the phenomenon, but itsinfluence will not be discussed until more is known with regardto rates of diffusion through celluloid.The author desires to emphasise the tentative nature of theabove obseivations. The primary object of this paper is to presentthe general nature of the phenomenon, rather than to give i t acomplete explanation.The author wishes to express his gratitude t o Sir William Ramsayfor the active interet taken in ths early stages of this research,and his great indebtedness to Professor F. G. Donnan and Dr.Whytlaw-Gray for help received throughout the work. He alsowishes to acknowledge the kind assistance of Mr. R. S. Felgate inthe determinations of rates of absorption.UNIVERSITY COLLEGE,GOWER ST., W.C