JOURNAL OF CHEMICAL EDUCATION
To the Editor: The modifications of equation (3) as stated by Dr. Goodwin are entirely correct and it is interesting to note that I have alreadv used his sueeested method of derivation (namely, the Tree body method) to check the first derivation by Archimedes' principle. In fact, I also liked the free body method much better and have prepared my subsequent paper using this method. Both methods of course give the same results, but the free body method is more fundamental. I t is unfortunate that Dr. Goodwiu fails to appreciate the importance and necessity of the more rigid derivations, and his facetious attitude concerning an algebraic marathon is out of place, since the mathematics involved are not above the high-school level. The necessity of these more exact relationships will become apparent when d e a h g with higher pressures as will be shown in my subsequent paper. I should also like to pbint out that the U-tube type of manostat with the sealed float is not at all analocrous to the Cartesian type. It is immediately appare;;t that the motion of the float is the same as the liquid surface in which it floats and that the sensitivity of the device a t low pressure is lost due to the insensitiveness of the motion of the float. No doubt Dr. Goodwin has encountered this trouble, as intimated in his letter. If Dr. Goodwin will analyze the action of the float in the Cartesian type of manostat he will realize that the sensitivity of motion of the float may be increased many fold by choosing the proper dimensions, or he may refer to the paper of Germann and Gagosl and obtain a good idea of the problem. I hope to present in a subsequent paper as I had promised in my first paper, a rigid analysis of this problem which I have already worked out in conjunction with the design of a combination high vacuum manostat and gage. I should state that it is not necessary to employ the calculus as was done by Germann and Gagos, and for this reason it may have pedagogical value when presented in simple algebraic form. Germann and Gagos have also assumed the cross-sectional area of the container to be sufficiently greater than the area of the float wall to give their simplified equation, which expresses the magnification as A2/A3 (using the symbols of my paper, and neglecting the area of the vent tube, which does not appear in their vacuum gage). The .more precise expression for this ratio is given by A2A/[A3(AI+A2)], which reduces to the simplified Considering the central expression when A1+A2+A. tube the ratio'is expressed by [A+Ao(AI/A%)]/&(1+A1/A2), where A, = area of central tube. Essentially what all this indicates is that the motion of the float becomes magnified as A3 is reduced in comparison to A2. I trust that I have not appeared unduly pedantic; however, I wish to stress the importance of all the details involved in the above problem because I see a big ~
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GEEMANN. F. E. E. AND K. A. G ~ c o sZnd. . Eno. Chem.. Anal.
future ahead for the application of these Cartesian devices both in industry as well as in the laboratory. To make a proper application of these devices, the smallest detail cannot be disregarded. ROGERGILMOKT THEEMILGREMERCOMPANY NEWYORKCITY
To the Editor: During my ten years of experience in teaching begiuning college chemistry, it has been discovered that there are always a few students that insist on writing chemical symbols with both the first and second letter capitalized such as MN for Mn. A good illustration, which I thought would help to overcome this, recently came to my mind when the initials H. C. L. were noted @na certain professor's brief case and when I asked him what it stood for, he said, "The high cost of living." As a result, it was decided that this illustration ~ o u l d help impress upon the minds of the students that the second letter of a chemical symbol is not capitalized. When it came to teaching chemical formulas, the letters HCL were written on the blackboard and the students were asked what these letters stood for. All the bright students with high-school chemistry raised their hands and, of course, the answer was "hydrocbloric acid." It was then pointed out that it does not stand for hydrochloric acid but instead it stands for the "high cost of living" and HC1 stands for hydrochloric acid. This comical illustration "did the trick" and so far I have not yet discovered any students writing the second letter of a chemical symbol with a capital letter. I would like to pass this idea on to other teachers. ARTHUR W. DEVOR
To the Editor: Finland has an excellent and keenly scientific minded Technical Institute, Teknillinen Korkeakoulu. During the mar its library was bombed and totally destroyed. On my recent trip to Finland for the American Friends Service Committee, I discussed the situation with Dr. Martti Levon, Director of the Institute. He said he would welcome gifts of Scientific and Technical Books and Periodicals from America to take the place of those destroyed. In the remarkable efforts for recovery that the Finns are making, the lack of technical library facilities is a very serious handicap. I t would be a practical act of friendship to a nation that holds America in high regard if Americans should contribute good technical books and periodicals to this library. Any such gifts should be marked for the Institute of Technology, Helsinki, and sent to the Legation of Finland, 2144 Wyoming Ave., N.E., Washington, D. C. Dr. K. T. Jutila, the Finnish Minister, will arrange for their being sent to Finland. ARTHUR E. M0R0.4~
