996
ANALYTICAL CHEMISTRY
burgh, a lecture on M o d e r n M e t h o d s of Analysis in t h e Training of the S t u d e n t ” was presented b y Christina C. Miller. T h e broad background against which t h e student must be taught was described, and the question of what t h e student should be taught was discussed. The training a t Edinburgh University of t h e potential honors graduate was then outlined, with particular reference t o t h e inorganic side, t h e lecturer’s own domain. Simple apparatus used by students for semimicroqualitative analysis, and for a few microquantitative experiments, was shown. T h e lecture was illustrated by slides.
The 4 0 t h meeting of t h e Physical M e t h o d s G r o u p was held April 14 in London. T h i s meeting was organized by t h e Polarographic Discussion Panel. T h e following papers on polarography were presented: Polarographic Determination of Fluoride. REYNOLDS, AND E. A. TERRY.
B. J. MACNULTY, G . F.
As it had been shown t h a t t h e effect of fluoride on t h e determination of aluminum was a sound basis for determination of fluoride, publication by Willard and Dean of the polarographic method for determining aluminum using pontochrome violet R.S. provided the basis for t h e polarographic determination of fluoride. T h e method consists of measuring the effect of an unknown amount of fluoride on t h e polarographic step produced from a standard amount of aluminum and dye, and comparing the observed effect with t h a t produced by known quantities of fluoride. It has been shown using standard instruments t h a t t h e effect of fluoride on the aluminum pontochrome violet polarographic step is quantitative down t o 0.1 microgram per ml., while the use of t h e cathode ray polarograph enables a lower limit for determination of fluoride in water solution of 0.001 microgram per ml. t o be reached. I n t h e latter case it is necessary t o allow t h e solutions t o stand for 24 hours prior t o polarographing, in order t h a t t h e slowly attained equilibria in t h e solution may be reached; otherwise results are meaningless. T h e method has been applied t o the determination of fluoride in hydrochloric and hydrobromic acids and bromine. Impurities which would otherwise interfere with t h e method-Al, Fe, etc.-are removed by shaking out with acetonyl acetone. I n certain cases the minute amounts of impurities still present after shaking out prevent formation of a flat t o p t o t h e polarographic step; this can be overcome by the addition of a small amount of cadmium. When t h e cathode ray instrument was used a t full sensitivity. considerable trouble was experienced due t o vibration of the mercury pool, but the use of a n external electrode avoids this.
A meeting organized jointly b y t h e Microchemistry G r o u p a n d t h e Scottish Section was held May 6 a t t h e University of Glasgow, at which the following papers were discussed. Geochemistry and Microchemistry. DAVIDT. GIBSOS. Many of t h e most valuable scientific advances have been made either by extending ordinary investigations to extreme lengths or by exploiting the borderlands between two so-called distinct sciences. Geochemistry may be regarded a s a combination of both these, for it extends the study of chemistry in space and time and temperature and it takes evidence from astronomy, biology, and geology. It is of particular interest t h a t it was by t h e microchemical determination of the rarer components of ordinary rocks t h a t Goldschmidt was able to rationalize the cycles of elements in space and time. Kearly all his work was done by quantitative emission spectroscopy and while it was rigorously controlled by comparison with synthetic specimens, it was of necessity limited in scope and by shortage of collaborators. A much more comprehensive survey of t h e possibilities of Goldschmidt’s methods is being envisaged in the U. S. As a preliminary, a large amount of carefully mixed natural rock standards is being accumulated. These will ultimately serve as a more dependable control for spectroscopic methods, but from the interim report (“Cooperative Investigation of Precision and .kccuracy in Chemical, Spectrochemical, and Modal Analyses of Silicate Rocks.” U. S. Geological Survey, Bulletin 9S0, 1951) it is evident t h a t much work on classical lines remains t o be done before a n adequate consensus of analytical opinion can be reached. Microanalysis of Silicate Rocks. Determination of Alumina. CHRISTINA C. MILLER AND ROBERTd. CH.4LMERS. The complications attending the classical method of determination of alumina in silicate rocks, and difficulties peculiar to t h e micro scale, were reviewed. Earlier attempts by microchemists to devise a n improved method for t h e determination of alumina were briefly described. A new procedure was presented for t h e separation and direct determination of alumina in 5-mg. samples of silicate rocks. Silica is eliminated by means of hydrofluoric and sulfuric acids, and the residue is fused with potassium bisulfate and extracted with acid. Several metals together are eliminated with cupferron and an organic solvent, and then aluminum is extracted as t h e acetylacetone complex, and finally converted into aluminum 8-hydroxyquinolinate. Microchemical Determination of Sulfur in Organic Compounds. WILLIAMS H. M ~ S S I E .
Organic compounds t h a t contain nitrogen in addition to sulfur give. on combustion in oxygen over platinum, a nonquantitative yield of Amperometnc Titration of Zinc and Its Application to Determination of Zinc in Lubricating Oils. D . PICKLES A X D C. C. WASHBROOK;. nitrous and nitric acids whose presence renders worthless the simple and rapid microtitrimetric procedure for sulfur as sulfuric acid. A method was described for the determinat.ion of zinc by ampero4 number of modified volumetric methods for the estimation of metric titration with disodium ethylenediamine tetraacetate (Versulfur in this type of compound have been described, but none is comsene) in a strongly alkaline solution containing cyclohexylamine, or in pletely satisfactory owing to involved technique or to defects inherent a buffered solution containing ammonium acetate. The method is in the method. applied t o t h e determination of zinc in new and used lubricating oils: A promising physicochemical titrimetric method, supported by interfering elements are either removed (copper, iron, barium, lead) analytical results, was advanced a s a suggestion for the direction of or suppressed (calcium). future work on this subject. Tentative Method for Determination of Calcium by Means of the Polarograph. BERTHA LAMB.
T h e Phy,sical M e t h o d s G r o u p held i t s 4 l s t meeting on M a y 8 at Ipsviich, joint w i t h t h e E a s t S n g l i a n Section of t h e Royal Ins t i t u t e of Chemistry. T h e follon-ing papers were presented a n d
T h e direct determination of calcium polarographically presents a certain amount of difficulty because the choice of a base solution is restricted t o the quaternary ammonium derivatives (owing t o t h e high negative decomposition potential required-greater than - 2.0 volts). T h e impurities frequently found in t h e base solution-i.e., mono-, di-, and trimethylamines-all have decomposition potentials in t h e same region as t h e calcium and therefore interfere with t h e determination of the calcium step. I n addition, there appears t o he some evolution of hydrogen, which creates a change in the p H of t h e solution in the immediate vicinity of t h e dropping electrode, even in solutions where the initial p H was greater than 7. This causes inconsistencies and nonreproducible polarograms. T h e addition of lithium or barium hydroxide improves the shape of t h e waves and it is possible t o determine calcium in concentrations ranging from 0.1 t o 1.0 millimolar. T h e final base solution consisted of 0.016 M tetramethylammonium bromide (specially purified) and 0.0016-0.0032 Ai’ lithium hydroxide. T h e concentration of lithium hydroxide has to be increased with increasing concentration of calcium t o eliminate the maxima and other irregularities which occur. Work using specially purified quaternary salts is continuing.
at Llandudno. K o r t h Wales, from J u n e 12 to 15. h paper entitled
I t a meeting of t h e S o r t h of E n g l a n d Section on Xlay 2 in Liverpool, W. Gordon C a r e y a n d J. G. S h e r r a t t discussed “ T h e .knalyeis of Waters, Sewages, a n d Effluents.”
“ R a n d o m Reflections on F o o d Legislation” was given b y C. -4. ..idams, Ministry of Food, F o o d Standards, a n d Lab$ling Division.
discussed. Semiquantitative Techniques in Spectrochemical Analysis. R . L. MITCHELL. Some Techniques of Presentation of Sample to the Spectrograph. A. H. C . P. GILLIESON. Applications of the Porous Cup Technique. L. G . Yor-sc. A t a meeting in London on May 20 the following papers w e r e presented. Determination of Ergosterol in Yeast. 1%’H. . C. SHAWL X D J. P. JEFFERIES. Estimation of Micro Quantities of Calcium. G . E . HARBIION .4ND W.H . A. RAYMOND. Ultraviolet Spectrophotometric Estimation of the Quality of Minerat J. €3. M. COPPOCK, .4XD Oils Extracted from Bread. M. A. COOKSON, R . SCHNCRXANN.
-1summer meeting of t h e S o r t h of E n g l a n d Section was held
