______- IND Us1’111 A L A X D EN(ilN&BRING CHEMISTRY
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Vol. 18, No. 11
Microcinematograms of Brownian Movement in Rubber Latex and of the Dissection of Single Latex Particles with the Micromanipulator’” By Ernst A. Hauser MBT*LI.UANB.FBINXFURT A X MAIN, GBPMANY
H E motioii picture, prepred in the of I h s t A. Ifauser and shown during the Raw Rubher Symposium, is divided into three parts.
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Examination of Latex under High-Power Microscope
The first reproduces the phenomena which are observed when I-Ievea latex is examined under a high-power microscope with dark field illumination. Numerous globular particles are in rapid zig-zag and vibrating motion, such as is always observed for minute suspended particles. This motion is called the Brownian molecular movement after the English botanist Brown, who first discovered the plienomenon in suspensions of pollen. Although many theories have been advanced to explain the cause of this motion, it is now generally agreed that it is the result of momentary shocks caused by the bombardment of the particles hy the molecules of the liquid medium. The important researches of Perrin and others have established the fact that the kinetic laws which govern gases also apply t o the motion of colloidal particles, even though one of these may have one hundred million timcs greater mass than a gas molecule. Perrin has actually determined the Avogadro number (number of niolecules in one niolecular weight) from measurements of Brownian movement. This inicrocinemat.ogram also clearly shows the wide diversity of sizes and shapes of the latex particles. I n Figure 1 an enlargement of one of the individual exposures is reproduced. The actual diameters vary from about 0.5 to 3.0 p (1 p = 0.001 mm. or about 0.00004 inch). Tlie smallest particles (0.5 t o 1.5 p ) are round but the larger ones (1.5 to 3.0 p ) are predominatingly pcar-shaped.
Figure I
Brownian Movement in Vulcanized Latex
The second part of the film shows the Brownian movement in vulcanized latex. The particles appear in somewhat more rapid motion for some renson not clearly understood. They arc predominatingly circular in shape, and more uniform in size than is true of the unvulcanized latex. Several clusters, forming and reforming, are clearly evident. An instantaneous glimpse is shown in the photograph reproduced in Figure 2. Dissection of Latex Particles
The third port.ion of the microcinematogram presents an experimental dissection of a latex particle. The beautiful researches of Hauser and Freundlich wit.h the micromanipnlator and the description of this instrnment are already widely known from the published papers.3 The micromanipulator consists essentially of a high-power microscope with special stage and facilities for illumination of the field, and very fine-pointed glass needles which may be used to move, puncture, or dissect any object observed t,lrrough the microscope. These needles are drawn out from glass by a special technic developed by Dr. IIanser. The points may be so fine that their presence is indicated only by interference fringes. Sunlight has proved to he by far t.he best source of illumination for these experiments. Dr. Hauser did much of the early work along these lines in the Far East. A solarstat or reflecting mirror system was adjusted so that it would automatically reflect the sun’s rays througlmut the day. So painstakingly was this adjustment originally made, in kcoping with all other phases
Figure 2
I Prerntrd undcr the title “The Disoectian ol the Latex Globule Recorded by Micro M o f i Pictures.” ~ :Dexripfioo by George L. Cbrk. Department of Chemical Iingineeiie%. Massachusetts Institute of Technolopy, Cambridge, Mar%.of motion picture ymsemted by Ernsf A. Hauser at the Raw Rubber Symposium.
Figure 3
of the experiments, that the mirror was in pedeet position at the end of three months. htex particie Kolloid-2.. 86. 16 (1925). amoog othera.
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I N D U S T R I A L AND ENGINEERING C H E M I S T R Y
about to he dkected by thc point of the glass needle. The motion picture shows the stroking of the particle with the point of the needle, and the resistance of the outer tough $%.tic skin to rnene.~ - ~ tratjon by the needle p o i n t , as though a toy balloon were bei n g i n d e n t e d by a rod. I”inally, t h e needle pierces the Ititex globule and on the point there is eviclcnce of the viscous liquid xhich constitutes t,he inbexior of t h c s e m i n u t e sacs. Tl,isfit;ige isindicated iii Figure 4. ~
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Interpretation of
Results This ingonious esI,criniorrt, r e q u i r i n g
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stitutes one of the greatest contributions to the knowledge of the nature of this most complex, interesting and useful material known as rubber. It has been established that t,hn 1nte.x dohtiln an mrtm . .~ ~~~~ ~ ~.... . . . .consist.; . ..... of .~ .-.. skin. ...., a ~ -~ solid rnhaw. --~~--, and evidently a high polymer of the hydrocarbon CsHS (isoprene), and an inner liquid phase, evidently a lower polymer of the same hydrocarbon, Outside of the polymerized hydrocarbon skin is a layer of protein which comes promiiieotlg into play in coagulation processes. Recent x-ray researches on rubber can be interpreted beautifully upon the basis of this structure as directly ascertained with the niic~maiiipulator. Tlic high polynier is the crystalline phase which appears when rubber is stretelred, and the lower polymer is the amorphous phase always clearly evident on the x-ray diagrams. Reference should he made also to the most rocerrt paper by IIausor and Mark4 in which the alternadivo theories of the structure of the latex particle are clcarly and critically considered. Whatever ma,y he the detailed int,erpretatiun of the phenomena in stretched rubber, the microcinematograrn is eloquent evidence of n‘ature’s achievement in constructing these latex globules so delicately and with sucii coinplcx interrelationships betxecn parts that sgntlictic reproduction in a lahorat,ory ~ e e m san almost howless t,ask. ~
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The Direct Use of Rubber Latex, Especially- Vulcanized Latex By Phillip Schidrowitz 57 Cxaicrinv LA^, LONOON, W C 2 , Ewm.mo
“Direct Use” by South American Natives
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N A most interesting paper on “Latex: Its Chemistry ~ ~ ~ l~i ~ ~ + , the ~ ~of lts Industrial ~ van Rossem, referring to the fact that the natives of the Amazon district used latex for waterproofing fabrics in ancient times, remarked most aptly that “what might be called the oldest ruhber industry of the world had for its crude mterial nothing else than rubber latex.” He states* that the first samples of native rubber products sent to Europe were made from latex-for instance, the suit of waterproof clothes which the Government of Para sent in 1750 to the King of Portugal. I think, however, that we may carry the date hack a little further, as it was pointed out by the writer3 that La Condamine, head of the expcdition sent forth to South America hy the Paris Academy of Science in 1736, sent home specimens of rubber, and referred to the fact. t,liat the natives in the Province of Quito coated linen with the “milk-white liquor” (termed by them “hevea”) and made boots with it which were water-tight. Still earlier than that, i t is on record that tho Spanish invaders of South America water-proofed their cloak3 with latex. The aboriginal uses of latex continue to this day, and Pearson’ gives a lively account of the practices of the natives in this connection. Thus (Chapter XVII) he says: It would be strange iii a rubber country if there were not some rubber manufacture. And there is much. Ncarly all of the Indian tribes make rubber nouches. kit-baes. and some vtrv curious toys. In making a iubber bag. they’first make a bag
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l’mnc. Ins,. Rubber I d , 1, 79 (lW251. Quoting fram Browne, “Rubber,” 1911. Schidrowifr, “Rubber;’ Methuen, 1911. p. 2. ‘‘‘Rubber Country 01 the Amazon,” India Rubber Publishing Co., 1
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N e w York, 1911.
bcjna~a~tablcspoonful isulfur, ~l ~ ~ the , ” zproportiins ~ ~ of sulfu; to ~ each
liter of latea. After stirring the liquid thoroughly, they apply it to the cloth with a leather, and give it a stin cure. If sulfur is not obtainable they use gunpowder.
StevensKanalyzed the rubber layer from fabric so treated, and found that a certain degree of vulcanization had taken place, the total sulfur content being 1.57 per cent, of which 0.9 per cent was combined. It is interesting to note that the exposure of a dried mass of “eaucho” (castilla) latex and sulfur to the sun does not produce a tacky compound. Probably, however, the exposure to the sun is of short duration, and such vulcnnization a6 takes place results rather from prolonged st.orage or use a t the high temperatures obtaining in the Amazon regions, than to t.he “sun cure.” IIancock‘s Work with Latex
Thorns Hancock’s patents of 1824, 1825, and 1830, the first for the manufacture of a species of artificial leather with latex, the second “for employing the liquid rubber in tho manufacture of ropes and cordage,’’ and the third for impregnating materials with latex for the purpose of making hats, shoes, and the like, have been frequently referred to in the literature,6 but it is not so well known that in 18.57 (Wright)O he pointed out the prinriple of adding coloring matters or dyes to the latex, with a view to making nonpoisonous children’s toys. It is curious also that a later English patent of Charles Hancock and Stephen Silver’ Bull. Rubbsr Crowns’ Asroc., 4, 105 (19221. % V a n Rorrem, loc. c i l . ; Wright, “Para Rubber.” p. 400; Hancock‘r “Personal Narrative,” pp. 14. 16, and 29, eic. 1 Ihifish I’ateni 3110 (1864).
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