INDUSTRIAL AND ENGINEERING CHEMISTRY
1150
Potentiometric Control The wiring diagram in Figure 3 of the potentiometric control used for bringing the mechanical zero and the electrical zero together is probably self-explanatory. A precision potentiometer is not necessary for this work, and an ordinary 400-ohm potentiometer made by the General Radio Company, intended primarily for amateurs for radio telephone work, has served the purpose excellently. The inexpensive rheostats used in radio work also serve admirably for the control of the X-ray tube filament current from storage batteries. This instrument is connected across a 2-volt 20-ampere-hour Exide storage cell. Dry cells were previously tried as a source of power a t this point, but gave difficulties due to their falling potential during the long runs, and the small investment required for the storage cell is far offset by the added certainty of operation. This control is located 6 or 8 feet away from the electrometer, together with the necessary high-tension battery for charging the needle of the electrometer and for mounting the high-tension electrode in the ionization chamber a t its proper potential. At this paint are also located the control for the make-and-break switch, the telescope and illuminated scale for reading the electrometer, and the necessary reversing and grounding switches used in making a run. General Comments All wiring in connection with the apparatus can well be shielded. Heavy high-tension automobile cable will be found satisfactory when run inside ordinary 3/4-in~hthin tubing. All metal parts of the apparatus which are supposed to be at the ground potential, including all shielding, can best be grounded to a common ground wire, thus eliminating any difficulties due to difference in potential between two grounds. High-tension dry batteries such as are used for radio work will be found entirely satisfactory as sources of high-tension energy for charging the electrometer needle and the ionization chamber electrode. Forty-five volts will usually be sufficient to use on the needle and anywhere from 90 to 200 can be satisfactorily used in the ionization chamber. Some difficulty may be experienced from vibration if the apparatus is set up on any floor other than a basement floor, and it is therefore rec-
Vol. 17, No. 11
ommended that installation be made on a firm foundation provided on a concrete floor in the basement of the building where the apparatus is to be used. Successful Uses of Spectrometer Installation This spectrometer installation is being successfully used in several chemical investigation^,^ of which the following are examples : (1) Evidences of chemical changes in valence from precision spectra including resolution of the KB lines into at least two components. (2) Fluorescent wave lengths of heavier elements, (3) Scattering and wave length shifts. (4) Secondary valence as revealed by the crystal structures of complex compounds. (5) Colloids: particle size from the widths of diffraction lines, and flocculation by rays of single wave length reflected from crystals. ( 6 ) Molecular orientation and dimensions from the structure of organic films as thin as lp and invisible to the eye. (7) Changes in metals on annealing and on hardening. (8) Mechanism of catalysis from a comparison of structures of metal catalysts of different activities depending upon method of reduction from oxides. (9) Polymerization of liquids from a study of the diffraction rings. (10) Study of possible structural differences in passive and active surfaces. (11) Crystal grain orientation in metals electrodeposited from widely different conditions of concentration, current density, etc. (12) Fundamental nature of rubber and similar products which show crystalline diffraction patterns when stretched.6 I n conjunction with the precision spectrometer use is being made of the usual powder diffraction, Laue, and monochromatic pinhole photographic methods. The last method has been developed with especially fruitful results and is the subject of another paper.6 4 For specific experimental results already obtained see Clark, "Photochemical and Ionization Studies," Proceedings International Congress of Radiology, London, 19.26, J. Am. Ckem. SOL (in press); Proc. N o t . Acad. Sci. (in press), 2. Elektrochem. (in press). 6 Katz, Ckem. Zfg., 49, 353 (1925). Six papers by Katz have been critically considered in a paper by Clark, India Rubber World (in press). 6 Clark, Brugmann, and Heath, Tma JOURNAL, p. 1142, this issue.
Determination of Asbestine in Lithopone Paint' By Frederick G. Germuth DEPARTMENT OF PUBLIC W O R K S , BUREAUOP
SAMPLE of lithopone paint, specified as containing 3 A per cent asbestine as a binder, was submitted to the writer for a complete chemical analysis, especially to ascertain the exact quantity of asbestine present. After the percentage of pigment and vehicle had been determined by the usual methods, and the zinc sulfide content of the pigment determined volumetrically with a standard solution of potassium ferrocyanide, 1 gram of the sample (dry pigment) was placed in a 250-cc. beaker and acid ammonium acetate added. As no lead was present and the barium sulfate and asbestine were insoluble in this medium, both were separated by filtration. Separation of these two constituents was then accomplished in the following manner: The filter with its contents was placed in a platinum crucible, ignited, and fusion mixture K&03) added and thoroughly mixed with the (NazCOa other contents of the crucible. The crucible was then heated
+
1 Received
September 9, 1925,
STANDARDS,
BALTIMORE, bID.
a t a temperature of 600" to 700" C. for 30 minutes. At the end of this time the barium sulfate had completely decomposed, and sodium and potassium sulfates and barium carbonate were formed. The asbestine remained unacted upon. The crucible was then placed in a beaker of water and heated to leach out the resulting mass. A slight excess of hydrochloric acid solution (1:l) was then added to convert the barium carbonate to barium chloride. The asbesthe wm separated by filtering off on a Gooch crucible, using the siphon. After heating the Gooch crucible a t 105' to 110' C . to constant weight it was weighed and the percentage of asbestine obtained. The filtrate was heated to boiling and then treated with sulfuric acid (1:1) to reconvert the barium chloride to barium sulfate, in which form it was determined. Both the barium sulfate and asbestine contents were determined in this manner, and the results of the asbestine determination obtained by this method on six samples of the material varied by only 0.1 per cent.
