T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Apr., 1916
t h e sample has been completely b u r n e d . Beyond this t u b e is placed a U t u b e containing zinc d u s t t o absorb all possible acid gases o t h e r t h a n carbon dioxide. T h e potassium hydroxide absorption b u l b is next a n d last i n t h e t r a i n . T h e r u b b e r s u b s t a n c e is burned in a s t r e a m of oxygen, a n d t h e potash b u l b is always weighed when full of oxygen. CIDHItj + IOCOZ This method on p u r e , fine p a r a g u m gave 96.19 a n d 96. j 7 per cent ( a v . 96.38). T h e value of 0.96 was t h e n used as t h e figure b y which t h e weight of ClaH16 should be divided i n order t o o b t a i n t h e weight of t h e r u b b e r f r o m which it c a m e . This factor was used o n t h e compounds m a d e with other varieties of gums w i t h o u t determinations o n those g u m s , a s t h e factor would be valueless unless it applied t o all high-grade r u b b e r gums. SAMPLE CALCELATION Loss due t o acetone extraction - 5.45 per cent Weight extracted with HC1 - 0.9850 g. Weight after HCI extraction - 0.6483 g . Weight burned - 0.2824 g. Weight of COS absorbed - 0.4232 g.
136x0 4232 = W t 440
of CioHin burned
-__ l : ~ O x x = OW ~ t .~of~rubber burned 136 0'4232 0'6483 = R = W t . of rubber t h a t would have been 440 X 0.96 X 0.2824 burned if all t h a t extracted with HC1 was burned
&'ow
-_ l,oOOo0.985OP - 0,0545 = W t . of unextracted sample which contained R
grams
of rubber 136 X 0.4232 X 0.6483 X 0.9455 .. . ___ 440 X 0.96 X 0.2824 X 0.9850
= 30,01 per cent
ANBLYTICAL RESGLTS
30 Per cent Fine Para Stock 30.31 30.12
....
--
Av.. 30.22
30 Per cent Cameta Stock 30.01 30.38 29,60
31 Per cent Ceylon Stock (Red Oxide) 30.50 30.87 ..., --
_-
30 00
30.69
30 49
__
31 Per cent Ceylon Stock (Black) ~, 30.18 30.80
....
COIiCLUSIOh-S
This method is f o u n d applicable t o high-grade compounds which do n o t contain l a m p b l a c k , s h o d d y , or r u b b e r s u b s t i t u t e s . If t h e compound should cont a i n lampblack, it is shown b y t h e d a r k color of t h e g u m when t r e a t e d with dilute hydrochloric acid. Otherwise, t h e g u m is grayish white. T h e presence of shoddies a n d rubber s u b s t i t u t e s m a y be detected, respectively, b y t h e d a r k color of t h e acetone e x t r a c t or a high alcoholic potassium hydroxide ( K O H ) e x t r a c t . Should t h e described method be used alone for specification work, t h e percentage of r u b b e r could be made t o a p p e a r falsely high b y a d d i n g ground leather, s t a r c h , egg albumen, or some o t h e r organic compounds which a r e insoluble in acetone, w a t e r , a n d dilute hydrochloric acid. B u t t h e addition of such substances would decrease t h e q u a l i t y of t h e comp o u n d a n d p r o b a b l y their presence could be detected b y qualitative chemical means or physical testing. Therefore, even t h o u g h this method is at present restricted t o positively high-grade stocks, it is felt t h a t its use m a y be made more general after f u r t h e r experimentation. RHODEISLAND STATECOLLEGE
KINGSTON
327
THE REDUCTION OF AsV TO Asiii BY CUPROUS CHLORIDE AND THE DETERMlNATION OF ARSENIC BY DISTILLATION AS ARSENIC TRICHLORIDE By R . C. ROARK AND C. C. MCDONNELL Received October 15, 1915
F o r t h e determination of arsenic i n arsenical insecticides, t h e Association of Official Agricultural Chemists has a d o p t e d methods for Paris green, London purple, a n d l e a d arsenate on1y.l I n recent years t h e r e have been placed on t h e m a r k e t other arsenical insecticides, such a s t h e arsenates a n d arsenites of calcium a n d zinc, a n d combinations of fungicides a n d insecticides which contain arsenic, such as Bordeauxlead arqenate, Bordeaux-Paris green, Bordeaux-zinc arsenite, etc. I n attem,pting t o find a m e t h o d for t h e quick a n d accurate determination of arsenic in these products, recourse was h a d t o t h e well-known distillation m e t h o d , * using ferrous sulfate a s a reducing agent. T h i s m e t h o d was carried o u t a s fo!lows: An a m o u n t of t h e sample containing n o t over 0.j g. arsenic calculated as AslOe a n d I O g. of ferrous sulfate was transferred t o a 500, cc. distilling flask, I O O cc. concentrated hydrochloric acid (sp. gr. 1.19) added, t h e solution heated t o boiling a n d t h e vapors distilled t h r o u g h a wellcooled condenser i n t o t h e arrangement of flasks shown i n Fig. I. When t h e volume in t h e distilling flask was reduced t o a b o u t 4 0 cc., a n additional jo cc. of concentrated hydrochloric acid was a d d e d b y means of a dropping funnel. This process was continued until 2 0 0 cc. of acid h a d distilled over. T h e distillate was t h e n m a d e u p t o I liter i n a g r a d u a t e d flask, a n aliquot of zoo cc. t a k e n , nearly neutralized with a concentrated solution of sodium hydroxide, sodium bicarbonate a d d e d in excess, a n d t h e arsenic trioxide t i t r a t e d with a n approximately N ; 2 0 iodine solution, using s t a r c h paste as a n indicator. On analyzing a commercial d r y lead arsenate in this way, only 26.3 per cent AszO:, was f o u n d ) whereas b y t h e Official method2 31.9 per cent was obtained. This low result was somewhat surprising i n view of t h e f a c t t h a t distillation of samples of Bordeaux-lead arsenate with ferrous sulfate a n d hydrochloric acid h a d yielded t h e s a m e a m o u n t of arsenic as other methods. I n order t o see if t h e copper salts present in t h e samples containing Bordeaux h a d a n y effect on t h e results, a n o t h e r distillation of t h i s lead arsenate was made, with t h e addition of j g. crystallized copper sulfate t o t h e I O g. ferrous sulfate. Distilling as before, 31.8 per cent A s 2 0 j was found. Cuprous chloride, as suggested b y Olsen,3 was t h e n tried as t h e reducing a g e n t , when, using t h e same procedure as before, 32.0 per cent A s 2 0 5was obtained. I n order t o t e s t this method f u r t h e r , a s a m p l e ' o f pure lead hydrogen arsenate4 (PbHAsOd) was analyzed Bur. of Chem., Bull. 107, Rev. (19081, 25-6. 28-9, 239; Bull. 132 (1910), 43-4; Jouv. A . 0. A . C., 1 (1915), 444-6. Bur. of Chem., Bull. 107, Rev. (1908), 239. 3 "Quantitative Chemical Analysis," 1910, p. 139. Prepared b y McDonnell and Smith, for use in another investigation, by precipitating potassium dihydrogen arsenate, KHnAsOa, with lead nitrate and recrystallizing from nitric acid.
328
T H E JOCRATAL O F Z i V D U S T R I A L A N D E N G I A - E E R I S G C H E J $ I S T R Y
Tal. 8,KO.4
by t h e distillation method, using cuprous chloride as t h e reducing agent, a n d 33.12 per cent Asz05 was obt a i n e d , which is exactly t h e theoretical for PbHAs04. B y t h e present Official method, 33.11 per cent was found.
or copper electrolytes; Heiduschka and Reuss' in the analysis of Paris green; and Brandt2 in the analysis of iron. It should be noted that in all these cases one or more of the following conditions obtained: ( I ) metallic copper or a salt of copper was present; ( 2 ) fhe arsenic was present only in very small HISTORICAL amount; (3) the arsenic was present largely (if not wholly) On looking up t h e literature on t h e distillation as metallic arsenic or as an arsenite and not as an arsenate. m e t h o d f o r arsenic it was found t h a t a n u m b e r of If the arsenic is present as an arsenite, no reducing agent is modifications h a v e been recommended. needed to effect its volatilization as arsenic trichloride, and, Fyfe,' Penny and Wallace,2 Schneider3 and van Kerckhoff4 as we have shown, where large quantities of arsenic are present determined arsenic by distillation as the trichloride, generating as arsenate, the presence of a copper salt greatly facilitates the the hydrochloric acid in the distilling flask by the action of reduction by means of a ferrous salt. Kern and Wen,3 using ferrous sulfate in the distillation of sulfuric acid upon sodium chloride, but in all cases the arsenic arsenic, obtained results which varied and were always low. was present as As"' and not as As". This method of distillation was also employed by Rieckher5 They also state that the distillation was difficult to control on account of the violent bumping which occurred as the soluto separate arsenious from arsenic acid in rosanilin. Arsenic in copper was detected by the distillation method tion became concentrated. Stead,4in determining arsenic in iron ores, steel and pig iron, as early as 1863 by Odling.6 The copper was dissolved in hydrochloric acid in the presence of ferric chloride, the mixture used ferrous chloride in the distillation with hydrochloric acid, distilled and the arsenic detected in the distillate with hydrogen and considered it superior to any other method. On the other sulfide or by boiling with a piece of copper foil. This method hand, Bishop,j in determining small quantities of arsenic in has been used to determine arsenic quantitatively in copper sulfuric acid, obtained unsatisfactory results by this method, and, owing to excessive bumping due t o the precipitation of by Thomas Gibb,' Clark,8 Platteqg and Ulke.lo Emil Fischer" was the first to propose the use of areducing ferrous sulfate, its use was abandoned. Hydrogen sulfide was proposed as a reducing agent by Piloty agent so as to make the distillation method applicable to the determination of arsenic when present as an arsenate. He and Stock,6 being passed through the solution, together with used ferrous chloride in the form of a saturated aqueous solu- hydrochloric acid gas, during the distillation. tion. His procedure was as follows: The solution containing Friedheirn and Michaelis' used methyl alcohol as a reducing arsenic was put in a distilling flask of about 600 cc. capacity; agent, and Cantoni and Chautems8 claimed to be able to remove I O to 20 cc. of a cold saturated solution of ferrous chloride, all the arsenic from a hydrochloric acid solution of arsenic and sufficient 20 per cent hydrochloric acid to bring the volume trioxide containing methyl alcohol by passing a stream of air to I j o cc. were added. The contents were then distilled through through a t ordinary temperature. C ~ l l i n s ,however, ~ found a well-cooled condenser into a large Erlenmeyer flask until the latter method to be of no value, and showed that if arsenic the residue in the distilling flask amounted to 30-3 j cc. Accord- was present as arsenate the method of Friedheim and Nichaelis ing to Fischer, as much as 1.0g. arsenic could be volatilized did not work. He used ferrous chloride as a reducing agent, by distilling four times. added the methyl alcohol in successive portions, and passed a Hufschmidt,'* on using Fischer's method, found traces of stream of hydrochloric acid gas during the distillations. Collins arsenic with hydrogen sulfide even in the tenth distillate. He substituted ethyl alcohol for methyl alcohol, but found it to modified the method by substituting 40 per cent for 20 per be only about one-half as efficient as the latter. At about cent hydrochloric acid, and used a Woulfe flask containing either the same time, Moser and Perjatel'O also showed that arsenic water or a solution of potassium hydroxide (sp. gr. 1.1 to 1.2) pentoxide is not reduced by methyl alcohol in hydrochloric to catch the distillate. The contents in the distilling flask were acid solution. Using ferrous sulfate together with methyl first saturated with hydrochloric acid gas, and the distillation alcohol for this purpose they obtained good results. Hilpert was carried out in a stream of the gas, which was generated and Dieckmannll likewise failed to obtain good results with the by the action of sulfuric acid on sodium chloride in a separate flask. Friedheim-Michaelis method. Classen and Ludwig13 substituted ferrous sulfate, or ferrous Stannous chloride as a reducing agent was suggested by ammonium sulfate, for the ferrous chloride, using about 2 5 Guedras," but Kern and %e'n1, found this to be objectionable g. to not over 0 .j g. arsenic calculated as AszO,. They likewise in that i t reduced the arsenic to the metallic state, in which condition it did not redissolve in the solution, and also some carried out the distillation in a strong stream of hydrochloric stannic chloride would pass over into the distillate. acid gas. The following writers record good results in distilling arsenic Distillation with hypophosphorous acid was originated in with the use of ferrous sulfate as a reducing agent: Ulke,14 1901 by A. E. Knorr, according to Butler,14 and has been used Heath,I5 Koch,16 Kann," and Bertiaux,18 in the analysis of copper successfully by Walter C. Smith,lj Heath, and Kern and Wen,1S 1 Philosophical M a g a z i n e , [ 4 ] 2 (18511, 487. who point out, however, that too much must not be used, otherz l b i d . , [4] 4 (1852), 361-5. wise i t will reduce arsenic t o the metallic state. In order to get. :Poggendorff's Annalen der Physik und Chemie, 86 (1852). 433-5. 4 Journal fuer praktische Chemie, 56 (18523, 395-400. 5 ZeiLschrift f u e v analytische Chemie, 9 (1870). 516-8. 6 Chem. N e w s . 8 (18631, 27-8, 7 Ibid., 45 (1882), 218. 8 J . Soc. Chem. I n d . , 6 (188i), 352-5. 0 Ibid., 13 (1894), 324-6. 10 Eng. and Min. Jour., 68 (1899). 727-9. 11 B e y . , 13 (1880). 1778-80;and Liebig's Annalen deu Chemie. 208 (1881), 182-95. 1: B e y . , 17 (18841, 2245-8. 18 Ibid., 18 (1885), 1112. 14 15
18 17
18
LOG.cit. J A m . Chem. SOC.,29 (19Oi),614. Z . fuer anal. Chem., 46 (1907), 35. Chem. Eng., 8 (1908), 159. .Innales de Chimie Analyligue, 18 (1913), 4 i 2 ; and 19 (19141, 49.
Zeitschrifl fner analytische Chemie, 60 (1911), 269. Chem-Zeit., 33 (1909:. 1114-5. 3 Met. and Chem. Eng., 9 (1911), 365-7. 4 Jour. of lhe Iyon and Steel Institute, No. 1, 47 (1895), 110-5. 6 J . A m . Chem. SOC.,28 (1906), 178-85. 6 Bey., 30 (189i),1649-55. 7 I b i d . , 28 (1895), 1414-22. 8 Annales d e Chimie Analyligue, 10 (1905). 213-4. Q Analyst, 37 (1912), 229-38. 10 Monats. fuer Chemie, 33 (1912). 797--820. 1
2
11 12
Bey., 46 (1913), 152-5, Res. g8n. Chim., 11 (1908), 251-2.
15
L a c . cit. Chem. Eng., 6 (1906), 66-7. Eng. and J l i n . J o u r . , 83 (1909). !06?-1.
16
THISJ O U R N A L , 3 (1911), 78-82.
13
'1
Apr., 1916
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
rid of the excess, these authors fume with sulfuric acid for onehalf hour before distilling with hydrochloric acid. Sodium thiosulfate, with and without ferrous sulfate, was tried by Kern and Wen and found to be without value. A stream of sulfur dioxide together with hydrochloric acid gas was successfully employed by Bishop in distilling arsenic from sulfuric acid. Hydriodic acid was proposed by Gooch and Danner’ as a reducing agent in the distillation of arsenic, but later Gooch and PhelpsZ found hydrobromic acid to be much better. RohmerS used hydrobromic acid in combination with sulfur dioxide, passing the latter, together with hydrochloric acid gas, through the solution during the distillation, Schurmann and Bottcher4 used Rohmer’s method in analyzing pyrites. Jannasch and SeideP use hydrobromic acid together with a salt of hydrazine to effect the reduction, and the arsenic in the distillate is titrated with potassium bromate according to the method of Gyory.6 This method has also been used by Billeter, and Kleine.8 The earliest recorded suggestion of the use of cuprous chloride as a reducing agent is that of Dittmar,9as cited by Clark.Io Clark also recommended the use of cuprous chloride, which he obtained by dissolving metallic copper in a strong hydrochloric acid solution of cupric chloride. He also made use of a mixture of cuprous and ferrous chlorides, obtained by dissolving copper in ferric chloride. Both of these methods were suggested by Odling for getting copper into solution, but not for the purpose of reducing Asv to Asiii. Platten made use of the copper-ferric chloride method, while Thomas Gibb modified the procedure by the addition of calcium chloride. This raised the boiling point and rendered the volatilization of the arsenic trichloride quicker. C. and J. J. Beringer” prepare a “ferric chloride mixture” by dissolving 600 g. of calcium chloride and 300 g. of ferric chloride in 600 cc. of hydrochloric acid and making up to I liter with water. Allan GibbI2used this method for determining arsenic, but substituted a saturated solution of zinc chloride for the calcium chloride when it was desired to determine antimony. The saturated solution of zinc chloride was mixed with an equal volume of hydrochloric acid containing 100 g. copper as cupric chloride per liter, and the mixture either concentrated or diluted in order that it should boil a t 108” C. Unless the sample under examination was metallic copper, there was added to the contents of the distilling flask 0 . 2 5 g. of pure copper which acted as a reducing agent. Skinner and Hawley13 use a distilling mixture somewhat similar to that of Allan Gibb, except that the proportions are: 300 g. cupric chloride in I liter of hydrochloric acid (sp. gr. 1 . 2 0 ) plus an equal volume of a zinc chloride solution which boils a t 180’ C. In determining arsenic in a sample it is first reduced with ammonium bisulfite, precipitated with hydrogen sulfide, and the arsenic distilled from the sulfide. The authors state that in the distillation some uncombined sulfur comes over, but no sulfurous acid or hydrogen sulfide. Ferric chloride was not as satisfactory as cupric chloride as it allowed hydrogen sulfide t o come over. 1
2
A m . Jour. Sci., 42 (1891). 308-12. Zeitschvifl fuer anovganische Chemie, 7 (1894), 123-6.
8
B e y . , 34 (19011, 33-8.
4
Chem.-Zeil., 37 (1913). 49-51. Ber., 43 (19101, 1218-23; J . f u e r 9raktische Chemie. 91 (1915), 133-73. Zeilschvift fuer analytische Chemie, 32 (1893), 415-21. Milleilungen aus dem Gebiete dev Lebensmitleluntevsuchung und Hy-
5 6
7
giene, 5 (1914), 280-7. 8 9 10
I1
Chem.-Zeit.. 39 (19153, 43. “Exercises on Quantitative Analysis,” p. 94. J . Soc. Chem. Ind., 6 (1887). 352-5. “Text-Book of Assaying,” 11th ed., 1908, pp. 384-5. J . SOC.Chem. Ind.. 2 0 (1901), 185. Eng. and Min. Jour., 74 (1902). 148.
329
Heath determines arsenic in copper by distilling with a mixture of zinc and cupric chlorides. This mixture he prepares as follows: “Dissolve 150 g. C. P. zinc in 140 cc. of hydrochloric acid (sp. gr. 1 . 2 ) and 440 cc. of distilled water, and evaporate until the bulk is reduced t o about 370 cc. Mix this solution with the solution of IOO g. of C. P. cupric chloride, dissolved in 330 cc. of concentrated hydrochloric acid.” Hilpert and Dieckmannl used cuprous chloride as a reducing agent in distilling arsenic from a mixture of arsenic and tungstic acids, and later2 they record the use of cuprous bromide, or cuprous chloride in conjunction with potassium bromide, for the same purpose. Schurmann and Bottche? have also used cuprous chloride. E XPE R I M E N TA L
I n order t o t e s t t h e action of different substances in reducing Asv t o Asiii t h e y were added t o a h y d r o chloric acid solution of pure lead hydrogen arsenate (AszOs = 33.12 per cent) a n d t h e solution distilled, using t h e a p p a r a t u s previously described. About 1.j g. of lead arsenate constituted a charge, a n d in each case zoo cc. of acid were distilled over. Some of t h e substances, e. g., t h e salts of manganese, nickel, cobalt a n d a n t i m o n y , were tried t o see if t h e y would a c t as catalyzers. T h e results are shown in Table I. T A B L E I-REDUCING ACTION OF VARIOUS SALTS ON LEAD H Y D R O G E N ARSENATE REDUCING Grams % A Z O , SUBSTANCE Used Found REMARKS 5 12.70) Ferrous chloride .... 10 15.60 Reduction not complete 30.601 25.10 18.50 Ferrous sulfate.. . . 2; 22.60 Reduction not complete 130 23.00
;:1‘
‘
i: 2;
i
Ferrous ammon- 1; nium sulfate.. . . { 20 Stannous chloride. Mercurous chloride Manganous chloride ... . . . . , , . , Cobalt chloride, . , Nickel sulfate.. . . . Antimony trichloride.. , . . , Cuprous chloride.. Ferric chloride. Copper foil.. . . , Cuprous chloride.. Antimony trichloride,,. , , , , , , ,
.
. .. . . . . . ... ..
2 1.70 Reduction not complete
(3:
53.10) 1 .OO Reduces AsV t o metallic arsenic None Reduces As” t o metallic arsenic Some HgClz in the distillate
5
No reduction No reduction No reduction
5
5 5
iione None None
5
5
None 33.12
‘!.5
!’ I4.’O {
5
1
0.44 J
33,10
o reduction small amount of antimony came over { UReduction complete
Metallic arsenic precipitates on the copper foil
