Mag, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
637
TABLB11. SUMMARY OF CLARIFIER TYPESAND PERFORMANCE Method of heating An le of bottom W i L or without baffles Heating surfacel sq. ft. Gross capac!ty, gal Soum caDacitv. nal. Liquor c'apachy;gal. Av. flow rate Gal. per hr, Gal. per min. Av. contact time. min.
Original Steam tubes at right anglea to flow of liquor
Williamson Clarifiers Modified A Modified B Steam tubes parallel to 1 steam chamber with flat bottom end top flow of liquor
Level With 100 1000 180 820
Level With 134 1000 180 820
Level With 72 1000 180 820
760
700
600
12.5 05
11.66
70
Three crystallizations of white sugar should be obtained, particularly if the original cane juice was sulfured lightly. This possibility should be very attractive for the smaller plants desiring to produce a white sugar far superior to the so-called plantation white sugars, without having to consider complete refining equipment. At present six North American refineries, with a combined melting capacity of 5000 tons daily, are using PlO6 and lime clarification as a pretreatment prior to bone char or activated carbon filtration with satisfactory results and considerable savings in operating costs. Thus far, continuous clarifica-
10.0 82
Modified C 1 steam chember with flat bottom and corrugated top Inclined With 210 990 180 810 700
11.60 69
Jacobs Clarifier
6 steam ohamberi im-
mereed in the liquor Inclined Without 400
760 160 600
1000 10.06 36
tion has been limited to sugar solutions made from washed sugars of high purity. A great deal of preliminary work and experimentation have been carried on to extend these limitations, and include products of lower purity. It is too early to report but we believe that prior limitations on continuous PzO6 and lime clarification will be extended to include the products of purity ranges considerably lower than has heretofore been found possible. PRES~XTB inDa group of papers on Filtration and Clarification before the Division of Sugar Chemistry and Technology at the 102nd Meeting of the AMERICAN CH~MICAL SOCIETY, Atlantic City, N. J.
SILVER PLATING OF OPTICAL GLASSWARE Triethanolamine as a Reducing Agent ROBERT D. BARNARD The Chicago Medical School, Chicago, Ill.
F
OR the uniform deposition of a layer of silver upon optical surfaces, the method of Brashear and the Rochelle salts process are most frequently used. The former employs sugar to reduce the silver ion to its metallic state, while in the latter the tartrates not only act as reducers but also probably serve to hold the alkaline silver complex in solution. Both of these methods have the disadvantage that the solutions are relatively unstable; there is also danger of silver fulminate forming from the action of ammonia, a possibility which, however remote, must always be taken into account. While investigating the utility of the ethanolamines as solvents for the alkaline copper complexes used in saccharimetry, we found that diethanolamine had no reducing action on cuprio hydroxide solution at 100' C. Triethanolamine did have a slight reducing action a t this temperature. This fact would place the reduction potential of triethanolamine at some point between that of alkaline tartrate and the reducing sugars. Its effect on silver ion bears out this conclusion. Since triethanolamine was found to be an excellent solvent for silver oxide as a preliminary to the reduction of the latter to metallic silver, the advantage of triethanolamine as a silver plating reagent was obvious. The cost of triethanolamine has been considerably reduced within recent years, chiefly because 'of the large demand for it as an emulsifying agent. It has therefore been adapted to a process of silvering glass which is felt to hold several advantages over those now commonly in use. Preparation of Optical Surface and Reagents. The surface should be cleaned with hot chromate-sulfuric acid solution and thoroughly rinsed with distilled water. It is unnecessary to use the application of caustic soda so often
recommended. If a drop of distilled water will spread evenly over the entire surface, it may be considered free from grease or other organic matter. About a half liter of (1) a 10 per cent silver nitrate solution containing one or two drops of concentrated nitric acid and of (2) a 10 per cent solution of technical triethanolamine are conveniently made up. Both solutions will keep indefinitely.
Method of Plating. The surface to be mirrored is placed face upward in a clean Petri dish of sufficient diameter to accommodate it. To25 cc. of solution 1in a large test tube are added 10 cc. of solution 2; then with constant agitation further additions are made of 2 or 3 cc. a t a time, just to the point where the precipitate which forms on the first addition clears completely. The mixed solution is poured immediately over the object to be plated so as to cover it by a layer of at least 0.25 inch. The deposition of silver begins within a few seconds. For the half-reflecting surface required for interferometers, a layer of silver which transmits about as much light as it reflects is ideal. Such a layer has a distinct violet tinge and appears within 10 minutes a t room temperature. It is advisable to have several surfaces in preparation a t the same time and being plated with the same mixture of reagent but removed from the bath a t graduated intervals, and to select the one which has the proper depth of coating rather than attempt to plate a surface additionally which has been found to have been immersed for an insufficient time. For completely reflecting surfaces, the immersion may last for 24 hours; this particular bath is unique in that the deposition seems to be continuous for that length of time. The Petri dish gives good visual control of the extent of
INDUSTRIAL AND ENGINEERING CHEMISTRY
638
plating, since deposition of silver occurs only on a surface and not through the body of the solution. It is possible that the low surface tension of the triethanolamine may be responsible for this phenomenon. When the desired thickness is deposited, the plated object is taken from the bath, only the edges being handled. The silver is removed from the under surface with dilute nitric acid. The mirrored surface is washed with absolute alcohol and then with xylene, and is covered with isobutyl methacrylate which, when allowed to dry, forms an optically inactive film which protects the silvering permanently.
Vol. 34, No. 5
Treatment of Exhausted Solution. I n most reagents for silver plating except those devised for electrodeposition, it is customary to throw away the exhausted solution to avoid the fulminate hazard or, if it is desired to recover the silver, to precipitate the latter as the chloride. With the triethanolamine reagent neither of these expedients is necessary. If allowed to remain in the container which constitutes the bath, all of the silver is ultimately deposited on its walls in metallic form. The container may then be rinsed with sufficient dilute nitric acid to dissolve this coating from which the nitrate may be recovered directly.
Optical Rotation of Petroleum Fractions M. R. FENSKE, F. L. CARNAHAN, J. N. BRESTON, A. H. CASER', AND A. R. RESCORLA2 The Pennsylvania State College, State College, Penna.
The rotatory power of distillate fractions from an Oklahoma crude is first evident in the gas oil range and reaches a maximum in the lubricant portion. Commercial neutrals from several crudes of various geographical origins evidence rotational maxima of widely different values in distillate fractions of about the same molecular weight and boiling point. As a primary means of concentrating optically active material, fractional solvent extraction seems to be less effective than fractional distillation, but the situation appears to be reversed for secondary operations or for fractions that have been originally concentrated in optically active components by distillation. A neutral oil subjected to treatment with anhydrous duminum chloride, clay, or sulfuric acid or to engine service changed little in rotation. The persistence of this characteristic in various refining procedures and in service makes it of value in the tracing or identification of lubricants.
T
HE optical activity of petroleum fractions was first studied along time ago; the results of much of this early work were reviewed by Gurwitsch and Moore (6). Specific optical rotations for certain portions of the lubricant fraction of a midcontinent crude oil are given by Mair, Willingham, and Streiff (11). Andre (b), Roche (IC), and Andre and Bloch (9) obtained optical rotations on fractions prepared by acetone extraction from lubricating portions of Venezuelan, Russian, Rumanian, and Texas crudes.
Rotatory power of crude oils or their fractions is of interest in geologic studies. The distribution and magnitude of optical activity in lubricants of various geographic origins are of great value and importance in the identification of these materials. The persistence of rotatory power in oils subjected to various refining procedures or to engine service makes the method particularly applicable to such purposes. The present work is concerned with the optical rotations of mineral oil fractions derived in various ways from the lubricant portions of different crudes, and with the effects upon a selected neutral oil of several refining procedures and of engine service. Optical rotation data were found on petroleum fractions classified as to molecular weight by fractional distillation procedures or considerably segregated as to molecular type through the application of selective solvent extraction. The method of hydrocarbon analysis of Vlugter, Waterman, and Van Westen (16) was applied to the fractions so obtained.
Determination of Oil Properties The determination of flash, fire, and pour points, gravity, kinematic viscosity, and dilution, and the conversion of kinematic to Saybolt viscosity were made through procedures listed by the American Society for Testing Materials ( 1 ) . Kinematic viscosity indices were calculated from the data of Hersh, Fisher, and Fenske (7'). Gravity indices of oils not considered to be narrow-boiling fractions (original neutrals, also products listed in Table VI) were evaluated from the data of McCluer and Fenske (IO). For the case of narrowboiling oil fractions a modification of this method was used. The results do not differ markedly from the earlier gravityindex data in magnitude, but the viscosity-gravity relations for narrow fractions are obviously not those prevailing for blended fractions. These viscosity-gravity relations for narrow-boiling fractions will be published presently. The Present address, United State6 Patent Office, Richmond, Va. Present address. Gulf Research and Development Company Harrnarville, Penna. 1 2
