INDUSTRIAL
and
ENGINEERING
CHEMISTRY ANALYTICAL EDITION
+
Earrison E. Eowe, Editor
Determination of Nickel in Allov Steels J
A Photometric Titrimeter W. J. BOYER, Research Laboratory, The Carpenter Steel Company, Reading, Pa.
T
HE volunietric determination of nickel in steel as pro-
The cyanide method, while rapid, is not entirely satisfactory if the end point is judged by visual means. Partridge posed b y Moore (6) has been investigated so often that (7) has demonstrated the use of the photoelectric cell as an further studies in this field mag appear to be unneceqsary. indicator in precise titrations. I n the present study, it wa5 However, the data are not very consistent, and apparently decided to employ the photronic cell for the determination no effort has been made to find what conditions are necessary of the end point in the cyanide titration method for nickel. to yield results on a basis of 1Si = 2.4g. Johnson (3) has reported extensively on the subject, alApparatus though his data do not include a study of such condition12s the permissible limits of nickel concentration, the amount A modified arrangement of Partridge's apparatus was assembled (Figures 1and 2), using a Leeds & Northrup students' of excess ammonia, and the range of temperature. The procedures recommended by Lundell, Hoffman, and Bright (5) type of potentiometer to measure the e. m. f. of the photronic and by the American Society for Testing Materials (1) are cell. The potentiometer was used !only to obtain the curves almost identical and are presumably the average conditions shown in Figures 3 and 4. All other titrations in this invesused by a large number of analysts in the field. Recently, tigation were made Kith ordinary radio potentiometers that Peters (5) has applied the cyanide titration for nickel to were made a n integral part of the completed apparatus. nickel-chromium alloys, but fails to specify the temperature The galvanometer used was a Leeds & Northrup instrua t which the titration should be made. The temperature is ment of the enclosed lamp and scale type with a sensitivity just as important as the amount of excess ammonia, as is of 0.02 microampere per mm. division. Figure 1 shows a shown below. Kolthoff (4) considered the optimum condiqchematic diagram of the apparatus along with the electrical tions necessary for the determination of alkali cyanides by circuits used. The lamp housing has a small 110-volt 15titration with d v e r nitrate in ammoniacal solution, using watt cwicentrated filament lamp with a reflector mounted d v e r iodide as an indicator. He recommended 4 to 6 ml. of rigidly in one end of a brass tube. The lamp voltage is kept constant with il Raytheon voltage iegulator of 60 Tvatt.' 7 . 5 N ammonia in ewe's. and 0.2 gram of potassium iodide per 100 ml. of solution. capacity. The nianuElectrolytic depof a c t u r e r claims an I .sVolts * i t i o n is recomoutput, of 115 volts f mended for umpirr 1 per cent. These nickel determinations regulators were found in high-nickel steel. much more conven(a), but this method ient than storage (*annot be used for batteries a n d h a v e 5003% control in a steelp r o v e d sufficiently Voltage Regulator making process hrconstant for this type ~ a u s eof the time rcof work. The other q i i i r e d . T h P rliend of the lamp h o i i h i n e t h y 1 g I y o x i ni c ing contains a .zmall method (1. .5) ronI m r , 3.5 cm. in rlisunies much less tinic arneter, to render the hiit has the disadlight rays parallel vantage of requiring The compartment small samples (aliquot for the glass cell i i portions) for highmade of fiber board, nickel alloys. An 6.3 mm. (0.25 inch) additional factor, too thick, and of such inoften neglected, is the side d i m e n s i o n s as solubility of the nickel just to accommodate dimethylglyoxime. FIQURE1. DIAGRAM OF APPARATUS the g l a s s c e l l . Its
1 7
t
t
INDUSTRIAL AND ENGINEERING CHEMISTRY
176
inside height is 14 cm., which is sufficient to shield the solution from stray light. The glass cells are of the museum jar variety with a total capacity of about 0.9 liter. While these cells are not optically perfect, they are nevertheless satisfactory since the potentiometer setting for each titration has its own initial zero. The photronic cell, manufactured by the Weston Electrical Instrument Corporation, is mounted directly opposite the lamp housing with a 3.5-cm. hole for the light to impinge on the cell. This area allows the activation of about 80 per cent of the photronic cell's surface. The stirring apparatus, marketed by the Arthur H. Thomas Company, is of the worm-gear drive type with a hollow spindle through which the glass stirring rod is fastened by a spring clamp. This has the additional advantage that it can be raised and lowered conveniently when changing the glass cells. All burets used were calibrated b y the National Bureau of Standards.
Reagents and Standard Solutions CITRICACID SOLUTION.Dissolve 200 grams of citric acid (U. S. P. grade) in 1000 ml. of water. IODIDE SOLUTION.Dissolve 10 grams of sodium iodide SODIUM in 100 ml. of water. COPPERSULFATE SOLUTION.This solution was prepared from a c. P. grade of CuS04.5Hx0, and was standardized by precipitating the copper as the sulfide and igniting to cupric oxide. Its strength was adjusted to equal 0.0002 gram of copper per ml. COBALTSULFATESOLUTION.The cobalt in a c. P. grade of CoS04.7Hz0was precipitated once as potassium cobaltinitrite (2) in order t o remove nickel. The potassium cobaltinitrite was decomposed with nitric acid and the solution fumed with sulfuric acid. I t was standardized by preci itating the cobalt with a-nitroso-p-naphthol and igniting to 80~04.Its strength was adjusted to equal 0.0002 gram of cobalt per ml. PUREMETALLICKICKEL. The nickel metal was a special metal prepared by W. A. Wesley of the International Nickel
VOL. 10, NO. 4
Company. The purity indicated, by difference, after chemical and spectroscopic examination was 99.98 per cent nickel. STANDARD SILVERNITRATESOLUTIOX.Dissolve 5.789 grams of silver nitrate in water and dilute to exactly 1000 ml. One milliliter of this solution is theoretically equivalent to 0.0010 gram of nickel. STANDARD SODIUMCYANIDESOLUTION.It is convenient to have two solutions on hand: For low-nickel alloys, dissolve 3.4 grams of sodium cyanide in 1000 ml. of water containing 1.0 gram of sodium hydroxide. For high-nickel alloys, dissolve 28.0 grams of sodium cyanide in 1000 ml. of water containing 1.0 gram of sodium hydroxide. Standardize by applying the method described in the section under recommended procedure. Cyanide solutions change with age and must be checked daily.
Recommended Procedure Weigh accurately a 1-gram Sam le of alloys containing from 5 to 35 per cent of nickel. For containin more nickel, use a weight equivalent to about 0.3 gram of nickef Transfer the Sam le to a 600-ml. beaker, treat with 20 ml. of diluted nitric acid to l), and heat until solution is complete. Dilute to 300 ml. with cold water and add 60 ml. of citric acid solution. Add diluted ammonium hydroxide (1 to 1) until just alkaline t o litmus, and then 5 ml. in excess. Transfer the solution to the glass titratin cell, and add 2 ml. of standard silver of sodium iodide solution. Dilute to nitrate solution and 10 500 ml. and adjust the tem erature to 30' C. Add standard sodium cyanide solution untiythe solution clears and then about 1 ml. in excess. Adjust the galvanometer to zero. Titrate the excess cyanide with standard silver solution until a permanent deflection of 25 mm. is obtained. A correction for the total amount of silver nitrate used must be made.
days
8
3.
Standardize the sodium cyanide solution by titrating an iron-nickel alloy of known nickel content. The calculation of the nickel titer of the cyanide solution is made according to Formula 1. The calculation for the per cent of nickel found is made according to Formula 2. Nickel titer =
grams of nickel
+
(ml. of AgNO, X 0.0010) (1) ml. of NaCN
Per cent of nickel = ml. of NaCN X Ni titer - (ml. of AgNOr X 0.0010) weight of sample
L
(2)
Although copper and cobalt consume cyanide, a correction can be made when the amounts are definitely known. The reaction with copper approximates the ratio, 2Cu = 7CN, and the nickel eauivalent can be calculated by multiplying by the factor 0.807. While the reaction with cobalt is not exactly 1Co = 4CK, it may be assumed to be so if the amount present does not exceed 5 mg. Chromium has no effect on the nickel titer if less than 0.1 gram is present. With high-chromium alloys, a sample that contains less than 0.1 gram of chromium must be taken or else an equal amount must be added to the standard used for determining the nickel titer of the cyanide solution.
Experimental The experimental work described below was done to determine the optimum conditions necessary for the development of the recommended procedure. A brief study of the effect of other elements is included. CYANIDEus. SILVEREND PoIw.. The curves shown in Figures 3 and 4 present comparisons between the nickelcyanide end point and the excess cyanide-silver end point. The titrations were made on weighed portions of 0.3 gram of pure nickel, 1.0 gram of 30 per cent nickel steel, and 0.4 gram of nickel-chromium (80/20) alloy. The conditions for the titrations were as follows:
FIQURE 2 . ASSEMBLYOF PHOTOTITRIMETER
The samples were dissolved in 10 ml. each of hydrochloric and nitric acids, diluted to 300 ml. Kith cold water, and treated with 120 ml. of the citric acid solution. The solutions were neutrahzed
APRIL 15, 1938
.4NALYTICAL EDITION
177
with 7.5 N ammonia, treated with 5 ml. in excess, and diluted to 500 ml., and the temperature was adjusted to 30" C. The solutions were titrated with standard sodium cyanide solution until the maximum point of inflection was reached. .4 small amount of cyanide was added in excess to show the effect of diluting the background color (iron and chromium citrates). The curves shown in Figure 3 were obtained by plotting the volume of standard sodium cyanide solution against the e. m. f . of the photronic cell. After titrating with the cyanide, the solutions were treated with 10 ml. of the sodium iodide solution and the excess cyanide was titrated with standard silver nitrate solution. Figure 4 shows the curves obtained by plotting the volume of standard silver nitrate solution against the e. m . f. of the photronic cell
T ~ B LI.E EFFECTOF A M M O S I ~CONCENTR~TIOS o s THE REACTION BETVEEN NICKELAND CYASIDE IONS (1-gram samples of iron-nickel alloy, 29 96 per cent niche1
Excess? 5 N Ammonia per 500 M1. of Solution
NaCS Added
Just alkaline
39,41 39.62 39.70 39.65 39,59 39.64 39.57 39.62 39.65 39.60
5.0 10.0 20.0
25.0 5
b
BnXOs
Nickela
Used
Found
Error
4.6 6.2 7.0 7.0
0.3000 0,3000
4-0.4 t0.4
b
....
, . .
6.6
0.2994 0.2989 0.2977 0.2980 0,2972 0,2977
-0.2 -0.7 -1.9 -1.6 -2.4 -1.9
7.4 8.1 8.2 9 2 8 3
...
All titrations made a t 30' C. NaCN solution = 0,007728 gram of Xi per ml.
The end point obtained with the silver solution is sharp and suitable for deflection end points. I n view of the data just presented, all the results in this investigation were obtained by using the cloud point (AgI formation) for the end point, as indicated by the photronic cell. SoDIcni CYAXIDE-SILVER SITR ITE RATIO. I n sodium cyanide-silver nitrate titrations the question naturally arises as to what conditions must prevail d i e n the relationship 1Ni = 2Ag holds. I t was found that the sodium cyanidesilver nitrate ratio is affected by alkalinity, temperature, the presence of citrates, and the concentration of silver. However, under the conditions of the recommended procedure, the nickel equivalent of the standard silver nitrate solution can be taken as 1Ni = 2=1g, since the amount of >ilver solution used in a determination is not enough to cause an appreciable error. EFFECTOF EXCESS; L \ n r o s ~i COXESTRATIOS.Table I shows the results obtained by the recommended procedure when the amount of 7.5 S ammonia was varied from just alkaline to 25 ml. in excess The conwmption of cyanide decreases with an increase in alkalinity.
"2)
A n excess of 5 ml. of 7.5 S ammonia used in all titrations. NaCN solution = 0.007666 gram of Si per mi.
EFFECTOF TEMPERATURE. Table I1 shows the results obtained by the recommended procedure when the tempera-
15 20 Volama of
25
NoCN
35
30
40
45
5
in milliliters
WITH
ture ivas Yaried from 10" to 50" C. The consumption of cyanide increases with an increase in temperature. EFFECTOF IROS ASDSICKEL CONCENTRATIOX. The data presented in Table I11 show that varying amounts of iron have only a slight' effect on the reaction between nickel and cyanide ions. A nickel concentration of 0.05 t o 0.4 gram per 500 nil. of solution does not affect the accuracv of the results obtained for nickel. It appears that the cciricentration of nickel could be considerably inereaped and still yield values which are correct t o within 0.1 per cent.
TABLE 111. EFFECT O F I R O s A S D S I C K E L CONCESTRbTIOS RE-ICTION BETWEES SICKEL ASD CYASIDEIONS XickelR Alloy Taken Gram
R . of 9.n
1.0000 1.0000
.... . .. .
0.8800
0.8800 0.7300 0.7300 0.5900 0.5900 0.4400 0.4400 0.2500 0.2500 0.1200 0.1200
c.
a b
IO
FIGCRE 3. PHOTOMETRIC TITRATION OF Xi(n"&++ NaCN
T-LBLE11. EFFECTOF TEMPERATURE OK THE RE.~CTIOS BETWEEN KICKEL ASD CYAXIDE IONS (1-gram samples of iron-nickel alloy, 29.96 per cent nickel) Temperature NaCS AgX03 Vickel'J of Solution Added Gsed Found Error Ml. MI. Gram MQ. 10 39,92 8 3 0.2977 -1.9 39.91 9.9 0.2961 -3.5 20 39.91 6 8 0,2992 -0.4 39.88 7.0 0.2987 -0.9 30 39.88 6.3 b 39.90 6.1 .... ... 40 39,89 5,9 0.2999 t0.3 39.91 5.9 0.3001 +0.5 50 39.88 5.0 0.3003 +0.7 39.92 5.6 0.3004 +0 8
5
5% Taken Gram
0.1200
. ...
0.2700
., . . . 0.5600 .,. 0.7500 ..., 0.8800 .., . ,
0 4100 ,
Nickel Present Gram 0.4134 0.4134 0 3638 0.3638 0.3018 0.3018 0.2440 0.2439 0.1820 0.1819 0.1035 0.1034 0,0498 0.0496
N a C N .igNO1 Added Used .U1. 311. 48 95 49 00 43 22 43.05 35.97 36.57 29.36 29.67 21.79 22.29 13.01 13.16 6.58 6.77
7.1 6.5 9
0.8 7.0 11.5 7.5 10.6 4.9 9.2 7.6 9.6 6.2 8.6
Sickelb Found Gram c
,
...
0.3639 0.3636 0,3015 0.3023 0.2443 0,2440 0.1819 0.1821 0,1037 0,1033 0.0499 0.0495
OS
Error .Wg.
...
... +O
1
-0.2 -0.3 +0.5 +0.3 f0.1 -0.1 +0.2 f0.2 -0.1 +0.1 -0.1
a Nickel alloy contains 41.34% X, O . O i % Cu. a n d 0.02% Co. National Bureau of Standards open hearth iron 5 5 , contains 0.019% Ni, 0.046% Cu, and 0.008% Co. 6 Corrected for copper a n d cobalt present. C N a C N solution = 0.008596 gram of Ni per ml., calculated from Ni
Co
+ (0.8
X CUI.
+
EFFECTOF COPPERAXD COBALT. During melting operations, nickel limits must be held within a very small range to control the final magnetic properties of the alloy. By correcting for small amounts of copper and cobalt known to be present in the mix, it is possible to control the nickel content within a range of 0.2 per cent. The copper corrections in
ISDLSTRI.4L k \ D ENGINEER13 G CHERIISTRITable IV n ere made by using the factor 0.807 to c o n v e r t i t t o its nickel equivalent. The theoretical relation of cobalt and c y nide is usuallv given as 1Co = 5 C S . In experiments where cobalt alone was 111 titrated according to c the recoinmended procedure, it beharetl ac=? 90 cording to the m i i E rated ratio. W i c n 0.7 E 85 .c. gram of iron Tvas added, E the reaction vas supbi 80 pressed to the extent I 0 $ that a relation of ap0.39 , pure nickel 2 75 p r o x i m a t e l y 1Co = * I1 I . O 9. 30 per c r n C 4CN was indicated. i nick81 steel 70 When large amounts of 1x1 0.4 9. nickel-chromum n i c k e l , s u c h a s 0.3 OllOrJ b 65 7 7 , I p c r c m t n i c r e l gram, were added with 19.5 per cant chromium the iron, the value9 for t h e iiicliel f o u n d 5 10 15 20 2 Volume of AgNdg In m#llrliters showed good recoveries d i e n corrected by usFIGURE4. PHOTOMETRIC TIi n g t h e r e l a t i o n of TRATION OF EXCESS CY- WITH 1 c o = 4CN. EFFECTo r C H R O J I I U J I . A solution of nickel sulfate was standardized by electrolytic deposition. An average of 0.3017 gram of nickel per 50 ml. of bolution was obtained, including the small amount of nickel remaining after electrolysis. The chromium was added by using a c. P. grade of sodium dichromate. It was reduced to Cr"' with a small excess of sulfurous acid and boiled. The solution was treated LTith bromine water and again boiled to expel the excess bromine. Large amounts of chromium are exceedingly hard to retain in ammoniacal solution, regardless of the amount of citric acid solution used. It was found that 0.3 gram of chromium could be held in solution with reasonable amounts of citrate if considerable ammonium chloride was also used. I n the experiments shown in Table V, 25 grams of ammonium chloride were used in conjunction n-ith the recommended procedure. Both Johnson (3) and Peters (8) claim that tlie end point cannot be determined accurately unless the chromium is first oxidized t o CrT'. K i t h the phototitrimeter, a good end point is obtained regardless of the valence or amount of chromium, but when more than 0.1 gram of chromium is present, the nickel titer, as obtained on pure nickel, 1s slightly low. For high-chromium alloys, therefore, a weight of sample should be taken which does not contain more than 0.1 gram of chromium.
,=
-----$
@A
were saturated xvith hydrogen sulfide to precipitate the copper, and filtered on small papers. The filtrates were boiled t o expel hydrogen sulfide, oxidized with bromine, and again boiled to expel the excess bromine. The residual iron was tviice precipitated n-ith diluted ammonium hydroxide and the filtrates were evaporated to a \ d u n e of 150 mi. An excess of ,35 ml. of ammonium hydroxide n-as added for the electrolysis. All determinations w r e corrected for the small amounts of nickel remaining after electrolysis. An average of four determinations gave a value of 29.96 per cent nickel. The sample was found to contain 0.10 per cent copper. The cobalt was determined by using Hoffman's procedure ( 2 ) to separate the iron, nickel, etc. TThen 25gram samples were used, less than 0.005 per cent of cobalt Tvas indicated. CYANIDETITRATIOS L~ETIIOD. Three 1-gram samples of tlie 30 per cent nickel ateel were analyzed for nickel by the recommended procedure. An average value of 29.96 per ceiit nickel was obtained. The cyanide solution was standardized on a synthetic mixture of 0.3000 gram of pure nickel and 0.7000 gram of Sational Bureau of Standards open hearth iron 55a. DIIIETHPLGLPOSIXIE I~ETHOD. The procedure used for the dimetliylglyoxime method was as follows: Accurately Twighed 1-gram samples \yere dissolved in 20 ml. of diluted nitric acid (I to I) and diluted to I liter in a calibrated flask. One huiidred-milliliter portions (0.1-gram samples) mere
transferred to 400-ml. beakers using a calibrated pipet. Ten milliliters of hydrochloric acid and 20 ml. of citric acid solution were added, and the solution mas dilut'ed to about 200 ml. and neutralized lvith diluted ammonium hydroxide (1 to 1). Seven milliliters of glacial acetic acid were added and the solution was heated to boiling. Forty milliliters of dimethylglyoxime solution (10 grams of dimethylglyoxime and 9 grams of sodium hydroxide dissolved in 1000 ml. of water) mere added, the solution was neutralized m-ith diluted ammonium hydroxide (1 to l), and then 5 ml. were added in excess. All solutions xere then
TABLE
IT'. BEHAVIOR O F COPPER AND COB.4LT TITRATIONS
I N NICKEL
(I-gram samples of iron-nickel alloy, 29.96 per oent nickel) NaCS AgSOa Nickela Copper Cobalt Used Found Error Added Added Added Mg. Mu. Ml, Xl. Gram M g , . . ... 41.91 8.5 b ... ... 41.94 8.7 .... ... 2.0 ... 42.22 9.1 0.2997 4-0.1 2 0 . .. 42.21 8.8 0.2999 +0.3 0.2996 tO.0 42.40 7.1 5.0 0.2992 -0.4 42.48 8.1 5.0 0,2997 +0.1 43.01 9.9 2.0 5.0 0.2995 -0. 1 4 3 . 0 0 1 0 . 0 2.0 5.0
. ...
Corrected f o r copper and cobalt added. t NaCN solution = 0,007351 gram of Ni per nil
0
CHROMIUM ON REACTION BETVEEN S I C K E L AND C Y A N I D E I O N S
TABLE\-. EFFECTOF
(50 ml. of S190r solution, equivalent t o 0.3017 gram of nickel) Chromium .kgso~ Nickela Added SaCN Used Found Error (CrIII) Added Gram Ml. 211. Gram MU. ... 36.84 14.4 b ... ,.. 36.82 14.4 ... ... 0 3016 -0.1 13.9 0.1 36.76 0.3010 -0.7 14.7 0.1 3 G . 78 0.2991 -2.6 16 9 0.2 36.82 0.2988 -2.9 17.4 0.2 36.84 0.2978 -3.9 18.7 0.3 36.S i 0.2973 -4.4 18.8 0.3 36.83
Comparison of Results b y Several Methods
ELECTROLYTIC METHOD. The 30 per cent nickel steel previously referred to was standardized electrolytically. The procedure used was as follows: Accurately weighed 1-gram samples were dissolved in 500-ml. Kjeldahl flasks with diluted hydrochloric acid (1 to 1) and oxidized with nitric acid. The solutions were evaporated to low volume and double ether separations made t o remove most of the iron. The acid layers were evaporated to fumes with sulfuric acid, cooled, and diluted with water. The solutions
\OL. 10. h0.5
+
1,
Recommended procedure 2 5 grams of NHICI. N a C N solution = 0.008683 gram of Ni per rnl.
APRIL 13, 1938
\\iLlTIO\L
allowed to digest for 30 minutes at about 75' C. The precipitates were collected in veighed platinum Gooch crucibles with asbestos beds, washed five t o six times I=,-ith hot (70" C.) distilled water, and dried at 110" C. for 1 hour. The factor 0.2032 was used to convert the weight of nickel dimethylglyoxime to nickel. The ayerage of five closely agreeing results gave a value of 29.82 per cent of nickel in the 30 per cent nickel steel. When an alcoholic solution of the dimethylglyoxime was substituted for the sodium hydroxide solution in the method just described, an average of two determinations gave 29.70 per cent of nickel. According to Lundell, Hoffman, and Bright ( 5 ) , alcohol has a greater solubility effect than ammonium hydroxide, ammonium salts, or alkali acetate. The difference between the electrolytic and the dimethylglyoxime value is large compared to the close agreement obtained by the cyanide method based on pure nickel. The following experiments were made to determine whether the difference could be due entirely t'o the solubility of the nickel dimethylglyoxime. One-gram samples of the 30 per cent nickel steel were dissolved in nitric acid, diluted to 1 liter, and divided into ten portions. The nickel in all ten portions n-as precipitated with dimethylglyoxime (sodium hydroxide reagent), filtered, washed, and run in all respects under the same conditions as the original dimethylglyoxime standardization. The precipitates were discarded and the filtrates evaporated to dryness. The citric acid, the excess reagent, and the ammonium salts were destroyed by oxidation with nitric and perchloric acids. The portions were combined and the remaining nickel was again precipitated in a small volume with dimethylglyoxime. An average of tm-o such runs gave a result of 0.12 per cent of nickel, t o which 0.01 per cent should be added to allow for the 0.13 = 29.95) h a 1 solubility. This corrected value (29.82 is in very good agreement with both the electrolytic and t'he cyanide values. A number of other cases seem worthy of reporting. A sample of Invar was found to contain 35.90 per cent of nickel by cyanide titration, based on pure nickel. The dimethylglyoxime method, using 0.1-gram samples (aliquoted from 1-gram samples), showed 35.62 per cent of nickel. In another case, an iron-nickel alloy was found t o contain 41.34 per cent of nickel by cyanide titration, based on pure nickel. The dimethylglyoxime method, using 0.08-gram samples (aliquoted from 1.6-gram samples), showed 40.99 per cent of nickel. An alloy of the 80 per cent nickel-20 per cent chromium type was analyzed for nickel by cyanide titration, using accurately weighed 0.4-gram samples, the cyanide solution being sbandardized against ure nickel. An average of 77.2 per cent of nickel was foun2 An average of 77.1 per cent of nickel was found by standardizing against 1-gram portions of the 30 per cent nickel steel (29.96 per cent of nickel). The dimethylglyoxime method, using 0.04-gram samples (aliquoted from 0.4gram samples), gave a value of 76.7 per cent of nickel.
+
EDITIOh
179
A determination of nickel by the recommended procedure in Sational Bureau of Standards 18 Cr-8 Ni steel 101 gave an average value of 8.49 per cent of nickel, after correcting for copper and cobalt. (Cobalt is not listpd on i h e certificate, but this laboratory obtained a value of 0.058 per cent. The certificate yalue for copper is 0.055 per cent.) The cyanide solution was standardized on a synthetic mixturc: of 0.2800 gram of the nickel steel ( S i = 29.96), 0.175 gram of chromium ( C r I I I ) , and 0.5 gram of Sational Bureau of Standards open hearth iron 55a. The certificate value of 8.44 per cent of nickel for this standard may be slightly low, since the dimethylglyoxime met,hodwas used by most of the cooperators listed on the certificate of analysis.
Conclusions
A photometric apparatus has been developed to detect the end point in the cyanide titration method for nickel and found to be greatly superior to the eye, particularly in analyses of high-chromium alloys. It is possible to run duplicate determinations in 35 to 40 minutes on iron-nickel alloys. High-chromium alloys necessarily require more time because of the difficulty of dissolving such samples. The accuracv that can be expected is of the order of 0.1 per cent. The solubility of nickel tiiinethylglyo?time is demonstrated and it is shown that less dependence should be placed on this method when applied to high-nickel steels where the highest order of accuracy is desired.
-4cknowledgment The author wishes to thank C. Sterling and W.A. Wesley of the International Sickel Company for the pure nickel used in this work. He wishes also to thank the officers of the Carpenter Steel Company for their encouragement during the progress of this work.
Literature Cited (1) Am. Sac. Testing Materials, "?Jethods of Chemical Analyses oi Metals," p. 34, 1936. (2) Hoffman, J. I., Bur. Standards J . Research, 8, 659 (1932). (3) Johnson, C. M.,"Chemical Analysis of Special Steels," 4th ed.. pp. 221-33, New Tork, John Wiley &- Sons, 1930. (4) Kolthoff, I. M., and Furman, N. H., "Volumetric Analysis," Val. 11, p. 239, New York, John Wiley & Sons, 1929. ( 5 ) Lundell, G. E. F., Hoffman, J. I., and Bright, H. A., "Chemical Analysis of Iron and Steel," pp. 277-87, S e w York, John Wiley &Sons, 1931. (6) Xoore, T., Chem S e u s , 72, 92 (1895). (7) Partridge, H. hl., ISD.ENG.CHEII.,Anal. Ed., 4, 315 (1932). (8) Peters, F . P., Chemzst-Analyst, 26, 76 (1937). ,RECEIVED January 4 , 1938.
The Symbol Dz to Signify Dithizone P. L. HIBBARD University of California, Division of Plant Nutrition, Berkeley, Calif.
C
OSSIDERABLE literature has accumulated in regard to use of diphenylthiocarbazone (phenylazothionoformic acid phenylhydrazide) as an analytical reagent, Users of this substance soon contracted the name t o dithizone, but so far as is known to the writer the only symbol proposed t o represent the name is D. Since this symbol is now commonly used to designate deuterium, the heavy isotope of hydrogen, it should not be uced to represent anything else.
The rvriter propobes the symbol Dz to represent dithizone. This will avoid confusion with anything else and will facilitate writing formulas or equations in which the radical dithizone occurs. TThen the XTord is used as the name of the reagent, diplien~lthiocarhazone. it should be spelled out "dithizone." R T C E I I E DFebruarv 15, 1938.
