ANALYTICAL EDITION
January 15, 1942
43
hydroxylamine hydrochloride in the controls by the original amount added. The weights of t h e nickel precipitates of the unknowns are divided by this factor to ascertain the actual recovery and likewise converted t o t h e equivalent weight of hydroxylamine hydrochloride. These differences from the original amounts indicate the amounts of amine t h a t reacted with the keto groups and when multiplied by 0.4029 equal the weights of these groups. These weights divided by the sample weights give the per cent value which is converted to per cent of triketocholanic acid when multiplied by 4.79.
bonyl groups in bile preparations, the gravimetric procedure based on the recovery of excess hydroxylamine was found to be the more consistent. However, when pigments were absent the titrimetric procedure was preferred because of its timesaving advantages.
Discussion
Literature Cited
The titrimetric method investigated, using a n indicator, has limited use in determining carbonyl groups in the presence of bile pigments. At times the formation of a precipitate obscures the end point. With the gravimetric method the use of a recovery factor t o account for incomplete reactions and losses due t o solubility was necessary. These methods may also be applicable to the various keto steroids related to
(1) Berman, A. L.,Snapp, E., Ivy, A. C., Atkinson, A. J., and Hough, V. S.,Am. J. Digestive Diseases, 7 , 333 (1940). (2) Berman, A. L.,Snapp, E., Ivy, A. C . , Hough, V. S., and Atkinson, A. J., Am. J. Physiol., 131, 752 (1941). (3) Bryant, W. M. D., and Smith, D. M., J. Am. Chem. SOC.,57, 5i (1935). (4) Hirschel, W. N., and Verhoeff, J. A., Chem. Weekblad, 20, 319 (1923).
the hormone field. I n accordance with existing data in the literature (8) it was found that of the natural sources studied, pig bile contains the largest number of carbonyl groups (Table
1). Of the two methods studied for the determination of car-
Volumetric Determination of Bismuth as Caffeine Tetraiodobismuthate (111) ROBERT S. BEALE AND G. C. CHANDLEE School of Chemistry and Physics, The Pennsylvania State College, State College, Penna.
A
XUMBER of organic bases are known to form insoluble
iodometallic compounds from which the metal may be determined by titration of the iodine from the complex ion. Several determinations of bismuth have been made by this method, Hexamethyldiiododiaminoisopropyl alcohol ( I ) , naphthoquinoline ( 2 , 8),&hydroxyquinoline (2, 4,10, 12), 8nitroquinoline (S), quinine ( 5 ) , quinoline (6), quinaldine ( 7 ) , dithiocyanato diethylenediamine cobaltithiocyanate ( I S ) , triethylenediamine cobaltichloride (14), and antipyrine methyleneamine (16) form complex compounds with bismuth and iodine and methods using these bases have been reported for the determination of bismuth. Preliminary tests with caffeine showed t h a t i t may be satisfactoxily used t o determine bismuth. An insoluble compound of caffeine, bismuth, and iodine is formed containing the atoms of bismuth and iodine in the ratio of 1 to 4. It was also found t h a t mercury formed no insoluble compound and hence i t was possible t o devise a method for the determination of bismuth in the presence of mercury. So far as i t has been possible to determine, similar methods for bismuth previously reported have all required the absence of mercury.
Solutions C A F F ~ I NSULFATE E SOLUTION.Dissolve 133 grams of caffeine in 570 mI. of 6 N sulfuric acid and dilute to 1 liter; 30 ml. of this solution contain 4 grams of caffeine. CAFFEINESULFATE WASHSOLUTION.Dissolve 1.5 grams of caffeine in 6 ml. of 6 N sulfuric acid and dilute to about 900 ml. Then add 1 gram of pure potassium iodide and bring the volume to 1liter. CAFFEINE KITRATE SOLUTION (for use in the presence of barium ion). Dissolve 133 grams of caffeine in 540 ml. of 6 11’ nitric acid and dilute to 1 liter; 30 ml. of this solution contain 4 grams of caffeine. BISMUTHXITR.4TE SOLUTION. Dissolve 2.79 granls O$ C. P. bismuth nitrate pentahydrate 111 10 ml. of 16 S nitric Had and dilute t o 1 liter. This \\-as standardized with concordant results by the phosphate and carbonate methods (25 ml. of this solution contain approximately 0.03 gram of bismuth). POTASSIUM IODATE SOLUTIOK.Dissolve exactly 2.0480 grams of c. P. potassium iodate t o make 1 liter of solution (1.00 ml. of this solution is equivalent to 0.0010 gram of bismuth). This solution was stable in accordance with studies by Jamieson ( 9 ) .
POTASSIUM CYANIDE SOLUTION.Dissolve 32.5 grams of c. P. potassium cyanide to make 1 liter of a 0.5 M solution. SODIUM HYDROXIDE SOLUTION.Dissolve 5 per cent by weight. POTASSILW IODIDESOLUTION.Dissolve 8.0 grams of U. S. P. potassium iodide to make 100 ml. of solution. ACID, 12 N . HYDROCHLORIC DIBUTYL ETHER. This must be free from peroxides, so as not to oxidize the iodine in the precipitate.
Procedure Dissolve the sample, containing about 0.03 gram of bismuth, in 10 ml. of concentrated sulfuric acid, remove most of any excess acid by evaporation, and dilute with water to 150 ml. in a 400ml. beaker. (Determinations were made in solutions containing as much as 6.5 per cent acid by volume but 1.5 to 2 per cent is preferable. Since sodium ion does not interfere, the acidity may be regulated, if necessary, by the addition of sodium hydroxide.) Add 30 ml. of caffeine sulfate solution and precipitate the bismuth by the dropwise addition, with vigorous stirring, of 25 ml. of the potassium iodide solution. Let stand for 10 minutes, then iilter by suction through asbestos in a Gooch crucible. It is not necessary to remove the precipitate which adheres to the beaker, since the same beaker is to be used for subsequent o erations. Wash five times with 15-ml. portions of caffeine sulkte wash solution and then four times xith 15-ml. portions of dibutyl ether. Place the Gooch crucible containing the washed precipitate in the beaker in which the precipitation was made, add 100 ml. of the sodium hydroxide solution, and heat to boiling to decompose the precipitate. Cool and add 23 ml. of 12 N hydrochloric acid, then add 8 ml. of the potassium cyanide solution, and titrate with potassium iodate solution to the iodine cyanide end point according to Lang’s method (11). This involves addition of potassium iodate until the color of the solution changes from the brown first obtained to a faint yellow, then addition of 10 ml. of starch indicator, and titration just to the disappearance of the blue starchiodide color. Six determinations on solutions containing 0.0300 gram of bismuth gave 0.0300, 0.0302, 0.0300, 0.0299, 0.0299, and 0.0300 gram by the above procedure. For verj7 small amounts of bismuth, proportionate amounts of reagents were used. Eight determinations on 0.00117 gram of bismuth gave 0.00116, 0.00118, 0.00116, 0.00120. 0.00118, 0,00119, 0.00120, and 0.00119 gram.
INDUSTRIAL AND ENGINEERING CHEMISTRY
44
IN THE PRESENCE OF NONINTERTABLE I. DETERMIXATIONS FERINQ IONS
Ion Added Gram
Ions Ca-+++ K + Sr hIg-Xa
Bismuth Present (as Nitrate) Gram
0.02 each
Xitrates
0.0300
0,0299 0 0300 0 0302 0 0300
0.02 each
Xitrates
0.0300
0.0296 0.0300 0,0300 0,0299
0.1
iiitrate
0.0300
+
.il + + h l n + Fe + + + Zn + crt++ h-i’t cot+ f
Hgtia
f
Bismuth Found Gram
0.0299 0.0298 0.0301 0.0299 0.0301
Vol. 14, No. 1
the usual 2.0 grams were adequate for the Yeparation of 0.03 gram of bismuth from as much as 0.20 gram of mercury. Lead, because of the formation of insoluble iodide, was p r e cipitated by addition of excess sodium sulfate and the lead sulfate removed by filtration before continuing with the determination of bismuth by the regular procedure. Barium gave no trouble in a solution free from sulfate ion. Barium sulfate was found to coprecipitate appreciable quantities of bismuth. A solution of caffeine nitrate was therefore used for precipitations instead of caffeine sulfate. Tin, in either the stannous or stannic state, offered no difficulty n hen sufficient hydrochloric acid was added to convert the tin largely to the complex chloride ion. For 0.1 gram of tin in either form, 2.5 ml. of 12 N hydrochloric acid were adequate. Antimony was found t o present no difficulty if tartrate ion was present. I n the following separations, 4 grams of ammonium tartrate were added prior to precipitation of the bismuth. Phosphate ion may not be present, of course, in sufficient concentration to exceed the solubility product of bismuth phosphate. I n the separations made in solutions containing this ion, the sulfuric acid present was never less than 3 per cent by volume. The results of the various separations are given in Table I.
Interfering Ions Bismuth could not be determined in the presence of mercurous ion. In addition to this, the determination could not be carried out in the presence of copper or silver because of the insolubility of their iodides. I n the case of copper, an insoluble compound is formed with copper, iodine, and caffeine.
Summary
0.0300
0.0301 0.0300 0.0302 0.0298
M004--
0.05
HaMoOn
0.0300
0.0303 0.0304 0.0301 0.0303
Po,---
0.14
NaNHdHPOa
0.0293
0.0294 0.0294 0.0294 0.0295
Precipitated by 3.0 instead of 2.0 grams of potassium iodide. recipitation Caffeine nitrate solution used instead of caffeine sulfate sorution. d 2.5 ml. of 12 . Y hydrochloric acid added before precipitation. a 4 grams of ammonium t a r t r a t ? added before precipitation. a
b Lead removed by precipitation with sodium sulfate before 0
A new method for the determination of bismuth has been developed in which the element is precipitated as caffeine tetraiodobismuthate (111) and subsequently determined by titration of the iodine. For solutions containing bismuth only, the method has been tested for as little as 1.2 mg. of bismuth. The method makes possible the determination of bismuth in the presence of mercury, a feature which does not apply t o other previously described methods for such analyses. Determinations of bismuth, by modified procedures in some cases, can be made in the presence of calcium, sodium, strontium, p,otassium, magnesium, beryllium, iron, uranyl, aluminum, mckel, cobalt, manganese, chromium, molybdate, zinc, arsenious, lead, cadmium, barium, vanadyl, stannic, antimonous, arsenate, stannous, and phosphate ions. Silver, copper, and mercurous ions interfere with the determination of bismuth by this method. Literature Cited
Determination of Bismuth in the Presence of Other Ions I n the majority of cases, the presence of other ions did not interfere with the determination of bismuth by the procedure described. Slight modifications were necessary in a few instances. I n the follon-ingseparations, synthetic samples were prepared by adding known amounts of pure salts to a standard bismuth nitrate solution containing 1 per cent of nitric acid by volume. Mercury in the biralent state did not interfere, provided sufficient potassium iodide was present to convert the insoluble mercuric iodide first formed to the tetraiodomercurate (11) ion. It was necessary, therefore, to boil with concentrated nitric acid to ensure complete oxidation of mercury. It was found that 3.0 grams of potassium iodide instead of
(1) Aurisicchio, G., Industria chimica, 7, 1358 (1932). (2) Berg, R., and Wurm, O., B e r . , 60B, 1664 (1927). (3) Canneri, G., and Dino, B., Ann. chim. applicata, 26, 455 (1936). (4) Farini, P., Boll. chim. f a r m . , 73, 284 (1934). (5) Francois, M., and Seguin, L., J. pharm. chim., [SI 2, 59 (1925). (6) Gapchenko, M. V., and Shefntzis, 0. G.. Zaeodskaya Lab., 4 , 835 (1935). (7) Hayes, J. R., and Chandlee, G. C., IND ENG. CHEX.,ANAL. ED., 11, 531 (1939). (8) Hecht, F., and Reissner, R., 2. anal. Chem., 103, 88 (1935). (9) Jamieson, G. S., “Volumetric Iodate Methods”, New York, Chemical Catalog Co., 1926. (10) Kolthoff, I. M., and Griffith, F. S., iwikrochim. Acta, 3,47 (1938) (11) Lang, R., 2. anorg. allgem. Chem., 122, 332 (1922). (12) Sazerac, R., and Pousergues, J., Compt. rend. SOC. baol., 109, 370 (1932). (13) Spacu, G., and Spacu, P., 2. anal. Chem., 93, 260 (1933). (14) Spacu, G., and Suciu, G., Ibid., 79, 106 (1929). (15) Tskaki,9 , and Takase, Y . , J.P h a r m . Soc Japan, 56,405 (1936).
