INDUSTRIAL AND ENGINEERING CHEMISTRY
656
The adaptation of these results to large-scale operation should not prove difficult. Other conditions being equal, the most important factor is the oxygen supply available to the organism. This supply is conditioned by the air pressure, the air flow through the fermenter, and the degree of agitation of the solution. I t is probable that the latter, because of the different dimensional relationships involved in the use of large equipment, may prove to be more adequately expressed in terms of peripheral speed rather than in revolutions of the fermenter. The construction of a much larger fermenter, similar in principle to the small fermenters used in this work, has now been completed. This equipment will make possible a study of the various factors involved in this process, on a scale
VOL. 29, NO. 6
closely approaching that which would be used in commercial operation.
Literature Cited (1) Herrick, H. T.,Hellbach, R., and May, 0. E., IND.ENG.CHEM., 27. 681-3 (1935). (2) May; 0. E., Herrick, H. T., Moyer, A. J., and Hellbach, R., Ibid.. 21, 1198-1203 (1929). (3) May, 0. E.,Herrick, H. T., Mouer. . . A. J., and Wells, P. A.. Ibid.. 26, 575-8 (1934). (4) Moyer, A. J., Wells, P. A,, Stubbs, J. J., Herrick, H. T., and May, 0. E., Ibid., to be published. RECEIVEDApril 8, 1937. Presented before the Division of Industrial a n d Engineering Chemistry at t h e 93rd -Meeting of t h e American Chemical Society, Chapel Hill, N. C . , April 12 to 15, 1037. This paper is Contribution 273 from the Industrial Farm Products Research Division.
COMPOSITION OF ZINC YELLOW A. A. BRIZZOLARA, R. R. DENSLOW, AND S. W. RUMBEL Krebs Pigment & Color Corporation, Newark, N. J.
T
HE wide use of zinc yellow Eight typical samples of zinc yellow amount of free zinc oxide. AIwere analyzed ; the indicated that though chemical specifications by paint manufacturers and the growing appreciafor pigment colors are recognized this pigment has the composition Kz0.- to be of less tion of its value in rust-inhibitthan practical ing paint formulations havemade 4Zn0.4Cr03.3HzO- The results, which tests related to actual use, the have been submitted to the National general importance of the subthe question of its chemical comBureau of Standards, are discussed in ject, as well as the interest of the position a matter of considerable i n t e r e s t . The National their relation to those found in the literaNational Bureau of Standards, Bureau of Standards is interested was sufficient to justify a rather in finding out how much zinc turem A system Of is e x t e n s i v e analytical study. yellow is present in rust-inhibiThe results have been reported tive paints submitted under a specification calling for a definite to the bureau, where they are now under consideration, and amount of zinc yellow; one reason for carrying out the present are reviewed briefly together with the analytical methods study was to develop data of possible interest to the bureau which are believed to be most reliable for the purpose. in this connection. Table I shows the composition of eight typical samples Pigment manufacturers have long known that the product of zinc yellow, representing the products of three American is a more or less complex salt containing not only zinc and pigment manufacturers. Although careful evaluation would chromium but also substantial amounts of potassium. It is indicate certain differences in pigment properties, tinting likewise basic in character. Simply mixing solutions of a strength, etc., all were quite similar and would be considered zinc salt and a soluble chromate results in a product of low typical examples of this pigment. tinting strength and generally poor tinctorial properties, The generally close agreement between the samples in lacking the clean green tone of the commercial products respect to composition is striking, particularly when the available on the American market. However, the formulas difficulty of some of the separations is considered and the reported in the early literature are conflicting and of doubtful additional probability of differences in manufacturing procsignificance. esses. The figures point to the (‘oxide formula,” K2O.An interesting paper by Ellis, Fox, and Hirst ( 1 ) which 4Zn0.4CrOs.3H~0,with a fraction of the chromate replaced appeared some years ago represents the first important by an equivalent amount of sulfate or basic sulfate. It differs attempt to determine the quantitative composition of the from the one suggested by Ellis et al., in that the latter contains a higher proportion of zinc, corresponding to an addipigment. The authors pointed out the importance of suitable analytical methods and indicated the possibility of tional mole of zinc hydroxide. What is designated as ‘(combined water” is apparently serious error in estimating any component “by difference.” On the basis of their experiments, they concluded that the very firmly held. Drying a t 110’ C. gave a loss in the range of 0.1 to 0.2 per cent, and a much higher temperature average product was 5Zn0.4Cr03.K20.4HzO but suggested that too much importance should not be attached to this is needed to effect the removal of the 6 to 7 per cent reported stoichiometric ratio. This caution was probably justified in Table I. Tests on the alkali metal residues indicated very little in view of the rather wide variations in composition between sodium to be present. Sample A, for example, contained the samples which they analyzed. only 0.51 per cent, undoubtedly an impurity. Preliminary analytical work in the present writers’ laboratory on various American zinc yellows indicated that Analytical Methods they are lower in zinc content (or more specifically, in the ratio of zinc oxide to chromic oxide) than those reported by REAGENTS. The reagents used were sulfuric acid ( 6 N ) , Ellis et al., suggesting that the latter might contain a certain hydrochloric acid (concentrated), potassium ferrocyanide,
JUNE, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
lead acetate (50 per cent), acetic acid (50 per cent), barium chloride (20 per cent), and ammonium hydroxide (concentrated and 1 to 10). The potassium ferrocyanide was prepared as follows : Dissolve 42.5 grams of the salt in 1 liter of water. Dissolve 0.4 gram of pure zinc in 25 cc. of concentrated hydrochloric acid and dilute to 300 cc. Keutralize with ammonium hydroxide, add 2 grams of ammonium chloride and 12.5 cc. of concentrated hydrochloric acid. Titrate with po-
2
37.2 42.5 2.9 6.1 1 1.4 __ 100.1
of Zinc Yellow D E F 37.2 37.2 37.6 43.1 43.2 41.9 2.1 2.3 3.1 6.6 6.7 6.7 1 1 . 4 1 1 . 8 1 1.2 __ __ 100.5 101.1 100.5
-
-Sample
A
"Zn calod. as Z n 0 70 Cr calcd. as GO;, SO&calcd. as SOa, Combined water Alkali metals cdci?as KzO, %
TOTAL ALKALIMETALS. Dissolve l gram of zinc yellow in 10 cc. of 1 to 1 acetic acid, add 25 cc. of water, and heat until dissolved. Dilute to approximately 250 cc. and heat to boiling. Add 20 cc. of 10 per cent lead acetate and allow to settle. Filter and wash well with hot water. Saturate the filtrate with hydrogen sulfide, observing the precautions as outlined under zinc. Zinc and excess lead will be precipitated. Filter and wash with cold water. (It is necessary to keep down the concentration of acetic acid to ensure
TABLEI. ZINC YELLOW ANALYSIS
-
~
B 36.9 43.6 1.4 6.6 11.4 99.9
C 36.8 43.6 1.8 6.4 11.5
100.1
tassium ferrocyanide using uranyl acetate as external and ferrous ammonium sulfate as internal indicator. The ferrocyanide is approximately 1.3 N. Calculate grams of zinc per cc. PREPARATIOK OF SOLUTION.Dissolve a 4-gram sample of zinc yellow pigment in 50 cc. of cold 6 N sulfuric acid (160 CG. of concentrated sulfuric acid per liter). It should dissdve completely a t this stage. Transfer the solution to a 500-cc. calibrated flask and make up to 500 cc. This gives approximately 0.1 N chromic acid. CHROMIUX To a 400-cc. beaker containing 200 cc. of water add 2 grams of potassium iodide (solid) and 5 cc. of concentrated sulfuric acid. Final acidity should be approximately 5 cc. per 100 cc. of solution. Pipet 25 cc. of the above solution into the potassium iodide-sulfuric acid solution, and after approximately 5 minutes titrate with standard thiosulfate solution, using starch as an internal indicator. Report as per cent chromic oxide. ZINC. After nearly neutralizing 100 cc. of the original snlution with ammonium hydroxide, add methyl orange indicator and continue the neutralization with weak ammonium hydroxide (1 to 10) until just neutral to methyl orange. No precipitate should be formed. The solution must be barely acid before beginning precipitation, and the acidity should not increase to more than 0.1 N due to the liberated sulfuric acid. Pass hydrogen sulfide through the solution at a rapid rate (at least eight bubbles per second) for a t least 40 minutes, keeping the temperature below 50 O C. Filter and wash with water. Dissolve the zinc sulfide precipitate in hot dilute hydrochloric acid (1 to 3). Wash the filter paper well with hot water. Boil out the hydrogen sulfide. Neutralize the solution with ammonium hydroxide and adjust the volume t o 300 cc.; add 2 grams of ammonium chloride and 12.5 cc. of concentrated hydrochloric acid. Heat the solution to boiling and titrate with standard potassium ferrocyanide solution, using uranyl acetate as an outside indicator on a spot plate and one to two drops of ferrous ammonium sulfate as an internal indicator. Report as per cent zinc oxide .calculated as follows :
+
K4F~(CN)a + 2ZnSOa = Zn2Fe(CN)6 2KZSO4 cc. KaFe(CN)6X grams Zn per cc. X 100 = %Zn wt. of sample yo Zn X 1.2447 = yo ZnO
657
~
H 39.2 42.8 1.3 7.3 1 0.4 __ 101.0
G 37.8 41.3 3.3 6.6 10.9 99.9
Calcd. for Kz0.4Zn0.4CrOa.3HrO Zn calod. as ZnO, Yo 37.2 45.8 Cr calcd. as CrOa, % 6.2 HzO % A1ka)li calcd. as K20, % 10.8 __ 100.0
complete removal of the zinc.) Boil to expel hydrogen sulfide. Add 3 cc. of sulfuric acid and boil down to a small volume. Transfer to a weighed silica dish and evaporate to dryness on a hot plate. Heat to complete dryness on a Bunsen burner. Add solid ammonium carbonate and heat until volatilized. Repeat four times, cool, and weigh. Add a few crystals of ammonium carbonate and again heat until volatilized. Cool, weigh, and repeat to constant weight. Report as per cent potassium oxide calculated as follows~ wt'
loo =
wt. of sample
% total sulfate (NanS04and K2S04)
% KzS04
X 0.541 =
% KzO
COMBINED WATER. The apparatus described by Fox and Bowles (3) is used. Weigh out 3 grams of pigment and transfer to a porcelain boat. Place in a combustion tube. Connect the apparatus and heat for 4 hours. The weight increase of the absorption tube represents the combined water. Report as per cent combined water. SULFATES.Dissolve 1 gram of zinc yellow in 15 cc. of concentrated hydrochloric acid. Heat to boiling and add 5 cc. of alcohol dropwise to ensure the reduction of the chromium. Boil to a low volume. Dilute to 300 cc. with distilled water and neutralize with sodium carbonate, adding 3 to 5 grams in excess. Heat to boiling and boil to ensure the conversion of the insoluble sulfates to the soluble form. Allow the precipitate to settle on a hot plate and filter. Wash with hot water. Keutralize the filtrate with hydrochloric acid and boil out carbon dioxide. Adjust the acidity to 2.5 per cent with hydrochloric acid and add 15 cc. of 20 per cent barium chloride dropwise to the solution, keeping the latter at a boil Allow to settle on a hot plate. Filter through a weighed Gooch crucible, wash, dry, ignite, cool, and weigh. The increase in weight represents barium sulfate. Report as per cent sulfur trioxide calculated as follows: wt. Bas04 X 0.343 X 100 = % so, wt. of sample
Literature Cited (1) Ellis, Fox, and Hirst, J . Oil Colour Chern. Assoc., 9,194 (1928). (2) Fox and Bowles, "Analysis of Pigments, Paints and Varnishes," p. 57, New York, D. Van Nostrand Co., 1927.
RECEIVED January 26, 1937.
