Vol. 3, No. 1
ANALYTICAL EDITION
106
nickel crucible if tantalum or columbium are present and fused with several grams of potassium hydroxide. The melt is dissolved in water and the determination completed as described for tungsten steels. Experimental Proof of Accuracy of Method
A number of experiments were carried out to obtain dependable dnta concerning the accuracy of the method. It is a well-known fact that unless hydrogen peroxide is added to peroxidize the titanium, it, will be carried down with the zirconium phosphate precipitate, and for this reason alone, when extreme accuracy is desired, the final zirconium phosphate precipitate should be tested for titanium. The procedure consisted in saltins a number of samples of plain carbon steels, a sample of Cr-W-V steel, and stainless steel of the 18 chromium-8 nickel variety known to be free of zirconiuni, with varying amounts of pure zirconium chloride. Five-, ten-, and twenty-gram samples, respectively, were used.
The accurately measured aliquot portions of the standard solution of pure zirconium chloride were added to the weighed samples of steel, which were then dissolved and otherwise treated as given in the description or the method. The results obtained are given in the table. EXPBRIMENT
2
Experiments to Test Accuracy of Method KIND
STEEL
Plain Plain c
STEEL
ZIRCoNIUM
TAKEN ADDED
Grams 20
Gram 0.00101 0.00101 0.0025 0 0025
FOUND
Gram 0 00095 0.00102
ERROR Gram -0 00006 $0 00001
20 5 0.0025 5 0,0025 10 0.0006 0 00058 -0'00002 6 18 Cr-8 Ni 6 0.00133 0.00132 -0.00001 (1 Bureau of Standards standard sample 50A of high-speed steel. Two 5-gram portions were taken and the precipitates combined after making the sodium carbonate fu4on t o separate the tungsten.
4"5
$;:Cr-W-Va !
Literature Cited (1) Lundell and Knowles, J . Am. Ckem SOC, 41, 1801 (1919)
-
Rapid Colorimetric Method for Determination of Molybdenum in Plain Carbon and Alloy Steels' ^,
Thos. R. Cunningham and H. L. Hamner UNIONCARBIDE AND CARBON RESEARCH LA~OEATORIES, I N C . , LONGISLAND CITY, N. Y
N ACCURATE colorimetric method for the deter-
A
mination of 'molybdenum in the presence of nickel, chromium, tungsten, and other elements, is given. It is best adapted to steels containing a maximum of 1 per cent molybdenum. However, good results have been obtained when the molybdenum content was as high as 2.5 per cent. One-half gram or one gram of the sample (if the molybdenum is 0.10 pes cent or less) is transferred to a 150-cc. covered beaker and treated with 25 cc. of sulfuric acid (1to 4) at a temperature of approximately 60" C. When all action appears to have ceased, 3 cc. of Perhydrol (30 per cent hydrogen peroxide) are introduced and the liquid is boiled for several minutes. The solution.is then filtered on a 9-cm. paper to remove carbon and the residue washed with water and discarded. The filtrate and washings are collected in a 250-cc. beaker and boiled down to a small volume to decompose completely the excess of Perhydrol. The Perhydrol destroys the hydrocarbons and partially reduces the molybdenum to a lower state; part of the molybdenum is oxidized by the air. I n the case of plain carbon or alloy steels, or steels containing tungsten, the above filtering operation is omitted. One gram of tartaric or citric acid is added (to tungsten steels only) and the solution made slightly alkaline with 10 per cent sodium hydroxide and then acid with an excess of 10 cc. of sulfuric acid (1 to 1). The tartaric or citric acid serves to hold up the tungsten. If only a small amount of tungsten is present this treatment may be omitted. The cold solution is transferred to a 250-cc. separatory funnel provided with a glass stopper, diluted to a volume of 100 cc. with cold water, and treated with 10 cc. of 5 per cent potassium thiocyanate solution. The stoppered flask and contents are shaken vigorously for several minutes, then treated with from 5 to 10 cc. of stannous chloride solution and again shaken vigorously for several minutes. The stannous chloride reduces the iron from the ferric to the ferrous condition and the molybdenum from the sexivalent 1
Received October 16, 1930.
to the quinquevalent or quadrivalent state. The potassium thiocyanate reacts with the reduced molybdenum to form a complex potassium-molybdenum thiocyanate, which imparts an amber to reddish brown color to the solution, depending upon its intensity. The solution is cooled to approximately room temperature, 50 cc. of ether added, and the separatory funnel stoppered and shaken vigorously for 30 seconds and then allowed to stand until the liquid has separated into two distinct layers. The lower or acid layer, which will contain the greater part of any iron, chromium, nickel, or tungsten, is drawn off and discarded, and the upper or ethereal layer, which will contain practically all of the molybdenum, is then drawn off into a 50-cc. Camp comparison tube. The tube is stoppered with a soft cork to prevent evaporation of the ether and its contents are mixed thoroughly by manipulating the tube in the usual manner. After standing for several minutes it is ready for comparison with the standard. Preparation of Standard for Comparison
With a little practice it is not difficult to estimate approximately the percentage of molybdenum in the sample. Twenty-five cubic centimeters of 8 per cent ferric sulfate solution are transferred to a 250-cc. separatory funnel and the standard molybdenum solution added from a buret. The solution is diluted with cold water to approximately 100 cc. and the development of the molybdenum color and extraction are completed as previously described. It is advisable to allow the molybdenum solution to stand in the comparison tube for several minutes before comparing with the standard, as the intensity of the color sometimes changes a t first but remains stable thereafter for 7 days and even longer if kept in the dark when not in use. The percentage of molybdenum in the sample is then determined by comparing the intensity of the color of the ethereal solution of potassium-molybdenum thiocyanate with that of the standard. The darker of the two solutions, the sample and the standard, is diluted carefully with ether
January 15, 1931
TNDUSTRIAL AND ENGINEERING CHEMILJTRY
and mixed thoroughly until they match exactly. The amount of molybdenum per cubic centimeter in the standard is then figured and the calculation of the percentage of molybdenum in the sample is obtained by multiplying the weight of molybdenum in each cubic centimeter by the number of cubic centimeters, dividing by the weight of sample taken, and multiplying by 100. The following example illustrates the calculations involved : I n comparing the standard with the sample, 15 cc. of the standard molybdenum solution (1 cc. = 0.0002 gram Mo) were used and diluted to 44 cc. with ether. Therefore, 15 X 0.0002 = 0.0030 gram Mo 0.0030 or - = 0.000068 gram Mo per cc. 44
The sample was diluted to 36 cc.; hence, 36 X 0.000068 = 0.00245 gram Mo in the 1-gram sample, or 0.245 per cent Mo
Solutions Required
STANDARDMOLYBDENUM SOLUTION-1 CC. = 0.0002 gram molybdenum. This solution is prepared by dissolving 0.430 gram of pure sodium molybdate in one liter of water containing 10 cc. of sulfuric acid (1 to l ) , and mixing thoroughly. One hundred cubic centimeters of this solution are measured carefully by means of an accurately calibrated pipet into a 250-cc. beaker, 12 cc. of sulfuric acid (I to 1) are added, and the solution is put through a Jones zinc reductor into 35 cc. of .ferric phosphate solution and titrated with a standard solution of 0.05 N potassium permanganate (1 cc. = 0.0016 gram Mo). A blank determination is run on the reductor and the solution of ferric phosphate (this usually amounts to about 0.2 cc.) by passing 100 cc. of 6 per cent sulfuric acid and 150 cc. of water (same amount as used in the analysis) through the reductor in exactly the same way as the molybdenum solution, and titrating the liquid with permanganate. The amount of 0.05 N potassium permanganate required to impart a pink tint to the liquid constitutes the blank to be deducted from the buret reading when standardizing the molybdenum solution. FERRIC SULFATESOLUTION (8 per cent)-Eighty grams of pure ferric sulfate are dissolved in one liter of 20 per cent sulfuric acid. The presence of iron is essential in the preparation of the standard since it has been determined by experiment that the ethereal solution of potassium-molybdenum thiocyanate is more comparable and also more stable than when it is omitted. The iron appears to have a catalytic effect.
107
STANNOUS CHLORIDE SoLuTIoN-Three hundred and fifty grams of stannous chloride are added to 200 cc. of hydrochloric acid (1 to 1) in a 500-cc. Erlenmeyer flask, the liquid boiled gently until the salt has almost dissolved, transferred to a liter bottle, and diluted with freshly boiled water to 1000 cc. A few pieces of metallic tin are introduced to prevent oxidation. FERRIC PHOSPHATE SOLUTION-Twenty-five grams of ferric sulfate are dissolved in 950 cc. of water containing 40 cc. of phosphoric acid (sp. gr. 1.72) and 10 cc. of sulfuric acid (sp. gr. 1.84). The accuracy of the method is indicated by the tabulated results obtained on several samples of steel and on Bureau of Standards standard sample 61 of ferrovanadium by the volumetric and colorimetric methods. Experiments t o Test Accuracy of Method MOLYBDENUM FOUND Volumetric Colorimetric WEIGHTOF SAMPLE SAMPLE method method Gvam % % .Steel 1 O:i7 0.6000 0.26 0.27 Steel 1 0.6000 0.27 Steel 1 0.6000 0.34 0.33 Steel 2 0.2500 0.34 0.5000 Steel 2 0.33 0.7500 Steel 2 Steel 2 1.000 0.33 Ferrovanadium standard 61‘“ 0.5000 0.72 0.73 4 The Bureau of Standards obtained a result of 0.72 per cent Mo by weighing as lead molybdate, and Electro Metallurgical Co., 0.72per cent by &e volumetric method when this standard was made in 1924.
The volumetric determinations were made on a 2-gram sample, the molybdenum being separated from the iron and vanadium with hydrogen sulfide by the present standard methods before passage of the sulfate solution through the Jones reductor. Time Required for Analysis
Comparison with standard.
.
. .
2
The above time may be reduced after one has become accustomed to the method. It has been found that the intensity of the color remains stable for at least a week. Therefore, by making up a sufficient number of fresh standards the beginning of each week, say within a range of 0.02 per cent, it will only be necessary to dilute the unknown until the colors match. Of course the standards should all be diluted to the same volume. This will aid in reducing the time taken for making the comparison.
Lots of Bromine in the Ocean Although practically all of the bromine produced in the United States has been obtained from salt brine deposits located in different states, the outstanding potential source of this chemical material is the sea, according to the United States Bureau of Mines. The rapidly increasing use of this material in motor fuel has attracted attention t o the bromine content of the ocean. Bromine occurs in sea water to the extent of 60 to 70 p. p. m., except where fresh water from rivers may cause local dilution near the coast. Since the area of the oceans is 139,295,000 square miles-almost two and one-half times the area of the land-and since the depth averages 3 miles, sea water represents a virtually inexhaustible source of supply of any chemicals that can be commercially extracted therefrom. Experiments have demonstrated that this bromine actually is available, and the importance of this discovery is evidenced by the fact that only 1 cubic mile of sea water would supply for 392 years all the requirements of a plant producing 100,000 pounds of bromine per month. Owing to the corrosive nature of the element it enters commerce largely in the form of its salt. Bromine is also sold as
“mining salt,” a mixture of sodium bromate and bromide. Solidified bromine has been used for laboratory work. Diatomaceous earth, formed with a suitable bihder and burned into coherent sticks, is saturated withtthe liquid. These porous sticks absorb 50 to 75 per cent of bromine by weight. Previous to about 1922 bromine was used principally in the form of sodium potassjum or ammonium bromide in photography and for medicinal purposes. The photographic trade usually buys ammonium bromide of U. S. P. grade. “Mining salt” was formerly used in some quantity in the extraction of gold from its ores, but this use has apparently greatly declined. Bromine is used in the production of certain dyes, and liquid bromine as well as many of its compounds is employed in analytical chemistry. During the war some hand grenades and gas bombs were loaded with bromine or with organic bromine compounds. The principal outlet for bromine a t present, however, is as ethylene dibromide used in tetraethyl lead and antiknock compounds. The world’s bromine has come chiefly From Germany and the United States, being produced in the United States as early as 1846.
