Electrically Operated Buret FREDERICK C. The
NACHOD
Atlantic Refining Company, Philadelphia,
Pa.
A series of experiments which were carried out several years of avoiding contamination of the titration liquid by stopcock grease was encountered. The solutions mainly consisted of bromine dissolved in light and “heavy” methanol (CHjOH and CH»OD), and were used in the determination of keto-enol equilibria {!).
INago, the problem
The apparatus employed, shown in the diagram, consists of a conical seal, S, which must be ground with great care; the male part of the seal is formed into a plunger, Pt which contains an iron core, C, suitably made of about 6 iron nails. This core is about 1.5 cm. long and 0.5 cm. in diameter. A top view of the upper cross section of the plunger is shown at the right. The four protrusions maintain the plunger in its vertical position during motion. Two solenoids, A and S, made from bell wire, and consisting of about 20 windings each, are connected over a 6-volt battery by means of a Morse key, K. If the key is released, solenoid B is actuated and provides magnetic “suction” for the seal; if the key is pressed down or tapped, the plunger rises and the solution is permitted to flow out of the buret. In preparing the assembly, it is recommended to start with the conical seal, to connect the seal to a calibrated buret, and then to slide in tne plunger. The apparatus described was made for a 10-ml. buret but can be adapted to larger burets.
LITERATURE CITED
(1) Nachod, F. C., Z. phyaik Chem., A182, 209 (1938).
Pbesented before the Spring Meeting oí the Philadelphia Section, American Chemical Society, June 13, 1945.
Titration of Boric Acid in the Presence of Mannitol MAX HOLLANDER
and
WILLIAM RIEMAN III, School of Chemistry,
IS well known that the titration of boric acid with sodium is satisfactory only in the presence of glycerol, mannitol, or some similar polyol. Although mannitol has been found most suitable for this purpose (5, 8), the literature contains no satisfactory report on the optimum quantity or concentration of mannitol. Schafer (6) recommends a mannitol concentration at least 0.2 Af, but the accuracy of his conclusion may well be questioned because he used a buret accurate to 0.01 ml. for titrations of less than 0.9 ml. Mellon (4) recommends the use of 1 gram of mannitol, while Kolthoff and Furman (8) and Kolthoff and Sandell (3) call for 0.5 to 0.7 gram of mannitol for each 10 ml. of solution, and Hillebrand and Lundell (J) ask for the addition of 1 to 2 grams. Scott (7) calls for the use of 1-gram increments of mannitol until a permanent phenolphthalein end point has
Rutgers University, New Brunswick, N. J.
mente of sodium hydroxide were 0.10 ml. The buret readings at the phenolphthalein end point (pH of 8.30) and at the steepest point of the titration graph (equivalence point) were observed. The difference in these readings is given in Table I under the heading of “Titration Error”.
IThydroxide
The results obtained from the titration graphs Table I.
are
given in
DISCUSSION
From Table I, it that with an initial volume of 100 ml., the proper quantity of mannitol is about 7 grams, corresponding to a ratio of 27 moles of mannitol per mole of boric acid. When the initial volume is 25 ml., 3.9 grams of mannitol, corresponding to a molar ratio of 15, will give satisfactory results. These conclusions show very clearly that the molar ratio of is obvious
been reached.
This paper presents a study of the effect of varying amounts of mannitol on the titration of boric acid with sodium hydroxide to the phenolphthalein end point. —
Table I, EXPERIMENTAL
Reagents. Boric acid, approximately 0.057 Af, was prepared by dissolving the Merck reagent in freshly boiled distilled water. Carbonate-free sodium hydroxide, approximately 0.045 N, was standardized with potassium acid phthalate. Mannitol, Eastman No. 155, was found to be neutral and used without further purification. Procedure. Twenty-five milliliters of the standard boric acid solution were diluted to a given volume and 2 drops of 0.03 Af phenolphthalein per 100 ml. of solution (volume at equivalence point) were added. A known amount of mannitol was added, and the solution was titrated potentiometrically at room temperature with a Beckman pH meter, laboratory model. In the vicinity of the equivalence point, the incre-
Volume before
Titration Ml. 100 100 100 100 100 100 100 100 100 25 25 25 •
Weight of
Mannitol
Titration of 25 Ml. of Standard Boric Add with Sodium Hydroxide Slope at pH at Molee of Mannitol Moles of Boric Acid
pH of
0.0 1.0 2.0
6.01 5.03 4.72 4.25 3.93 3.62 3.43 3.18 3.01 3.80 3.02 2.88
Oramt
0.00 0.26 0.52 1.04 2.08 4.16 8.32
16.64
33,3®
Ml.
4.0
8.0 16.0
32.0
64.0
0.49 1.9 7.6 1.97 15.2 3.98 This quantity did not dissolve entirely.
602
Equiva· Equivalence Point Point 10.29 9.91 9.70 9.45 8.82 8.48 8.18 7.65 7.36 10.01 8.67 8.50
0.12 0.22 0.88 0.82 1.48 2.70 4.50 5.60 6.70 1.04 3.5
8.4
-14.47 7.27 -
-
-
-
2.13 0.50 0.05
+ 0.03 + 0.12 4- 0.19 -
-
-
5.46 0.06 0.01
ANALYTICAL
September, 1945
mannitol to boric acid is not the deciding factor in determining the amount of mannitol necessary for a good titration. The concentrations of mannitol at the equivalence point are 0.30 and 0.38 M with initial volumes of 100 and 25 ml., respectively. Shabpness of End Point. The sharpness of the end point is determined by the slope of the graph at the equivalence point. If the pheholphthalein end point is to be satisfactory, the slope should be at least 3.0 pH units per ml. Table I shows that the slope at the equivalence point exceeds 3.0 in both cases if the recommended quantities of mannitol are used. CONCLUSION
If the mannitol is present in a large excess over the boric acid, concentration of about 0.35 mole of mannitol per liter of solution at the equivalence point will yield both a small titration error and This observation agrees very well with the a sharp end point. recommendations of Kolthoff and Furman (#) and Kolthoff and Sandell (S). a
EDITION
603 ACKNOWLEDGMENT
The authors are indebted to the Armstrong Cork Company for financial assistance in this work. LITERATURE CITED
(1) Hillebrand, W. F„ and Lundell, G. E. F., “Applied Inorganic Analysis", p. 616, New York, John Wiley A Sons, 1929. (2) Kolthoff, I. M., and Furman, N. H., “Volumetric Analysis", Vol. II, p. 122, New York, John Wiley A Sons, 1929. (3) Kolthoff, I. M., and Sandell, . B„ “Textbook of Quantitative Inorganic Analysis", revised ed., p. 560, New York, Macmillan
Co., 1943. (4) Mellon, M. G„ “Methods of Quantitative Chemical Analysis", p. 237, New York, Macmillan Co., 1937. (6) Mellon, M. G., and Morris, V. N„ Ind. Eno. Chem., 16, 123 (1924).
(6) Schafer, ., Z. anorg. allgem. Chem., 247, 96 (1941). (7) Scott, W. W., “Standard Methods of Chemical Analysis", ed. by N. H. Furman, 5th ed., Vol. I, p. 179, New York, D. Van Nostrand Co., 1939. (8) Van Liempt, J. A. M„ Z. anorg. allgem. Chem., Ill, 151 (1920).
Recommended Practice for Microscopical Reports Crystalline Materialsz in A.C.S. Publications committee of the Division of Analytical and Micro Chemistry was appointed to present a recommended procedure for reporting microscopical crystallographic data. The members were: W. M. D. Bryant, Experiment Station, E. I. du Pont de Nemours A Company; Mary L. Willard, Pennsylvania State College; E. F. Williams, Research Laboratory, American Cyanamid Company, and C. W. Mason, Cornell University, Chairman. After considerable discussion, and correspondence with other microscopists and with the American Mineralogical Society, the recommendations given below were formulated and presented to the Division at the Cleveland meeting, April 4, 1944, where an n 1942 a
the increasing
use
of microscopical crystal studies in re-
search and technology, and the wider knowledge of the underWith such information
should be more lying experimental techniques, frequently and extensively published for the benefit of those chemists who have come to depend on it as a primary or supplementary means of identification. Authors should be encouraged to give detailed crystallographic descriptions (geometrical and optical) of crystals, in all-papers where crystallinity is reported; the editors should consider such data as deserving of space as is conventional chemical information, and where necessary for clarity should allow the publication
of drawings or photomicrographs. When feasible, crystal descriptions may well be reviewed separately. The author may be advised to extend his report, or on the other hand to clarify it for the benefit of those not well versed in the condensed style of formal crystallographic terminology. The term amorphous should not be used as synonymous with “very fine grained” or “unresolvable”, unless qualified—for example, “apparently amorphous”, “microscopically amorphous within the limits of visual (or ultraviolet, or electron) micros-
copy”, etc. The term crystal may be applied to any solid possessing a single continuous lattice structure throughout its extent, whether the crystal exhibits faces (euhedral) or is irregularly bounded (anhedral) or is a cleavage fragment. Twinned crystals properly are only those in which the differently oriented portions bear a specific geometrical relationship to each other: accidently adhering or intergrown crystals are not considered twins. Crystal habit or mode of development should be stated in conjunction with the conditions of formation. The particular habit of a given substance can vary markedly with the method of crystallization, solvent, temperature, rate, associated impurities, etc., which should be reported. For crystals grown on a micro-
on
informal ballot was taken, to submit them for the approval of the Executive Committee of the Division. The recommendations were also discussed with the A.C.S. Committee on Nomenclature, which voiced no objections, and became an official action of the Division of Analytical and Micro Chemistry by authority of its Executive Committee. They are published for the guidance of authors, upon whose willingness to follow them depends their success in bringing more clarity and accuracy of expression to a field where ambiguity has been all too prevalent. They will also serve as an established reference for the use of reviewers and editors when dealing with papers in microsC. W. Mason copy. scope slide from solution or fusion, the common view or preferred orientation should be given. Drawings or photomicrographs may well be used to describe the habit, particularly if it is consistent and significant for descriptions. If several different sets of similar faces (“forms” in crystallographic terminology) are exhibited, their relative sizes should be indicated; it is customary to list the dominant ones first. Cleavage, skeletal or dendritic habit, and any other readily observable and characteristic features should be included in the report. Where clSavage is reported, it is desirable that the number of directions and their mutual angular relationship (true, or traces on a given face) be stated. Crystallographic studies are based primarily upon direetionai properties; directions and orientations must be unambiguously designated if the description is to have meaning. If crystallographic axes and Miller indices of faces are used the assumed setting of the axes should first be stated, with reference to some conspicuous geometrical or optical features, and in accordance with conventional crystallographic practice. Descriptive terms such as “prisms” or “rhombofiedra , which connote a specific crystal form (a group of faces having the same relationship to the crystallographic axes) should be avoided or used in quotation marks unless the faces of these particular forms are
present.
If axial ratios are given, the method of measuring the essential angles should be stated. Axial ratios calculated from microscopical measurements have little value. Angles should be measured wherever possible, but care should be taken that the particular angle involved is clearly and unambiguously designated, preferably on a drawing. Distinction should he made between silhouette (“profile”) angles and true interfacial angles, tod between microscopical and goniometric data. In order to avoid confusion with the symbols for refractive indices, the angles of inclination between the inclined crystal-
