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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 16, No. 7
left from lithopone when the zinc sulfide is eliminated with hydrochloric acid. The index of refraction of blanc fixe is higher than that of bromoform. Blanc fixe is eliminated with hot, concentrated sulfuric acid.
( b ) If both lead sulfate and zinc oxide have been found, it is necessary to decide whether or not these substances are in combination as a leaded zinc oxide. Disregard this point for the time being, pass to VII, and complete the analysis. After the analysis is completed, note whether any other substances except zinc oxide, lead sulfate, and obvious SCHEME OF MICROCHEMICAL ANALYSISFOR MIXEDWHITE inerts have been found. PIGMENTS AND INERTS (c) Only lead sulfate, zinc oxide, and inerts are known to be present. Make Paravar test. If every particle (except 1-If the pigments and inerts are present in paint, remove particles that are obviously inerts) shows discoloration, then vehicle according t o method given under A-1. the pigment is leaded zinc oxide. If distinct squarish par11-Make a damar mount (A-3) with the dry material. ticles stand out without discoloration, basic lead sulfate is Examine carefully and note those pigments and inerts that present and the pigment is composed of either pure zinc oxide can be recognized by the presence of characteristic particles. plus basic lead sulfate, or leaded zinc oxide plus basic lead 111-Prepare a number of turpentine dispersions. It is sulfate. If the Paravar reaction is light, in all probability convenient to have some of these dispersions of heavy and the zinc oxide is presekt as high-leaded zinc oxide; if the resome of light density. action is strong, then the pigment may contain pure zinc IV-Take a heavy dispersion and eliminate with hot, oxide or low-leaded zinc oxide. Any further microchemical concentrated sulfuric acid. ( a ) No residue; pass to V. analysis of these particular combinations is impossible in (b) Residue. Wash, dry, and mount in bromoform. Ex- the present state of development of the science. amine for Titanox, Asbestine, and Silex. Note -It is impossible to aistinguish by microchemical test between a
Titanox. Small roundish particles; 0.4 micron average diameter; very high index of refraction. Asbestine. Elongated particles. See further 3-10. Silex. As a rule, if Asbestine is present, Silex cannot be determined. If Asbestine is absent, any inert remaining will be Silex or siliceous material such as infusorial earth. See further
B-9.
V-(a) Immerse two dispersions in 50 per cent acetic acid to remove possible zinc oxide. Remove and test one slide with Paravar. If it shows no reaction for zinc oxide, test the other dispersion for lithopone according to method in B-2. (6) In testing an unknown sample of pigment for zinc oxide it must be borne in mind that if lithopone is present a Paravar reaction will be given by the film of zinc oxide on the zinc sulfide part of the lithopone particle. This reaction is light, however, and even when carried to extremes the lithopone particles are clearly and sharply seen in the discolored areas. On the other hand, a pure zinc oxide particle is so greatly attacked by the Paravar that the particle, especially if small and deflocculated, loses its outline, and it becomes impossible to focus on it sharply. This distinction between the reaction of oxidized lithopone and the pure zinc oxide particle with Paravar is quickly learned. If desired, however, the analyst may wash the sample with dilute acetic acid for a time that is sufficient to remove the oxide film from possible lithopone particles but not of great enough duration to remove an appreciable quantity of possible pure zinc oxide particles. See V(c). If no lithopone was found under V ( a ) , test a dispersion for zinc oxide according t o B-1. ( e ) If lithopone was found, immerse a dispersion for 10 seconds in 10 per cent acetic acid. Wash, dry, and test for zinc oxide according to B-1. VI-(a) Immerse a dispersion for two minutes in hydrogen sulfide water to which a few drops of ammonia have been added. Examine for lead pigments. Basic lead sulfate (sublimed white lead). Particles have turned black. Average about 0.6 micron in diameter. (The presence of large, black particles, several microns or more in length, probably indicates normal lead sulfate, which occurs only when the basic carbonate is present as one of the principal ingredients.) PArticles squarish. Basic lead carbonate (corroded white lead). Particles have turned light brown and are considerably larger in size than the basic sulfate of lead. Particles hexagonal.
mixture of zinc oxide plus high-leaded zinc oxide on the one hand, and lowleaded zinc oxide on the other.
(d) Materials other than those in VI(c) are known to be present. Make Paravar test. Note the particles that stand out without discoloration. If these particles can be recognized to be either Titanox, Timonox, or basic lead carbonate, then the lead sulfate present is in combination with the zinc oxide as a leaded zinc oxide. If some of the particles that do not react with the Paravar resemble basic lead sulfate in size and appearance, then follow the procedure given in VI (c) where basic lead sulfate is known to be present. VII-Immerse a dispersion for 5 minutes in cold, 50 per cent acetic acid. Dry, mount in glycerol, and examine. The presence of well-defined acicular crystals, and especially the presence of triangular crystals, indicates Timonox. VIII-Take an extra dense dispersion and eliminate with hydrochloric acid (1: 1). Wash, dry, and make a half elimination with hot, concentrated sulfuric acid. Note by macroscopic examination whether the immersed half has become less dense than the other. If SO, barytes or blanc fixe is indicated. Mount in bromoform. See that the cover glass overlaps both fields. If the denser field contains large particles of an inert (of higher index of refraction than the mounting medium) that are absent in the lighter field, barytes is present, If these particles are very small and difficult to see, blanc fixe is present. IX-Examine a medium dense dispersion for Foraminifera shells. Their presence indicates whiting. ACKNOWLEDGMENT The author wishes to acknowledge his indebtedness to C. Hall for his assistance with the laboratory work in connection with this paper.
Bayer 20.5 At the meeting of the Soci&i? de Chimie Industrielle held on May 13, M. Fourneau, of Pasteur Institute, exhibited a moving picture film showing ina veryingeniousmanner the development of the structural formula of the secret Bayer 205 preparation for the cure of sleeping sickness. The pictures of the formula were taken as written on a blackboard, with such substitntions and rearrangements of radicals as would be performed by the lecturer before an audience. The point of particular interest is that this wonderful new secret remedy, which the Germans offered t o sell to the Allies a t a fabulous price, has now been synthesized by French chemists and its unlimited production made possible. A T H ~ R T OSEIDELL N
