1130 and a new electrode stand designed for this work. Tables showing the reproducibility and ~ C C U P B D Yof single determinations were presented. Mention was made of other metallurgied samples analyved and of various diffioulties already overcome in the application of the method t o the complete snalysis of soluble miscellaneous residues rtshas, and corrosion products.
An ordinary meeting of the society was held May 20, in London. T h e following papers were presented and discussed. Determination of Ergosterol in Yeast. W. H. C. SXAWINDJ I’ JEPFERIES.
ULTRA~IOLET ASSORPTION OF PURXFIED ERGOSTEROL. Most published records agree on the wave lengths of the three main peaks in the ultraviolet absorntion curve of erzosterol. but there are discreeancies in the extinction values reported for the various maxima. apparently beoause of the diffioulty of preparing pure ergosterol by direct recrystdlisation of the commercial material and t o a lesser extent because of small variations in the moisture content of the hydrated sterol. Simple recrystallisation does not ralws,ys yield a pure product; the best means of purifioation is by recrystallising a suitable ester, with subsequent regeneration of the sterol. The preparation and purification of ergosterol benzoate were described and the physical properties and ultraviolet %hsobsorption (in various solvents) of s purified speoimen of ergosterol were recorded. DETEBMINAT~ON BY SAPONIFICATION AND ULTRAYLOLET ass on^ T ~ SPECTROBCOPY. N Part of the ergosterol found in yeast occurs in a combined form, and treatment to liberate the free sterol is a %acesmry preliminary to its determination. Most published methods make use oi alcoholic or aqueous alkali hydroxides for this purpose. and the variety of strengths prescribed suggested that further investigation was necessary. The oonditions for the destruction of the yeast cells and maximum reoovery of ergosterol have been studied. Boiling under reflux with alcoholic sodium or potassium hydroxides did not break down the yeast sufficiently. Aqueous sodium hydroxide a t strengths from 10 to 50% w./w. gave low a i d erratio results. additiond ergosterol being recovered by subsequent alcoholic saponification of the residue. Concentrations of potassium hydroxide above 20% w./w. i n aqueous solution proved sstiefactory. the strength required depending on thelength of boiliigunderreflux. For the method described 40% w./w. aqueous potassium hydroxide has been selected. as it makes possible eonsidemble latitude in time and concentration The ergosterol in the extracted unsqponifiable matter is Separated hy digitonin precipitstion from nonsterol substances that show irrelevant absorption in the same region as ergosterol. This preoipitation has been shown to be quantitative, the separated sterol digitonides iielding solutions speotroseopically indistinmishable at wave Iewths above 260 ma from those of purified ergosterol. CoRREcnoNs FOR IRRELEv*NT ABBORPTIONI N SOLUTIONS O F Encos~mno~.The unsaponifiable matter of yeast normally oontains substances that po6sess ultraviolet absorption in the same region as ergosterol. so that the ertinct,ion at the ergosterol maximum (282 mi” in absolute alcohol) cannot be used directly as a measure of the eonoentration of ergosterol present. Although digitonin purifiestition may be used for separating ergosterol in a spectroscopically pure oondition. considerable time can be saved by applying a cormction prooedure to the gross absorption. , Two suoh prooedures have been studied: (1) a eorreotion of the Morton and Stubbs type. based on the 282-mi” maximum m d two subsidiary wave lengths at which the purified compound ~ossesszs maximum absorption, and (2) a new four-point correction based on the three ergosterol maxima (271.5, 282, and 293.5 ma) with 8. fourth reading at 310 mi”, where eraosterol shows very little absorption. Procedure 1 suffers from the disadvantage that the maxima in the absorption curve of ergosterol are sharp and observations a t the subsidiary wave lengths must be taken on steep portions of the curve. In omsequence, small errors in measuring wave lengths have a large effect on the oorrection factor and any instrument used for this procedure must be calibrated with pure ergosterol. Procedure 2 is free from this disadvantage but requires 8; greater range of wave lengths and linearity of absorption must be assumed over it. Results by both corrective procedures were compared with those by the full digitonin method. The degree of agreement is generally good, but depends on the shape and amount of irrelevant absorption, which ha8 been determined on %numberof differentstrains of yeasts. The &eSnom METXODBASEDON U m a n v i o m ~ABSORPTION. ourate method for determining ergosterol in yeast described above has proved too lengthy for the examination of large numbers of samples. A short semimioromethod involves saponifying a portion of the yeast sample oontsjning about 1 mg. of ergosterd with a small volume of 40% w./w. aqueous potassium hydroxide in a epeoially designed flask and extracting the unsaponifiable matter with a single
A N A L Y T I C A L CHEMISTRY accurately measured volume of oyoloheamne. The filtered extraot is suitable for speotroscopic enaminhtion. The four-point correction procedure is applied to allow for irrelevant absorption; the ergmterol content of the sample is calculated from the corrected extinotion a t 252 ma (man.). The method requires much less manipulation time than the full digitonin procedure but. because a geometrical correction and a single extraction only are used. gives results slightly lower and n standard deviation of .s single determination a little greater than sre go%with the full method.
The Estimation of Micro Quantities of Calcium. G. E. HAREISON W. H. A. RAYMOND. A micromethod for the estimation of odoium is based on the colorimetrio estimation of a molybdenum thiooyanate. An aceur~oyof bett.er than 10% is attained for solutions containing as little as 4 y of calcium. The method is especially useful for the estimation of serum calcium in young children or smaI I laboratory mimals. A comparison of the results with those found by other methods was AND
given. Ultraviolet Spectrophotometric Estimation of the Quality of Mineral Oils Extmeted fmm Bread. M. A. C O O X ~ J. I NB. , M. COPPOCX, AND R. S C ~ N U W A N N . A method has been developed hy which the degree of refining of a mineral oil that has been absorbed by a dough during bread making may be determined in the resultant bread. The method consists basically of sulfating. under controlled conditions, the unsqponifiable fraction of the total oils extracted from bread, 80 that the natural saponifiable matter is destroyed without completely removing the unsaturated hydrocarbon constituents inherent in mineral oils of different degrees of refining. The recovered mineral oil is then examined by ultraviolet absorption speotrophotometry to determine its quality. A spectrophotometric criterion was suggested for the wa1ity of mineral oils that could be regarded as satisfactory for the lubrication of plant used in bread production.
Merck Fellowship Award Donald H. Vilkins of Park Rapids, Minn., a graduate student at the University of Illinois, was selected for the fifth annual $2500 Merrk Graduate Fellowship in Analytical Chemistry. Farrington Daniels, President of the AMERICAN CHEMICAL SOCIETY, presented the award at the 123rd meeting of the Society in Los Angeles, Calif. Mr. Wilkins, who received his M.S. in 1052, has completed two years of research under the supervision of G. Frederick Smith. Pending publications resulting from this work are on the following subjects: a new copper-specific reagent; 2,4,6-trinitrobeneoic acid as n primary standard in acidimetry; and D. Wi’kins spectrophotometrio studies of substituted 1,lO-phenanthrolines as their ferrous chelate complex ions. He will continue t o work rtt the University of Illinois on the chelate complexes of various series of compounds with spec metric reagent.8 for t tion indicators, and a
Microdetermination of 3-(p-Chlorophenyl)-l,ldimethylurea in Plant Tissue-Correction In the article on “Microdetermination of 3-(p-Chloraphenyl)1,l-dimethylurea in Plant Tissue” [Young, E. Y., and Gortner, 5’.A,, AXAL.CHEM.,25, 800 (1953)l in the sixth line under the heading Reagents, the listing should hawe been: N-(1-Xaphthyl). ethylenediamine dihydraehloride, 2%.
