38
Vol. 16, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
CRESOL. Add 2 drops of a freshly prepared 10 per cent aqueous solution of ferric chloride to 5 ml. of the test solution. Phenol and m-cresol produce clear bluish-purple colors, ocresol produces in about 10 minutes a slightly cloudy urine yellow or brown solution, while p-cresol produces a cloudy blue solution. The sensitivity for each compound is about 10 mg. in 5 ml. MODIFIC.4TION O F LIEBERMAKN'S TEST( 5 ) FOR DETECTION OF CRESOL. To 3 ml. of the unknown aqueous solution add slowly and with shaking 1 ml. of the reagent (6 per cent solution of sodium nitrite in concentrated sulfuric acid). A cloudy orange solution develops in about 5 minutes if p-cresol is present. Phenol and m-cresol yield clear, and o-cresol very slightly cloudy brown or yellowish-brown solutions. The sensitivity of this test is about 5 mg. in 3 ml. MODIFICATION OF COTTON'S TEST(1) FOR DETECTION OF' pCRESOL. To 3 ml. of an aqueous solution, add 1 ml. of concentrated ammorliam hydroxide (sp. gr. 0.901) and 4 drops of the freshly prepared reagent (10 ml. of concentrated hydrochloric acid and 0.5 gram of potassium chlorate added to 40 ml. of water). Phenol and 0- and m-cresol produce in 5 to 10 minutes clear light blue colors; p-cresol produces a clear light straw-yellow color. The sensitivity is about 10 mg. in 3 ml. of solution. HYPOCHLORITE TESTFOR DETECTIOK OF O-CRESOL.To 5 ml. of the test solution, add one drop of sodium hypochlorite solution. In the presence of o-cresol the solution will immediately turn a cloudy yellowish-n-hite; in the presence of phenol, and wa- and p cresol, it will remain clear and colorless. The sensitivity k about 4 mg. in 5 ml. of solution. (Excess of hypochlorite must be avoided because it may produce faint cloudiness with p cresol.)
Stability
OF
DISCUSSION
It is reasonable to assume that all reagents discussed in this paper will also react with some compounds other than phenol, or 0-,m-,or p-cresol. Therefore one must make certain that the test solution is comparatively free from compounds related to phenol or cresol. This may require preliminary precipitation, extraction, or distillation procedures. Millon's test, even though it makes specific differentiation between phenol and the three cresols difficult, is of value because of its simplicity, as a preliminary test. This should be followed by the modified tests of Melzer and Guareschi, which will identify the compound. The conclusions drawn from these latter two tests may be checked by the hypochlorite and ferric chloride tests or by the modified procedures of Liebermann and of Cotton. LITERATURE CITED
(1) Cotton, S., BUZZ.soc. chim., 21,8(1874). ( 2 ) Deichmann, Wm., and Schafer, L. J., Am. J. Clin. Path., 12,129 (1942). (3) Deickmann, Wm., and Scott, E. W., IND.ENG. CHEM.,ANAL. ED.,11, 423 (1030). (4) Guaresclii, cited by H. Schiff in Correspondensen, Ber., 5, 1055 (1872). (5) Liebermann,C.,Ber., 7,248,1098 (1874). (6) Meher, H., 2.anal. Chem., 37,345 (1898). (7) Millon, M.E., Compt. rand., 28, 40 (1849). (8) Schiff, H.,Ann., 159,158(1871).
Standard Solutions OF Copper Perchlorate and Potassium Iodate JOSEPH J. KOLB Lankenau Hospital Research Institute, Philadelphia, Penna.
W
HENEVER sodium thiosulfate is used in titration work
of high accuracy frequent restandardisation is necessary. I n order to avoid the troublesome and wasteful necessity of preparing fur each standardization a fresh solution of a primary standard [iodine, potassium iodate (S),copper perchlorate (8)1, a standard in the form of a solution of a primary substance of dependable stability is desirable. The work reported here deals with the possibility of using potassium iodate or copper perchlorate (8) for such a purpose. In considering the stability of such solutions it is necessary to distinguish between changes due to chemical instability, presumably resulting in decrease of active concentration, and changes due t o evaporation from the container, which will cause increases of concentration. In the study of Berman ( I ) , for instance, on the stability of potassium iodate, it is impossible to distinguibh the role of these two factors. However, his data suggest thrct evaporation has been an appreciable factor in his results, and that, in some cases, an apparent stability has resulted from the opposing effects of evaporation and decomposition. In a recent paper (4) on the stability cf sodium thiosulfate solutions no account was taken of the possible effect ol' exgoration. A graphical study of the data on stability shows that in the first 60 days there is approximately a 0.3 per cent increase in normality. After that the values drop. Again two antagonistic tendencies, evaporation and decomposition, tend to produce a false picture of the stability of thiosulfate solutions. The evaporation factor can be eliminated if, a t the beginning of the experiment, samples of the solution to be examined are pipetted into separate flasks, and some of these are titrated a t once, while others are titrated after a suitable lapse of time. The extent of evaporation, on the other hand, can be measured by
suitable weighings of the vessels containing stock solutions. If the solution is chemically stable, it is then possible to calculate the theoretical normality a t any time from the initial normality and the loss of weight that has occurred. A P P A R A T U S AND REAGENTS
A 50-cc. buret and one 10-cc. pipet were carefully calibrated and were used throughout the experiments. Details of the preparation and use of the copper perchlorate and potassium iodate are given in (2) and ( 3 ) ,respectively. EXPERIMENTAL
All titrations were carried out in duplicate. The amount of active substance present in solutions when they were fresh, and after they had stood for various lengths of time, was always determined by titration with thiosulfate (0.025N), newly standardized against two freshly prepared cupric perchlorate solutions (8). ~~
Table
~
1. Stability of O.1N Copper Perchlorate and Potassium Iodate Solutions
Solution Cu(C1OSr
KIOI
5
b
Days 6r~1,d.n: 565 565 289 454 565 565 565 289 454
Normality Initial Final" 0.1007 0.1007 0.0993 0,0993 0.1027 0.1027 0,1027 0.1007 0.1007
0.1002 0.1004 0.0992 0.0993 0.1021 0.1013 0.0983 0.1002 0.1004
Conditions Thymoi, glass atoppers Glass stoppers Cork stoppers, spore6 on corks Glass stoppers Thymolb, glass stoppers Cork stoppers, spores on corks
Final normality calculated on basis of its initial volumo. Only one sample; others are average value found for two samples.
ANALYTICAL EDITION
January 15, 1944 Table Loss of Weight per
% of W r i g h t of solution present 0 0-85
....
0:740 0.679 0,445
1:iis 0,898 0.534
0.1011 0.1026 0.1033
85-290
0:Cj75 0.488 0.506
1:ii2 0.671 0.576
0.1009 0,1019 0.1028
o:ois
0: Oil
0.1007
290-455 0 0-185 0 0-373 373-1159
0 : 033 0.083
...
0 0-8 5 85-453
0
0-368 588-768
0 0-157 157-557 0 0-238 0 0-165 0 0-855
.... ....
....
0:ois 0.075
0.0994 0.1001
o:iii
0.1007 0.1011
....
C , 053 0.095
0.166
0:032 0.021
0 004 0,036
0.1329 0.1030
0:0;1 0.085
0 : 083 0,050
0.1002 0.1003
o:oi1
0:040
0.1028
0:022
O:O36
0.1028
0:i i o
o:ii3
0.1040
:
Copper Perchlorate 0.1005 Glass-stoppered Pyrex about 12 years old 0.1013 0.1025 0.1084 0.1003 Glass-stoppered, flint 0.1009 0,1023 0.1034 0.1007 Rubber stopper, Pyrex 0.1007 0.0993 Glass stopper, Pyrex, sealed with paraffin 0,0994 0.0997 Potassium Iodate 0.1007 0.100:
0.1010
eolulion present
Go.
CC.
250
155
500
165
200
120
250
145
Glass stopper, flint glass; mold after several months
MK)
265
Brown, glass stopper. paraffined
500
195
....
0.1001 0.1000 0,0997 0.1027 0.1027 0.1027 0.1013 0.1028 0.1037
Standard interchangeable glass stopper, Pyrex
250
160
Glass stopper and ground-joint cap (“ether bottle”) Rubber stopper
500
185
250
165
1 liter
85
....
.... ....
Evaporation Snlution
Approximate Volume of Solution
0.1025 0.1026 ‘1.1021
Ill. Effect of Storage under Conditions of Minimum Loss of Weight Day8 per 100 Daya % of weight of
Bottle Capaoity
....
In the experiments summarized in Table I, 10-cc. samples of freshly prepared cupric perchlorate and potassium iodate solutions were pipetted into 125-cc. Erlenmeyer flasks. Some solutions were titrated a t once, while other flasks were closed R-ith either glass stoppers or fresh cork stoppers and protected against dust by paper caps. These flasks were stored in the laboratory in a cabinet that was opened frequently and thus provided no protection against possible contamination from the laboratory atmosphere. The temperature was 22” to 35” C. The last of these solutions were titrated after 19 months. As a possible prevention of mold growth, about 10 mg. of thymol were added to some of the flasks.
Table
Container
Grams
85-290
290-355 0 0-85
Stability of Solutions in Glass-Stoppered Bottles
Normality Calculated Found
100 Days
DSYS
11.
39
Normality Initial Final
Flint, glass stopper, turbid, deposit of inorganic material on walls
titrated as above. The bottles were then reweighed and the above procedure was repeated a t intervals. From the data given, one can readily calculate the initial weight of the solutions. In some cases, portions of the solutions were removed for other purposes. The bottles were weighed before and after such removals and due corrections were applied in the calculations. I n order to keep evaporation a t a minimum the following procedure was tried. A tared 250-cc. glass-stoppered bottle containing about 100 cc. of copper perchlorate solution was weighed. The bottle, placed in a dry beaker, was stored in a desiccator over a portion of the same solution. One year later the bottle was taken from the desiccator, wiped, and carefully weighed as before. Duplicate 10-cc. samples were then titrated. A potassium iodate solution was treated in the same manner. A comparison of the results obtained (Table 111) with those shown in Table I1 shows that by the use of good glass-stoppered or rubberstoppered bottles nearly the same results can be attained as by the desiccator method.
Conditions
CONCLUSIONS
Cu(C103r
368
0.018
Grams 0.019
0.1022
0.1018
KIOI
392
0,0018
0.0018
0.1002
0.0999
Glass atopper. Pyres Glass stopper, flint
Table I shows the results. I t appears that copper perchlorate solutions possess a high degree of stability, while potassium iodate solutions show a pronounced tendency to become weaker. In either case thymol has a harmful effect, presumably because it is oxidized, while in the copper perchlorate solutions, even the presence of black, sporelike spots on the cork stoppers was not associated with any loss of titer. I n the experiments summarized in Table 11, samples of freshly prepared copper perchlorate and potassium iodate solutions were titrated with thiosulfate. The remaining portions of the solutions were transferred to clean, dry, tared, glass-stoppered reagent bottles and weighed with an accuracy of * 5 mg. After standing for varying periods under the conditions described above, the bottlcs were carefully dusted and about half an hour later weighed. A pair of 10-cc. samples were withdrawn and
Solutions in glass-stoppered bottles may lose weight by evaporation. This loss in weight has a tendency Bo give some types of solutions an appearance of stability. Results of expcriments indicate that solutions of copper perchlorate are more stable than those of potassium iodate. For use as permanent standards copper perchlorate solutions should be stored in good glassstoppered or rubber-stoppered bottles (evaporation losses should he determined by weighing, and normalities should be corrected accordingly). Iodate solutions must be stored in glass-stoppered bottles. Thymol should not be used as a preservative for either copper perchlorate or potassium iodate solutions. ACKNOWLEDGMENT
The author wishes to thank G. Toennies of this institute for his encouragement and suggestions. LITERATURE CITED
Berman, S. M., J. Assoc. Oficial Agr. Cham., 20, 590 (1937). (2) Kolb, J. J., IXD. ENG.CHEM., ANAL.ED.,11, 197 (1939). (3) Kolthof?, I. XI., and Sandell, E. B., “Textbook of Quantitative z4nalysis”, p. 593, New York, MliLcrnillan Co., 1936.
(1)
(4) Rue, 8.o., IND.&:SG. CHmf., h
L L .
ED., 14,804 (1942).
