acid until free from soluble silver salts. The filtrate and wash water were then combined and titrated with a standardized solution of ammonium sulphocyanate (using ammonium-ferric alum as indicator) and the amount of hydrogen cyanide present in the original gak mixture calculated from the volume of ammonium sulphocyanate used. The contents of the third and fourth absorption tubes was transferred into a beaker and a known volume of a standardized solution of silver nitrate added. The silver nitrate must be in excess of the amount required to precipitate all of the potassiuni cyanide in the solution as silver cyanide. The solution and the suspended precipitate were then thoroughly stirred, and dilute nitric acid added until the precipitated silver oxide redissolved and the solution became slightly acid The precipitate of silver cyanide was now filtered off; precipitate and filter paper were washed with very dilute nitric acid until all soluble silver salts were removed, and the filtrate and wash water combined and titrated with a standardized solution of ammonium sulphocyanate using ammonium-ferric alum as indicator. The cyanogen present in the original gas mixture was then calculated, the reactions involved in the calculation being: (CN), 2KOH = KCN KCNO H,O KCN AgNO, = AgCN KNO,. AgNO, K C N S = AgCNS KNO,. The results of some determinations of cyanogen and hydrogen cyanide are given in the following table, the analyses being expressed in terms of the ratio of hydrogen cyanide to cyanogen b y weight because by this means mistakes arising either from error in the determination of the volume of the small containing tubes or from the presence of gases other than cyanogen or hydrogen cyanide in the gas mixture are eliminated.
+ + +
Tube. 1
2
+ + +
Mixture h-0. 1. Weight HCN. Weight (CN)?. 0.0177 0 00586
0.009005 0.00296
+
Ratio. 1.96 : 1 1.98: 1
Mixture N o . 2. 1
2
0.00134 0,00044
0.0116 0,0038
I
: 8.65 I:863
The results of the investigation may be summarized as follows: I . Hydrogen cyanide is rapidly and quantitatively absorbed by a slightly acid solution of silver nitrate with the formation of silver cyanide. 2 . Cyanogen is not absorbed by a slightly acid solution of silver nitrate and any cyanogen that may be dissolved as such in the solution is quantitatively removed when a current of air is passed through the liquid 3. Cyanogen may be detected in the presence of hydrogen cyanide even when the total volume of cyanogen in the gas mixture is as small as 0 . 3 cc. The method is applicable to the detection of small amounts of cyanogen in the presence of hydrogen cyanide and large volumes of air. 4. Hydrogen cyanide and cyanogen may be determined rapidly and accurately in the presence of each other. I wish t o express my indebtedness t o Professor
Dennis for the assistance and encouragement that he has given me in this work. CORNELL UNIVERSITY. ITHACA, N. Y.
RAPID AND ACCURATE METHODS FOR DETERMINING PHENOL. AND E. 0. RHODES. Received July 3, 1912.
H y I-. 17. REDMAN
I n 1871 LandoltI made the first successful attempt to determine phenol quantitatively by precipitation as tribromphenol, and since that time numerous attempts have been made to obtain an accurate and easy method of determining phenol each experimenter working under varying conditions to suit his particular purpose. As a result of these investigations, many methods have been submitted for which claims of more or less accuracy and rapidity have been asserted. The time of the reaction period in most cases is too long for rapid determination. A method has been suggested by Lloyd* in which he substitutes a hypobromite solution for Koppeschaar’ss bromide-bromate solution. In his paper he shows that the tribromphenol is formed almost instantaneously and quantitatively (and that the time of the reaction period is reduced practically to zero). This hypobromite method has been adversely criticized by Olivier,4 who in 1909 and 1 9 1 0 published results which do not agree with Lloyd’s. He did not find as high a percentage of error when a large excess of hypobromite was added to the phenol as did Lloyd, and he doubts the accuracy of Lloyd’s numbers and methods. He shows also that the length of time required for Koppeschaar’s method, using a bromidebromate solution, may be reduced from one-half hour to nine minutes. More recently, Wilkiej has published a method for the rapid determination of phenol, in which he used iodine in cold sodium carbonate solution. The reaction period for this method is 5-10 minutes. I t has the disadvantage of requiring that the iodine solution be restandardized each time a phenol determination is made. A more complete bibliography on phenol determination may be found in Lloyd’s’ paper of 190j or Wilkie’s papers of 1911-1912. Our object in undertaking this research was to shorten if possible the time required for a determination of phenol by the bromide-bromate method and compare the hypobromite method with the bromidebromate method for accuracy, ease of manipulation and time required for a determination. Apparatzts.-The apparatus used consisted of a shaking machine driven by a water motor, several five-liter bottles fitted with glass siphons, D. R. burettes and one-half liter ground stoppered bottles from the common stock in which the phenol determinations were made. Berichle. 4, 770 (1871). J . A m . Chem. Soc.. 27, 16 (1905). 2. Ann. Chem., 15, 233 (18i6). 4 Rec. Trau. Cham., BE, 362 (1909). [I J . S o c . Chem. I d , 30, 399 (1911). 1 2
The shaking machine, is ii long. n x r m v a n d shailo\v liquicl hnimine dissolved in five litcrs oi S / q potassium moorim box r z o c u i . V iutions i,f sodium thiosulphate, potassium hypobromite. a mixture of sodium bromide, and bromatc and phenol, concentrated hydrochloric acid (sp. gr. L Z ) , ii 2 0 per cent. potassium iodide solution ani1 a starch solution used as an indicator. The thiosulphate solution was prepared by [lissolving i zj grams of sodium thiosulphate (S:i,S,0a.5H,0) in five litcrs oi waicr; 40 g r a m s oi
K1 IICI
20 nrr ccet. 1.2 si'. in.
Thc above results indicate that the time o i shaking has very little cffrct upon the perccntages of phenol as determined. I t will be noticed that the values ior onc minute's shaking are as correct as those for one hour. There is no result in the table which varies irom thc correct value by more than 0.6 of I pcr cent. and the average varies by 0 . 2 per cent. This is the degree of accuracy claimcd by Lloyd for the hypobromite method. In Table 11 are given the results obtained when the concentration of phenol wit.h repect to the total
volume was varied but the relative concentrations of phenol and hypobromite were kept constant. I n each case the time of shaking was I minute and the total dilution I O O cc. So.
la lb 2a 26 3a 3b 4a 4b
TABLE11. Time. KI. H20. HCI. CGH50H. KOBr. Min. 61 61 * 83.5 83.5 90.4 90.4 92.7 92.7
5 5 5 5 5 5
5 5
15 15 5 5 3 2 1 1
19.0 1 19.0 1 1 6.5 5.5 , 1 3.9 1 2.6 1 1.3 1 1.3 1 Solutions-See
Time. Min. Xa&03.
5
5 5 5 5 5 5 5 Table I.
3 3 3 3 3 3 3 3
3.97 3.97 1.50 1.50 0.92 0.60 0.32 0.31
Per cent. 100.14 100.14 99.79 99.79 99.14 99.71 98.90 98.81
The results obtained indicate t h a t amounts of phenol as small as o.oooo15 gram per cubic centimeter may be determined within I per cent. by this method and with a reaction period of one minute. Table I11 shows t h a t shaking for. one minute is sufficient by the method used for a n accuracy not greater than four parts per thousand. Each test was run with a total volume of I O O cc. and in each the concentrations of the various solutions were the same. The six determinations were a single series. 'All six are submitted, none rejected, thus giving a fair estimate of the amount of the error to be expected generally in a laboratory determination. TABLEIII.-HYPOBKOMITE. Xo,
1 2 3 4 5
6
Time. Time. Min. Sa2S20s. Per cent. H 2 0 . HC1. CoH50H. KOBr. Min. K I . 5 3.99 100.3 19 1 3 61 5 15 19 1 5 3 3.98 * 100.4 61 5 15 5 3 4.02 99.6 19 1 61 5 15 1 5 3 19 4.00 99.8 61 5 15 1 5 3 19 4.01 99.7 61 5 15 5 3 5.00 99.8 20 1 61 5 15 Solutions-See Table I.
Attention is called t o the fact t h a t in each of these tables, the phenol was first diluted with water before the hypobromite solution was added t o it. This is of interest because of the fact t h a t a number of authors state t h a t in the determination of phenol b y bromine,I a red compound is formed in the white precipitate which is probably tetrabromphenoquinone. Only once or twice in all our determinations did the precipitate show even a light pink shade, never yellow which would indicate tribromphenol bromide, and in all the other cases the precipitate was perfectly white. I n every case where the red compound is mentioned the phenol solution was used with greater concentration than *Y/Ioo; i t was found that diluting the phenol t o approximately A'/IOO reduced the formation of this compound t o zero and possibly increased the accuracy of this method. T h e Pervnanemy of a Hypobromite SaIutioTi .-In estimating phenol, conflicting determinations were obtained b y us when i t was assumed that a fresh hypobromite solution retains a constant quantity of available bromine. Allen2 states that a hypobromite solution made alkaline by dissolving 62.2 grams of pure KaOH (this is 50 per cent. more caustic than is necessary to react with the bromine according t o the zIVaOH = zNaBrO + H,O) and made equation, Br,
+
Beckurts. Arch. P h a r m . , 5 , 24, 561 (1886); from J. SOC. Chem. I n d . , 6, 5, 546 (1886). 2 J. SOC. Chem. I n d . , 3, 65 (1884).
up to 0.16075 -Y loses not more than 0.8 per cent. of its bromine by boiling it for one hour. Lloyd1 assumes from Allen's paper that the available bromine in a solution of hypobromite is fairly constant. This is true if the bottle is kept full of solut'on and corked with a ground stopper. But if the ordinary 5-liter bottle be fitted up with a paraffined bark cork, siphon and inlet for air, the hypobromite solution changes its strength. A fresh solution made up in this laboratory by dissolving 8 grams of bromine per liter in .Vj4 KOH changed its strength in thirty-two days from o 0 8 6 5 -1: t o 0.0781 *Y, a decrease 0.3 per cent. strength per day. A second fresh solution of strength 0.1654 changed in 1 2 days to 0.1584 .Y,t h a t is a change of 0.33 per cent. per day A third solution, which was kept in a ground stoppered brown glass bottle in a dark compartment, changed from 0.1346 to 0.1340 N in fifty-seven days I t is evident that this solution. which was quite yellow and smelled of free bromine. retained its strength when kept well corked in a brown glass bottle. This may account for the conflicting statements made regarding available bromine in a hypobromite solution. Owing to the possibility of bromine evaporating from a strongly alkaline hypobromite solution i t is necessary to test this strength of hypobromite after each determination if these are more than a few hours apart. especially if the solution has a n inlet for air t o allow the siphon t o operate, or if the bottle is badly corked. T h e Acidity of the Phenol Hyp,obrotnite Solution-It is imperative, if hypobromite is used in determining a phenol solution as tribromphenol, to have the solution acid both before and after the hypobromite is added. Otherwise the phenol ring is brokeno up in alkaline hypobromite and passes over into carbon tetrabromide and possibly higher homologues. a\7
'
TABLEIT'.-ALKALINE
No. Ia IIa IC JIc. Id IId le IIe Ig IIg Ii IIi
H20. 64.5 64.5 64.5 64.5 64.5 64.5 64.5 64.5 64.5 64.5 64.5 64.5
PHENOL HYPOBROMITE. Time. CeHjOH. KOBr. Xa&Os. Time. HC1. K I . Min. 2.5 18 1 min. 5 5 3 19.81 2.5 18 1 min. 5 5 3 19.78 2.5 18 5 mins. 5 5 3 19.04 2.5 18 Smins. 5 5 3 19.06 2.5 18 10mins. 5 5 3 18.96 2.5 18 10mins. 5 5 3 18.94 2.5 18 20mins. 5 5 3 18.90 2.5 18 20mins. 5 5 3 18.89 2.5 18 1 hr. 5 5 3 18.79 2.5 18 1 hr. ' 5 5 3 18.76 2.5 18 18.011 18 hrs. 5 5 3 2.5 18 18 hrs. 5 5 3 18.07 Solutions. Phenol . . . . . . .. . . 0.1022 pi KI 20 per cent. HC1 1.2 sp. gr. K O B r . . . . . . . . . . 0.1318 X
Per cent. 167.84 169.01 197.25 196.86 200.39 201.17 202.74 203.13 205.49 208.22 234.51 234.90
18 cc. 0.1318 N K O B r = 23.72 cc. 0.1 N K O B r 2.5 cc. 0.1022 N phenol = 2.55 cc. 0.1 N phenol
I n Table IV the acid was not added until after the hypobromite. Column 5 shows the time during which the solution was alkaline. The table shows the rate at which the bromine is used up in an alkaline phenol solution. The last column gives the per cent. of Br disappearing, calculating as IOO per cent. the amount of Br required t o form tribromphenol, when the solution is acid. J . Am. Chem. Soc., 27, 10 (1905). 2
Olivier, Rec. Trav. Chim.. 29, 294 (1910); Collie. J.
SOC.Chem.
P. 264 (1894); Wallach, Ann. Chem., 276, 147 (1893); 159, 322.
Ind.,
The above table indicates that if the solution be alkaline for only one minute after the hypobromite is added, a n error as great as 67 per cent. may be introduced in the determination, and a longer period gives a greater error. Lloyd uses sufficient acid to keep this solution strongly acid although he does not mention the attendant danger if the solution were alkaline. OlivierI rather inconsistently expresses surprise a t the amount of acid used by Lloyd and a t the same time shows that if the solution become alkaline an error of 1 2 j per cent. may be introduced in a single determination. I t may be noted t h a t no precipitates appeared after adding the acid. THE
B R 0 M ID E - R R O M A T E M ET 1-10 11.
This method is similar in many respects to the hypobromite method. Instead-of using a solution of hypobromite as in the first case, a solution consisting of a mixture of potassium bromide and potassium bromate (Koppeschaar’s solution) was used. This is the standard solution used by the United States Pharmacopoeia and is made a s follows: 3.5 grams of potassium bromate and 5 5 grams of potassium bromide are dissolved in water and then diluted up t o I liter. This solution has considerable advantage over the hypobromite solution in that it contains no free bromine and therefore does not have the objectionable odor of the hypobromite solution. For the same reason, i t is much more stable than this solution2 and does not require to be standardized with each operation. The chief objection t o the use of the bromide-bromate solution, however, has been t h a t i t was too slow. Koppeschaar recommends I j minutes shaking and the U. S. P.30 minutes, before the K I solution is added. As shown b y the following tables i t is not necessary to shake for one-half hour to obtain a n accuracy of three parts per thousand. The order of adding the solutions is shown in each table reading from left to right. TABLEV.-BROMIDE BROMATE.
No. H 2 0 . HC1. CeH:OH. 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61
la
lb 2a 26 3a 36 4a 46 Sa 56 5c 56
6a 6b
7a 76
5 5 5 5
Bromide Time. Time. bromate. Min. K I . Min. Sa2S203. 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19
15 15 15 15 15 15 15 15 15 15 15
1 1 5
5 10 5 10 5 15 5 15 5 20 5 20 5 20 5 20 5 15 30 5 15 30 5 15 60 5 15 60 5 15 Solutions. 0.1022 N Phenol Bromide bromate 0.09493 N Thiosulphate.. . 0.09816 N-
........ . .
.
5 5 5 5
5 5
5 5 5 5 5 5 5 5 .5
5
3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
2.80 2.75 2.80 2.77 2.80 2.79 2.78 2.77 2.73 2.85 2.75 2.82 2.70 2.74 2.70 2.71
Per cent. 99.72 100.04 99.72 99.92 99.72 99.79 99.85 99.92 100.11 99.72 100.04 99.60 100.30 100.11 100.30 100.30
KI 2 0 p e r cent. HC1 1.2 sp. gr.
Table V was prepared t o determine the effect of time of shaking upon the results obtained when the 1 2
Olivier. Rec. Trav. Chin.,29, 294 (1910). See P a r t V, SUMMARY, page 6 5 9 ; also page 657.
total dilution, volume of phenol and volume of bromide bromate are kept constant and the solution acid. I n Table V the constant volumes of water, phenol, acid and bromide-bromate solution were used, but the time of shaking varied. I t will be noticed t h a t for no test was there a greater error than 0.6 per cent. and that with one exception all the results are within 0.3 per cent. The results obtained for one minute’s shakinq are as accurate as those for ~j minutes, 30 minutes and I hour. I n order to confirm the one-minute determinations, a series of’five tests were run exactly similar to those in Table V. The five results, are submitted, none rejected, thereby giving a n idea of the magnitude of the errors t o be expected in a n ordinary laboratory determination by this method. The results given below in Table VI show an average error of 0.3 per cent., the greatest error being 0.4 per cent. for a reaction period of only I minute. TABLEVI.-BROMIDE BROMATE. Bromide Time. Time. No. H?O. HCI. CcHjOH. bromate. Min. K I . Min. Na&O:+ 5 20 1 1 61 5 15 3 5.81 5 18 1 2 61 5 15 3 3.88 5 18 1 3 3.90 3 61 5 15 5 18 1 4 61 5 15 3 3.92 5 18 1 3 3.90 5 61 5 15 Solutions. Phenol . . . 0.08815 W K I 20 per cent. Bromide bromate 0 , 0 9 4 9 3 X HCl 1 . 2 sp. gr. Thiosulphate. . . . 0,09816 h-
Per cent. 100.4 100.4 100.2 100.3 100.2
Table VI1 like Table I1 varies the concentration of phenol with respect to the total volume, but keeps the relative quantity of bromide bromate with respect t o the phenol constant. I n this table the time of shaking was taken as one-half hour. This length of time was chosen according t o the U. S. P.. as Table VI1 was completed before Tables IV and V. TABLEVII.-BROMIDE
BROXATE.
Bromide Time. Time. S o . H20.HC1. CcH30H. bromate. Min. K I . Min. Na&Oa. la
Ib 2a 26 3a 36 4a 46
5a 5b
61. 61. 72. 72. 83.5 83.5 90.4 90.4 92.7 92.7
5 5 5
5 5
5
15 15 10 10 5 5
5
2
5
2
5 5
1 1
19. 30 5 30 5 19. 30 5 13. 5 13. 30 30 5 6 5 30 5 6.5 30 5 2.6 30 5 2.6 30 5 1.3 5 30 1.3 Solutions-See Table V.
3 3 3 3 3 3 3 3 3 3
2.70 2.74 2.12 2.15 1.02 1.08 0.39 0.43 0.19 0.21
Per cent. 100.36 100.11 100.39 100.10 101.15 100.00 102.02 100.05 102.50 100.58
The results for I and z cc. of phenol are seen to be less concordant than those for larger amounts. However, as one drop is a n error of 5 per cent. in I cc., and as the phenol solution was measured out from a burette and not weighed, the agreement is fairly good. The table shows t h a t O . O O O O I ~ gram of phenol per cubic centimeter may be determined by this method with a maximum error of z per cent. The method is probably much more sensitive than this if more dilute solutions are used. From these tables we have come to the following conclusions for work requiring an accuracy not closer than 0.3 per cent. First, it is not necessary t o shake the acidified phenol solution with Koppeschaar’s solution (bromide bromate) or with Lloyd’s hypobromite solution for a longer time than one minute
if a continuous shaker is used. Seco?zd, if the conditions of dilution, etc., are those given in the preceding tables no red or yellow compounds are observed in the white tribromphenol precipitate. I n addition to the above experiments, tests were run by the two methods to determine the error which might be introduced in the determinations due t o chemicals, evaporation of bromine due t o the use of ordinary one-half liter bottles, methods of working, etc. Thus, an error might be introduced b y running the hypob. omite solution into the phenol without shaking if the region where the hypobromite was most concentrated became alkaline. Several tests were made to determine this, but no appreciable effect was noticed. A series of six determinations to find the effect of titrating back with the thiosulphate after periods of 1 , 2 and 3 minutes (continuous shaking) from the time when the IC1 was added, gave results which showed a maximum error of o 5 per cent. within themselves. Accordingly a n error of not more than 0.5 per cent. is introduced if the solution is shaken only I minute after adding the potassium iodide. Blank experiments were run under the same conditions as the original determinations which showed that the maximum error introduced by the solutions, manipulation, bottles, etc., was 0.3 per cent. Direclioizs.-( I ) ,\'/IO sodium thiosulphate and a -V/IOof either hypobromite or bromide bromate. 20 per cent. K I and I / : ~ per cent. starch solutions. ( 2 ) Into a joo cc. bottle, fitted with a ground glass stopper, put 60 cc. water, 5 cc. hydfochloric acid (sp. gr. 1.2) and then add 15 cc. of the unknown phenol solution which is t o be determined and which has previously been diluted t o about -Y;Io. If the solution is weaker than L Y / ~ ono previous dilution is required. Add quickly enough X / I O hypobromite or bromidebromate solution to make the solution yellow and then add in addition ' I O per cent. of the amount already added. Place the stopper in the bottle and shake continuously for one minute. Add t o the solution in the bottle 5 cc. potassium iodide solution ( I O per cent.) and again shake for three minutes. Wash down the stopper and sides of the bottle and titrate the solution with the -V/IO thiosulphate, using starch solution as an indicator. The starch must not be added until enough thiosulphate has been run in t o make the solution almost colorless. The quantity of thiosulphate used represents the quantity of free iodine, and therefore the quantity of excess bromine. The difference between this quantity and the known quantity of bromine added gives the amount of solution present. Each cubic centimeter of .V/IO bromine used up is equivalent t o 0 . 0 0 1 5 6 gram of phenol. SUMMARI'.
I . The results show that by the above methods of manipulation, either with the hypobromite . o r with the bromide-bromate solution. phenol determinations can be made within an error of 0 . 3 per cent. with only one minute of continuous shaking after the solution containing the bromine is added, i. e . , the reaction
period may be reduced from 30 minutes to I minute without sacrificing accuracy. 11. The phenol in each case was diluted until it was approximately .Y/IOO before the determination was made. The resulting precipitate with the hypobromite or bromide-bromate solution was white and flocculent in each case and the precipitate showed no traces of red tetrabromphenoquinone or yellow tribromphenol bromide. 111. I n order to secure correct results, the phenol solution must be acid after the bromine is added. If i t is alkaline, a n error is introduced which increases as the concentration of the phenol in the solution diminishes and the reaction period increases. IV. The error introduced by shaking the solution for only one minute after the IC1 solution is added before titrating back with thiosulphate is 0.j per cent. Three minutes shaking eliminates this error and longer shaking has no effect. Y. The bromide-bromate solution has the advantage over the hypobromite of being permanent. When the solution used was first made, its strength was 0.0949,3 After three months duplicate tests gave o 09495 The hypobromite solution weakened one-third per cent. every twenty-four hours for the first few days Lfter the solution was made. The bromide-bromate solution has not the unpleasant odor or free bromine. A\7.
DEPARTMENT OF INDUSTRIAL
RESEARCH,
vUIVERS1TY O F KAPI'SAS.
LAWRENCE
THE COLORIMETRIC DETERMINATION OF IRON IN LEAD AND ITS OXIDES. B y J O H N -4.SCHAEFFER
Received June 20, 1912.
The determination of the small percentage of iron always found in lead and its oxides must frequently be made by chemists working in industries where any appreciable amount of iron in raw materials has a deleterious effect on the finished product. This is especially true in the use of red lead and litharge in the manufacture of high-grade cut glass, and lead and its oxides in the manufacture of lead accumulators, where the determinations are constantly made The gravimetric determination of this constituent necessitates a lengthy and a more or less inaccurate analysis, owing t o the many operations entailed. A volumetric determination is also in many cases not sufficiently accurate and rapid for estimating the very small percentages which are often present. The following colorimetric method was developed to fill this need and i t has been found that no other method compares with i t in rapidity, ease of manipulation, or in accuracy for the estimation of the small percentages of the above constituent present in lead and its oxides. The method is a modification of Thomson'sI method, so adapted as to be readily applied t o the above mentioned analysis. I t is carried out in the following manner: I n the analysis of litharge or metallic lead, treat one gram of the sample in a beaker with 1 5 cc. of water 1
J . Chem. SOC.,1886, 493.
,
