Sept., 19581 WOOD AND CLARK 509 Determination of Copper in Titanium, Zirconium and Their Alloys BY D. F. WOOD AND R. T. CLARK (Research Department, Imperial Chemical Industries L t d . , Metals Division, Kynoch Works, Witton, Birmingham, 6 ) A rapid direct absorptiometric method, based on the blue colour produced by the reaction of copper ions with biscyclohexanone oxalyldihydrazone, has been developed for the determination of copper in titanium, zirconium and their alloys. The method is suitable over the range 0.005 to about 3 per cent. of copper. In order to provide a method for determining less than about 0.005 per cent. of copper, a procedure depending on the formation of a copper - diethyl- dithiocarbamate complex has been investigated and shown to be satisfactory over the range 0.0005 to 0.01 per cent.Interference by iron and nickel is overcome by forming complexes of these metals with disodium ethylene- diaminetetra-acetate. THE amount of copper contamination in titanium, zirconium and their alloys is of metal- lurgical interest, particularly in zirconium used in pressurised-water nuclear reactors, in which only small amounts of copper, not more than about 0.005 per cent., can be tolerated because of its effect in reducing corrosion resistance to water a t high temperatures. Interest has also been shown in the effect of alloying amounts of copper in these materials. These considerations have necessitated the development of procedures for the determination of copper in the range 0.002 to about 2 per cent. in titanium, zirconium and their alloys.Absorptiometric procedures based on the use of sodium diethyldithiocarbamate,l 2 : 9-dimethyl-1 : 10-phenanthroline (neocuproine)2 and 2 : 2'-diquinolyP are used in the examination of a variety of materials and are usually applied over the range 0.002 to about 1 per cent. of copper. Both the diethyldithi~carbamate~ and neocuproine5 methods have been recommended for the determination of copper in titanium, but they involve extraction of the copper-organ0 complex with an organic solvent. More recently, details have been published of methods based on the formation of a blue complex when copper ions react with biscyclohexanone oxalyldihydrazone, a reaction first suggested by Nilsson,6 and later applied to the examination of paper,i plant materialspg and steel.1° The complex is formed in a solution controlled at about pH 9 by means of a buffer of either ammonium hydroxide and ammonium citratesJO or sodium hydroxide and sodium b ~ r a t e .~ This procedure does not involve extraction of the complex, and, in this respect, is more rapid than the earlier methods. In order to provide a simple and rapid method for determining copper over the required range in titanium, zirconium and their alloys, the biscyclohexanone oxalyldihydrazone procedure has been investigated. Colour development of the copper complex is inhibited by high salt concentration, which imposes a limitation on the amounts of acid solvent and sample that can be used in the determination; consequently, the procedure is limited to amounts of copper above about 0.005 per cent.Application of the diethyldithiocarbamate method4 to zirconium and its alloys has also been investigated, in order to provide a more accurate procedure for the determination of copper below about 0.005 per cent. EXPERIMENTAL BISC~C~OHEXANONE OXALYLDIHYDRAZONE METHOD FOR COPPER IN TITANIUM PRELIMIXARY EXPERIMENTS- Initial tests with an ammonium hydroxide - ammonium citrate buffer solution permitted conditions to be established for determining copper in the presence of major amounts of titanium only. ~ These tests confirmed that the presence of a high concentration of ammonium ions caused low resultsi; the 0.5-g sample was, therefore, dissolved in a minimum volume of acid (15 ml of diluted hydrochloric acid (2 + 1) and 1 ml of fluoroboric acid) in order to avoid the formation of an excessive amount of ammonium salts when the solution was neutralised.510 WOOD AND CLARK: DETERMINATION OF COPPER [Vol.83 Subsequent tests showed that aluminium, manganese and tin caused both low and erratic results, whereas with the alternative pro~edure,~ in which the complex was formed in a sodium hydroxide - sodium borate buffer solution, no such interferences were observed. The alterna- tive procedure was therefore further investigated; preliminary experiments were made (a) to establish the wavelength at which maximum absorption of the copper - organo complex occurs, and (b) by using this wavelength, to prepare a calibration graph. (a) Absorptiolz curve-A 0.5-g portion of hlgh-purity copper was dissolved in 25 mi of diluted nitric acid (1 + 1) and the solution was boiled for 2 or 3 minutes to expel nitrous fumes; it was then cooled, transferred to a 1-litre calibrated flask and diluted to the mark with water.1 ml = 0.01 mg of copper. To 2.0 ml of this copper nitrate solution in a 50-ml calibrated flask were added 5 ml of 10 per cent. ammonium citrate solution and then 1 drop of 0.05 per cent. neutral red indicator solution. Sodium hydroxide solution (10 per cent.) was added until the colour of the solution changed from red to yellow, and then 5 ml of a sodium borate buffer solution and 0.5 ml of 0.5 per cent. biscyclohexanone oxalyldihydrazone in ethanol - water (1 + 1) were added. The solution was diluted to the mark a,id optical-density measurements were made with a Unicam SP600 spectrophotometer in 4-cm cells at wavelengths between 5000 and 6500 A.It was confirmedlo that the wavelength at which maximum optical density occurs is (b) Calibration gra$Jh-Portions of the copper nitrate solution ranging from 0 to 4.0 ml were transferred t o 50-ml calibrated flasks and Ieagents were added in accordance with the procedure described in (a). These solutions were diluted to the mark and their optical densities were measured at 5950.4 in 4-cm cells; a linear calibration graph was obtained. Tests were then made in the presence of titanium. A 0.5-g sample of copper-free titanium was dissolved in a mixture of 15 ml of diluted hydrochloric acid (2 + 1) and 1 ml of fluoroboric acid. The solution was oxidised with a few drops of nitric acid, sp.gr.1.42, boiled to expel nitrous fumes, cooled, transferred to a 50-ml calibrated flask and diluted to the mark. Five 5-ml portions were transferred to 50-ml calibrated flasks and portions of the copper nitrate solution ranging from 0 to 4.0 ml, am- monium citrate solution and neutral red indicator solution were added as before. On addition of sodium hydroxide solution, however, titanium hydroxide was precipitated, because the amount of ammonium citrate was insufficient t o react with all the titanium. Further tests showed that about 8ml of 20 per cent. ammonium citrate solution were sufficient for this purpose, and, with this modification, a calibration graph was prepared, which was identical with that obtained in the absence of titanium. This graph is suitable for amounts of copper in the range 0.005 to 0.08 per cent.A 10-ml portion of this solution was diluted to 500 ml, so that- 5950 A. EFFECTS OF TEMPERATURE, REAGENT CONCENTRATION AND OTHER FACTORS- No significant variation in optical density OF the complex occurs over the range 18" to 24" C, and strict control of solution temperature during optical-density measurement is therefore not essential. Full colour developmeiit is achieved within about 5 minutes of adding the reagent solution, and the colour is stable for at least 3 hours. The use of different amounts of diluted hydrochloric acid (2 + 1) between 10 and 16 ml has no significant effect, but amounts between 16 and 30 ml of the acid solvent result in a sharp decrease in optical density. Different amounts of fluoroboric acid between 0.5 and 2 ml have no effect on the optical density of the complex.In the range 7.5 to 9.5 ml, the volume of 20 per cent. ammonium citrate solution has a negligible effect on the optical density, but, above this upper limit, optical density decreases with increase in ammonium citrate concentration. Below 7.5 ml, precipitation of titanium hydroxide occurs when the acid solution is neutralised. In subsequent tests 8.0 ml of 20 per cent. ammonium citrate solution were added. Amounts of 10 per cent. sodium hydroxide solution in the range 0.5 to 5 ml, added after neutralisation, have no significant effect on the optical density, but the colour of the complex develops more rapidly in the presence of 1 to 5 ml of this reagent, full colour development being achieved within about 2 minutes.Therefore, in subsequent tests, an excess of 1 ml of 10 per cent. sodium hydroxide solution was added; the pH of the solution at this stage will he nhmit Q4Sept., 19581 IN TITASICM, ZIRCONIUM AND THEIR ALLOYS 51 1 No effect on the optical density was observed when different amounts of sodium borate buffer solution between 3 and 10ml were used, and the pH of the solution remained at 9.0 i 0.05. When 2.5ml of this buffer solution are used, full colour development is not achieved (the pH of the solution was 8.8) ; 5 ml of the buffer solution were added in subsequent tests. Amounts of biscyclohexanone oxalyldihydrazone solution between 0.5 and 3 ml have no effect on the optical density. Experiments were made on solutions containing 50 mg of titanium and the equivalent of 0.005 or 0.08 per cent.of copper to determine the effect of common alloying constituents and likely impurities. It was established that no interference is caused by the presence of at least 20 per cent. of manganese or tin, 10 per cent. of aluminium or 5 per cent. of chromium, iron, nickel or molybdenum. Vanadium above 2.5 per cent. causes a decrease in optical density and the presence of 10 per cent. of vanadium completely inhibits colour development. Interference of vanadium up to about 5 per cent. can be overcome by taking a smaller aliquot of the sample solution, so that the amount of vanadium in the final solution does not exceed 1.25 mg. DETERMISATION OF LARGER AMOUNTS OF COPPER- Tests showed that, by using a smaller sample weight and smaller cells, or smaller cells only, the procedure can be extended to the determination of up to about 3 per cent.of copper. BISCYC~OHEXANONE OXALYLDIHYDRAZONE METHOD FOR COPPER IN ZIRCONIUM Calibration graphs covering the ranges 0.005 to 0.08 per cent., 0.02 to 0.32 per cent. and 0.2 to 3.2 per cent. of copper prepared in the presence of copper-free zirconium are identical with those prepared in the presence of titanium. Effects of temperature, acidity, concentration of reagents and stability of the complex were studied in the presence of zirconium, and results agree with those from similar experiments relating to the determination of copper in titanium. Effects of common alloying constituents and likely impurities were also investigated on solutions containing 50 mg of zirconium and the equivalent of 0.005 or 0.08 per cent.of copper. It was established that up to at least 30 per cent. of tin or 5 per cent. of magnesium, chromium, iron, nickel or molybdenum do not interfere. Vanadium above 2.8 per cent. causes low results, but interference up to 5 per cent. can be overcome by taking a smaller aliquot of the test solution. TABLE I DETERMIXATIOK OF COPPER I N TITASIUM ALLOYS, ZIRCONIUM AND ZIRCALOY 2 Kominal composition Copper Standard added, Coppw found, deviation, % "A % Titanium +- 5 per cent. of aluminium + 2.5 per cent. of tin (317 alloy)* . . .. . , 0.010 0.011 - cent. of tin (371 alloy)* . . . . . . 0.010 0.010 - cent. of manganese (314-1 alloy)* . . . . 0.010 0.010 - 0.080 0.080 Titanium -?; 2.5 per cent.of aluminium + 13 per 0.080 0.080 Titanium $- 4 per cent. of aluminium + 4 per 0.080 0.052 Zirconium + 1.5 per cent. of tin + 0.12 per cent. of iron + 0.1 per cent. of chromium + 0.05 per cent. of nickel (Zircaloy 2)" . . .. 0.010 0.010 - 0.080 0.080 Titanium 317 alloy? .. . . .. , . Nil 0.0178, 0.0180, 0.0182, +0.0002 0.0182, 0.0178, 0,0178 0.0156, 0.0154, 0.0154 Zirconium? . . .. .. .. . . . . Xi1 0.0152, 0.0154, 0.0152, - * Presence of copper compensated for by using an equivalent amount of sample in the t Sample taken from experimental ingot. compensating cell. APPLICATION OF THE BISCYClOHEXANONE OXALYLDIHYDRAZOXE METHOD The results were satisfactory when the recommended method was applied to solutions of titanium alloys and Zircaloy 2 to which the equivalent of 0.01 and 0.08 per cent.of copper512 WOOD AiVD CLARK: DETERMINATION OF COPPER [Vol. 83 had been added. Samples of titanium 317 alloy and zirconium were also examined, and, as shown in Table I, the results were reproducible, the standard deviation at the 0.02 per cent. level being +0.0002 per cent. SODIUM DIETHYLDITHIOCARBAMATE METHOD FOR COPPER I N ZIRCONIUM The diethyldithiocarbamate procedure as applied to the determination of copper in titanium4 was used as a basis for investigation In this procedure, sulphuric acid is used as the solvent, but, as this acid does not readily dissolve zirconium, a mixed sulphuric acid - fluoroboric acid solvent was used in the experiments described. PRELIMINARY EXPERIMENTS- Preliminary experiments were made (a) to establish the wavelength at which maximum absorption of the copper - organo complex occurs and (b) by using this wavelength, to prepare a calibration graph.(a) Absorption curve-A 0.5-g portion of copper-free zirconium was dissolved in a mixture of 25 ml of dilute sulphuric acid (1 + 4) and 0.5 ml of fluoroboric acid; a few drops of nitric acid, sp.gr. 1.42, were added and the solution was boiled to expel nitrous fumes. To the cooled solution, 5 ml of copper nitrate solution (1 ml E 0.01 mg of copper) and 5 ml of 60 per cent. citric acid solution were added. Ammonium hydroxide, spgr. 0.940, was added until the solution was neutral to litmus paper; an excess of 2 ml of ammonium hydroxide was then added. Ten millilitres of 0-1 per cent.sodium diethyldithiocarbamate solution were added, the solution was transferred to a separating funnel and the complex was extracted with two 10-ml portions of chloroform. The combined extracts were diluted to the mark in a 50-ml calibrated flask containing about 1 g of anhydrous sodium sulphate. The optical density of the solution was measured with a Unicam SP600 spectrophotometer in 4-cm cells at wavelengths between 4000 and 4 8 0 0 ~ . The wavelength of maximum absorption was found to be 4 4 0 0 ~ . (b) Calibration graph-Solutions containing 0.5 g of copper-free zirconium and amounts of copper nitrate solution (1 ml = 0.01 mg of copper) ranging from 0 to 5.0 ml were prepared and reagents were added as described in (a). The optical densities were measured at 4400 A in 4-cm cells and a linear calibration graph suitable for determining copper in the range 0.0005 to 0.01 per cent.was obtained. EFFECTS OF TEMPERATURE, REAGEKT CONCENTRATION AXD OTHER FACTORS- Tests with separate 10-ml portions of chloroform showed that about 75 per cent. of the copper - organo complex is extracted in the first 10 ml, about 23 per cent. in the second and about 2 per cent. in the third; the aqueous and organic layers were shaken for 1 minute before each separation. In further experiments, therefore, the complex was extracted with three separate 10-ml portions of chloroform, which were subsequently combined. No significant variation in optical density of the complex occurred over the range 18” to 24” C, and strict control of solution temperature during measurement of optical density is therefore not essential.Sandelll states that “exposure to light, of solutions of copper diethyldithiocarbamate in carbon tetrachloride or isoamyl acetate, causes fading,” but experiments in our laboratories showed that the complex in chloroform is stabk for at least 2 hours in diffused daylight. Increase in the amount of 60 per cent. citric acid solution over the range 2 to 10ml has no significant effect on the optical density of the complex; 1 ml, however, is insufficient to react with all the zirconium, and, on addition of ammonium hydroxide, a faint cloudiness appears owing to precipitation of zirconium hydroxide. Different amounts of ammonium hydroxide, sp.gr. 0.940, in the range 0 to 3 ml, added after neutralisation, have no significant effect on the optical density, but, above 3 ml, optical density decreases with increase in ammonium hydroxide concentration, and this is attributed to incomplete extraction of the complex.More than 0.5 per cent. of iron and 0.005 per cent. of nickel cause high and erratic results. According to Sedivec and Vasak,ll the addition of disodium ethylenediaminetetra-acetate (EDTA) solution overcomes interference by iron tiid nickel, and tests showed that interferencr by nickel up to 0.5 per cent. and iron up to 2.5 per cent. can be overcome by adding 5 ml of 0.75 per cent. EDTA solution before neutralisation. ilddition of this amount of the reagent was therefore made in all subsequent tests, and it was established that up to at leastSept., 19581 I N TITANIUM, ZIRCOSIUM AND THEIR ALLOYS 513 20 per cent.of tin or molybdenum, 10 per cent. of aluminium or 5 per cent. of magnesium, chromium or vanadium do not interfere. Manganese above 0.25 cent. interferes by forming a pink colour in the organic layer. This interference can be overcome,l up to at least 20 per cent. of manganese, by extracting both the copper complex and manganese in chloroform, returning the combined extracts to a separating funnel and shaking for about 10 minutes with dilute ammonium hydroxide solution (1 + 10). Manganese hydroxide is precipitated in the aqueous layer and the copper - organo complex remains unchanged in the chloroform. EFFECT OF EDTA CONCENTRATION- Addition of 0.75 per cent. EDTA solution over the range 2.5 to 10.0ml to solutions containing 0.5 g of zirconium and the equivalent of 0.008 per cent.of copper had no effect on the optical density of the copper complex, but similar tests in the absence of zirconium gave low results, as shown in Table 11. These tests indicate that EDTA solution, in excess of that required to react with interfering elements, inhibits colour development, but this excess of EDTA forms a stable zirconium - EDTA complex and hence does not interfere. TABLE I1 EFFECT OF EDTA CONCENTRATION Zirconium present, EDTA solution added, Copper added, Copper found, g ml % % Xi1 0.5 Nil 0.5 Nil 0.5 Nil 0.5 2.5 2.5 5.0 5.0 7.5 10.0 10.0 c - i ’ D 0.0080 0.0080 0.0080 0.0080 0.0080 0*0080 0.0080 0.0080 0.0075 0.0080 0.0074 0.0080 0.0075 0.0079 0.0076 0.0081 APPLICATION OF THE SODICM DIETHYLDITHIOCARBAMATE METHOD The recommended method was applied to samples of commercially pure zirconium and Zircaloy 2 ; as shown in Table 111, the results were satisfactory, the standard deviation at the 0.005 per cent.level being +O.OOOl per cent. This method differs from that published for the examination of titanium4 in that the sample is dissolved in a mixture of sulphuric and fluoroboric acids and EDTA is added. A calibration graph prepared from solutions containing 0.5 g of copper-free titanium and copper over the range 0.0005 to 0-01 per cent. was identical with that obtained in tests with zirconium solutions. Further tests confirmed that the effects of reagents and other metals were the same as those from similar experiments relating to the determination of copper in zirconium.TABLE I11 QETERMINATION OF COPPER IN COMMERCIALLY PURE ZIRCONI~~M AND ZIRCALOY 2 Sample Xo. Copper found, % 1 0.0052, 0.0052, 0.0054 0.0031, 0.0033, 0.0032 0.0020, 0.0020, 0*0020 0.0055, 0.0057, 0.0056, 0.0056, 0.0057, 0.0058 Zirconium . . ..{ ; 4% 1 0.0041, 0.0041, 0.0040 -{ 2 0.0035, 0.0035, 0.0033 Zircaloy 2 . . * Standard deviation jO*OOOl per cent. METHODS BISCYC~OHEXAXONE OXALYLDIHYDRAZONE METHOD REAGENTS- sp.gr. 1.18, and mix well. Hydrochloric acid, diluted ( 2 + 1)-To 100 ml of water, add 200 ml of hydrochloric acid514 WOOD AND CLARK: DETERMINATIOY OF COPPER TVol. 83 Fluoroboric acid-To 280 ml of hydrofluoric acid maintained a t 10" C add, in small Nitric acid, spgr. 1.42. Ammonium citrate solution, 20 per cent.-Dissolve 50 g of ammonium citrate in about Neutral red indicator solution, 0.05 per cent.---Dissolve 0.5 g of the reagent in about 50 ml Sodium hydroxide solution, 10 per cent.-Dissolve 25 g of sodium hydroxide in 150 ml Sodium borate buffer solution-Dissolve 15.46 g of boric acid in 250ml of water and Dissolve 2.0 g of sodium hydroxide in 75 ml of water and amounts, 130 g of boric acid.Store in a polythene bottle. 100 ml of water and dilute to 250 ml. of water and dilute to 100 ml. of water and dilute to 250ml. dilute to 500 ml (solution A). dilute to 100ml (solution B). in 50 ml of ethanol - water mixture (1 + 1). acid (1 + l), boil for 2 or 3 minutes to expel nitrous fumes, cool, and dilute to 1 litre. 10ml of this solution to 500ml. To 400 ml of solution A , add 60 ml of solution B, and mix well.Biscyclohexanone oxalyldihydrazone solution, 0.5 per cent.-Dissolve 0-25 g of the reagent Standard copper solution-Dissolve 0.5 g of high-purity copper in 25 ml of diluted nitric Dilute 1 ml = 0.01 mg of copper. PREPARATION OF CALIBRATION GRAPHS- Graph 1 : For copper contents between 0.005 and 0.08 per cent.-Add, separately, 0.5, 1.0, 2.0, 3.0 and 4.0ml of the standard copper solution to each of five 50-ml calibrated flasks. Proceed with each solution and a blank as follows Add 8.0 ml of ammonium citrate solution, 1 drop of neutral red indicator solution, and then shake. Continue to shake, add sodium hydroxide solution slowly from a burette until the indicator changes from red to yellow, and then add an excess of 1 ml of sodium hydroxide solution.Add 5 ml of sodium borate buffer solution and 1 ml of biscyclohexanone oxalyldihydrazone solution, and then dilute to the mark. Measure the optical density at 20" C at a wavelength of 5950 A in 4-cm cells. Graph 2: For copper contents between 0.08 and 0.32 per cent., and 0.32 and 3.2 per cent.- Proceed as described for the preparation of graph 1, but make the following modifications- (i) Use 2.0, 4.0, 8.0, 12.0 and 16.0 ml of standard copper solution. (ii) Measure the optical density in 1-cm cells. Take the appropriate weight of sample, as follows- PROCEDVRE- Copper contents, yo . . . . 0.005 to 0.08 0.08 to 0.32 0.32 to 3.2 Sample weight, g . . . . 0.5 0.5 0.1 Dissolve the sample in 15 ml of diluted hydrochloric acid ( 2 + 1) and 1 ml of fluoroboric Oxidise with a slight excess of nitric acid, sp.gr.1.42, Cool, transfer (For copper in the range 0.32 t o 3.2 per Transfer a 5-ml portion (see Note) to a 5o-rfil calibrated flask, add 8.0 ml of ammonium Calculate the copper content of the sample from the appropriate calibration graph, by vanadium (up to the equivalent of 5 per cent ) can be overcome by taking a 2-ml portion. acid; warm gently to assist dissolution. added dropwise, and then boil for 2 or 3 minutes to expel nitrous fumes. t o a 50-ml calibrated flask and dilute to the mark. cent., use a 100-ml calibrated flask.) citrate solution and continue as described for the preparation of graph 1 or 2. SoTE-vanadium above 1% mg (equivalent ';o 2.5 per cent ) causes low results Interference SODIUM DIETHYLDITHIOCARBAMATE METHOD REAGENTS- 1.84, mix well and cool.Sulphuric acid, dilute (1 + 4)-To 400 ml oi water, add 100 ml of sulphuric acid, sp.gr. Fluoroboric acid-Prepare as described previously. Nitric acid, sp.gr. 1-42. Ammonium hydroxide, sp.gr. 0.940.Sept., 19581 I N TITANIUM, ZIRCONIUM AND THEIR ALLOYS 515 Citric acid solution, 60 per cent.-Dissolve 60 g of citric acid in about 80 ml of water and dilute to 100ml. EDTA solution, 0.75 per cent.-Dissolve 3.75 g of crystalline disodium ethylenediamine- tetra-acetate dihydrate in water and dilute to 500 ml. Sodium diethytyldithiocarbamate solution, 0.1 per cent.-Dissolve 0.1 g of the reagent in about 50 ml of water and dilute to 100 ml. Standard copper solution-Prepare as described previously.PREPARATION OF CALIBRATION GRAPH FOR COPPER CONTENTS BETWEEN 0.0005 AND 0.01 PER Transfer 0.5-g portions of zirconium (or titanium) refined by the iodide process to each of six beakers and dissolve in 25-ml portions of dilute sulphuric acid (1 + 4) and 0.5 ml of fluoroboric acid; warm gently to assist dissolution. Oxidise with a slight excess of nitric acid, spgr. 1.42, and boil for 2 or 3 minutes to expel nitrous fumes. Cool, and add, separately, 1.0, 2.0, 3.0, 4.0 and 5.0 ml of the standard copper solution; use the remaining solution as a blank. Add 5 ml of citric acid solution, 5 ml of EDTA solution and ammonium hydroxide, spgr. 0.940, from a burette until the solution is neutral to litmus paper. Cool, add an excess of 2 ml of ammonium hydroxide and 10 ml of sodium diethyldithiocarbamate solution Transfer the solution to a 100-ml separating funnel, add 10 ml of chloroform, shake for about 1 minute and then allow the two layers t o separate.Remove the lower chloroform layer, which contains the copper complex, to a 50-ml calibrated flask containing about 1 g of anhydrous sodium sulphate. Extract with two further 10-ml portions of chloroform, combine the extracts and dilute to the mark with chloroform. Xeasure the optical density at 20” C at a wavelength of 4400 A in 4-cm cells. PROCEDURE- Dissolve 0.5 g of sample in 25 ml of dilute sulphuric acid (1 + 4) and 0.5 ml of fluoroboric acid; warm gently to assist dissolution. Oxidise with a slight excess of nitric acid, sp.gr. 1.42, and boil for 2 or 3 minutes to expel nitrous fumes.Cool, add 5 ml of citric acid solution (see Note) and continue as described for the preparation of the calibration graph. CENT.- Proceed with each solution as follows. Read the copper content of the sample from the calibration graph. XoTE-when manganese is present above 0.25 per cent., return the combined chloroform extracts to a separating funnel, add 50ml of dilute ammonium hydroxide (1 + lo), and shake for about 10 minutes. Remove the lower chloroform layer containing the copper - organo complex and continue as described for the calibration graph. CONCLUSIONS The direct absorptiometric method with biscyclohexanone oxalyldihydrazone is suitable for determining 0.005 to about 3 per cent. of copper in titanium, zirconium and many of their alloys.Vanadium above about 2.5 per cent. causes low results, but this interference (up to about 5 per cent.) can be overcome by taking a smaller aliquot of the sample solution. The procedure is simple, rapid and particularly suitable for control analysis. About 30 deter- minations can be made in 8 hours by one analyst. The standard deviation at the 0.02 per cent. level is about +0.0002 per cent. The sodium diethyldithiocarbamate method is suitable for the determination of copper in the range 0.0005 to 0.01 per cent. in titanium, zirconium and many of their alloys. This procedure can be extended to the determination of larger amounts of copper by using a smaller sample weight, but it is recommended primarily for amounts of copper below about 0-01 per cent. Interference by nickel up to 0.5 per cent. or iron up to 2.5 per cent. is overcome by forming complexes of these metals with EDTA. We thank Mr. W. T. Elwell, Division Chief Analyst, for helpful suggestions and assistance in the preparation of this paper. REFERENCES 1. 2. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Second Edition, Interscience Crawley, R. H. A., Anal. Chim. A d a , 1955, 13, 373. Publishers Inc., New York and London, 1950, Volume 111, p. 304.516 POLLOCK: A PHOTOMETRIC METHOD FOR [Vol. 83 3. 4. 5. 6. 7. 8. 9. 10. 11. Elwell, \V. T., Analyst, 1955, 80, 508. “The Analysis of Titanium and its Alloys,” Imperial Chemical Industries Ltd., First Edition, Frank, A. J., Goulston, A. B., and Deacutis, A. A., Anal. Chem., 1957, 29, 750. Nilsson, G., Acta Chem. Scand., 1950, 4, 205. Wetlesen, C., and Gran, G., Svensk Papperstitlning, 1952, 55, 212. Xf’illiams, T. R.. and Morgan, R. R. T., Chem. 6- I n d . , 1954, 461. Somers, E., and Garroway, J. L., Ibid., 1957, 395. Haywood, L. J. A., and Sutcliffe, P., Analyst, 1956, 81, 651. Sedivec, V., and Vasak, V., Coll. Czech. Chem. Comm., 1950, 15, 260. London, 1956. Received March 7th, 1958