SEPTEMBER 15, 1935
ANALYTICAL EDITION
advantage over the usual gravimetric method that the vapors are constantly removed from the evaporating surface.
Summary Trends in the field of protective coatings emphasize the importance of the evaporation rates of the solvents and thinners used in their manufacture and application. A survey of existing methods reveals that for the slower evaporating types they are time-consuming, lacking in control of air flow, temperature, and humidity, or costly to establish for control purposes. d volumetric method has been described which is rapid, sufficiently precise for control purposes, reasonably inexpensive and which embodies positive control of air flow, temperature, and humidity. The results so obtained, by virtue of the constant removal of vapor from the evaporating surface, are believed to be somewhat more practical than those obtained by methods in which this feature is lacking.
293
Acknowledgment The authors are indebted to C. F. Rassweiler and H. H. Hopkins, under whose jurisdiction this work was conducted.
Literature Cited (1) Durrans, T. H., “Solvents,” New York, D. Van Nostrand Co., 1930. (2) Gardner, H. A., “Physical and Chemical Examination of Paints, Varnishes, Lacquers, and Colors,” 6th ed., pp. 701-3, Washington, Institute of Paint and Varnish Research, 1933. (3) Ibid., p. 703. (4) Lowell, H. J., IND. ENQ.CHEM.,Anal. Ed., 7, 278 (1935). (5) Rubeck and Dahl, Ibid., 6,421 (1934). (6) Wilsonand Worster, IND.ENG.CHEW,21, 592 (1929). R E C ~ I V EJune D 7, 1935. Presented before the Diviaion of Paint and Varnish Chemistry at the 89th Meeting of the American Chemical Society, New York,N. Y., April 22 t o 26, 1935.
Determination of Mercury in Iodinated Organic Compounds of Mercury I J
Application of Spacu and Spacu Copper Sulfate Propylenediamine Reagent R. B. SANDIN
T
AND
E. T. MARGOLIS, University of Alberta, Edmonton, Alberta, Canada
HE determination of mercury in mercurated organic compounds is of considerable importance, because of the increasing use of such compounds in medicine. Numerous procedures are available, but in the majority of them the halogens and especially iodine are interfering elements and must be gotten rid of. In the potassium thiocyanate titration of mercury, all the halogens must be absent and to accomplish this Kharasch and Flenner (3)have developed a very satisfactory method. If iodine is present, mercury cannot be precipitated by Jamieson’s reagent, but the procedure of Fenimore and Wagner (3) obviates this difficulty. Finally, in the determination of mercury as the sulfide, iodine must be removed by such methods as those of Dunning and Farinholt (1) and Tabern and Shelberg (5). In three of the above procedures (2, 3, 5 ) interfering halogens are eliminated by precipitating the mercury in solution as metallic mercury, which is then redissolved and determined by an appropriate method. Recently Whitmore and Sobatzki (6) have developed a new and very direct method for the determination of mercury in organic mercury compounds such as organomercuric halides, by which none of the halogens are interfering elements. Because of the difficulty mentioned above, it was thought that an adaptation of the method of Spacu and Spacu (4) might have possibilities. This paper describes a satisfactory procedure, whereby organic mercury in the presence of iodine is finally determined by the copper sulfate-propylenediamine reagent. The organic mercury compound containing iodine is oxidized in a bomb tube by the well-known Carius method. However, a method of oxidation such as that of Tabern and Shelberg (5) should be satisfactory, provided mercuric iodide is not allowed to escape. The only special reagent required is propylenediamine which is obtainable from the Eastman Kodak Company as a 70 to 75 per cent aqueous solution. The copper sulfatepropylenediamine reagent is prepared by dissolving 2.5 grams
of crystalline copper sulfate in water, then adding 2 grams of
the propylenediamine solution. It should be made up as needed.
Procedure Weigh out a sample, corresponding to at least 0.3 gram of mercury, in a small Pyrex weighing tube similar to that used in the Carius halogen determination. To a Carius bomb tube add 3 cc. of fuming nitric acid, transfer the weighing tube carefully to the bomb tube, and proceed as in a halogen determination. After the bomb tube hab been heated and cooled (and before opening), heat the capillary end of the bomb tube gently with a gas flame (using goggles), to prevent the loss of any mercuric iodide, which has condensed in that part of the tube, when the capillary is opened. Cut off the end of the tube, add 20 cc. of water and 15 cc. of concentrated ammonium hydroxide, and an amount of solid potassium iodide (plus an excess), sufficient to dissolve the mercuric iodide. Transfer the solution to a 400-cc. beaker and wash out the bomb tube thoroughly with water. Do not allow the total volume t o exceed 200 cc. If the solution is brown, owing to free iodine, carefully add clear dilute sodium hydroxide solution until the color is a pale yellow. Heat the solution t o boiling and add an excess of hot copper sulfate-propylenediamine reagent. Cool for several hours in an ice-water mixture. Filter the blue precipitate on a weighed Gooch crucible and wash from three to four times with an aqueous solution containing 0.1 per cent of potassium iodide and 0.1 per cent of the copper sulfate-propylenediamine reagent. Then wash three to four times with 2-cc. portions of 96 per cent alcohol and finally two t o four times with 2-cc. portions of ether. Dry in a vacuum desiccator and weigh. The precipitate contains 21.81 per cent of mercury. Considerable preliminary work was carried out t o determine whether the method would be satisfactory. A few typical analyses, listed in Table I, are the average of two or more closely agreeing determinations, and indicate the real value of the method. The calculated percentage of mercury is given for compounds I and I1 which were pure. The remaining compounds were of unknown purity and, for that
INDUSTRIAL AND ENGINEERING CHEMISTRY
294
Aclrnowledgments
TABLE I. TYPICAL ANALYSES Calcd. Knownor I Mercuric chloride I1 Tolylmercuric. iodide I11 Chloromerouriphenol IV p-Mercury ditolyl V Phenylmercuric chloride V I Phenylmercuric nitrate
VOL. 7, NO. 5
Found by
Spacu Spacu Method and
%
%
73.88 47.93 60.66 52.07 56.14 62.80
73.90 47.90 60.50
The writers wish to thank N. M. Stover of this laboratory for his valuable suggestions, and the Carnegie Corporation Research Fund for a grant which enabled the purchase of certain reagents.
Literature Cited
52.04
56.03 62.87
reason, the mercury content was determined by a sulfide precipitation or by a thiocyanate titration. Compound 11 was the only one to contain iodine, and therefore, 0.2 to 0.3 gram of diiodofluoresceinwas added to all the others.
(1) Dunning and Farinholt, J. Am. Chem. SOC., 51, 804 (1929). (2) Fenimore and Wagner, Ibid., 53, 2468 (1931). (3) Kharasch and Flenner, Ibid.,54,674 (1932). (4) Spacu and Spaou, Z. and. Chem., 89,188 (1932). ( 5 ) Tabern and Shelberg, IND.ENG.CHEM.,Anal. Ed., 4, 401 (1932). (6) Whitmore and SobatZki, J *Am. Chem. SOC., 55, 1128 (1933).
RECEIVED June 13, 1935.
Microchemical Analysis of Solid Fuels J
W. R. KIRNER, Coal Research Laboratory, Carnegie Institute of Technology, Pittsburgh, Pa.
T
HE history of the development of Pregl's methods of quantitative organic microanalysis is familiar to everyone interested in this field. These methods were developed by carrying out analyses on pure organic compounds of known composition. Only after Pregl had demonstrated that his methods were able greatly to reduce the expenditure of time, energy, material, and hence money, and that the results obtained were as accurate and precise as the older macromethods, were the methods accepted by other chemists. Their introduction into industrial laboratories was a t first viewed with a good deal of skepticism by industrial chemists, their main argument being that it was impossible for a microsample to be actually representative of the total substance whose analysis was desired. Certain difficulties are encountered in the elementary macroanalysis of solid fuels, as well as of many other natural substances, such as agricultural and biological products, alkaloids, etc., which are almost entirely absent in dealing with pure organic compounds. In the first place, solid fuels have a complex composition, and all samples, besides containing carbon, hydrogen, and oxygen, also have present nitrogen, sulfur, and mineral matter and sometimes phosphorus and chlorine. Some of these constituents are present in very small amounts, which makes their determination difficult by any method of analysis. In the combustion the mineral matter is converted into ash which may cause certain complications in the analysis. The combustion of solid fuels often leads to the formation of exceedingly combustion-resistant cokes which, a t times, makes complete oxidation of the sample extremely difficult. During the expulsion of the volatile matter by the action of heat, large volumes of gas are evolved, consisting primarily of methane, hydrogen, and carbon monoxide, and special precautions must be taken during this part of the combustion to insure their complete oxidation. Another difficulty involved in the analysis of solid fuels concerns those methods which require solution of the sample. Solid fuels are relatively insoluble and there is no solvent known which dissolves them completely a t a moderate temperature and without reaction. The difficulties connected with the elementary analysis of solid fuels by the usual macromethods have been known for some time and certain modifications of standard methods, as developed on pure compounds, were made by fuel analysts to render the results more certain, consistent, and accurate. In the light of the development of micromethods applied to
pure substances, it is now recognized that the conversion of a macro- to a micromethod involves much more than the mere diminution of the size of the sample taken for analysis, Errors which are of no significance in macromethods often assume gigantic proportions in micromethods and much tedious work is necessary for their elimination. It is this rationalization, however, which gives micromethods their accuracy and precision. If such difficulties are encountered in converting macro- to micromethods applied to pure substances, it is only reasonable to expect that the difficulties will be still greater when dealing with complex, heterogeneous substances such as solid fuels. For the purpose of a systematic discussion, the individuai determinations necessary for the complete microanalysis of a solid fuel will be considered.
Sampling Solid Fuels for Microanalysis Since Pregl, in his development of the methods of quantitative organic microanalysis, was primarily interested in the application of these methods to pure substances, he did not mention in his book the problem of sampling heterogeneous materials for microanalysis. In dealing with pure substances, the microsample taken for analysis is directly a true, diminished representative of the whole. The problem of sampling solid fuels for microanalysis has been fully discussed elsewhere (85). In order to obtain homogeneous, representative microsamples, solid fuek must be subjected to extremely fine grinding and thorough mixing. One difficulty in the fine grinding of solid fuels concerns the extremely troublesome appearance of electrostatic charges induced on the finely ground particles. Great care must be exercised in grinding samples which exhibit this phenomenon, since rather large amounts of the finer particles may be lost from the agate mortar. Various attempts have been made to overcome this difficulty with but moderate success. Such charges can also seriously affect the accurate weighing o f microsamples.
Determination of Moisture The method generally used in this laboratory for determining moisture consists in drying the sample in a microdesiccator at a temperature of 110" to 115" C. for 15minutes in an atmosphere of nitrogen. The microdesiccator is fitted with a bubble counter which in turn is connected with a Pregl
