JULY 15, 1937
ANALYTICAL EDITION
16 to 25 years of analytical laboratory experience. I n every instance the results by the volumetric method were completed in the specified time, but those by gravimetric methods were 'lot the day* A great number Of precise gravimetric tests in triplicate were made on coal and no was higher than any Obtained by the proposed method. In tests performed by the present method, there was no instance when a definite end point could not easily be secured within a range of 0.1 to 0.2 cc. No interference was experienced when common ions were present. The strontium ion if present may interfere with obtaining the true end point, as it gives a red-colored precipitate with axyquinone compounds; however, this precipitate is soluble in dilute acetic acid. From the qualitative experimental evidences presented, it appears that the method can be applied not only for the accurate determination of sulfur or sulfate in inorganic technical products, but also in biochemical laboratories (urine analysis, etc.), and in the organic chemical industries-for instance, for the rapid determination of free sulfuric acid and sulfonated components in phenol and naphthalene sulfonation mixtures.
333
-
Acknowledgment As the analytical part of this work was carried out in the Central Testing Laboratory of the City of New York, the author wishes to express appreciation to Stroud Jordan and the entire staff of the laboratory for their cooperation. He is indebted to Stanley Mayer for many encouraging suggestions, and to Martin Lang and Harry Dash for their assistance and performance of a great number of gravimetric checks. At the same time the author feels it his duty to express his sincere thanks to the Ba-Re Company, 185 Madison Ave., New York, N. Y., for the liberal supply of stable solution of oxyquinone compounds, which courtesy enabled him to achieve the foregoing work of research.
Literature Cited
,.;'E(.:
~ ~ ~ ' ~ ~ ~ ; Anal. , ~Ed.,; 5,.403~(1933), ~ \ ~ ~
(3) Strebinger, Zombory, and pollak, (1936).
z,
anal. Chem., 105, 346
RECEIVED February 3, 1937. Part of a paper presented first at the regular meeting of the ohemists of the Central Testing Laboratory of the City of New York, January 9, 1937.
A Simple Gas Thermoregulator R. M. KINGSBURY Bureau of Chemistry and Soils, U. S . Department of Agriculture, Washington, D. C.
T
HERE are occasions in many laboratories when, if for
any reason an electric thermoregulator is not convenient or available, a gas regulator could be used. I n most gas regulators now in use, the flow of gas is controlled by a column of mercury which is adjusted to close a small inlet a t the temperature desired. A common fault of these regulators is that the current of incoming gas causes small globules of mercury
I 1
t o rise and adhere to the sides of the tube, thereby causing a rise in temperature above that which is desired. The accompanying sketch illustrates a gas regulator in which the flow of gas is controlled by a glass valve, 2, which closes or opens the inlet opening as the mercury column rises or falls because of changes of temperature. Thus, any splashing of mercury and consequent change of temperature are prevented. The regulator can be adjusted to the desired temperature by turning the thumbscrew, 7, as in other gas regulators. The principal dimensions are indicated on the sketch. Tubes 1, 4,6, and 9 are of 5-mm. inside diameter, the mercury bulb, 5 , and the valve chamber, 3, are of 15- and 8-mm. inside diameter, respectively, and the valve, 2, is of 4mm. outside diameter. The opening in the inlet tube which acts as a valve seat is prepared before sealing by cutting the tube off square and filing, if necessary, to make it perfectly flat. A small notch about 0.25 mm. deep is made across one edge, and the end is then uniformly polished in a flame. The valve is made by drawing out a thinwalled tube to a diameter of 1 or 2 mm. and sealing it so as to leave a prong about 1 cm. long. The tube is heated carefully and a slight bulb is blown at the point where the tube starts to taper. The opposite end is then drawn out and sealed about 3 em. from the bulb. The valve is then inserted and the inlet tube is sealed in lace. i n y thumbscrew taken from a small ringstand clamp can be used for an adjusting screw. A small nut, selected to fit the screw, is filed down t o about 6 or 7 mm. in diameter and cemented into the enlarged opening in the side arm, 6, with a thick litharge and glycerol cement. In order to permit accurate adjustment for all temperatures, the top of the mercury in the adjusting arm should be about 5 mm. below the level of the mercury in the main column when at room temperature. Other details of construction are evident from the sketch. A regulator of this type has been in use for more than a year, and controls the temperature of a 12-liter water bath within a range of 50" to 100" C., with a variation of about *0.5" C. RECEIVED May 3, 1937
2,4-Dihydroxyacetophenone as a Qualitative Reagent for Ferric Iron S. R. COOPER, Howard University, Washington, D. C.
ride, and aluminum chloride containing ap roximately 100 mg. (3) approximately 21$)solutionsof hydrochloric, nitric, and sulfuric acids.
S
EVERAL methods have been proposed for the qualitative detection of ferric iron, but the ferrocyanide and thiocyanate methods of Wagner (5) are commonly employed in systematic analysis. Necki and Sieber (I) prepared 2,4dihydroxyacetophenone and observed that it gave a red color with a solution of ferric chloride. The purpose of this investigation was to ascertain if this color reaction could be used as the basis for a sensitive qualitative detection of ferric iron.
of metal ion per ml.;
Sensitiveness of Test for Iron One milliliter of the iron solution to be tested was placed on a colorless watch glass, and 2 drops of the reagent were added. The coloration produced was compared with 1 ml. of the same solution to which 2 drops of alcohol had been added. All the solutions of ferric iron were made from the stock solution by proper dilution with distilled water. The results are given in Table I. The limit of detection was 0.002 mg. of iron in 1 ml. of solution, or 2 parts of iron in 1,000,000 parts of solution.
Preparation of Reagents The 2,4-dihydroxyacetophenone was prepared and according t o the method given by Necki and Sieber (If?%:: and five-tenths parts by weight of anhydrous zinc chloride were dissolved in 1.5 parts by weight of glacial acetic acid, through the application of heat, and to the solution one part by weight of resorcinol was added. The mixture was heated on a sand bath until it had started to boil (145' t o 150'C.). Then the flame was removed and the reaction allowed to complete itself while the mixture remained on the sand bath. The temperature was kept below 150' C. in order to prevent the formation of resinous products, Upon diluting the reaction mixture with cold water, the crystalline compound separated. These crystals were washed with a cold dilute solution of hydrochloric acid to remove the zinc chloride. The substance was further purified by mixing it with dilute hydrochloric acid solution and animal charcoal, and boiling for a few minutes. The hot solution was filtered, and upon cooling the compound precipitated. This procedure was repeated several times, giving a final product which consisted of white needles. The melting point of the compound was 142' C. A solution consisting of 10 grams of the compound dissolved in 100 ml. of 95 per cent ethyl alcohol was made. The following solutions were prepared and standardized: (1) a solution of ferric chloride containing approximately 2 mg. of iron per ml. and 5 ml. of 6 M hydrochloric acid per liter; (2) solutions of copper nitrate, mercurous nitrate, mercuric nitrate, chromic nitrate, cobalt nitrate, nickel nitrate, manganese chloTABLEI. SENSITIVENESS OF TESTFOR
IRON WITH HYDROXYACETOPHENONE
Weight of Iron
Observation
MI.
MQ. 0.0040 0.0033 0.0025 0.0022 0.0020 0.0018
Light red color Light red color Light red color Very light re3 color Faint red color No visibIe color
1 1 1
Solutions of salts of silver, lead, mercury, bismuth, copper, cadmium, arsenic, antimony, tin, divalent iron, aluminum, chromium, cobalt, nickel, manganese, zinc, barium, strontium, calcium, sodium, potassium, magnesium, and the ammonium radical were tested with the reagent to observe if any reactions occurred, No reactions were noted except in the following cases: mercurous nitrate gave a light yellow precipitate upon standing, mercuric nitrate gave a white precipitate upon standing, and aluminum and manganese chlorides gave white precipitates. Tests were next made t o ascertain the maximum quantity of the interfering metal salts, which could be present without interfering with the detection of the iron. For these tests 1ml. of a mixture of the ferric iron solution and the interfering substance was placed on a watch glass, and 3 drops of the reagent were added. The colors produced were compared with 1 ml. of the mixture containing 3 drops of alcohol and placed on a similar watch glass. The results are given in Table 11. I n the cases of chromium, cobalt, nickel, and copper, the color of the solutions interferep with the detection of the red color. Similar tests were made to obtain the maximum quantity of the common acids which could be present without affecting the reaction. The results are shown in Table 111.
2,4-DI-
Volume of Solution 1 1 1
Action of Foreign Salts and Acids on Color Test
Discussion By the use of an alcoholic solution of 2,4-dihydroxyacetophenone it is possible to detect 2 parts of ferric iron in 1,000,000 parts of solution if no other metallic salts are present. This compares favorably with the 2.1 parts per 1,000,000for the thiocyanate, and 2.6 parts per 1,000,000 for the ferrocyawhich were nide tests as reported by Nichols and Cooper (I), performed under similar conditions. Copper, cobalt, nickel, manganese, mercuric, mercurous, aluminum, and chromium salts interfere, either because of the color of their solutions, or because they give a precipitate with the reagent. Mercurous, mercuric, aluminum, and manganese salts give a precipitate with the reagent. However, the interference which these metallic salts offer is not great, since the iron can be detected in the presence of 300 times as much copper, 1800 times as much cobalt, 400 times as much nickel, 25,000 times as much manganese, 30,500 times as much mercurous mercury, 11,440 times as much mercuric mercury, 32,500 times as much aluminum, and 225 times as much
TABLE11. SENSITIVENESS OF T E ST IN PRESENCE O F INTERFERING METAL IONS Salt . .
Cu(N0a)r Co(N0a)z Ni(N0s)z MnCIz Hgz NOdz A HBd(NOah I 18 Cr(N0s);
Limit of Detection for Iron Mg./ml. 0.2857 0.0571 0.2000 0.0041 0.0034 0.0097 0.0031 0.5000
Weight of Interfering Metal Present Mg./ml. 86.71 102.34 88.11 101.49 103.65 110.94 100.69 112.53
Ratio of Metal t o Iron 300
1,800 440 25,000 30,500 11,440 32,500 225
TABLE111. LIMITING CONCENTRATIONS OF COMMON ACIDS Acid
Limiting Concentration
Weight of Iron
H C1 HNOa HzSOr
N 0.0606 0.0608 0.0314
1.000
MU * 1.000 1,000
334
