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J anuary 15,1929 IND USTRIAL AN D ENGINEERING CHEMI STRY 7A quartz condensing lens serves to concentrate the lightfrom the arc on the slit and to exclude that from the incan-descent carbons, whose strong continuous spectrum would beobjectionable, Suitable adjustments are provided, whichpermit the arc to be moved both horizontally and verticallyso as to keep itproperly centered during the exposure. Con-stant arc length isinsured by keeping the tips of the electrode

images always at the same points above and below the aper-ture in the slit diaphragm. With a reasonably constant linevoltage in the power supply, this control of the arc length isall that is necessary to maintain constant current and voltagedrop in the arc.I n order that the operator's attention may be concentratedon keeping the arc properly centered, an automatic timingdevice has been installed. This consistsof an electric clock soconnected through a system of relays that it operates onlywhile the arc is burning, and extinguishes the arc as soon asa predetermined exposure time has elapsed. This is particu-larly valuable in photographing the spectra of very volatilematerials, which often yield almost explosive arcs, difficultto keep burning continuously. If it were necessary for theoperator to keep track of the intermittent exposures thatresult under such conditions, he could not give proper at-tention to the centering of the arc, which is one of the most im-portant factors in insuring that all spectra shall be accuratelycomparable.Using a large L ittrow-type quartz spectrograph, with anobjective of 70 mm. aperture ando170 cm. focal length, thespectrum from A2350 to A3400 A. is photographed on aplate 10inches (25.4cm.) long. This s the spectral range thathas been found the most generally useful for much of the workthat is encountered in the average metallurgical laboratory.Other ranges may be utilized, if desired, by a simple changein the adjustment of the instrument, but experience has shownthat at least 95per cent of the work can be done within theselimits. Persistent lines of most of the elements are foundthere, and the dispersion is great enough to insure accurateidentificationof lines. The most complete and accurate listsof lines are available for this region, and ordinary plates aresensitive to these wave lengths without special treatment,such asbathing in sensitizing dyes or f luorescent oils.Smaller instruments can be used for a great deal of work.Several makers put out quartz spectrographs in which thefu l length of the photographable spectrum isincluded withinthe length of a single 10-inch (25.4-cm.) plate, and excellentresults can be obtained with them on many materials. Oc-casions do arise, however, when only the larger instrument

can resolve closely coincident lines of two elements, whichmust be separated to permit the certain identif ication of oneconstituent and i ts estimation, free from the possibil ity oferror due to an overlapping line of another. I n general,therefore, any laboratory which has alarge amount of workadapted to the spectrographic method will find that theadditional cost of the larger instruments is fully justified bythe greater certainty of the results which may be obtainedand by the wider range of possible applications.Three-minute exposures are given with most materials,using an arc carrying 10amperes with a 60-volt drop acrossthe arc terminals. This length of time is sufficient to insurethe complete evaporation of the sample, or at least the expul-sion of all of the constituents to be determined, It is quitenecessary that none be left in the electrode, otherwise erraticresults will be obtained.Slow photographic plates give the best results. Theirfine grain makes it easy to compare line intensities, and theirfreedom from fog is an important consideration, particularlywhen comparing extremely weak lines.

ConclusionNo hard and fast rules can be given for methods applicableto the determination of all elements in all kinds of materials.Some of the general methods have been sketched, whichhave been found useful in a laboratory devoted mainly tothe study of problems connected with the production and useof zinc and zinc-bearing materials. Each type of analysisrequires individual study to find the most suitable detailsof technic. The main purpose of this paper is to call to theattenti on of the chemists of this country the apparently li ttle-appreciated fact that in the spectrograph they have a power-ful tool, capable of yielding information of the greatest value,with a speed and certainty that cannot be matched by anyother means. A few laboratories have installed the necessaryequipment and are finding new uses for i t almost daily. I nthat of The New J ersey Zinc Company several hundredspectrographic analyses are made each month, mostly quanti-tative estimations, and many of them are daily routine andcontrol analyses.

AcknowledgmentGrateful acknowledgment is made to George W. Standen,whose painstaking care and attention to details have beenimportant factors in the progress of this work.

Simple Pressure Regulator for Vacuum Distillations'Henry L . Cox*

MELLONN S T I T U T E O F I N D US T R I A L R E S E A R C H , U N I V E R S I T Y O F P I T T S B U RG H , P I T T S B URG H , PA.

HE chemical li terature of the past two decades containsnumerous descriptions of devices designed to maintain aconstant pressure in a vacuum distillation apparatus.Most of these devices are not entirely satisfactory in thatthey are not sufficiently accurate for the intended purpose orthe construction is so complicated as to discourage use in allexcept the most, exacting investigations. Several of thememploy mechanically or electrically operated valves requiringa high precision in their manufacture and subject to the

T disadvantages inherent in such devices-for instance, cor-rosion and sticking or breakage.The apparatus described in this paper is to a large measurefree from most of these disadvantages. It contains no valvesor moving parts other than an efficient motor-driven pumpand a relay, the armature contacts of which are of sufficientsize to carry the electric current required to operate the motor.The apparatus is entirely automatic, requires little attention,and maintains any desired pressure constantly within *O.lmm. of mercury.1 Received August 3, 1928.* Senior Industrial Fellow, Mellon I nstituteof IndustrialResearch. A closed-arm mercury manometer containing a sealed-in

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8 A,YALYTIC'AL EDITIO-AT T'ol. 1,so . 19iRELAY

IIOYOLT LINEv] MOTOR

contact and an adjustable contact is connected in series witha relay and a battery as shown in the accompanying figure.The armature of the relay is connected to the motor whichdrives the vacuum pump. When the manometer circuitis closed by the mercury rising to the end of the adjustablecontact, the relay is actuated and the motor is stopped.When the pressure within the system rises, thus breaking themanometer circuit, the pump is started and continues tooperate until the pressure is reduced to the desired magnitude.

Satisfactory regulators have been constructed using com-mercial laboratory pumps driven by '/c-horsepower, 110-volt,a. c. motors. In the writer's laboratory, one of these main-tained a constant reproducible pressure of 15 mm. with thepump operating ess than 1per cent of the time. A ny desiredpressure between atmospheric and approximately 2 to 3 mm.may be maintained i f care is taken to prevent leaks in thesystem. Obviously, this device is limited to the use ofmechanically operated pumps which may be stopped withoutallowing air to leak back through the pump mechanism intothe system.The manometer should have an internal diameter of about8 mm. in order to minimize the curvature of the mercurymeniscus. The use of a reservoir between the pump and thedistillation system reduces the fluctuation in pressure to suchan extent as to render it almost unobservable on the man-ometer.Obvious changes in the construction and the use of apressure pump will enable pressures above atmospheric pres-sure to be readily obtained.The apparatus as described was designed by the wri terwhen at the laboratories of the Standard Oil Company(Indiana) at Whiting, Ind., in 1923, and has given satisfactoryresults during the past four years.

Analysis of M aple Products','D. E. Fowler and J . F. Snell

MACDONALDOLLEGE, CGILLUNIVERSITY, A CDONALDOLLEGE . O., P. Q. ,CANADA

X-Study and Modification of the Canadian Lead MethodETHODS for the detection of adulteration of mapleproducts, dependent on measurements of the quan-M i ty of precipitate produced by treatment of thediluted sirup with basic lead acetate, were fi rst proposed in1904 by J ones3 and by Hortvet14who measured the volumeafter centrifugal collect,ion. I n 1906 the more accuratemethods at present recognized by the L4ssociat'ionof OfficialAgricultural Chemists3 were originated by Winton andKreidern and by t'he chemists of the Laboratory of the Cana-dian Inland Revenue Department17particularly A. valin.Studies on three sirups by Snell and Scott8 ndicate that infalling off more rapidly in adulterated sirups than the maplecontent, the Canadian lead value has an advantage over allthe other values used for the detection of adulteration withrefined sugar. But that the method lacks in precision, asevidenced by comparison of duplicates, is well known,8 meandifferences of 0.10 and 0.09 between duplicates by a single

1 Received August 16, 1928. For reference to previous papers, seeIND. NG .CHEM.,19, 275 (1927).2 The experimental work reported and much of the comment are

derived from a thesis presented by M r. Fowler to the Faculty of GraduateStudies and Research o McGi lI University in May, 1928, in partial fulfil-ment of the requirements for the M . Sc. degree.

3 J ones, Vermont Agr. Expt. Sa. , 17th Ann. Rept., 1903-4, p. 446.4 Hort%et, . Am. Chem. Soc., 26 , 1523(1904).: ssocn. Official Agr. Chem., Methods, 1926, p. 204. I n 112 the quan-

ti ty of water to be used in the preparation of the basic acetate solution shouldbe 600cc.

e Winton and Kreider, J . A m. Chem. Soc., 28, 1204 (1908).7 Laboratory Inland Revenue Dept. (Ottawa), Bull. 120 (1906);140 (1907). The Food and Drugs Laboratories o the Department of

Health are successors to this laboratory.8 Snell and Scott, J . IND. NG.CHEM., , 993 (1913).Laboratory Inland Revenue Dept. (Ottawa), Bull. 140 (1907);

228 (1911).

observer, of 0.13 between the means of two observers, of 0.16between duplicates in another series of experiments (printedfigures give 0.19) and occasional differences as great as 0.20(equal to 10 per cent in a lead number of 2.0) being found.The experiments of Valin, reported by Snel1,lo indicated thatactually different quantities of lead mere precipitated in theduplicate determinations. On the other hand, Lancasterllhas expressed the opinion that the variations between dupli-cates are probably due mainly to irregularities in the washing.I n the present work the effectsof temperature and quantityof reagent, as well as methods of washing, have been studiedwith a view to improving this simple and useful determination.M aterials

The lead subacetate solution was made from Horne's saltaccording to the A. 0.A. C. directions. It contained 0.2243gram lead per cubic centimeter. The rati o of neutral tobasic leadlo was 1.88.The sirups were collected in Ontario and Quebec by dis-trict representatives of the Provincial Departments of Agri-culture, instructed to collect only samples of unquestionablepurity. A few (4 to 9)were supplied by A . Valin, analyst ofthe Dominion Department of Health in charge of the Mon-treal Laboratory.T ime Required for M aximum Precipitation

Except for the time of standing, the prescribed method6was closely followed. The results are recorded in Table I.Except in sirup 2 at one-half hour, the results show no varia-10 Snell, J . Assocn Oficial Ag u Chern , 4, 428 (1921).11 Lancaster, Ibzd , 8, 372 (1926).