ANALYTICA L EDITION
428
of the water or of a water extract is very low, however, the electrometric titration is preferable as it is considerably more sensitive.
SUMMARY Comparative analyses of the chlorides of the leaf and stem saps of plants were made electrometrically and volumetrically after ashing and by an electrometric titration of the unaltered saps. The two methods are in close agreement when used upon the acid extracts of plant materials or of their saps, The electrometric titration of chlorides in such acid extracts is preferred to the volumetric method because it is timesaving and because of its greater sensitivity. Chlorides in the saps of some plants can be titrated directly by the electrometric-method. T h e ashing step must be in-
Vol. 6 , No. 6
cluded in juices, such as those of citrus fruits, that contain appreciable amounts of the salts of weak acids. The electrometric titration of chlorides in ground waters, which contained traces of sulfides and appreciable amounts of sulfates, checked closely with the chromate volumetric method and had a more sensitive end point. LITERATURECITED (1) Assoo. Official Agr. Chem., Official and Tentative Methods, 1930. (2) Best, R. J., J. Agr. Sci., 19,35 (1929). (3) Clark, W. M., “Determination of Hydrogen Ions,” Williams & Wilkins Co., Baltimore, 1920. (4) Snyder, E. F.. Soil Sci., 35,43 (1933). R ~ C B I V HApril ~ D 2, 1034. Presented before the Division of Agrioultura and Food Chemiatry at the 86th Meeting of the American Chemical Society st. Petersburg, ~ i a . March , 26 t o 30,1934.
Determination of Tellurium in Tellurium Lead and Tellurium Antimonial Lead W. J. BROWN,National Lead Research Laboratories, Brooklyn, N. Y.
A
LTHOUGH lead has been known since the earliest times, it is today one of the most useful of metals, finding extensive application as cable sheathing, water pipes and drains, tank linings, and heating coils. Hence, any treatment, whether physical or chemical, that improves the physical properties of lead is rendering industry a real service. The properties ( l a ) that commend lead are its pliability and resistance to corrosion. Metallurgists have long known that small amounts of another metal may increase the hardness and tensile strength of lead. A lead containing a maximum of 0.08 per cent of copper and sold to the trade as “chemical lead” is harder, has more tensile strength, and is believed by many users to be more resistant to corrosion than pure lead. Singleton and Jones (18) claim that tellurium not only increases the tensile strength of lead and antimonial lead to a greater extent than copper does but also increases its resistance to corrosion. Tellurium lead and tellurium antimonial lead, each containing not less than 0.06 per cent nor more than 0.08 per cent of tellurium, are now marketable products, the patent rights for their manufacture in the United States being held by the National Lead Company. The introduction of tellurium lead and tellurium antimonial lead creates an unusual problem for the analyst-the exact estimation of small amounts of tellurium in these products. Tellurium is regarded as a rare element. Textbooks on analytical chemistry allot little or no space to its consideration, and the chemist in most commercial laboratories seldom has occasion to make a determination. Indeed, he rarely in the course of his work considers it as an interfering element. Low consumption and restricted output, no doubt, have contributed to this general opinion. Volumetric methods of determination have been developed depending upon the reduction of telluric acid (H2Te04)t o tellurous acid (H2Te08),and conversely the oxidation of tellurous acid t o telluric acid. Gooch (8) makes the reduction with potassium bromide in a sulfuric acid solution, while Browning (8)uses stron hydrochloric acid. The liberated bromine in the one case an8 the liberated chlorine in the other are passed into a solution of potassium iodide, the iodine set free being titrated with sodium thiosulfate. Gooch (7’) oxidizes tellurous acid with a measured excess of potassium permanganate and titrates the excess with oxalic acid. Tellurous acid may also be determined by a volumetric precipitation method using potassium iodide as the precipitant, the end point being reached when n o precipitation of tellurous iodide takes place upon further addition of the potassium iodide (10). Evans (6) reduces tellurium to the elemental
form and then dissolves it in sulfuric acid in the presence of a measured excess of iodine solution and titrates back with standard arsenite solution. Tellurium may be determined gravimetrically by reduction to elemental tellurium, by conversion to the sulfate ( I ) , as tellurium dioxide (S),and by the treatment of tellurous acid with potassium iodide in the presence of hydrochloric acid and a weighed amount of finely divided silver, whereby tellurium is precipitated and the liberated iodine is absorbed by the silver. From the increased weight of the insoluble material the tellurium may be calculated (17). Tellurium may also be determined electrolytically (19). Tellurium is generally determined gravimetrically as elemental tellurium. There are a number of reducing agents used to make the precipitation, the most common being sulfur dioxide, sodium sulfite, stannous chloride, titanium trichloride, hypophosphorous acid, hydrazine hydrochloride and several of the metals in acid solutions, and grape sugar, hydroxylamine hydrochloride, and hydrazine hydrochloride ih alkaline solution. (Brukl and Maxymowicz make a reduction with sodium sulfite in an alkaline solution, 4). Lenher and Homberger (14) use both sulfur dioxide and hydrazine hydrochloride t o make the reduction. MacIvor (15)discusses the merits of several of the reducing agents alone and in combination and points out that the amorphous precipitate of tellurium oxidizes when exposed to the air. For this reason Gooch (9) prefers t o weigh tellurium as tellurium dioxide. Clauder (5) finds that oxidation of amorphous tellurium takes place, but states the difficulty may be overcome by precipitating the tellurium in a crystalline form by proper control of conditions. Treadwell (20) claims that tellurium thrown down with sulfur dioxide will not oxidize t o any appreciable extent during the drying of the precipitate at 105” C. In an attempt to work out a method for the determination of tellurium in pig lead the method of Lenher (IS) was chosen as a starting point. Lenher effects solution with nitric acid and removes the bulk of the lead with sulfuric acid and the remainder by evaporating to fumes. The tellurium is then precipitated as a disulfide, dissolved in sodium sulfide, reprecipitated with sulfuric acid with the aid of hydrogen sulfide, dissolved in nitric and sulfuric acids, again taken to fumes, again precipitated as a disulfide, dissolved in hydrochloric acid and potassium chlorate, and finally thrown down with sulfur dioxide and weighed. The experience of this laboratory with hundreds of analyses of commercial leads has shown that bismuth in ordinary lead and copper in chemical lead are the only impurities present in sufficient amount to interfere to any appreciable extent. In removing them by means of the alkali sulfide separation the author found that a small amount of tellurium due to the dissociation of tellurium disulfide (16) remained behind with
November 15,1934
I N D US T R IA L A N D E N G I N EER I N G C H E M I ST R Y
the bismuth or copper residue, the amount depending upon the temperature of the solution and the duration of the digestion, and that this small amount could be recovered without contamination by either bismuth or copper. The procedure in testing for tellurium was to dissolve weighed amounts of tellurium, copper, and bismuth in nitric acid and make the separat)e solutions up to a definite volume. Measured volumes were then added to a weighed portion of a very pure lead prepared by this laboratory. A description of the method in detail and the results obtained (Table I) are given below.
DETERMININQ TELLURIUM IN TELLURIUM LEAD Weigh 12.5 grams of the lead sawings into a 500-cc. graduated flask, add a measured volume of the tellurium solution and a measured volume of the copper or bismuth solution, and then add 100 cc. of nitric acid (1 to 4). Heat on a water bath until solution is complete. Cool somewhat, add 25 cc. of sulfuric acid (1 to l), cool to room temperature, make up to the mark with water at room temperature, and mix. Filter 400 cc. of solution through a dry paper (discarding the first 20 cc. of filtrate) into a 600-cc. beaker and evaporate to fumes of sulfur trioxide. Cool, dilute to a volume of 50 cc. with water, add 5 grams of tartaric acid, and bring to boiling. Cool, allow to stand for 2 hours, filter, and wash. Discard the residue. Through the filtrate pass hydrogen sulfide, filter, and wash with hydrogen sulfide water. Wash the precipitate back into the original beaker with as little water as possible, add a gram or two of sodium bicarbonate and 5 cc. of a 10 per cent solution of sodium sulfide, and digest in a warm place. Filter and wash. Reserve the residue. Make the filtrate slightly acid with dilute sulfuric acid and again pass in hydrogen sulfide. Filter and wash as before. Wash the reBidue back into the original beaker with as little water as possible, add an equal volume of hydrochloric acid (sp. gr. 1.19) and about a gram of potassium chlorate, and bring to boiling. Filter through the same paper as before and wash several times with hot water. Gently heat to expel free chlorine, add a few cubic centimeters of nitric acid (sp. gr. 1.42), and evaporate to dryness on the water bath (11). Take up with 100 cc. of hydrochloric acid (9 to 1), add a gram or two of tartaric acid, just bring to boiling, pass in sulfur dioxide for 15 minutes, add 100 cc. of boiling water, and continue in passing in sulfur dioxide for 30 minutes. Allow to stand in a warm place 1 hour, again pass in sulfur dioxide for 20 minutes, filter through a prepared Gooch crucible, and wash several times with hot water. Do not allow the pad to become dry between washings. Finally wash once with 95 per cent grain alcohol, dry at 100’ C. for 1 hour, cool, and weigh as elemental tellurium. Treat the residue held in reserve with hot hydrochloric acid to which potassium chlorate has been added, and proceed as described above. The final preci itate of tellurium may be filtered separately or combined wit{ the main portion. In Table I the tellurium in the residue and that found in the main portion were filtered separately. The first three columns represent amounts added that should be present in the aliquot portions. TABLE I. DETERMINATION OF TELLURIUM IN LEAD TELLURIUY COPPER TAKEN ADDED Dram Dram 0.0100 0.0100 0.0100 0.0100 0.0100 0.0100 0.0060 0.0060 0.0100 0.0100
a
....
.... .... ....
0,0050 0.0050 0.0050 0.0050
....
TELLURIUM FOUND BISMUTH In I n mam portion ADDED residue Gram Gram Gram
.... .... .... .... .... .... ....
0.0005 0.0006 0.0005 0.0004 0.0025 0.0234
0.0150 0.0150
0.0012 0.0010
....
0
0.0096 0.0096 0,0094 0.0097 0.0075 0,0069 0.0060 0.0062 0.0090 0.0093
ERROR Gram
+o.
0001
+0.0002 -0.0001 +o ,0001 0.0000
4-0.0003 0.0000 +0.0002 4-0 .oooz
.... 4-0.0003 Tellurium in the residue combined with that in main portion.
This method is not adaptable for the determination of tellurium in antimonial lead. Nitric acid is not a suitable solvent for antimony alloys nor is hydrochloric acid an efficient solvent for lead alloys. The prospect of effecting decomposition of 10 grams of material with boiling concentrated sulfuric acid did not seem to hold much promise of success. The common practice of bringing alloys of antimony and lead into
429
solution is to employ mixed acids-either hydrochloric and nitric or nitric and tartaric acids. The former mixture was used in the method given below. The method is applicable for 6, 8, and 10 per cent antimonial lead. The results obtained are shown in Table 11.
DETERMINING TELLURIUM I N ANTIMONIAL LEAD Weigh 10 grams of the sawings into a 250-cc. beaker and add about 175 cc. of bearing metal solution. [Bearing metal solution is prepared by dissolving 40 grams of potassium chloride in 1000 cc. of water, adding 400 cc. of hydrochloric acid (sp. gr. 1.19) and 200 cc. of nitric acid (sp. gr. 1.42), and mixing.] Heat until lead chloride begins to crystallize out and then decant the solution into a 400-cc. beaker. Again add 175 cc. of bearing metal solution and heat to complete solution of the alloy. Allow both portions to stand in the cold overnight and filter through the same paper into a 600-cc. beaker. Wash with cold hydrochloric acid (1 to 1). Discard the residue. Evaporate the filtrate to dryness on a water bath, take up with 100 cc. of hydrochloric acid (9 to l),just bring to boiling, pass in sulfur dioxide for 30 minutes, add 100 cc. of boiling water, and continue passing in sulfur dioxide for 30 minutes. Allow to stand in a warm place an hour and again pass in sulfur dioxide for 20 minutes. Filter through a Gooch crucible and wash a few times with hydrochloric acid (1 to 2); finally wash a few times with water. Detach the asbestos pad, transfer both pad and crucible to a small beaker, add 10 cc. of nitric acid (sp. gr. 1.42) and 10 cc. of sulfuric acid (sp. gr. 1.84), warm until the tellurium precipitate is completely dissolved, cool, remove and wash the crucible, filter, and wash. Evaporate the filtrate to fumes of sulfur trioxide, cool, dilute to a volume of 50 cc., add 5 grams of tartaric acid, and bring to boiling. Cool, allow to stand an hour or so, and filter and wash if a precipitate has formed. Discard the residue. Through the filtrate pass hydrogen sulfide and proceed exactly as in the determination of tellurium in lead.
In Table I1 are shown the amounts of copper, bismuth, and tellurium added to pure lead (samples I to IV). Samples V and V I are antimonial lead to which tellurium alone has been added. TABLE11. DETERMINATION OF TELLURIUM IN ANTIMONIAL LEAD TELLURIUM FOUND TELLURIUMCOPPER BISMUTH In I n main S A M P L ~ TAKEN ADDED ADDED residue portion ERROR Gram Gram Gram Gram Gram Gram 0.0100 I 0.0050 .... 0.0014 0.0085 -0.0001 I1 0.0100 . . . . 0.0013 0.0050 0.0084 -0.0003
I11
IV VI
V
0.0100 0.0100 0.0100 0.0100
....
.... .... ....
0.0050 0.0050
.... ....
0.0012 0.0010 0.0005 0.0004
0.0085 0.0086 0.0094 0.0093
-0.0003 -0.0004 -0.0001 -0.0003
LITERATURE CITED (1) Browning, P. E., “Introduction to the Rarer Elements,” 2nd ed., p. 156, John Wiley & Sons, N. Y . , 1909. Ibid., p. 157. Browning, P. E., and Flint, Mi.R., Am. J . Sci., 28, 112 (1909). Brukl, A., and Maxymowicz, W., 2. anal. Chem., 68, 14 (1926). Clauder, 0. E., Ibid., 89, 270 (1932). Evans, B. S., Analyst, 58, 453 (1933). Gooch, F. A., “Methods in Chemical Analysis,” 1st ed., p. 394, John Wiley & Sons, N. Y., 1912. Ibid., p. 401. Ibid.,p. 402. Gooch, F. A., and Morgan, W. C., Am. J . Sci., 2, 271 (1896). Heath, G. L., “The Analysis of Copper and Its Ores and Alloys,” 1st ed., p. 235, McGraw-Hill Book Co., N. Y., 1916. Hiers, G. O., Trans. Am. Inst. Chem. Enyrs., 20, 131 (1927). Lenher, V., Trans. Am. Inst. Mining Met. Engrs., 69, 1051 (1923). Lenher, V., and Homberger, J . Am. Chem. SOC.,30, 387 (1908). MacIvor, R. W. E., Chem. News, 87, 17, 163 (1903). Ibid., 87, 209 (1903). Perkins, C. C., Am. J. Sci., 29, 540 (1910). Singleton. W., and Jones. B., J. Inst. Metals, 51, No. 1, 71 (1933). Smith, E. F., “Electro-Analysis,” 6th ed., p. 189, P. Blakiston’s Sons & Co., Philadelphia, 1918. Treadwell, F. P., and Hall, W. T., “Analytical Chemistry,” 6th ed., Vol. 11, p. 259, Jphn Wiley & Sons, N. Y . , 1924. \ - - - - ,
R ~ C E I V EApril D 4, 1934.
