1865
V O L U M E 2 4 , N O . 11, N O V E M B E R 1 9 5 2 t o the many readers whose original paper-bound copies have fallen t o pieces through use, t o those who find t h e foreign language of t h e French edition a handicap, a n d , finally, t o all interested in t h e applications of x-ray crystallography who are n o t already familiar with its contents. T h e durable a n d attractive binding, t h e larger t y p e size, and t h e high quality of the paper used also contribute t o make it an excellent publication for which Hilger a n d K a t t s , Ltd., are to be congratulated.
HAROLD P. KLUG Principles a n d Methods of Chemical Analysis. H . F . W a l i o n . 435 pages. Prentice-Hall, Inc., i o Fifth Avr., 1st ed. ix Kew York, 1;.Y., 1952. Price, $7.00.
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This book, which is designed for advanced undergraduatc o r graduate courses in analytical chemistry, is really an advanced survey of noninstrumental methods of analysis. After a sho1.t introductory chapter, t h e next three chapters discuss various asperts of precipitates and cover subjects which are not found in m a n y textbooks b u t should be useful t o anyone interested in gravimetric analysis. T h e next chapter on electrical methods revicivs the theory of simple electrodeposition, and rather brieflJt h e fundamentals of deposition a t a controlled potential, internal electrolysis, and coulometric titrations. Organic precipitants, complex ions in analytical chemistry, ion exchange methods, anti separation b y vaporization and extraction are t h e subjects of t h e next four chapters. T h e last ten chapters are devoted t o subj w t s related t o volumetric mr~thods. T h e emphasis in t h t w chapters is principally on t h e theory and method of detecting end points, both visually and by electrical methods, in the) variou‘ types of volumetric determinations. T h e author ha’s assumed t h e reader t o have a knowledge of physical cheniistry and ronscqucmtly gives more advanced interpretations of the various principlcs of analysis than are found in elementary tests. Furthermorr,, each chapter is \vel1 documented with numerous references t o t h e rheniical literature. A numiicr of problcms is given a t t h e end of each chapter and answers to t h r numerical prohlenis arc’ found in t h e .Ippendis. Actual procedures for carrying o u t specific determinations are not given, even though thr: theorcxtiral aspects of many procedures are discussed. T h e book is remarkably free of errors; on])- one incorrect sentence was found. An author index t o t h e m a n y references given throughout t h e t e s t as well as a good subject index cover t h e last tv-elve pages of t h e book. T h e book should not only find wide acceptance as a tcixt for advanced courses in noninstruniental methods of anal! should be valuable to a n y chemist interested in t h e thc:orc.tical side of gravimetric and volumetric determinations.
CLARK E. BRICKER
Merck Graduate Fellowship in Analytical Chemistry .%pplications are again being received for t h e 1lerc.k Graduate Fellowship in Analytical Chemistry, financed by U e r c k & Co., Inc., a n d administered b y the AVERICAXCHENICALSOCIETY. T h e annual stipend is 52500. T h e place of study must be a n institution m-hose undergraduate course of instruction in chemistry is approved by t h e Society. I n Canada, t h e institution selected must be approved by the Chemical Institute of Canada and t h e AMERICAS CHEMICAL SOCIETY. A fellowhip will be awarded t o t h e applicant believed capable of contributing most to t h e advancement of the theory a n d practice of analytical chemistrj- during t h e fellowship a n d in t h e future. It ill be voted contingent upon the successful candidate’s obtaining acceptance from t h e institution a n d professor selected for t h e s t u d y program sponsored.
hpplication blanks m a y be obtained from t h e ARIERICAK CHEMICAL SOCIETY, 1155 Sixteenth St., N.W., Washington 6, D. C. T h e y should be completed a n d returned to t h e Merck Fellowship Committee, a t t h e same address, along with letters of recommendation a n d transcripts of credits. Deadline d a t e for receipt of all material is February 1, 1953.
Electron Microscope Society Hh tenth annual m?eting of t h e Electron llicroscope Sovietv
hmerica was hpld a t Cleveland, Ohio, S o v e m b e r 6 to 8, 1952. Secretary of the society is T. G. Rochov-, Research Laborat01 ies, American Cyanamid Co., Stamford, Conn. Abstracts of t h r papers of special interest t o analysts are given below.
Photographic Emulsions and Electron Diffraction Photographic Emulsions Electron Microscopical Studies of Photographic Grains. Specimen Preparation Techniques. F. -1.H a M M AND J. J. COMER,General Aniline and Film Corp., Easton, Pa. This paper described several preparation techniques which yield specimens useful in the study of latent image theory. Examination of the grains per se or of various types of replicas furnishes only a limited amount of important information. Fortunately, the silver halide grains in many photographic emulsions are encapsulated by a thin film of gelatin complexed with silver ions. .Idrantage of this relatively insoluble capsule is taken in studying the partially developed latent image. Two general types of del-elopment are dewribed: (1) “arrested organic” development, and ( 2 ) gold derelopment. The important results of the electron microscopical study depend. i n the final analysis, upon the utilization of the silver gelatinate capsule during the specimen preparation. Some emphasis was placed on demonstrating the identity of this capsule. A few independent csperinients were described. Contrast and Grain of Electron Micrograph Negatives. C R\ V . L T H , Shell Development Co., Emeryville, Calif.
A. 51.
The denaity and grain of electron micrograph negatives were measured over the practical range of exposure and development times for lide medium plates in Dektol, DK-50, D-19, and D-11, and points for other emulsions and developers. Both contrast and grain behave differently from expectations derived from light lihotography. The contrast, or slope of the H a n d D curve, increases with increasing density, instead of approximating a constant, -y, in one negative. It is nearly the same function of density, however, for different emulsions, developer formulas, and development times, provided that exposure is not too great. Grain differs greatly between emulsions. For lantern slide medium plates, which were as fine as any tried, the grain a t given density and exposure was about the same for different developers, but the optimum exposures differed. .ipplications of the data to practical problems were shown. The new .sen>itometric procedure used was described. Evacuating Plates and Films for Use in Electron Microscopy, J. H. REISNERAND E. G. DORNFELD, RC-4 Victor Division, Radio Corp. of -Imerica, Camden, S . J. Pump-down speeds were compared for plates and films commonly used in electron microscopy. d comparison was made for acetatebacked and nitrate-backed film. The relative contribution of emulsion and hacking to pumping times was discussed. Means of improving pumping speeds for photographic materials in the microscope by prepumping, temperature elevation, and desiccation were dihcussed and evaluated along with the physical changes produced in the photographic material. Experiments were described as carried out on hoth Type EMU and Type E M T microscopes. A roll film camera for use with the E M T microscope was described and its pumping characteristics were given. Electron Diffraction Some Factors Affecting the Precision Attainable in Electron Diffraction Studies. S. G. ELLIS,RC.4 Laboratories Division, Princeton, N. J. The precision of measurement when using the RCA Model EMU electron microscope as an electron diffraction camera was discussed and illustrated. I n most cases an error less than 1% can be at-
ANALYTICAL CHEMISTRY
1866 tained. 0.1%.
Where the rings are sharp, the error can be made less than
Effect of Some Factors on the Quality of Powder Patterns by Electron Diffraction. N. R. MUKHERJEE AND OLIVERRow, Engineering Experiment Station, University of Washington, Seattle 5, Wash. I n an attempt t o determine the critical thickness of any substance for an optimum quality transmission electron diffraction pattern [Mukherjee, N. R., and Row, O., J . A p p l i e d Phus., 2 2 , 681 (1951)], the influence of the following factors was studied. Films were prepared by high vacuum evaporation on Elvanol and the diffraction samples were made from the substrateless film. The position of the film of critical thickness was varied with respect to the source of evaporation, but the critical thickness for a substance was the same in all cases. No change in critical thickness was observed when the film was exposed to either maximum or minimum heat. Neither age nor electron bombardment had any effect in changing the critical thickness, though, in some cases, poorer quality pictures were obtained. Several other plastics were used as substrates and dissolved from the film in their respective solvents, after evaporation, with no change in the critical thickness, but with some mechanical difficulty in making the diffraction sample. Increase of the accelerating voltage by a small amount broadens the range of critical thickness of the sample and improves the quality of the optimum picture, while decreasing the accelerating voltage reverses the effect. The critical thickness of the film appears to be an inverse function of density of the substance. A Specimen Heater for Electron Diffraction.
R. G. PICARDAND
E. G . DORNFELD, RCA Victor Division, Radio Corp. of America, Camden, N. J. An electric specimen heater for diffraction studies a t temperatures up to 600° C. was described. Specimens up t o 0.5 inch square may be heated by the element which fits the vacuum chamber upon the regular stage of an EMD-2 diffraction camera. The principal problem is the reduction of stray magnetic fields from heater wires to a negligible value. This is achieved by using low current in high resistance wire and reverse winding the heater coils. Radiation and conduction losses are cut to a minimum by enclosing the heater element in Maronite or Electro-bestos except for a window over which the specimen is mounted. D.c. power is taken from the power supply for the valving system. During the initial heating cycle a period of from 30 minutes t o an hour is required t o outgas the heater. Subsequent pumping times are very much shorter. A High Temperature Chamber for Electron Diffraction Studies. M ~ P N A RJ.D COLUMBE, General Engineering Laboratory, General Electric Co., Schenectady, N. Y. A high temperature specimen heating chamber for use with electron diffraction instruments was described, provisions being made for accommodating both transmission and reflection samples. It is capable of being adjusted to temperatures ranging from ambient to 1000° C. The chamber is adapted to the manipulator of the diffraction instrument to permit alignment of the sample with the electron beam, being a complete plug-in unit. Samples may easily be changed without removal of the chamber from the manipulator. A thermocouple for measuring the sample a t any desired level is included. A Diffraction Study of Micro Crystals by Use of the Le Poole Lens Arrangement. NORMANM. WALTER,General Electric Research Laboratory, The Knolls, Schenectady, N. Y. An RCA EMB electron microscope equipped with an intermediate lens with adjustable aperture and independent power supply is used to inrestigate the diffraction patterns of single micro crystals. A suitable crystal is selected in the field of view of the microscope and then its diffraction pattern recorded after suitable adjustment of the aperture and lens current. Specimens are dispersed in nitrocellulose and draw-downs made on glass. In this way a fairly random distribution of orientations is achieved. The method of investigation has particular merit in its application to x-ray diffraction powder specimens which have given poor results because of particle size. Other results were cited. Special Techniques, Applications Microtomes Some Developments in Ultrathin Sectioning Techniques. JAMES HILLIERAND GEORGECHAPMAN, RC.4 Laboratories Division and Princeton University, Princeton, hT.J. A simple microtome of the “single pass” thermally controlled advance type has been developed. The thickness of the sections can be controlled accurately, so that precise serial sectioning can be done. A comparison between glass and steel knives has been made which
has shown them to have equal cutting abilities. The steel knife is preferred because of the technical conveniences afforded by its long straight edge. Hardness of the blocks was shown to be of secondary importance and hence may permit adjustment t o the cutting properties of the tissue. Failure t o dry thoroughly the gelatin capsules commonly used has been identified as one cause of irregularities of polymerization. A number of examples were shown. Development and Use of a Simple Ultramicrotome in Cancer Research. CLIFFORDE. GREYAND JOHN J. BIESELE,Sloan-Kettering Institute for Cancer Research, New York 21, N. Y. A simple ultramicrotome has been built around the inexpensive, direct-drive Spencer microtome. This incorporates advantages of recent developments, has a magnetic drive and a modified specimen support, and eliminates contact of the specimen with the knife except during actual cutting. Initial phase- and electron-microscopic studies of ascites tumor cells and other cancer tissues illustrate the utility and great promise of this instrument. New Ultramicrotome for Thin Sections of Tissue. MARK E. GETTNER AND LEONARD ORNSTEIN, Department of Zoology, Columbia University, ?Jew York, N. Y. An entirely new ultramicrotome was described incorporating many novel features. The specimen is mounted in a rotating head. The advance is accomplished by a rotating inclined plane bearing against a traveling nut. The screw which leads the nut is driven a t constant speed. The rate of specimen advance and thus the change of section thickness are obtained by varying the angle of the rotating inclined plane. The section advance can also be changed from 0.1 to 1.0 micron by a simple gear change. The instrument has two feed ranges, 0.05 to 1.0 micron in the lower range, and 1.0 to 10.0 microns in the higher range. It can thus provide the cytologist with phase microscope sections for comparison with electron microscope sections. Replica Techniques
A Replica Technique in the Study of Chemical Precipitation Processes. ROBERTB. FISCHER AND JOSEPH E . ELLINGER,Indiana University, Bloomington, Ind. A modified replica technique was described for the replication of particles of precipitates formed by mixing chemical reagent solutions. The replica is formed while the particles are still suspended in the mother liquid. The interpretation of the resulting micrographs was discussed. The technique was applied to several types of precipitates, and its realm of useful applicability was assessed. “Extraction Replica” Technique for Electron Metallography. R. M. FISHER, Research Laboratory, U. S. Steel Co., Kearny, Ir;. J. This paper described and illustrated a new technique for studying and identifying fine precipitates in metals. I t has been found possible to free from the metal the precipitate particles that are partially embedded in the replica plastic by etching the sample a second time through the plastic. Thus the replica contains the actual precipitate particles, avoiding the loss in resolution inherent in any replica technique. These replicas can be shadow-cast, resulting in one-step positive replicas. Modifications of the RCA EMU were also described that permit electron diffraction examination of small areas of the replica so that unknown precipitates can be identified by diffraction means. -4number of examples of applications to ferrous metallurgy were illustrated, including identification of the boron phase in boron steels and of the precipitate causing embrittlement of high-chromium steels during service a t 885’ F. Preshadowed Replicas for Electron Metallography. W. L. GRCBE S.R. ROUZE,Research Laboratories Division, General Motors Corp., Detroit, Mich. Direct-stripped, preshadowed replicas of metallographic surfaces can be prepared when a surface-active, parting layer is used as sugJ . A p p l i e d Phys., 20, 1209 (194911. gested by Kaye [Kaye, W., These replicas may be either plastic or all metal and are free from strain marks when wet-stripped. Since plastic structure is not visible in them, resolution is not limited by this factor. The technique used for the preparation of preshadowed replicas was described, and the differences in interpretation between this type and the usual shadowed-plastic replica were discussed. Applications of preshadowed replicas to the study of microstructures of steel were presented.
AND
Metallic, Direct-Stripped Grating-Replicas as Internal Calibration Standards for the Electron Microscope. S. R. ROUZE,Research Laboratories Division, General Motors Corp., AND JOHNH. L. WATSON, Edsel B. Ford Institute for Medical Research, Henry Ford Hospital, Detroit 2, Mich.
1867
V O L U M E 2 4 , N O . 11, N O V E M B E R 1 9 5 2 I t was shown earlier [Watson, J. H. L., and Grube, W. L., J. A p p l i e d Phys., 23, 793 (1952)l that plastic grating replicas mounted upon eighth-inch specimen screens were practical internal standards and that they could be accurately calibrated independently by spectroscopic means. Metallic replicas of diffraction gratings have been made by a direct-stripped method. These can still be direct-stripped easily and without damage to the original grating, and the optical quality of these preshadowed, all metal replicas is better than that of the plastic replicas. Because of their superior optical properties, the spacing can be determined spectroscopically more conveniently and with greater accuracy. I n addition, the metal replicas are more stable than the plastic ones. A report was also given on the electron microscopy of the metallic replicas and the accuracy and constancy of their magnification measurement. Applications Electron Microscopy of Synthetic Elastomer Latices. ROBERTR. AND M a x SWERDLOW, National Bureau of Standards, STROMBERQ Washington, D. C. Particle size distributions, ranging from approximately 100 t o 2100 A., were determined for four synthetic elastomer latices by means of electron microscopy. These lat'ices are copolymers of butadienestyrene, butadiene-acrylonitrile, and butadiene-styrene-acrylonitrile. The effect on the apparent size and distribution arising from the method of specimen preparation, shadow-casting, distortion of the shape of the elastomer particle, and other artifacts were described. The use of a single, accurate, and reproducible method of examination for all four latices was statistically evaluated. Qualitative and semiquantitative information is provided by the results. An Electron Microscope Study of the Skin on Cellulose Acetate Fibers. VIRGILPECKAND WILBURKAYE,Research Laboratories, Tennessee Eastman Co., Eastman Kodak Co., Kingsport, Tenn. The nature of the surface layer of cellulose acetate fibers has been studied in the electron microscope by the use of high resolution aluminum-beryllium alloy replicas. Chemical etching of the surfaces showed the nonuniformity of the surface layer. Breaking of the fibers in tension showed the effects of draft and spinning temperatures. The skin consists of a highly oriented layer which is caused by drafting while solvent is still within the core of the fiber. It is nonuniform around the circumference of the fiber and is less extensible than the core. I n general, higher draft causes formation of a thicker skin which is made up of layers. Yarns broken in tension show very jagged cracks and hairlike protuberances. Particle Size Studies of Ultrafine Ferromagnetic Powders. A. D. FRASKLIN, R. B. CAMPBELL, AND J. A. WEINMAX, Laboratories for Research and Development, Franklin Institute, Philadelphia, Pa. Particle size distributions have been measured for several ferromagnetic powders with particles in the diameter range from 200 A. to 2 microns. The complete distributions were obtained with the electron microscope. They were compared B-ith the average sizes determined from: (1) the broadening of x-ray diffraction lines, and ( 2 ) the surface area per gram measured by nitrogen adsorption. I n all cases, the electron microscope data gave average particle sizes somewhat greater than those obtained from the x-ray data, and somewhat less than those from the nitrogen adsorption experiments. The over-all agreement was reasonable.
The Morphology of Kaolinite Clay. L. A. WOODWARD, State Engineering Experiment Station, Georgia Institute of Technology, Atlanta, Ga. The general description of the particle shape of kaolinite is that it occurs in small, flat, hexagonal plates. Electron micrographs were shown to indicate that, while this is the basic form in the smaller pieces, there is a composite form that exists in the larger pieces. Evidence that this change in form is related to particle size and other physical properties was also presented. A further series of electron micrographs was shown to illustrate the physical effects of calcination of the clay. This in addition showed the use of the heating effects of the electron beam as a tool for investigation.
X-Ray Microscopy and General X-Ray Microscopy X-Ray Shadow Microscope. 1 ' . E. COSSLETT AND W. C. KIXON, Cavendish Laboratory, Cambridge, England. The shadow projection method of x-ray image formation has been developed using a point source of x-rays produced by a two-lens electron optical system t h a t reduces the electron source t o a fine beam 0.5 micron in diameter. This electron spot strikes a 1-micron tung-
sten foil target that also forms the vacuum wall or the x-ray tube. A specimen placed close to this target casts an enlarged shadow image on a distant photographic plate with a resolution in the image equal to the x-ray spot size. Fresnel diffraction of the x-rays is reduced below the geometrical resolution if the spot-specimen distance is less than 0.1 mm. All of the specimen is in focus a t once and stereographic presentation of the micrographs reconstructs the threedimensional form of the specimen. Magnetic electron lens aberrations are avoided by using a small angular aperture in the final reducing lens and by stabilizing the high voltage used for accelerating the electrons. The energy balance in the foil target is very favorable and no forced cooling is needed. The emission current density of the filament and not the heat dissipation of the target limits the total x-ray intensity. Living and dried specimens have been imaged as well as specimens stained with heavy metals. The best results were obtained by freeze-drying various insects; no distortion occurs and the internal detail shows up very clearly, especially in stereographic presentation. An improvement in the 0.5-micron resolution is possible a t the expense of increasing the exposure time from the 5 minutes used a t present. Microradiography a s an Approach to X-Ray Microscopy. STERP. NEWBERRY, General Engineering Laboratory, General Electric Co., Schenectady, N. Y . Recent improvements in photographic emulsions and x-ray sources warrant a re-examination of our approach to x-ray microscopy. Advantages of microradiography over other methods include large field of view, short exposures, reliable operation, and simple equipment. Relative merits of direct contact and shadow projection microradiography were explained. X-ray micrographs were shown. LINQ
General Propagation of Metallic Vapors in Shadow Casting by Vacuum Evaporation of Aulg8and C+. L. E . PREUSS, Edsel B. Ford Institute for Medical Research, Henry Ford Hospital, Detroit 2, Mich. A special method was introduced for quantitatively determining the mechanism of metal evaporations using metallic gold and chromium tagged with pileproduced Au198 and Cr". This tracer method provides a powerful tool in the study of the distribution of the evaporated metal. The deposition and propagation of the evaporated metal are analyzed under a variety of conditions both in the normal process of evaporation and under simulated shadow-casting conditions. Autoradiographic studies are made of the deposited film structure and quantitative radioactive tracer techniques are applied. The methods allow an analysis of the deposition with measurement errors of approximately i 2 % . Athene Specimen Screens. ERNESTF. FULLAM, General Electric Research Laboratory, The Knolls, Schenectady, N. Y. A very useful type of electron microscope specimen screen, designated as Athene electron microscope specimen grids, new type, in tubes of 100 each, has been obtained from England. The screens, made individually of electrolytically deposited copper, are highly polished on one side and have a marked center as an aid in locating any particular screen opening. A relatively wide border provides support to the 20-micron thick screening. Xecessary modifications of conventional techniques were given for using these specimen screens in electron microscopy.
A Device for Automatic Recording of Magnification Settings. H. FROULA A N D E. BOWLER, Department of Engineering, University of California, Los Angeles 24, Calif. To an RCA EMU electron microscope a device was added which automatically records on each individual micrograph the settings (1 to 10) of the magnification control. This is accomplished by means of a mechanical linkage between the magnification-control knob and a small pointer which slides along one margin of the photographic plate. A shadow cast by this pointer can be seen in the processed micrograph, the position of the shadow indicating the setting of the magnification-control. A Method of Preparing Tungsten Points for the Field Emission Microscope. SELBYE . SUMMERS, General Engineering Laboratory, General Electric Co., Schenectady, N. Y . Points were made by electrolytically etching 0.005-inch tungsten wire. It was found that a 110-volt Variac and a suitable electrolyte produced points with radii approximately 10-6 cm. The 0.005-inch tungsten wire was first etched a t about 25 volts and finished off with 1.5 volts. These points were mounted in a special holder and placed in the electron microscope to be checked. The same points were used in the field emission microscope. This gives a simple method for producing points.
1868
ANALYTICAL CHEMISTRY
Bibliographies of Electron Microscopy. DANH. MOORE, Columbia University College of Physicians and Surgeons, KENNETHT. MORSE, New York Society of Electron Microscopists, New York Academy of Sciences, AND A. R. T. DEXUES,Sloan-Kettering Institute for Cancer Research, New York, N. Y. A survey of bibliographies of electron microscopy was presented, together with a report of the organization and function of the bibliographic service of the New York Society of Electron Microscopists. College Instruction in Electron Microscopy. ROBERTL. WEBER, The Pennsylvania State College, State College, Pa. Instruction in electron microscopy in fifteen representative universities was described briefly. Recommendations were presented regarding principal instrumental techniques (in order of importance), specimen techniques, laboratory equipment, and student supplies. A brief list of books and manuals was suggested as helpful in setting up a syllabus suited to local facilities and student interests. These recommendations evolved from seven semesters of a course in electron microscopy at Penn State, and from an inquiry [Weber, R. L., -4m. J . Phys., 20, 301 (1952)] among those practicing electron microscopy in academic and industrial laboratories.
Biology Techniques C. A Freeze-Drying Technique for Electron Microscopy. ROBLEY WILLIAMS,Virus Laboratory, University of California, Berkeley, Calif. A new technique has been developed for rapid freeze-drying of biological specimens in order t o preserve their three-dimensional structure. Quick freezing is accomplished by spraying minute droplets of material upon the surface of a cold, collodion-filmed metal block. The freezing time of the droplets is estimated to be second. Vacuum sublimation is completed in about 20 minutes at a temperature of -50’ C. The filmed surface of the block is then shadowed, and the collodion transferred t o microscope grids. The suspending medium for the biological objects must be completely volatile and must have a eutectic point well above -50’ C. Distilled water (if biologically tolerable) and ammonium benzoate are satisfactory suspending media. This method of freeze-drying appears to preserve three-dimensional structure about as completely as does the criticalpoint method developed by Anderson. I t s primary merit resides in the rapidity with which biological materials and reactions can be physically “fixed” and effectively examined in the fixed state. Examples were,shown of frozen-dried cells, fibers, and virus particles.
Society of Public Analysts
A’
A meeting of the Society of Public Analysts and Other Analytical Chemists held in London October 1, the following papers were presented a n d discussed.
Spectroscopic Properties of Vitamin As. Application to Assay of Cod Liver Oil. H . R. CAMAAND R. A. MORTOK.
Vitamin As, made by reduction of retinenes with lithium aluminum hydride, shows a main ultraviolet maximum near 351 mp (E;?&,, about 1400) and a secondary peak near 287 mp (Et?&,. about i50). The blue solution (antimony trichloride reagent) shows A,,. 693 mp, about 3900. The intensities of adsorption a t different wave lengths for different solvents have been measured and expressed as fractions of the maximum intensities. The biological potency of vitamin A2 is taken to be 1.33 X lo6 international units per gram, and that of vitamin A1 3.33 X 1C6units. Fish liver oils in general contain much more A 1 than As, depending on the species. I n cod liver oils vitamin 4 2 may account for n,bout one seventh of the total vitamin A (molecule for molecule). By determining E:?&,, 693 mp (42) and 620 mp (SI) in the antimony trichloride color test (applied to the unsaponifiable fraction) and the 326, 351, and 286 mfi in the ultraviolet, oils can be tested for both vitamins. The 693 mp absorption measures AB directly and from it the As contributions to ultraviolet absorption at 351 and 327 mp can be calculated. A conversion factor is given for obtaining the probable Az contribution t o the potency. h cod liver oil typical of those studied by spectrophotometric methods, corrected for all irrelevant absorption, gave an estimated vitamin A potency about 6.57, lower than the estimate which included the possible vitamin Az contribution. Estimation of Carbonyl Compounds by Semicarbazide and Hydrox-
ylamine with Special Reference to Fatty Acid Oxidation Products. A. J. FECELL AND J. H. SKELLON.
A volumetric method of determining aldehydes and ketones with semicarbazide has been developed, which is suitable for carbonyl compounds that readily precipitate semicarbazones, but is not applicable to oxidized fatty acids and esters. For estimation of the carbonyl groups in the products of oxidation of fatty acids and esters by gaseous oxygen, a modified hydroxylamine method was described. The modified method is especially useful in dealing with colored samples. Simultaneous Determination of Pentose and Hexose. W. K. FERNELL h X D H. K. KING. Pentose and hexose may be estimated when present together by heating with orcinol and acid, both with and without ferric chloride. The colors produced are measured at suitable wave lengths and the results are obtained directly from the colorimeter readings by means of a nomogram.
.4t the summer meeting of the Biological Methods Group, hcxld June 13 a t Not,tingham, the following paper was read. Assay of Pertussis Vaccines for Antigenicity and Toxicity. P. IT. MCGGLETON. A laboratory assay of pertussis vaccines is required to select those of acceptable antigenic potency and to reject others unlikely t o give adequate protection. It is not conclusively established which parts of the complex antigenic structure are essential if a vaccine is to give good protection, and vaccines should therefore be prepared from strains that produce all the known biological components. The vaccines, after being checked for detoxification by injection into animals, are assayed as a routine for their ability t o protect mice by the “immunization and challenge” method. I n addition, they may be tested on rabbits for agglutinin and antihemagglutinin response and by the complementfixation test. I n the mouse assay, groups of 15 to 20 animals, given single intraperitoneal injections with graded doses of the vaccines, %’ere formerly challenged by the intranasal route [Burnett, F. M., and Timmins, C., Brit. J . Ezptl. Pathol., 18, 83 (193i)l. More reproducible results are now obtained by a modification of the intracerebral challenge method [Kendrick, P. L., Eldering, G., Dixon, M. K., and hlisver, J., Am. J . Pub. Health, 37, 803 (1947)l. A standard vaccine is always tested contemporaneously to permit valid comparison of successive assays: over a period of 18 months, the results have been found reproducible within reasonable limits. Despite the undoubted artificiality of the assay method, clinical field trials have shown that batches giving good protection to mice also confer a high degree of protection on children. Experience has shown that a vaccine consisting of whole cells should produce a survival rate of over 60% in mice receiving an immunizing dose of 1000 X 106 organisms if it is of acceptable potency. Moreover, the technique of assay is sufficiently flexible to be successfully modified t o suit vaccines of different types-e.g., plain suspensions, adsorption products.
A4ta meeting of the North of England Section held at Liverpool on October 25 a paper on “Detergents” was read by C. B. Stuffins.
I
Society for Experimental Stress Analysis. Annual meeting and exhibition, Hotel McAlpin, New York, N . Y., December 3 to 5 Sixth Annual Symposium on Modern Methods of Analytical Chemistry. Louisiana State University. Baton Rouge, La., February 2 to 6, 1953 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. William Penn Hotel, Pittsburgh, Pa., March 2 to 6, 1953 American Chemical Society. 123rd National Lfeeting, Los Angeles, Calif., March 15 to 19, 1953 Sixth Annual Summer Symposium. Rensselaer Polytechnic Institute, Troy, N. Y., June 1953
