A N A L Y T I C A L CHEMISTRY
APRIL 1 9 5 6
NEWS
Technicol sessions, describing the latest in analytical and rpectrogrophic techniques, were well attended. Left: Dinner speoker, Wallace R. Brode, National Bureau of Standards (center),discusses program with E. M. Du Bois (left) and W. S. Bates of the conference publicity committee
Pittsburgh Conference Sets Record Attendance RECORD
crowd of nearly 3000 an-
A alysts and spectroscopists at the
Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy had the opportunity to hear papers describing the latest in analytical theory techniques and to see, firsthand, the newest in analytical equipment. Of particular interest during the meeting was gas chromatography, a method hailed b y many as having great possibilities for development and application. This interest n.as reflected in several instruments displayed \vhich utilize this principle, some of which are in the prototype stage, and in the Symposium on Gas Partition Chromatography. Analysts had a good opportunity to evaluate the merits of units now becoming available. The partition symposium discussions indicated a trend toward greater utilization of this new analytical technique, which, although developed and used in Europe for several years, has only recently been applied here to any significant extent. Responsible, to some degree, for development in the United States was industry itself. Many companies, learning of this new technique, found it relatively simple t o construct their own models. Instrument makers have started producing a t a cost they hope will be sufficiently attractive to
justify purchase rather than participation in what may he called a "do it yourself movement."
Principle of Gas Chromatography. Generally speaking, the ne\!. method involves the separation of componentin a narrow column packed with an inert granular support, previously coatedwith a high boilingorganicliqiiid. When a small amount of the mixture of gases or vaporized liquids to be analyzed enters the apparatus, the individual components partition, or divide. hetween the gas phase and the liquid phase. Elution with an inert carrier gas makes the components move with characteristic velocities. This movement depends upon partition coefficients of the various components. Since this varies for different substances, a separation takes place in the column. Materials so removed are detected by a thermal conductivity cell as they leave the separation unit. Basically, anything which can potentially be distilled can be analyzed by gas chromatography, said L. V. Guild of Burrell Corp. Separation of liquids with boiling points up to 200" C. is possible. However, most applications to date have centered around gas analyses of gasoline refinery butane cuts; separation of isomers-pentanes and hexanes-and the trace analysis of components. I n this latter application, Guild ex-
V O L U M E 2 8 , NO. 4, A P R I L 1 9 5 6
plained, the instrument can be used to pick out a control component of particular interest. The balance of the mixture can then be grouped together or come off later, depending upon the sample. An example i s nitrogen in natural gas. Here, the N2 component can he determined first, followed by the other materials. Also, the new chromatographic equipment, added Guild, is a very useful supplement for other methodsthe analysis of cuts from liquid-vapor distillation and separations for further annlysis. Extended Utilization. One method for modifying equipment, suggested by D. H. Lichtenfels of Gulf Research and Development. is applicable to analyzing gasolines. Previous methods involved either distillation of the gasoline to separate the volatile components, followed by an infrared or mass spectrometry analysis for component identification, or a low temperature distillation. Lichtenfels uses two chromatography columns mounted in series. The first strips light fractions, while the second provides a more complete study of the light ends in g a s o l i n e usually propane, isobutane, butane, pentane, and isopentane. Heavier components are retained in the "stripper," and are either removed or prevented from interfering 15 A
NEWS
vith the lighter substances in subsequent runs by bsckflushing with a carrier gas, while the conventional separation of the light fractions is in process. Results obtained in less than a n hour per sample by this modified technique, added Lichtenfels, are comparable to those from the former method of distillation followed by mass spectrometry analysis which usually required 2 to 3 hours. Further evidence of interest in extended utilization was given hy R . W. Neuzil of Universal Oil Products Co. Neuzil proposes the separation of 4methoxyphenol in 2-tert-butyl-4-methoxyphenol b y application of partition chromatography and ultraviolet spectroscopy. The procedure is used to detect and identify as little as 0.03% of the 4-methouy, said the Universal Oil chemist. Separation depends upon a 500 to l ratio of partition coefficients for the two components in a water-carbonte trachloride system. After elution, the two phenols are determined b y their ultraviolet band at 2910 A. Neuzil said that the mixture is added to the top of a 100 by 12 mm. column packed with silica gel and forced through b y percolation with carbon tetrachloride, the mobile phase. Rate of travel through the apparatus depends upon the partition coefficients-the 2-twt-butyl separates first, followed b y a phenol-free fraction, and then the 4-methoxy. New Instrument Department. Many difficulties encountered by analysts in measuring the moisture content of gases can be eliminated by
using a n instrument developed by Du Pont, reported E. K. Keidel. Speaking before the Symposium on New Instruments, Keidel said that this new tool provides a simple, yet accurate, method for absorbing and electrolyzing water present in sample streams entering the apparatus, continuously and quantitatively, at concentrations down to fractions of a part per million or to a dew point of less than -80" C . The new tool, applicable to process streams, can also be used in the laboratory. Continuing, the Du Pont chemist explained electrolysis current is directly related by Faraday's law t o the mass rate of the flow of water into the instrument. Flow can he regulated by available restrictors and regulators. Indications are proportional only to the water concentration, which is conveniently expressed as parts per million. The absorbing material takes the form of a viscous film, placed around a spirally wound platinum electrode wire on the inside of a tetrachloroethylene resin tube. Absorbed mater is electrolyzed quantitatively to hydrogen and oxygen at the electrode by d.c., thus providing a continuous indication of moisture content and maintaining the film in a n absorbent condition. Unusual feature of the instrument, added Keidel, is t h a t it responds nearly twice as rapidly to increasing concentrations as i t does to decreasing ones. This may well be due t o the diffusional properties of water in the absorbent film. Temperature effects are minor.
Much interest war shown in the exhibits of 50 manufacturers of modern laboratory equipment 16 A
This new instrument, while designed primarily for measurements on gases such as air, nitrogen, Freon, hydrogen chloride, chlorine, ethylene, and hydrogen, may he used to determine water in many liquids using vaporization or stripping techniques, he said. Du Pont is not manufacturing the instrument hut mill make it commercially available under a licensing arrangement. At the exposition Beckman showed its unit and a few other instrument manufacturers indicated they had plans to bring out models soon. X-Ray Fluorescence. X-ray fluorescent techniques, which permit spectroscopists to determine traces of metallic components in the parts-permillion range, have been applied to determining small concentrations of germanium (usually 0.1%) in minerals and coal. W. J. Campbell of the Bureau of Mines, speaking at the trace analysis symposium, said t h a t chemical analyses for the metal are often difficult and unreliable. A new fluorescent x-ray spectrographic technique, however, can detect quantities to within 10% of the amount present, in a concentration range of 5 t o 100 p.p.m. Basically, continued Campbell, the germanium is separated from the original material by distillation as the tetrachloride. Cinchonine germanomolybdate precipitates the distillate as an organic complex. The product is then collected on filter paper and compared with standard germanium solutions. X-ray comparison, using either a quartz or topaz analyzing crystal, is used to provide sufficient resolution of the GeK alpha line from the 2nd order MoK beta line.
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NMR Still Mysterious. About 10 years ago, Felix Block and E. M. Procell discovered a useful analytical tool called nuclear magnetic resonance. Their efforts were rewarded with the Nobel Prize in 1952. Since then, some 40 N M R instruments have been installed in laboratories throughout the world. But, there are questions-what does i t do? What are its advantages? One outstanding advantage, added Baker, is that, unlike ot,her spectrographic methods, it is not necessary to have a material of known composition in order to aid in identification. Many structural features of some compounds are revealed in a way characteristic to this new analytical tool. This may, in some cases, cause difficulties in interpretation and in other cases, may be an advantage. ANALYTICAL CHEMISTRY
Newest Methods to Be Stressed at Ninth Summer Symposium wastes, rapid A methodsofofindustrial analysis, and analytical
he placed on newer instrumental techniques for specific materials. problems encountered in biological sysChairman of the Saturday session, tems will he the principal subjects covdealing with analytical problems enered during the Summer Symposium on countered in biological systems, will he Analytical Chemistry at the University Taft Y . Torihara, associate professor of California at Los Angeles, June 14 to of analytical chemistry at the University 16,1956. of Rochester. Speakers at this session The 3-day meeting is the ninth annual will emphasize nen. developments in symposium sponsored by the Division micromethods for separating and anof Analytical Chemistry of the AMERI- alyzing biological systems. CAN CHEMICAL SOCIETY and ANALYTICAL Robert L. Pecsok, associate professor CHEMISTRY. of analytical and inorganic chemistry I n addition to three technical sessions, a t UCLA, is chairman of local arrangeother events scheduled include an introments. John Mitchell, Jr., senior superductory lecture on coulometry by Fisher visor in charge of the Analytical Group, Award winner Ernest H. Swift, CaliPolychemicals Department Research fornia Institute of Technology and Division, Du Pout, is general chairman. honorary chairman of the symposium. The complete program, including Also scheduled is a modest exhibit of abstracts, will he distributed a t the instruments by local manufacturers meeting. Manuscripts will be conand supply houses, three group lunchsidered for publication as a group in eons, a ladies’ program, and a banquet. ANALYTICAL CHEMISTRY. The banquet speaker will he Herbert hleyer, chief chemist of the Motion Picture Research Council which serves nine of Hollywood’s major studios. Dr. Meyer, formerly associated with I. G. Farben, Agfa Berlin, and Agfa Ansco Corp., will describe the critical role played by chemistry in all phases of motion picture production and major unsolved problems. The first of the three technical sessions, that on analysis of industrial wastes, will he chairmaned by Richard D. Hoak, science fellow a t Mellon InstiE. H. Swift, R. L Pecsok, Local NALYSIS
Meetings will he held in UCLA’s new chemistry building where registration will begin at 8:OO A.M., Thursday, June 14. Registration fees will he $4.00 for ACS members, full time students, and nonchemists; $8.00 for nonmember chemists or chemical engineers. Room reservations should he made before June 1, using the preregistration coupon.
Program Technical Session
Thursday, June 14,
11:OO ~.mr.-4:30 P.M.
Analysis of Industrial Waster
Analytical Techniques in Air Pollution Control. M. D. THOMAS. Stanford R e search Institute Spectrometric Investigations of AtmosBureau pheric Pollution. R. A. FRIEDEL. of Mines
Continuous Nitric Oxide and Nitrogen Dioxide Recorder. L. H. ROGERS.Air Pollution Foundation Evaluation of Published Methods for Atmospheric Omne Analysis. W. A. DuPRAW, Armour Research Foundation Fixation of SO. as Disulfitomercurate(I1) and SubsequentColorimetric Esti-
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Honorary Chairman
Arrangements
John Mitchell, Jr., General Chairman
Herbert Meyer, Banquet Speaker
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I I I I II
R.
D. Hoak
tute. Discussions will include sensitive chemical and spectroscopic analyses for trace components in air and aqueous wastes. The second day’s sessions, devoted to *‘PId methods of analysis, will he headed Kelley, director of Chemistry Division National Laboratory.
1
Preregistration Coupon-Ninth
I I I I I I I I I I
Annuol Summer Conference
Division of Analytical Chemistry and ANALYTICAL CHEMISTRY University of California, 10s Angeles
June 14-1 6, 1956
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Name (print) Address (print). Date and time of arrival.. Date and time of departure..
M. T. Kelley
I I Fraternity House Hotel* I II 0 single at $3.00 single at $4.00-5.00 lunch at $1.50 Thurs. Fri.. I sat...... I I 0 double at $2.50 0 double ot $3.50-4.00 0 Banquet at $4.00 I Name of roommate, ifany.. I I 0 Share double roam if singles exhausted. Ladies‘ Program I I *Please enclose $5.00 deposit for hotel roam, payable to Analytical I Conference, ACS. Send coupon to R. 1. Pecsak, Department of Chemistry, I UCLA, Lor Angeles 24, Calif. I RESERVATIONS
... .....
i T. Y. Toribara
by ,Myron T. the Analytical of Oak Ridge Emphasis \\ill
I I I I I I
V O L U M E 28, NO. 4, A P R I L 1 9 5 6
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17 A
NEWS
mation. P. If7. WESTASD G. C. GACKE, Louisiana State University Recent Advances in Waste l17ater Analysis. W. A. MOORE A X D AI. B. ETTISGER~ Public Health Service Determination of Trace Amounts of Alkylbeneenesulfonates in Water. E. A I . SALLEE,Procter & Gamble Co. Spectrophotometric Determination of Alkylbenzenesulfonate Detergents in Sewage and River Waters. J. D. FAIRINQ AND F. R. SHORT,hIonsanto Chemical co. Direct Spectrophotometric Method for Chloride. P. W.WESTA N D HANSCOLL, Louisiana State University
KJELDAHL A P ~ A ~ A ~ U ~
Friday, June 15, 9:OO A.M.-4:30
6 APPARATUS I
Saturday,
DISTILLATION APPARATUS
Run Complete KJELDAHL DETERMINATIONS with these three units 0
Electrically-heated Digestion Unit holds 12 flasks: standard types, NPN tubes or newIy-designed expansion-bulb flasks. Rotary design eliminates former difficulty of cold-end flasks. Special heating feature prevents condensation in fume hood, and aids in fume exhaustion. Distillation Apparatus is avaiIabIe with interchangeable sntrance tubes and vacuum-jacketed distilhtion flasks permitting a wide range in sample sizes.
0
STEAM GENERATOR
Steam Generator consists of a 2-liter Pyrex flask ant1 an immersion type heating coil.
June 16, 9:OO A.M.-12:30 P.M.
Analytical Problems Encountered in Biological Systems Application of Paper Chromatography to Steroid Analysis. A. ZAFFARONI, Syntes-S. A., hlesico, D.F. Newer Developments in Microelectrochromatography. P. L. KIRK,University of California Problems Involved in Assaying Drugs in Biological AIaterials. B. B. BRODIE, National Heart Institute Use and Abuse of pH AIeasurements. I. FELDMAN, University of Rochester Analytical Problems in the Determination of Amino Acids. M. S. DUNN, University of California Special Events
Thursday, June 14 10:30 A.M. Coulometry. ERNEST H. SWIFT,California Institute of Technology 12:30 P.hf. Group Luncheon, UCLA Religious Conference Building 12 30
P . M . - ~ :00 P.M.
Friday, June 12:30 r.nr.
Instrument Display
15
Group Luncheon, UCLA Religious Conference Building
12:30 P.X.-G:OO G:30
Write for New Bulletin No. 2271-H
P.M.
Rapid Methods of Analyses Rapid Rock Analysis. LEONARD SHAPIRO, U.S. Geological Survey Optical and X-Ray Quantometry. J. W.KEMIP,Applied Research Laboratories Flame Photometry. V. W.MELOCHC, University of Visconsin Rapid Mass Spectrometer Methods as Applied to the Oil Industry. M. J. O’NEAL,Shell Oil Co. Radioactive Methods Based on Gamma Ray Spectrometry. R. E. CONKALLY, General Electric Co.
P.X.
P.M.
Instrument Display Banquet, Hotel bliramar, Santa Monica Speaker, DR. HERBERT MEYER,Motion Picture Research Council Subject, Hollywood Has Chemical Problems
Saturday, June 15 r
For further information, clrcie number 1 8 A on Readers’ Service ICard, page 61 A
18 A
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10 :00 A.31.-2 :00
P.31.
Instrument Display 12:30 r.nf. Group Luncheon, UCLA Religious Conference Building An informal ladies’ program will be arranged, consisting of tea on the campus, lunch, and shopping tour, and sightseeing in Beverly Hills-Westwood area. ANALYTICAL CHEMISTRY
PHOTOVOLT pH METER
A full-fledged line-operated pH Meter of remarkable accuracy at the UNPRECEDENTED price of
.
made possible b y receni advances in electronic tubes and circuits.
0
SIMPLE
in operation and maintenance. 0 FAST and dependable in
Write for Bulletin #225 lo
0 FULLY stabilized for , wide r a n g e of l i n e fluctuations.
For further information, circle number 19 A-1
voltage
on Readers’ Service Card, page 61 A
PHOTOVOLT Li n e - 0 p erat ed for Partition Chromatography and Paper Electrophoresis
A photoelectric-precision instrument for the rapid and convenient evaluation of strips and sheets of filter paper in partition chromatography and paper electrophoresis.
Multiplier
FLUORESCENCE METER
Mod. 540
High-sensitivity for measurement of low concentrations (fullscale for 0.001 microgram quinine sulphate) Micro-fluorimetry with liquid volumes as low as I ml Low blank readings, strict linearity of response Universally a plicable due to great variety of available filters, sample hoherr, and other accessories Interference Filters for high specificity and for determining spectral distribution of the fluiorescence High-sensitivity nephelometry far minute turbidities Fluorescence evaluation of powders, pastes, and solids, also in spot-tests on filter paper without dution Write for Bulletin #392 t o
PHOTOVOLT CORP.
95 Madison Ave. Circle No. 19 A-2 on Readers’ Service Card, page 61 A
Circle No. 19 A-3
N e w York 15,
N. Y.
on Readers’ Service Card, page 61 A
19 A
V O L U M E 28, NO. 4, A P R I L 1 9 5 6 For further ioformation, circle number 21 9, on Rieaders’ Service Card, page 61 A
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Y
The ACTUAL LOT ANALYSIS Every ‘Elaker Analyzed’ Reagent carries the ACTUAL LOT ANALYSIS 011 the label. Purity is defined to the decimaZnot merdy maximum limits !
The AXTUAL LOT ASSAY More than 325 ‘Baker Analyzed’ Reagents now carry a LOT ASSAY.. .more than any other brand. Note these are actual assays-not just range assays! And more are on the way!
MODERN, PROTECTIVE PACKAGING All ‘Bakw Analyzed’ Reagents are packaged in safe, functional containers.
FAST, C 0 NV EN I ENT AVA I LAB 1 L ITY Your laboratory supply house carries a full line of Baker laboratoiy chemicals-as close as your telephone.
Your LSR knows ‘Baker Analyzed’ Reagents are manufactured and labeled to meet your need for greater speed with improved accuracy. Consider for example ‘Baker Analyzed’ Reagent Acids : their purity to the decimal is delineated right on the label. To insure against accidental contamination in your laboratory, labels and clo:,ures match in color. For maximum safety, the Acid-Tite closure provid& a leak-proof, double seal.
OUR L S R ...A GOOD M A N TO KNOW B E T T E R ! Your LSIt is hand-eicked and trained v i t h care. His job: to bring the thousands-of items in his firm’s catalogs to your door-to supply you with the laboratory chemicals, equipment and services you need, when you need them. The ne>t time he calls, ask him about his company’s many extra benefits. He represents one of 88 leading laboratory sup and can help you fill all your needs for apparatus, equipment and glassware. as well as for ‘Baker Analyzed’ Reagents.
whenever you see this you know it stands f o r complete laboratory supply sertiicethe j n e s t products, the leading brands.
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'Baker Analyzed' REAGENTS . . . p referred for your - work
ANALYTICAL CHEMISTS.. .
f:
-
the ACTUAL LOT ANALYSIS urd lot assay speed testing, improve accuracy You can work faster. . . zcith confidence. . . because both assay and significant impurities are defined to the decimal (not jus1 as maximum limits). You have an accurate, time-saving basis for your preparation and calculation.
ELOPMENT CHEMISTS.. . This new CAP SEAL helps ithe transition.from pilot-plant to production This new SEAL appears on the bottle caps o€ more than 200 Baker laboratory chemicals. It tells you that the same Baker chemicals you use in your laboratory are also available in tonnage quantities, at economical prices. This seal works for you in minimizing the variables which often complicate the change-over from pilot plant operation to full-scale production. Write for your list of the 200 Baker laboratory cliemicals which carry the new CAP SEAL.
J. T.Bak& Chemical Co. REAGENT
FINE
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Phillipsburg, N e w Jersey
Actually, this unit does the same work, in less time, than the two separate units you may now be using. It does combustion sulfur analysis (A.S.T.M. E30-47) and also has a gravimetric absorption system for carbon analysis. Sulfur contents up to .300/,can be analyzed with a one gram sample. Sulfur analysis can be made alone, in 3 minutes or less, by disconnecting the absorption system. It’s easy to clean this unit, because the sealed titration vessel has fill and drain tubing connections. This also reduces the chance of breakage, since the vessel does not have to be removed for cleaning.
Errors are eliminated because you do not have to remember the initial color or shade before titration. It has a mirror surface that permits color end point comparison. The Lindberg Combined Sulfur-Carbon Determinator cuts equipment costs way down-and a t the same time saves plenty of work hours. This makes it just about perfect for the small lab, or for the lab that must analyze both carbon and sulfur on every sample. If you want to know more about this unit, just call your nearest Lindberg laboratory equipment dealer. He will be happy to give you full details.
&iN@@gR6LAB0RAT0 RY EQUIPM ENT DIV I SI0N Lindberg Engineering Company, 2440 West Hubbard Street, Chicago 12, Illinois For further information, circle number 21 A on Readers’ Service Card, page 61 A
22 A
ANALYTICAL CHEMISTRY
NEWS
Experimental Biology Meeting in April Several subjects of interest t o analysts will be included in the 2000 papers to be presented a t the 40th Annual Meeting of the Federation of American Societies for Experimental Biology. The meeting, to be held April 16 to 20, a t Atlantic City, mill consist of 155 scientific sessions, symposia, and panel discussions. An exposition showing recent developments in the pharmaceutical, chemical, food, publishing, apparatus, and equipment industries will be shown. Participating societies are the American Physiological Society, American Society of Biological Chemists, American Society for Pharmacology and Experimental Therapeutics, American Society for Experimental Pathology, American Institute of Nutrition, and American Association of Immunologists. Symposia will include one on toxicological and nutritional studies on irradiated foods, one on progress and developments in biochemistry, and one on interpretation of data obtained on studies with isotope-labeled proteins of biological significance. Further details and the program will be available from the Federation Headquarters, 9650 Wisconsin Ave., i1"ashington 14, D.C.
Symposium on Molecular Structure and spectroscopy This year marks the tenth anniversary of the annual Symposium on RIolecular Structure and Spectroscopy a t the Ohio State University, Columbus, Ohio, to be held June 11 to 15. The mornings are to be devoted to invited papers by scientists from a t home and abroad, made possible by the cooperation of the National Science Foundation, Office of Naval Research, and the Graduate Scliool of the university. The Joint Commission on Spectroscopy of IUPAP and IAU will be meeting concurrently with the symposium, and the National Research Council on Atomic Spectroscopy is planning a conference a t the same time. Abstracts of communications, in duplicate, must be submitted not later than April 20. Harold H. Nielsen, Department of Physics and Astronomy, The Ohio State University, Columbus 10, Ohio, is chairman. Papers include: Ultraviolet Spectra of Simple Polyatomic Molecules. G. HERZBERG,National Research Council, Ottawa, Canada. Recent Developments in the Molecular Quantum Theory. PER-OLOV LOWDIN, University of Uppsala, Uppwla, Sweden. Case History of the NO Molecule. J. H.
V O L U M E 2 8 , N O . 4, A P R I L 1 9 5 6
YOURS FREE
ANALYST'S CALENDAR American Chemical Society. 129th Meeting, Dallas, Tex., April 8 to 13, 1956. Symposium on Crystallography. International Union of Crystallography. Madrid, Spain, April 2 to 7. Scientific Apparatus Makers Association. Belleair, Fla., April 8 to 12. Congress on Low Temperature X-Ray Crystallography. Oxford, England, April 12 and 13. Sixth International Colloquium on Spectroscopy. Royal Netherlands Chemical Association and Dutch Natural Sciences Society. Amsterdam, May 14 t o 19. Symposium on Molecular Structure and Spectroscopy. Ohio State University, Columbus, Ohio, June 11 t o 15. Joint Commission on Spectroscopy. International Council of Scientific Unions, Columbus, Ohio, June 11 t o 15. Ninth Annual Summer Symposium on Analytical Chemistry. Division of Analytical Chemistry, ACS, and ANALYTICAL CHEMISTRY. University of California,LosAngeles, Calif., June 14 to 16. Gordon Research Conferences. American Association for the Advancement of Science. Instrumentation, New London, N. H., July 23 to 27. Analytical Chemistry, New Hampton, N.H.,August 6to10. InfraredSpectroscopy, >feriden, N. H., August 20 t o 24. American Society for Testing Materials. Annual meeting, Atlantic City, N. J., June 17 to 22, including 12th Exhibit of Testing and Scientific Apparatus and Laboratory Supplies. Second Pacific Coast national meeting, Hotel Statler, Los Angeles, Calif., September 16 to 22. Fifteenth International Congress of Pure and Applied Chemistry. Analytical Chemistry. International Union of Pure and Applied Chemistry. Lisbon, Portugal, September 9 t o 16.
SSS Membrane Filter Folder Detailed information and iimple directions for use of membrane filters. This folder describes the new SlLS "BacT-Flex"', flexible membrane filter with a larger, green-colored grid designed for easier, more accurate bacteria count.
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T h i s desk-sized chart shows at a glance which filter paper to uae for a \ given analysis. Gives rela1 tive retention valuer of S L S Analytical F i l t e r I: Papers and other brandr.
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