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together through the 3-way stopcock. If the copper block is a t room temperature, the meniscus will fall in the right leg and rise - - in the leftleg. '

The copper block is then cooled by direct immersion in liquid air until the meniscus in the right leg is back to a Dosition near the upper tungsten contact. Theliquild air is remdved, a glass test tube slipped over the copper block, and the test tube immersed in liquid air. The position of the mercury in the manometer then turns the heater current off and on, so as to maintain the meniscus near the contact point. The rheostat in the heater circuit and the depth of the liquid air around the test tube are adjusted so that the off and on periods for the heater are approximately equal in duration. Whe: roperly adjusted the temperature remains constant to *0.3 8

When it is desired to increase the temperature of the distil1in.g tube to the next value, the height of the mercury in the left leg is reset to the proper position with the mercury in the right leg still a t the tungsten contact. Without further attention the tpm- perature quickly rises to the desired value and then is auto- matically maintained constant at this point.

DISCUSSION

This control unit has been found to be a very satisfactory means of both adjusting and controlling the temperature required for isothermal distillations at low temperatures. The operation of the thermometer is very simple and it requires a minimum of attention from the operator. The apparatus should also be applicable to the control of low temperatures as required in other problems.

A N A L Y T I C A L C H E M I S T R Y

For use as both a method of temperature measurement and temperature control the 120" type 3-way stopcock in the man. ometer should probably be replaced with a T-type stopcock. This type of stopcock has an advantage when measuring tempera- tures, as it permits adding mercury to both legs of the manometer simultaneously until the meniscus in the right leg just touches thP contact point. However, when the main application is the pre- setting of the control point a t some particular temperature and the control of the temperature a t this point, the 120" type s top cock is believed to be preferable. Although the location of the stopcock above the bottom of the manometer makes somewhat inconvenient the removal of all the mercury as required when filling the thermometer with helium, it has the advantage of per- mitting relubrication of this stopcock without loss of the helium from the reservoir.

LITER4TURE CITED

(1) Buffington, R. M., and Latimer, TV. M., J . Am. Chem. SOC., 48,

(2) Savelli, J. J., Seyfried, W. D., and Filbert, B. M., IND. ENQ

(3) Scott, R. B., J . Research .VatZ. BUT. Standards, 25, 459 (1940). (4) Shepherd, M., Ibid. , 2, 1145 (1929); 26, 227 (1941). (5) Southard, J. C., and Miluer, R. T., J . Am. Chem. SOC., 55, 4384

(1933). (6) Ward, E. C., IND. ENG. CEIEM., ANAL. ED., 10, 169 (1938).

RECEIVED Maroh 1, 1948.

2305 (1 926).

CHEM., A N ~ L . ED., 13, 868 (1941).

Quantitative Colorimetric Microdetermination of Methanol with Chromotropic Acid Reagent

R. N. BOOS, Merck & Co., Znc., Rahway, N. J .

.4 rapid, accurate, and specific method for the quantitative determination of methanol is described in which the methanol is oxidized to formaldehyde and the latter measured colorimetrically with chromotropic acid. The method per- mits the determination of methanol with a relative error of <2'3&.

OBMALDEHYDE when heated with chromotropic acid F (1,8-dihydroxynaphthalene-3,6-disulfonic acid) in the pres- ence of sulfuric acid gives rise to an intense violet-red color (1 , 2, 4) . The formation of this color is the basis for the analy- tical method for methanol described below (7 ) . This method was developed in connection with a problem requiring a rapid, ac- curate, and specific determination of methanol for which other available methods, including the Zeisel method for alkoxy1 groups, were unsuitable. The specificity of the reaction is indicated by the fact that the,following aldehydes do not react with chromotropic acid to give a colored solution: acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, isovaler- aldehyde. crotonaldehyde, chloral hydrate, glyoxal, beneal- dehyde, and phthalaldehyde. Glyceraldehyde gives a yellow color (4) .

Methanol, reagent RIerck. Dilute phosphoric acid, 10 ml. of 60% acid diluted to 100 ml. Potassium permanganate, 57, aqueous solution. Sodium bisulfite, reagent Merck, saturated Rolution. Concentrated sulfuric acid.

Chromotropic acid, Eastman Kodak (P-1613), 2% aqueous solution. Ten milliliters of the acid solution are prepared and stored in a brown bottle. The solution darkens rapidly on stand- ing unless preserved by cold storage.

REAGENTS

PROCEDURE The organic material is weighed into a distilling flask with 4 ml.

of water and distilled. Three milliliters of the distillate are col-

lected and diluted according to the expected methanol content (the test solution). One milliliter of the test solution is trans- ferred to a 10-ml. volumetric flask, to which are subsequently added 3 drops of dilute phosphoric acid and 5 drops of potassium permanganate solution (5). The solution is kept a t room tem- perature for 10 minutes with occasional swirling to ensure oxida- tion of the methanol to formaldehyde. Sodium bisulfite is then added dropwise to the solution to reduce the excess permanganate.

The solution is cooled by swirling the flask in an ice bath while 4 ml. of cold concentrated sulfuric acid are added. If a buret is used for the measurement of the sulfuric acid, the stopcock should be lubricated with concentrated sulfuric acid only.

Four drops of chromotropic acid reagent are added to the solu- tion and the 10-ml. volumetric flask is placed in a water bath at 60' C. for 15 minutes, during Tvhich time the flask should be swirled occasionally. The flask is removed from the water bath and cooled in an ice bath. Distilled water is added to bring the level to within 2 mm. of the mark on the flask. The flask is stoppered, shaken, and allovied to stand until the solution is at room temperature, Sufficient distilled water is then added to bring the level of the solution to the mark.

A blank is run on 1 ml. of distilled water each day, as chromo- tropic acid solution darkens with time. The solutions under test and the blank are transferred to t t e cells of a Beckman spectro- photometer and compared a t 5800A. (5) . (Evelyn and Coleman photometers have also been employed successfully.) The quan- tity of methanol in the test solution is then read from an optical density-concentration curve which is determined as follows: A series of aqueous methanol solutions containing from 20 to 100 micrograms of methanol per milliliter of solution is prepared and treated according to the above procedure. The colored solution6 are stable for a t least 3 days.

V O L U M E 20, NO. 10, O C T O B E R 1 9 4 8

The following results are typical of the agreement obtained between the Zeisel and the proposed colorimetric method when methanol was the only alcohol present:

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termined by the procedure described. The results showed 2.0 moles of methanol as compared with a theoretical value of 2 moles.

LITERATURE CITED

(1) Boyd and Logan, J . Bid . Cham., 146, 279 (1942). (2) Bricker and Johnson, ISD. ENG. CHEM., AN.4L. ED., 17,400 (1945’ (3) Eegriwe, E., MGcrochim. Acta, 2, 329 (1937). (4) Eegriwe, E., 2. anal. Chem., 110, 22 (1937). (5) MacFayden, D. A,, J . BioZ. Chem., 158, 107 (1945). (6) Snell and Snell, “Colorimetric Methods of Analysis,” Vol. 11, p

(7) U. S. Pharmacopoeia, 12th rev., p. 428. 1932. RECEIVED October 2 5 , 1947.

17, New York, D. Van Nostrand Co., 1937.

Zeisel, Colorimetric, 70 70

5 . 5 5 . 0 , 5 . 2 4 . 8 5 . 0

The procedure here described may be employed to advantage In the determination of methoxyl groups in methyl esters ( 6 ) .

As an example, a sample of dimethyl tartrate was saponified with 4 ml. of 5 S sodium hydroxide. After 3 ml. of distillate had been collected, the latter was diluted and its methanol content de-

ELECTRON MICROSCOPE GONIOMETRY A. F. KIRKPATKICK AND EVELYN G.4GNON D.4VIS

Stamford Research Laboratories, American Cyanamid Company, Stamford, Conn.

The frequent occurrence of unknown crystals in electron microscopical samples presents the problem of their identification. Their relatively small size severely limits the ordinary methods of identifica- tion. The silhouette angles observed on the screen or photographic plate are practically all the data available to the electron microscopist. These angles are functions of the interfacial angles of the crystals and the orientation with respect to the screen or plate. The interfacial angles, constants of

H h frequent occurrence of unknown crystals in electron T microscopical samples presents the problem of identification. The microscopic size of the crystals or the nature of the sample severell limits the ordinary methods of identification. Pre- cipitated materials, pigments, and by-products, such as calcium carbonate, which is used as the illustration in this paper, are an example of the occurrence of microscopic sizes. Crystals as- sociated vi th other materials in such a manner that separation is not possible, such as crystals attached to fibers or even to other crystals, especially when common ions are present, illustrate the limits due to the nature of the sample. The history of the samples usually limits the number of possibilities and the problem then can be reduced to confirmation of a suspected identity. The authors were presented with the problem of identification of crystals in electron micrographs n ith the suggestion that the silhouette angles, practically all the data available to the elec- tron microscopist, be considered as data for the confirmation of identity. It was then realized that crystallographical concepts could be applied to this problem.

ORIGIN AND NATURE OF PROBLEM

Electron micrographs of industrial sludges from the carbon dioxide and sulfuric acid processes for the extraction of cyan- amide from crude, commercial calcium cyanamide showed out- lines of relatively small crystals (ca. 3 to 5, in breadth). The nature of the sample suggested that the crysta!s might be calcite. The confirmation of this hypothesis by a determination of some physical property was desired. The identification of the crystals as the calcite phase of calcium carbonate was confirmed by the use of electron microscope goniometry.

Its general appearance suggested that the crystal might be one of calcite lying on a rhombohedral face.

Figure 3 is an orthographic projection of a calcite crystal show- ing only the unit rhombohedron, r { 1071 ]. The projection plane is parallel to the face r,(lOil) and the crystal is lying on r6(iOlT).

Figure 1 is an electron micrograph of one of the crystals.

a suspected compound as obtained from the litera- ture, can be used to calculate the angles of an ortho- graphic projection of the crystal, which is observed with the electron microscope. A comparison of the angles measured with those calculated may estab- lish the identity of the crystal. It may be possible to determine directly axial elements (axial ratios and interaxial angles) and interfacial angles of unknown crystals. This represents the determination of physical constants with the electron microscope.

The solid lines represent the viaible edges, and the dotted lines represent the edges not directly visible.

All faces in this form are identical; however, in the projection, faces parallel to the projection plane show their true size, whereas those at an angle are reduced in size. -4ngle A is the angle be- tween edges T2T6 and w 6 , and showvs the true value. Angle C i p the angle between the projections of edges Tar6 and ~ 3 r d . The plane formed by these edges in space is a t an angle to the projec- tion plane: therefore, the angle between the edges as projected ie different from the true value. The calculation of this angle, from the axial elements and others such as B and C’, is the problem for the electron microscopiht. (In this paper interedge angles arc considered as internal angles.)

Donnay and O’Brien (4) showed how the apparent interedge angles of crystals observed with the optical microscope could be correlated with true interfacial angles and the axial element,. They demonstrated how known methods of crystal drawing and B

knowledge of the spherical projection and its derivatives, the stereographic and cyclographic projections, could be applied to graphical calculations.

In electron microscopy, the silhouette angles of crystals are practically the only determinative data available. In this paper are presented the application of microscope goniometry to the study of electron micrographs and the use of silhouette angles for the determination of physical constants by means of the electron microscope. The calculations follow the methods pre- sented by Donnay and O’Brien (4 ) .

Figure 4 is a stereographic projection of a calcite crystal showing only the unit rhombohedron { loill. I t is derived from the interfacial angle (OOOl):(lOil), which is 44” 36’ (Dana, 2). This projection was constructed with the use of the Wulff net (Donnay and O’Brien 4).

Point C is the projection of the polar axis of the fundamental sphere of projection and of the c crystallographic axis. The three points, UI, a2, and u3, are the positive poles of the three horizontal axes of the hexagonal system. (double circles), are the stereographic projections of the face poles which are above the equatorial plane of the fundamental sphere.

Calculation of Angles of Orthographic Projection.

The three points, r l , TP, and