LETTERS T h e Periodic (?) Table
few attempts to actually change the law in the light of more recent knowledge. It is hardly scientific to To the Editor: maintain that Mendeleeff's original statement is One of my students asked me the other day: "Is it sacred and subject to no modification whatever forevertrue that the periodic law has been discarded as ob- more. solete?" He had just been reading the paper by W. F. The only concrete difficulty Professor Cadbury Luder in the January issue of this JOURNAL entitled mentions is that "the resemblances between magnesium "Electron Configuration as the Basis of the Periodic and zinc and between sulfur and chromium, as shown rable." Since I was already somewhat irate on the by sulfates and chromates, are not so much as sugsubject of this paper, the remark induced me to gested in this chart." This objection is conclusively write this letter. answered by a glance a t the chart, where it is perfectly Among the reasons for my irritation was my belief obvious that both chromium and sulfur have six that there have been too many pet "periodic charts" valence electrons and that magnesium and zinc have published in recent years, including the same chart by two. Furthermore, the chart immediately makes the same author in this JOURNAL in 1939. Another plain the reason why chromium does not have a valence reason was the optimistic claim made for the merits of of minus two as sulfur does! this latest chart: "The chart . . . overcomes all . . . the When the chart was first proposed in 1939 (based on defects . . without introducing any new difficulties." Ebel's suggestion in this JOURNAL) I was not aware of Among the new difficulties which occur to me is the Gardner's chart published in Nature in 1930. Gardner fact that the resemblances between magnesium and was among the first to realize that the solution to the zinc and between sulfur and chromium, as shown by problem of pet periodic charts demanded a change in snlfates and chromates, are not so much as su~zested the law to one based upon our knowledge of atomic . . in this chart. structure. After becoming acquainted with Gardner's The strongest objection, however, is that although chart and the other atomic structure charts discussed this chart is an interesting wav of classifving the in the second article, I noticeathat Mitra's goal of a elements, it is not a periodic table. * A periodic tabye is a combination of the periodic table with the table of graphical representation of this important natural law: electron configuration was realized simply by adding to that the properties of the elements are periodic the top of the original form of my chart the s, p, d, f functions of their atomic numbers. The Luder chart divisions of the electrons. I repeat: A chart of the places elements with similar properties in the same elements based upon electron configuration is not vertical column, but i t does not bring out the all- merely another rearrangement of the Mendele& chart. important fact of periodicity; in fact i t abandons It is a modification of the periodic law made necessary periodicity altogether. Hence the completely false by the confusion arising from the many attempts to impression as to the present status of the periodic law merely rearrange Mendeleeff'schart to conform to new registered by the student quoted above. Let us retain experimental facts. the periodic table as a representation of the periodic W. F. LUDER law. N O R T H E A S TUEN~ I V E R S ~ BOSTON. MASSACHUSE~~S WILLIAM E. CADBURY, JR.
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Cubic Centimeters a n d Milliliters
To the Editor: Professor Cadbury's imtation is revealed not only by his frank declaration of it, but by the fact that his two principal objections to an electron configuration chart are merely matters of opinion. They are also niutually contradictory. According to Professor Cadbury too many pet periodic charts have been published in recent years, yet this one is not a periodic chart. The whole point of my article lies in this contradiction. The very f a d that so many modifications of Mendeleeff's chart have been suaaested indicates the need of some modification of the ld;ig:nal statement of the periodic law. The article gathered together the
To the Editm: On page 149 of the March number of your excellent Journal, V. T. Jackson makes the claim that the term cubic centimeter is preferable to the "tongue twisting and confusing milliliter" although he admits that the liter has been defined by the International Commission of Weights and Measures as the volume occupied by a kilogram of water a t its maximum density. It is true that the original intent was to make the liter exactly 1000 cubic centimeters and the error in accomplishing this is surprisingly small. Few of us can work within 0.03 of one per cent in any of the measurements we make.
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I think i t was in 1910 that I wrote to a maker of chemical apparatus asking him why he marked all of the measuring instruments in ml. rather than cc. He replied "Ask the Bureau of Standards." I wrote a letter to Dr. Stratton, who was then Chief of the Bureau of Standards, and he replied very positively that the liter was not properly defined as one thousand cubic centimeters and that the milliliter was the proper term for one-thousandth of a liter. He informed me of the fact that the emor was 0.03 of one per cent and to this I replied that I had read about the error but had no idea it was so slight. I told him that I thought it was very silly to insist upon the distinction. However, no one to whom I talked failed to agree with the logic of Dr. Stratton's remarks. Since that time I have never seen a new measuring instrument that was not marked in ml. rather than cc. Unfortunately, chemists had for quite a number of years been using the Mohr liter which was the volume occupied by a kilogram of water a t 17.5'C. Moreover, Wagner thought that this temperature was too far below the average laboratory temperature and he proposed the temperature of 20°, which is the temperature a t which measuring instruments are today assumed to be correct. Others preferred to use true liters as defined by our Bureau of Standards. When the Bureau of Standards asked the makers of measuring instruments to use ml. rather than cc., there were a t least three different kinds of liters in fairly common use-the true liter, the Mohr liter, and the Wagner liter; and there were three different abbreviations used for the thousandth part of the liter, namely, c.c., cc., and ~ r n . The ~ error between the cubic centimeter and the milliliter is least with the true liter. I am certain that the Bureau of Standards thought they were making things simpler and better by asking instrument makers to calibrate their instruments in terms of the true liter and to use the abbreviation ml. rather than c.c., cc., 01 c m 3 A few years ago, the leading English journal on analytical chemistry, The Analyst, instructed all persons submitting papers to use the abbreviation ml. unless they actually meant a cubic centimeter. The prefix milli is commonly used to represent onethousandth of the whole. Thus we have milligram, millimicron, millifold, millifarad, milligrade, millistere, milli-equivalent, etc., and these terms are not difficult to understand. The idea that the six syllables of cubic centimeter can be pronounced more quickly and with less use of the tongue than the four syllables of nzilliliter is interesting, but not true. The idea that cc. can be written more quickly and easily than ml. is certainly true in the case of the amateur typist who rarely uses more than two fingers in his typewriting but of no other typist and certainly the reverse is true in writing longhand. There is a tremendous amount of inertia against doing anything differently from that done by our forefathers. Thus scientists for about one hundred and fifty years have been telling folks that the metric
system is better than the English system of weights and measures hut, except in times of war when we have to make ammunition and machines to correspond to those made with the metric system, progress toward making its adoption universal is very slow. Our textbooks, particularly those for beginners, are tenihly conservative and the authors explain things the way they were taught irrespective of any results ,of modem investigations. Thus youth is still being taught that sodium is first set free when a solution of sodium chloride is electrolyzed although M. Le Blanc in about 1890 showed that such an idea is preposterous; youth is still being taught that the electric current flows in a north to south direction although most every scientist knows that the electric current is really a stream of electrons flowing in a south to north direction, and, as a result of the same sort of conservatism, many texts still teach that a liter is one thousand cubic centimeters. It has been over forty years since I began to say milliliter instead of cubic centimeter, and I have certainly taught thousands of students to do the same thing. As far as I know, none has offered any argument against this practice. It is true to be sure that in 1910 the United States Pharmucofileia adopted the abbreviation mil. instead of cc. and this caused so much confusion and provoked so much opposition that the editors never have dared to use anything but cc. in subsequent editions. WILLIAM T. HALL Rowr~s~en, MASSACHUSETTS Ultraviolet Tyndallorneter To the Editor: Your articles are always a source of interest to me, but one in the February, 1943, issue has especially attracted my attention. I t is entitled "A simple and permanent tyndall cone apparatus," by Abrahams and Dubner. You will be interested to know that this instrument can also be employed as an "Ultraviolet Tyndallometer," and the effects produced with it used for a wide variety of purposes as well as for spectacular lecture demonstrations. The ultraviolet Tyndallometer is an instrument of my origination, being first described in detail in the hook "Ultraviolet Light and Its Applications." The Abrahams and Dubner apparatus can be used without modification, except that a small amount of visible light fluorescing substance is added to the solution to enhance the features of the cone. Betamethyl umbelliferone is very satisfactory in this regard. However, by substituting an ultraviolet source for the small light globe, and a quartz or pyrex lens for the glass lens, it is possible to construct a simple ultraviolet Tyndallometer which will show properties of a solution such as its absorption characteristics, the Tyndall effect, and qualities in regard to fluorescence intensity. JACKDE MENT Coucn BUILDING PORTLAND. OREGON
