I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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Vol. 16, No. 9
Fluorine Determination in Nickel-Depositing Solutions'" By L. D. Hammond BUREAUO F SThNDARD.3,WASHINGTON. D .
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NASMUCH as fluorides have recently been employed in salt, to which in some cases nickel sulfate and boric acid were nickel-depositing solution^,^ a method for the analysis of added. Such portions of the procedure as were required by such solutions is desirable. In this paper a method is de- the constituents present were employed. The results are scribed by which fluorine can be determined in the presence shown in Table I. of nickel sulfate, boric acid, and other usual constituents of From Table I i t is seen that the results are fairly reproducinickel baths. ble, but are usually somewhat high. It does not appear If the nickel is removed by electrolysis of the ammoniacal feasible to obtain by this method with reasonable precautions solution, and any precipitate of ferric hydroxide is filtered out, an accuracy greater than about 1per cent of the amount presthe filtrate will contain, chiefly as ammonium salts, fluoride, ent. This accuracy is, however, usually adequate for works borate, sulfate, and possibly chloride. The problem there- control of nickel-plating solutions. fore involves the determination of the fluorine in such a soluPROCEDURE tion. The precipitation and filtration of calcium fluoride, either Application of this method to a nickel solution is as follows: d i r e ~ t l yor , ~together with calcium carbonate,6or with calcium (The method may require modification if unusual constituents oxalate,6 proved so slow as to be unsuitable for control are present.) analysis. To a 25-cc. sample add 50 cc. of water and 25 cc. of amAttempts were made to apply a volumetric method7 in monium hydroxide (specific gravity, 0.90), and remove the which, after the addition of sodium chloride, the fluoride is nickel by electrolysis in the usual way. Filter the solution titrated with ferric chloride, forming a precipitate of sodium into a 250-cc. graduated flask and wash the precipitate ferric fluoride (NaaFeFe). This method was inapplicable, (chiefly ferric hydroxide) with hot water. Add a few drops of because it was not found possible to regulate the pH of the a 0.4 per cent aqueous solution of bromophenol blue,1° and solutions containing ammonium borate so that the solution was neutralize the solution with nitric acid. Add enough nitric neither acid enough to dissolve the double fluoride nor acid-e. g., 5 cc. of 5 N HNO3-to make the solution approxialkaline enough to precipitate basic ferric compounds. mately 0.1 N in nitric acid. I n order to precipitate the sulMethods based upon the evolution of volatile compounds of fate as PbSOr, add a slight excess of a lead nitrate solution fluorine were not attempted, as they would probably not be (2 N ) , the volume of which may be calculated approximately adaptable for laboratory control work. from the nickel content if no other sulfates are present. The The method found most satisfactory is an adaptation of that lead sulfate must be precipitated in an acid solution in order to proposed by Stark,8 and subsequently confirmed by A d ~ l p h , ~avoid co-precipitation of lead fluoride or chlorofluoride. for the determination of fluorides in neutral solutions. This The solubility of lead sulfate in 100 cc. of 0.1 N nitric acid is method depends upon the precipitation of lead chlorofluoride about 11 mg. Some of this is probably precipitated subse(PbFC1) by the addition of lead chloride solution. As this quently with the chlorofluoride, which may account for the precipitate is appreciably soluble in pure water, it is washed high results. with lead chloride solution, in which it is less soluble. Dilute the solution to the 250-cc. mark, mix well, and pour at once into a Pyrex beaker, which is less attacked by the free TABLE I-DETERXINATION OF FLUORINE hydrofluoric acid than is ordinary glassware. Filter the soluWEICKTOF PhFCl tion without washing the precipitate, and use 100-cc. portions COMPOSITION OF FROM i o c c . SOLUTION Calcd. Found of the filtrate for duplicate analyses. To each 100-cc. porExpt. NaF €LBO& NiSOi Grams Grams tion add about 2 cc. of N sodium chloride solution, to insure .. .. 0,5233 0.5295 1 0 2 N .. *. 0.5233 0.5297 2 0.2N that any precipitate formed during the neutralization will be .. .. 0,5233 0.5290 3 0 . 2 AJ lead chlorofluoride and not lead fluoride. Add a few drops of 4 0.2N .. 0.5233 0.5291 5 0 . 2N 0 : i 34 .. 0.5233 0.5300 bromophenol blue, neutralize most of the excess acid with 5 N 0.5 M 6 0.2N 0.5233 0.5301 O.5M 2'N 0,5233 0.5253 7 0.2N sodium hydroxide, and finally add gradually 0.1 N sodium 8 0.2 2 N 0.5233 0.5213 0.5 M hydroxide until a fresh drop of the indicator assumes a deep blue color when it enters the solution. This shows that the pH The sodium fluoride used in the following experiments was is greater than 4.6. To make sure that the solution is not prepared from a C. P. salt which was free from sulfates, sufficiently alkaline to precipitate lead hydroxide, add a drop chlorides, and carbonates, but contained a small amount of of a 0.4 per cent solution of bromocresol purple, which should calcium fluoride. This was removed by filtration and the turn yellow, showing that the pH is less than 5.4. solution was evaporated to dryness in a platinum dish. The During the neutralization some lead chlorofluoride may product was powdered and kept in a platinum crucible within separate. To precipitate it completely, add 300 cc. of 8 a desiccator. saturated solution (0.08 N ) of lead chloride and allow to stand Determinations of fluorine were made in solutions of this overnight. Filter through a weighed Gooch crucible, wash 1 Received July 11, 1924. by decantation with a half-saturated (0.04 N ) solution of lead 2 Published by permission of the Director, U. S . Bureau of Standards. chloride, and finally with about 20 cc. of cold water. Dry * Blum, TYUWS. Am. Elecfrochem. SOL.,39, 459 (1921). a t 150" C. for 2 hours, cool, and weigh. 4 Berzelius, Schw. J . , 16, 426 (1816). The factor for computing from PbFCl to XaF is 0.161. 6 Rose, A n n . , 72, 343 (1849). Stark and Thorin, Z. anel. Chem., 51, 14 (1912). The weight of PbFCl froma 10-cc. sample-i. e., 100 cc. of the 7 Guijot, Compl. rend., 71, 274 (1870), Greeff, B E Y .46, , 2511 (1913). 250 cc. of solution prepared from a 25-cc. sample-multiplied AT
6
8
Z. unorg. Chem., 70, 173 (1911).
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J . A m . Chem. Soc.. 37, 2509 (1915).
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Clark, "The Determination of Hydrogen Ions," 2nd ed., 19!22, p. 80.
September, 1924
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
by the factor 0.382 gives the fluoride normality in the original sample. In those cases in which the volume of the lead sulfate precipitate in the 250-cc. flask is appreciable, an appropriate correction should be made. This may be roughly calculated, as the volume of the lead sulfate (specific gravity 6.2) is about 0.024 cc. for each cubic centimeter of normal sulfate solution originally present. In Expts. 7 and 8 (Table I), with
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25 cc. of a 2 N nickel sulfate solution, this is equivalent to 2 x 25 X 0.024 = 1.2 cc. of PbS04-i. e., 0.5 per cent of the 250 cc. The results given for these experiments include deductions of 0.5 per cent (0.0025 gram) based on this correction.
ACKNOWLEDGMENT Acknowledgment is due to William Blum, under whose direction this work was conducted.
Variation of Stress-Strain Properties of NitrocelluloseCamphor Mix with Its Composition'" By Paul Heymans and George Calingaert MASSACHUSETTS INSTITUTE OP TECHNOLOGY, CAMBRIDGE. MASS.
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T I S of interest for photoelastic work to be able to obtain celluloids of any specified elastic proper tie^.^ It is well known that the physical properties of celluloid vary with its composition. Nishida4 has studied the comparative elastic properties of celluloids made with cellulose of different origins. As the various materials which he examined did not have as sole variable the origin of the cellulose, his results do not allow a reliable interpretation. Nishida states, as a general qualitative condition, that the physical properties of celluloid are much affected by the several operations during the manufacturing processes, and especially depend upon the nature and properties of the loading materials.
only by varying its composition when manufactured. Different samples of celluloid were prepared, care being taken to use raw materials of the same origin and to put them through the same manufacturing processes, varying the content in camphor and adding ester gum in one case. The stress-strain curves were determined on specimens of rectangular cross section measuring 1 inch by 0.25 inch, and 4 inches in gage length. The results, together with the relative content of camphor and ester gum, are summarized in Table I and Figs. 1 and 2. The elastic limit was taken a t the point where the stressstrain curve departs from a straight line. A more accurate definition of the elastic limit, such as a given increment of the elongation per unit of charge, could not be made on account of the plasticity of the materials. Single variations of the elongation differed appreciably, while the mean slope of the stressstrain curve was still constant. TABLE I
SamDle A B C
D E
TESTSON CELLULOIDS OF VARYIXG COMPOSITION From preliminary tests it appeared that homogeneous celluloid of different chemical compositions could be obtained 1 Presented before the Division of Cellulose Chemistry at the 67th Meeting of the American Chemical Society, Washington, D . C., April 21 to 26, 1924. * T h i s work was undertaken b y the Photoelastic Laboratory of the Massachusetts Institute of Technology at the request of the Research Laboratory of the General Electric Company. a Heymans, Am. Mech. Eng., 44, 513 (1922). 4 THISJOURNAL., 8, 1099 (1916).
Camphor Per cent 9.5 8.8 17.8 24.2 38.6
Ester gum Per cent 0 7.2 0 0 0
Young's modulus of elasticity Elastic limit Lbs./sa. in. Lbs./su. in. 350,000 2450 337,000 2025 387,000 2425 308,000 1875 254,000 1825
Although the elastic limits should, therefore, not be considered too accurate, the moduli of elasticity are more reliable, since for a given stress-strain curve a slight displacement of the elastic limit will affect the value of the modulus much less. Comparing Samples A and B, in which the ratio of camphor to nitrocellulose is the same, the only difference being the addition of ester t gum, it is seen that ester gum lowers the elastic limit and the $ modulus of elasticity. & Samples A , C, D, and 8 E constitute a series in which the percentage of &#cm f " P ? camphor varies from 9.5 to 38.6. Fig. 2 shows the effect of the camphor content on the elastic limit and the modulus of elasticity. It is seen that the modulus of elasticity does not vary constantly with the.percentage of camphor. A maximum is reached a t
