I&EC REPORTS & COMMENTS Nucleation in action-the technology of candy Through the maze to the substrate Partnership with the microbes
Confectionery Crystallization Although it has neither the glamor of polymer chemistry nor the dramatic impact of chemical electronics, crystallization in confections and sweets is economically important and obviously has wide appeal. The complexities of the phenomena that govern the manufacture of sweets are every bit as challenging as those involved in corrosion or crystallization in glasses. I n fact, the latter subject is closely allied to candy manufacture. Crystallization, be it in candy or in germanium melts, is necessarily dependent on nucleation. The broad spectrum of the principles of nucleation, so vividly brought out in the recent Nucleation Symposium, is, thus, applicable to the technology of confections. The energetics of nucleation, reviewed by Uhlmann and Chalmers in this issue, is the first to treat nucleation, although not any specific system is discussed. The crystallization of sweets is chiefly of interest in producing uniform products. Most candies seem to be varieties of mixtures containing crystalline sucrose and amorphous sirups in varying proportions. T o ensure long storage life and uniformity, it is necessary to produce a stable mixture; and stable mixtures are usually those in which crystallization from the amorphous phase is either complete or artificially and permanently prevented. Most research into crystallization of sweets appears to be concentrated on boiled sweets and fondants with only occasional and unrelated efforts being devoted to jellies, creams, fudges, toffees, and caramels. This is to be expected since boiled sweets and fondants are the simplest systems: The simplest system of all is
probably "khandi" which is made by simply dipping lengths of string into sucrose solutions maintained at 70" Brix and 80" C. and allowing the crystals to grow on the string. This represents the classical case of crystallization from solution. I n the case of boiled sweets, which are prepared from a mixture of sucrose and either confectioners' glucose or invert sugar, the manner and extent of crystallization are quite sensitive to the amount of water present. The phase relations in such a system must be very complicated, especially when small amounts of modifiers are present. One of the reasons for the complication is the existence of a stable amorphous phase. A typical boiled sweet will contain up to 2% moisture physically combined in voids and fissures. The remainder is amorphous sucrose which exhibits a tendency to crystallize in different forms depending upon the conditions. The principal variable controlling the crystallization is the moisture content in the ambient environment. The development of crystalline sucrose has been the subject of some sophisticated investigations. The most widely accepted mechanism is probably that of Campbell and Clothier presented in 1926 in which the moisture controls the primary step of water adsorption on the surface of the sweet. The adsorbed water is present as a film which rapidly dilutes the surface of the sweet. Nucleation in the diluted amorphous mass is thus begun, and crystallization proceeds with the release of additional water which, in turn, dilutes more of the amorphous phase. The progressive crystalliza-
tion proceeds until the advancing sirup front has passed through the entire mass. I n the crystallization of fudge, one of the more significant effects is the migration of fatty material to the region of small crystal size, usually the surface of the sweet. Robert Lees of the British Food Manufacturing Industries Research Association has collected the known works dealing with the crystallization of sweets and sililar materials and critically discussed the significant trends in the research. The excellent summary illustrates beyond question that there are many areas of practical interest and importance which might benefit from the great pool of knowledge about crystallization.
Migration-Free Condensation Observed The condensation of atoms onto single crystal surfaces is receiving widespread attention because of its basic importance to the understanding of surface phenomena. Surface interactions that take place during the process of condensation are being studied by scientists who hope to gain a better understanding of the atomic structure of matter. A recent study by Theodore Gurney, Franklin Hutchinson, and Russell Young [ J .Chem. Phys. 42 (11), 3939 (1965)], has shown that, contrary to what might be expected, condensing atoms do stick in the first lattice site they encounter-at least in the case of tungsten condensing on its own substrate at temperatures
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NO. 9 S E P T E M B E k 1 9 6 5
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below 77" K. The study was under the sponsorship of the Advanced Research Projects AgencS-, the Kational Institutes of Health, and the American Cancer Society, and was carried out at the NBS Institute for Basic Standards I n the case of tungsten deposited on tungsten, condensing atoms approach a surface with only a few tenths of a n electron volt of energy. but, because of the stroiig attractive force near the surface, strike with a much greater energy-the kinetic energy of collision. In order for the atom to stick in the first lattice site it encounters, it would have to give up over half of its total energy in the first collision with the substrate. Such an occurrence uould seem unlikely, so that the possibility of an atom making several lattice jumps before coming to rest could be considered quite likely. The results of the present work, however, show that migration-free condensation occurs. An ultrahigh-vacuum field ion microscope, heated to more than 400"C., was used in the initial study. The advantages of clean singlecrystal surfaces, high resolution, and visual observation render this tool ideal for such an investigation. Tungsten was evaporated onto the tungsten field emitter by means of an evaporating coil and the deposited atoms were then field evaporated in several steps. Photographs of the field emission pattern were taken before and after the tungsten deposition, and after each evaporation, in order to provide a step-bj--stepvisual representation of the entire process. A study of the successive photographs below led to the conclusion that the early pictures, taken after deposition (Photograph .4)showed third layer deposited atoms. Later pictures, taken after some field evaporation, showed second-layer deposited atoms (Photograph B), while still later pictures (Photograph C) showed the first layer deposited atoms. Photograph D shows the I
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
A
B
C
D
clean, tungsten substrate before deposition. I t is evident that the transition from Photographs A to C indicates the emergence of the clean substrate. Under the assumption that the above conclusions were correct, an atom count was made from the photographs and it was found that the third deposited layer contained onlv a few atoms, the second de-
USE YOUR
I&EC REPORTS Sturtevant Equipment
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WATER
It’s kind of like washing your hands. You get some crud and some smudges on you in the course of work - so you wash it off and your hands are as clean as new. Does it occur to you that you can “wash” your process or rinse water, too? I n some places there i s a lot of perfectly good value going, literally, down the drain. Plants are sending used treated water to the sewer that is actually in better condition than their raw supply water. Here’s a tip they can put this so-called “waste’) water back through their de-ionizer (if they use one) again and again and again. Recirculation is a great idea, and a lot of places could use it. I n communities where there are water shortages - temporary or permanent, a s the case may be recirculation and re-treatment of water can solve a lot of problems.. Industries that are considering deionization of water supply should look into de-ionization plus recirculation. It could save money, and water also. Toxic substances in waste water can sometimes be concentrated into manageable batches by de-ionization, rather than dumping them to the sewer or attempting treatment with vast quantities of water. Cost of waste treatment can then be reduced, along with the cost of water. Current national programming is emphasizing the preciousness of our water supply. The ideas above fall right in line with this effort. It will be no effort a t all - a pleasure in fact - for us to tell you more about it. Please address yourself to Mr. W. S. Morrison, ILLINOIS WATER T R E A T M E N T CO., 840 CEDAR ST., ROCKFORD, ILL., 61101. Circle No. 30 on Readers’ Service Card
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posited layer only several tenths of a monolayer, and the first deposited layer was only 2/3 to 3/4 filled. These findings suggested that condensing atoms were bound in the first atom site they encountered, but this explanation was considered unlikely, so further verification was sought. Dr. Young and NBS Physicist D. C. Schubert performed a Monte Carlo calculation using an idealized rectangular grid of 400 atom sites (potential wells) equally spaced in the lattice. Atoms were assumed to arrive randomly at the sites. If the site was occupied, the atom was then randomly deflected to an adjacent site, unless the adjacent site was occupied, in which case it was further deflected to another nearby site. The outstanding feature of the calculation is the drastic lowering of population in the second and third layers when the rules are changed from no allowed jumps to one allowed jump and then to two allowed jumps. The force of the argument lies not in the perfection of the model used for analysis but in the drastic way in which the character of the deposit changes with the number of jumps the atom is permitted to make.
Interim Report on Waste Treatment In contrast to sedimentation techniques and biological oxidation, the Advanced Waste Treatment Research Program of the Public Health Service is investigating a variety of physico-chemical separation processes that will remove dissolved salts and complex synthetic organic wastes unaffected by standard treatments. The AWTR Program has been in effect since June 1960 and the latest interim report, covering the period (Continued on page 76)
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NOW-A 20/’ Air Separator for Laboratory Use or Small Production Accurate extrapolation of lab results is now possible with the new 20-inch Sturtevant Air Separator. No longer does our industry have to use small production units for pilot and lab work. The 20-inch Sturtevant Air Separator will classify from ounces to hundreds of pounds a n hour, depending upon feed, feed rate and required particle size. True lab work at Sturtevant or a t your own plant - is now a reality, The20-inch unit fills out Sturtevant’s comprehensive line of air separators, Besides the lab unit, a three-foot model for pilot and moderate production is available. Larger-scale separators range from six to twenty feet in diameter and classify in tonnage quantities. All are available with fully external adjustment devices which allow shiftover from coarse to fine selection in minutes, without shutdown of the separator! Write for Bulletin 087. Or let us know about your plant problems.
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STURTEVANT MILL COMPANY 15 Sturteuant St., Boston, Mass. 02122
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Slurteant snglnoers and fobricobl I full line Of dry prP(W:* Inp epulpmeot~ alr oparrtors, bltndort Bnd mixers, con. nyors, crusher and grindor:, nuid anorgy mills, impact mill:.
Circle NO. 42 on Readers’ Service Card
NO. 9
SEPTEMBER 1965
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He just washed an accident
a lot of trouble never happened Floods o f w a t e r can p r e v e n t serious i n j u r y t o contaminated eyes, face and body.. .can mean the difference between perman e n t and costly i n j u r y o r j u s t temporary i r r i t a t i o n . Send f o r Haws “First Aid on Tap” catalog for information on the entire line of eye/face-wash fountains and emergency drench showers. Haws Drinking Faucet Company, 1443 Fourth Street, Berkeley, California 94710.
EMERGENCY EQUIPMENT Circle No. 14
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from January 1962 through June 1964 has just been issued. Broadly speaking the program is attempting to adopt both conventional and newly emerging chemical engineering separations processes to the solution of large scale water purification problems. Processes studied to date include : adsorption, electrodialysis, foaming, distillation, solvent extraction, emulsion separation, freezing, hydration, chemical oxidation, ion exchange, electrochemical degradation, and reverse osmosis. After initial examination of the various methods, four of them are currently considered to have good prospects for being developed for large-scale use. These early indications are particularly encouraging because the projected treatment costs on a scale-up basis are not greatly out of line with current costs associated with the municipal use of water. Adsorption by activated carbon for the removal of organic compounds has been shown highly effective. Regeneration of the carbon has been proved possible. Despite the relatively high cost of activated carbon, the current outlook indicates that with a feed free of suspended solids, satisfactory results are attainable for a cost under 10 cents per 1000 gallons of product water at the 10 million gallon per day scale. At present, a 290,000-gallon-per-day pilot plant is under construction. Foam separation is a process that takes advantage of the foaming properties of a waste stream by passing air bubbles through the stream and causing surface active organic impurities to concentrate at the bubble surfaces. A 500,000-gallon-per-day pilot unit has been operated for six months, and the process looks promising as a method of removing up to 30 or 40y0 of the organic contaminants from a conventionally treated waste effluent. I t also reof the synmoves 70 to thetic detergent present. Costs
on Readers’ Service Card
INDUSTRIAL AND ENGINEERING CHEMISTRY
should be less than 3 to 5 cents per 1000 gallons at the 10-million-gallonper-day scale. Electrodialysis although not practical for removing organic molecules, it is highly effective in removing dissolved inorganic salts and would work well as part of a two-stage organic-inorganic separation system. Exclusive of brine disposal, this process is expected to cost about 15 to 20 cents per 1000 gallons of product water in a 10-million-gallonper-day plant. The outlook is sufficiently promising to justify a pilot plant study, and plans are under way for an experimental unit handling 80,000 gallons per day of feedwater. Distillation is expected to be adaptable to municipal waste waters containing certain volatile contaminants that may be carried over into the product. Although this situation constitutes a significant drawback to this process, the possibility of follow-up polishing treatments to remove trace impurities offers a practical solution. Costs for treatment by distillation are still uncertain but probably will be somewhat less than $1 per 1000 gallons at the 10-million-gallon-per-day capacity. Even though this is a much higher unit cost than those for other processes under consideration, application of a “blending principle” can lead to sizable savings (perhaps 50% or more) when a “total removal” process such as distillation is employed in the proper system configuration. Final disposition of wastes must be made without polluting either surface or underground water supplies. Possible solutions considered to date include : subsurface disposal into permeable strata or cavities; wet oxidation ; incineration; conveyance to selected dump sites (e.g., the sea) by barge, truck, or pipeline; and recovery of waste materials to make useful products.
