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INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 7. NO. 4
Discussion
Literature Cited
The purpose of special analytical technics is to increase the economy of analysis. Emich (6) has enunciated this as a general principle:
(1) Benedetti-Pichler, A., 2.anal. Chem., 73, 257 (1928). (2) Brenneis, H., Mikrochmie, 9,385 (1931). ENG.CHEM.,23, 1301 (1931). (3) Clarke, B. L., IND. (4) Clarke, B. L., and Hermance, H. W., J.Am. C h m . SOC.,54, 877 (1932). (5) Emich, F., “Lehrbuch der Mikrochemie,” 2nd ed., Munich, J. F. Bergmann, 1926. (6) Goubau, R., Chimie & industrie, 17,170 (1927). (7) Grassner, Mikrochemie (2), 4,255 (1931). (8) Hermance, H. W., Bell. Lab. Record, 13,81(November, 1934). (9) Kirner, W. R., IND.ENG.CHEM.,Anal. Ed., 5,363 (1933). (10) Moser, L., Mikrochemie, 1,l (1923). (11) Niessner, W., Ibid., (2), 4, 271 (1931). (12) PetBrfi, Naturwissenschaften,6,81 (February, 1923). (13) Titus and Gray, IXD. ENG.CHEM.,Anal. Ed., 2,368 (1930).
Auf allen Gebieten menschlichen Schaff ens kommt dem Prinzip der Okonomie die grosste Bedeutung au. Dieses Prinaip verlangt bekanntlich, dass man sich bemiihen muss, ein gegebenes Ziel mit einem Minimum von Material- und Energieaufwand, von Zeit und von Denkarbeit zu erreichen.
Perhaps the most characteristic feature of micrurgy is its employment of direct observation instead of inferential deductions from indirect observations. The organic chemist, wishing to determine the position of a substituent, is not able to make direct microscopic observation but must rely on circumstantial evidence. Similarly, a paper chemist, if limited to macroanalytical methods, might conclude from analyzing the ash of two condenser papers that the one with the higher iron content would be functionally the poorer. But micrurgical examination of the papers might disclose that the one with lower iron contained actual metallic particles, greatly reducing the breakdown resistance, while the iron in the other was evenly dispersed as the relatively innocuous iron oxide. Again, a lead-cable-sheath corrosion product, examined by “test tube” methods, might show no active ion, and the analyst would be a t a loss to diagnose the corrosion cause. Under the microscope, however, tiny pockets might be found which contained a high chloride concentration, easily detected micrurgically because the test is made in situ and not after dilution below the sensitivity of the test. Many other similar instances could be given where analytical data are useless or even misleading when the factor of distribution is not taken into account. Many materials are made up of minute structural elements, upon the nature and interrelation of which depend most of their gross mechanical properties. In such cases micrurgical methods are necessary no matter how large the available sample. Petrographers and metallographers preceded analytical chemists in recognizing the importance of this in analysis.
Conclusions 1. Directors of analytical laboratories should strive to provide a t least some facilities for the use of all analytical technics, so as to allow some freedom of choice in a given problem. 2. The natural tendency is to use samples and apparatus of a size convenient to handle. The principle should be inculcated that following this tendency is often the way of inefficiency and sometimes results in gross error. The analyst should shape the apparatus and methods to the job, not to his hands. While the authors cannot fully agree with Benedetti-Pichler (1) that no special skill is necessary for the use of micrurgical methods, it is certainly true that much good micrurgical work can be done by any conscientious, welltrained analyst. 3. Teachers of microanalysis should impress upon their students that the operations of sampling and preparation in industrial micrurgy frequently require more time and skill than microchemical tests proper. 4. Finally, the authors would urge manufacturing engineers and research directors to adopt a more critical attitude towards analytical results. They will thus come to appreciate both the possibilities and the limitations of chemical analysis, and will be able properly to appraise the value of analysis to manufacturing and research. The prestige of the profession of analytical chemistry will not suffer from this appraisal.
RECEIVEDMay 3, 1936. Presented before the Division of Physical and Inorganic Chemistry, Symposium on Recent Advances in Microchemical Analysis, a t the 89th Meeting of the American Chemical Society, New York, N. Y., April 22 to 26, 1935.
An Efficient Vacuum Pump Check Valve ROY L. MOBLEY Lacto-Yeast Co., Inc., Baton Rouge, La.
IN
MANY instances the laboratorian is not aware of the availability of mechanical devices of professions associated with his, and their most efficient adaptability to his purposes. Such an instance is evident in the use of the water-operated vacuum pump. Of the valves used for this purpose, none have ever consistently filled the requirements over any period of time. The writer, constantly working with this type of laboratory apparatus, desired a perfected valve, which was easily had by using simple pipe and fittings with a ballcheck valve. The materials required include one 0.125-inch brass ballcheck valve, one 0.125 X 3 inch brass nipple, one 0.125 X 8 inch brass nipple, and two 0.125-inch brass street ells. Determine the direction of flow through the valve and start
the street ells in either end. Then insert the shorter nipple in the exit ell and the longer in the entrance, so that the longer of the two will be placed in the trap bottle and the shorter will lead t o the pump. Tighten the joints well with a wrench, being sure to leave the valve in its upright position and horizontally in the assembly, otherwise it will not work. Then insert in the stopper of the trap bottle and connect to the pump by means of tubing. The trap serves as a further safety device, should the valve leak a bit. Such a valve has given very satisfactory service when used on a pump maintaining from one to three funnels under a vacuum of 10 to 20 inches of mercury. RECEIVED May 10, 1936.
