1NDUSTRIAL AND ENGINEERING CHEMISTRY
January 15, 1931
ball bearing and grinding chamber is surrounded by babbitt metal. It is lubricated by vaseline through a hole in the center of the bearing and is driven by a 1-inch pulley attached to the end opposite the grinding chamber. Operation
One of the difficulties encountered in early trials was that of keeping the material in motion. The small size of the rotating knife made it necessary to drive the mill a t the rate of 5600 r. p. m. to give sufficient surface speed to keep the material agitated. A plug of metal (not shown in Figure 1) to fill in the angle between the wall of the grinding chamber and the stationary blade helped to prevent the material from gathering a t that point The use of more than the one stationary blade in the wall of the chamber in order to increase the cutting speed of the mill is impossible due to the tendency of the material being ground to gather on the top of the blade. A slightly eccentric collar was placed on the shaft at the pulley end to furnish enough vibration to ensure that the finely ground material would pass through the sieve. Since a temperature increase during grinding might be detrimental to the material by causing moisture loss, etc., the mill was provided with a water-cooling system surrounding the shaft. So far it has been unnecessary to use it, as the large bulk of iron in the main body of the mill tends to take up and conduct away the small amount of heat developed. A second experimental mill made with a smaller body did need a water-cooling system to prevent overheating. A nickel-plated brass face was used for that portion containing the grinding chamber.
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This grinding mill has been found very satisfactory for grinding small samples of material difficult to grind. I n grinding wheat kernels it is necessary to break them up in a mortar to prevent them from tearing the copper mesh by hitting it too suddenly. It is better to cut leaves, also, into rather small pieces convenient for loading. The capacity of the mill is about five to eight kernels of wheat or several wheat leaves at one charge, and the operation can be performed practically without loss of material, with proper precautions] so that a representative sample may be obtained for microanalysis. It is rapid in operation. At an operating speed of 5600 r. p. m. and a clearance of l/No inch between the rotating and stationary blades, a single charge of material is reduced to pass an 80-mesh sieve in from 3 to 4 minutes. The simplicity and accessibility of the grinding chamber permits thorough and rapid cleaning between samples. The homogeneity of ground wheat leaves or kernels has been demonstrated by more than 200 analyses for total nitrogen content, successive 20-mg. samples having been found to check within a few hundredths of 1 per cent of nitrogen, Analyses were made according to the ter Meulen and Heslinga hydrogen method (1). The Arthur H. Thomas Company of Philadelphia has designed and is about to place on the market a micro-grinding mill involving the main principles of construction of the mill described in this article. Literature Cited (1) Meulen, ter, and Heslinga, "Neue Methoden der organisch-chemischeo Analyse," Akademische Verlagsgesellschaft, 1927 (2) Wiley, IND.END.CHEM.,17, 304 (1925).
Determination of Aluminum in Ferrochromium and Chromium Metal' Thos. R. Cunningham UNION CARBIDE A N D CARBON RESEARCH LABORATORIES, INC., LONGISLAND
I
N THE following method iron is separated by means of cupferron while chromium is oxidized by evaporating the solution with perchloric acid, and aluminum is separated by precipitation with ammonia. Two and one-half grams of the sample are t,ransferred to a 250-cc. covered beaker and treated with 15 cc. of hydrochloric acid (sp. gr. 1.19). If the aluminum content is less than 0.1 per cent it is necesgary to work on a 10-gram Pample. This is accomplished by dissolving four 2.5-gram portions of the sample and subsequently combining the four aluminum hydroxide precipitates, obtained as described below, by filtering on a single 9-em. paper and washing with a 2 per cent ammonium chloride solution. The solution is warmed to about 60" C. until all action has ceased, when 3 cc. of Perhydro1 (30 per cent hydrogen peroxide) are added and the liquid boiled down to a sirup. Thirty cubic centimeters of hydrochloric acid (1 to 1) are introduced, the solution heated until all salts have dissolved, diluted with water to 50 cc. and filtered on a 9-cm. paper containing home ashless paper pulp into a 400-cc. beaker, and reserved. The paper and residue are washed 18 to 20 times with hot water and ignited in a 30-cc. platinum crucible. Five drops of sulfuric acid (1 to 1) and 2 cc. of hydrofluoric acid (48 per cent) are introduced and the silica is volatilized by evaporating the solution to the complete expulsion of the acids. 1
Received October 16, 1930.
CITY,
N. Y
The residue is fused with 2 grains of sodium carbonate and the melt dissolved in 25 cc. of hot sulfuric acid (1 to 4). If four 2.5-gram portions are taken for analysis the residues may be combined and only one fusion made, increasing, of course, the weight of sodium carbonate used to 8 grams. The solution is boiled to expel carbon dioxide, approximately 2 grams of arnmonium chloride and a very faint excess of dilute filtered ammonium hydroxide (1 to 3) are then introduced, and the solution is boiled for no longer than 1 or 2 minutes. The precipitate is filtered on a 9-cm. paper containing some ashless paper pulp and washed thoroughly with hot 2 per cent ammonium chloride solution. The paper holding the precipitate is transferred to the 400-cc. beaker containing the main solution and macerated to a pulp by means of a glass rod. The liquid is then heated just short of boiling for about .5 minutes to insure the complete solution of the precipitate. The solution (which should have a volume of about 100 cc. and an acidity of approximately 15 per cent) is cooled to approximately 15' C. and the iron precipitated by the addition of a slight excess of a freshly prepared, cold 6 per cent solution of cupferron (ammonium nitrosophenylhydroxylamine, CtHj(NO)ONH4), whilc all aluminum and chromium will remain in solution. A brownish red, partly amorphous, partly crystalline, precipitate separates out. As soon as a drop of the reagent cawes the formation of a transient snowwhite crystalline precipitate] all of the iron is down. The
ANALYTICAL EDITION
104
solution is filtered on an 11-cm. paper containing some ashless paper pulp, the paper and precipitate washed well with cold 5 per cent hydrochloric acid, and discarded. The filtrate and washings are collected in a 600-cc. beaker and boiled down to a volume of about 50 cc. Fifty cubic centimeters of nitric acid (sp. gr. 1.42) are introduced and the boiling continued until the volume has been reduced to approximately 10 cc. Twenty cubic centimeters of nitric acid (sp. gr. 1.42) and 30 cc. of perchloric acid (60 per cent) are added, the solution evaporated to strong fumes of perchloric acid, and heated for an additional 30 minutes to insure the complete oxidation of the chromium to chromic acid. One hundred cubic centimeters of water are introduced, the solution is warmed, filtered on a 9-cm. paper, and the silica washed with warm water. The filtrate and washings, which should not exceed 175 cc., are collected in a 400-cc. beaker. The solution is nearly neutralized with filtered ammonium hydroxide (1 to 3) and heated to boiling. Approximately 5 grams of ammonium chloride and some ashless paper pulp are added and the solution treated with dilute ammonium hydroxide (1to 3) drop by drop until the color just changes to a distinct yellow. The solution is boiled for no longer than 1 or 2 minutes and immediately filtered on a 9-om. paper. The paper and precipitate are washed thoroughly with hot 2 per cent ammonium chloride solution, transferred to a 150-cc. beaker and treated with 15 cc. of hydrochloric acid (1to 2). The solution is heated to boiling for several minutes, diluted with warm water to 100 cc., and treated with a brisk stream of hydrogen sulfide for 15 minutes to precipitate platinum. Any precipitate that forms is filtered on a 9-em. papel, washed 10 to 12 times with hydrogen sulfide water containing I per cent hydrochloric acid, and discarded. The filtrate contained in a 400-cc. beaker is boiled to expel hydrogen sulfide, 5 cc. of perchloric acid (60 per cent) are added, and the solution is evaporated to strong fumes of perchloric acid and heated for an additional 15 minutes. One hundred cubic centimeters of warm water are added and the solution is nearly neutralized with filtered ammonium hydroxide (1 to 3) and heated to boiling. Approximately 2 grams of ammonium chloride, some ashless paper pulp, and several drops of an 0.2 per cent alcoholic solution of methyl red are introduced and the solution treated with dilute filtered ammonium hydroxide (1 to 3) drop by drop until the color just changes to a distinct yellow. The solution is boiled for no longer than 1or 2 minutes and immediately filtered on a 9-cm. paper. The paper and precipitate are washed thoroughly with hot 2 per cent ammonium chloride solution. The precipitate is ignited in a weighed platinum crucible first a t a low temperature and finally over a blast lamp for 5 minutes or in an electric furnace a t 1150" C. for 15 minutes. The crucible covered with a closely fitting lid is allowed to stand in a desiccator until cool and then rapidly weighed. A second heating of equal duration is advisable, especially as it permits more rapid weighing and consequently more accurate results. Ignited alumina is very hygroscopic, and absorbs within the first 10 minutes' exposure to the air a large proportion of the total water which it will take up in 24 hours, A well-fitting crucible cover is quite efficient in preventing the adsorption of moisture by the alumina while the crucible is in the desiccator or on the balance pan. Elimination of Phosphorus
The precipitate obtained as described will contain part or all of the phosphorus in the alloy (depending upon the aluminum content) but rarely contains chromium; should it be colored, indicating the presence of chromium sesquioxide, it is fused with 1 to 2 grams of sodium carbonate. The melt is dissolved in the least necessary amount of hot water and the
Vol. 3, No. I
chromium determined colorimetrically. A small amount of sodium peroxide is added and the liquid is boiled for a few minutes and cooled. The chromate solution is transferred to a Camp comparison tube. The volume should now be about 15 cc. To the other comparison tube there is added from a 10-cc. buret an amount of standard potassium chromate solution (1 cc. = 0.00050 gram Cr.) which contains slightly less chromium than the sample, and sufficient water to make their volumes exactly equal. After having mixed each, the intensity of the two solutions is compared. The color of the sample should be slightly more intense than that of the standard. An additional smaIl amount of the standard chromate solution is added to the tube containing the standard, and an equal amount of water to the tube hoIding the sample. After having mixed the contents of the tubes the intensities of the colors are again compared. These operations are repeated until an exact match is obtained. The number of cubic centimeters of the chromate solution used, multiplied by 0.00050, multiplied by 1.4615, gives the weight of chromium sesquioxide to be deducted. After having determined the chromium colorimetrically, the solution from the sodium carbonate fusion is transferred to a 300-cc. Erlenmeyer flask and made acid with an excess of 2 cc. of nitric acid (sp. gr. 1.42). The solution is heated to boiling to expel carbon dioxide and the chromium reduced to the trivalent state by the addition of a sufficient amount of sulfurous acid, and by boiling. The liquid is cooled to 40" C., approximately 5 grams of ammonium nitrate, 0.05 gram of ferrous sulfate (free from phosphorus), and 40 cc. of molybdate solution added, and the phosphorus precipitated as ammonium phosphomolybdate by 5 minutes of vigorous shaking. The precipitate is allowed to settle and the phosphorus is determined by either the alkalimetric or the molybdenum reduction (Emmerton) method. The weight of phosphorus found, multiplied by 2.2887, is the weight of phosphorus pentoxide to be deducted from the weight of the alumina precipitate. The weight of the alumina precipitate, less the weights of chromic oxide and phosphorus pentoxide found, is multiplied by 52.94 and divided by the weight of sample taken to give the percentage of aluminum in the alloy. A blank should be run on all the reagents used and any aluminum found deducted from the result obtained as above described. Experimental Proof of Accuracy of Method
I n order to test the accuracy of the method a number of experiments were carried out. The procedure consisted in salting several samples of the Bureau of Standards standard sample 64 of high carbon ferrochromium2 with varying amounts of pure aluminum chloride. The accurately measured aliquot portions of the standard solution of pure aluminum chloride were added to the weighed samples of ferrochromium, which were then dissolved and otherwise treated as given in the description of the method. The results obtained are shown in the table. Experiments to Test Accuracy of Method FERROEXPERICHROMIUM ALUMINUM ALUMINUM ALUMINUM MENT TAKEN ADDED FOUND RECOVERED5 Gmmr _ _
1 2 3
5
5 10
.
Gram
Gram
Nil Nil Nil Av.
5
Gram
Gram
0.021%
0.00228 0.00339 0.00234 6 0.0039 0.00498 0.00393 5 After correcting for 0.021 per cent AI in alloy.
4 6
ERROR
0.00106 0.00100 0.00220
+O.OOOOS +0.00003
9 The Bureau of Standards obtained a result of 0.020 per cent aluminum,and Electro Metallurgical Co.,0.022 per cent, when this standard was
made.
