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Experimental Demonstration of the Refining of Metals by Oxidation' James Silberstein 844 GRACEST., CHICAGO, ILL.
I
N THE Bessemer converter iron is refined by blowing air
through the molten metal. The elements phosphorus, sulfur, and carbon, which have a greater affinity for oxygen than has iron, are thereby oxidized and removed from the metal. Similarly, copper is refined and the impurities, such as lead, tin, arsenic, and sulfur, pass into the slag or fumes. Everyone who has had some experience in the refining of metals knows that part of the metal is oxidized along with the impurities and that this part increases with the purity to which the metal must be refined. The explanation is as follows: When their concentration is relatively large, the impurities are oxidized either directly by oxygen or indirectly by the metal oxide which has been formed by the metal and oxygen. The impurities are therefore removed without affecting the metal. With decreasing percentages of impurities, however, such large amounts of the metal are oxidized with the impurities that part of the metal oxide passes into the slag without reacting with the unoxidized impurities. Let us suppose, for instance, that lead is to be removed from copper and the concentration of lead is 1 atom per 1000 atoms of copper. Blowing air through this metal causes the formation of copper oxide with lead oxide, and, as it is a technical impossibility to bring about such an intimate mixing of metal and slag that all the rest of the unoxidized lead is brought into reaction with the copper oxide formed, copper oxide appears in the slag while there is still lead in the metal. The writer, who knows of no previous simple experiments to show this condition on a laboratory scale, has found that f
Received August 28, 1928.
the removal of sodium from lead furnishes a good and easy demonstration. Pure lead on melting is covered with a bluish oxide film, which, especially a t somewhat elevated temperatures, turns grayish black. If 0.2 to 0.5 per cent sodium is added to the lead and the temperature is kept not too high above the melting point of the lead, the surface appears a t first bright metallic because of the deoxidizing effect of the sodium. Soon, however, the surface is covered with a thin white film of sodium oxide. It is not necessary to blow air through the metal in this case. Exposure of the metal in the molten state to the atmosphere will bring about the refining. (Simple exposure is sufficient, but stirring and drawing off the oxide film, so as to expose the metal more intimately to the atmosphere facilitates the oxidation process.) If the film is removed, the bright metallic surface appears again, but it is soon covered with the oxide film. At this stage sodium alone is being oxidized by the oxygen of the atmosphere. Later the milky white film assumes a bluish tint, indicating that lead as well as sodium is being oxidized. Still later the color changes to a bluish gray, with a milky appearance. Despite the great affinity that sodium has for oxygen in comparison with lead, a rather long time elapses before the oxide film loses the characteristic color which is imposed upon i t on account of the presence of sodium. This experiment illustrates clearly the procedure of the refining of metals on a practical basis. Much metal passes into the slag when the element to be removed has for oxygen an affinity not very different from that of the metal to be refined. A case in point is the removal of nickel from copper.
Sampling Apples in the Orchard for the Determination of Arsenical Spray Residue' A Statistical Study J. W. Barnes INSECTICIDE DIVISION,BUREAUOF CHEMISTRY
N T H E analysis of arsenical residue on apples there seems to be some difference of opinion regarding the size of sample necessary. The investigation here reported was carried out to aid in solving this problem. The number of apples taken was large enough beyond reasonable doubt to reduce the probable error well below the accuracy of the method of analysis. Three hundred apples were picked a t random from four trees and culls were discarded, but no other selection was made. These apples had received four applications of lead arsenate in a spray of 2 pounds to 50 gallons of water, the last treatment having been applied July 1. They were gathered the middle of October.
I
1 Presented as a part of the Insecticide Symposium before the Division of Agricultural and Food Chemistry at the 75th Meeting of the American Chemical Society, St. Louis, Mo., April 16 to 19, 1928.
AND
SOILS,WASHINGTON, D. C.
The apples were peeled, and the peelings were oxidized by sulfuric and nitric acids. The solution was made to volume, and the arsenic was then determined by the Gutzeit method. There are some variations in the details of this method in use by different chemists dealing with arsenical residue on fruit., I n our work 5 cc. of concentrated sulfuric acid, a solution containing 1 gram of potassium iodide, and 3 drops of 40 per cent stannous chloride solution in hydrochloric acid were added to a solution of the sample in the reaction chamber, the whole amounting to approximately 35 cc. The addition of the strong acid heats the solution to 35"or 40" C. This is allowed to stand for an hour instead of being heated to 90" C. for a few minutes, The zinc is sensitized by washing with acid containing a few drops of the stannous chloride solution. The strips are sensitized with mercuric bromide. As a rule,
February, 1929
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of the weight of the apples, the area of the apples,
Figure 1-Frequency
Distribution of Weight
an aliquot of 25 cc. from 500 cc. was used, but smaller portions were a t times necessary. The total arsenic2 found was calculated to grains, and the weight of apple was converted to pounds, which allowed the results to be expressed in grains per pound, the common commercial terminology. As the amount of residue in the fruit is primarily a matter of surface and not of weight of the fruit, a quick method was sought for determining the relative areas of the apples from the weight and density. Any method of measuring the surface seemed to take so much more time than weighing that it appeared impracticable. The simplest figure obtained by revolving a cardioid is a good approximation to the shape of an apple. Calculating the area in terms of the volume, and convertng from square centimeters to square inches A = 0.755 ( V ) 2 ' 3= 0.755 = 0.755 where A = area in square inches V = volume in cubic centimeters W = weight in grams D = density
Table As201 Grains per lb. 0.000-0.007 0.008-0.012 0.013-0.017 0.018-0.022 0.023-0.027 0.028-0.032 0.033-0.037 0.038-0.042 0.043-0.047 0.048-0.062 0.053-0.057 0.058-0.062 0.063-0.067 0.068-0.072 0.073-0.077 0.078-0.082 0.083-0.087 0.088-0.092 0.093-0.097
(h)2'3(W)2/3
As under ordinary conditions the sample would consist of apples of the same variety and approximately the same development, the density derived from a few apples may be used in this equation. In this particular case the density appeared as 0.85. Substituting, the equation becomes A = 0.842 (W)2'3 This equation gave results differing by less than 5 per cent from those obtained by direct measurement. A small square stamp with cutting edges was used t o mark off as many squares as possible without overlapping. The areas of the smaller irregular spaces were determined by comparison with cross-section paper. 2
- The extreme variation ingrains per pound was from 0.004 to 0.095, a factor of 24. A factor of a t least 15 is common, however. The weights of the individual apples varied from 0.20 to 0.70 pound, 95 per cent being between a quarter and a half pound. From this series of 299 apples (one having been lost) was obtained the arithmetic mean in grains per pound (0.031) and then the residuals for the individual value. This gave a standard deviation (root mean square) of 0.017 (0.0168) and from this the probable error of a single observation 0.011 and of the mean 0.001 (actually 0.0008). The probable error of the mean is considerably below the accuracy of the method, which shows that this lot of fruit was sufficient for the purpose.
Arsenic is calculated as the trioxide, AszO3.
Table 11-Section
.
SAMPLE 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
from Record Illustrating Variations i n Individual Apples AszOa AszOa AszOa Grains per Grains per Grains per Grams aoole lb. 1000 so. in. 167 0.008 0.022 0.32 145 0,029 0.009 0.40 164 0.043 0.62 0.015 167 0.006 0.09 0.002 0.002 125 0.008 0.11 132 0.014 0.048 0.64 148 0.015 0.047 0.74 132 0.017 0.059 0.78 0,009 128 0.033 0.44 158 0,022 0.008 0.32 150 0.011 0,032 0.46 138 0.016 0,005 0.22 115 0.032 0.008 0.41 158 0.021 0.007 0.30 166 0.019 0.007 0.27 I57 0,018 0.006 0.25 135 0.011 0.036 0.49 145 0.003 0.010 0.14 125 0 002 0.007 0.09 0.008 136 0.003 0.11 148 0.009 0.003 0.12
WEIGHT
The relation between the probable error of the mean, the standard deviation ((r), and the number of individuals is:
PE
N =
=
0.6745 -%
.\/N .~ (p)' 0 6 7 4 5 ~ = (-)67.4%
(PE).M
A r e a d f I n d i v i d u a l A p p l e s [Spunre I n t h e & ] Figure 2-Frequency Distribution of Area
2
where PE = probable error of mean (by weight) (PE)'= probable error of mean (by per cent) CJ = standard deviation M = mean N = number of individuals in sample
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Figure 4-Frequency Distribution (Arsenic per Unit of Apple Surface)
Gmtns
Figure 3-Frequency
/L,&
per
pound of h u r t
Distribution Pound)
(Arsenic per
Under the conditions of this investigation the results are accurate to one unit in the second significant figure. Substituting in the equation, it is seen that to gain this accuracy for the mean would require a sample of 120 apples. An accuracy of 2 in the second figure (15 per cent for this mean) could be obtained from 30 apples. For an accuracy of 5 per cent (1.5 units in the second significant place) 50 apples will suffice. It will probably be necessary to carry out further investigations to determine whether 50 apples can be picked from-an orchard with sufficient degree of randomness to obtain a representative sample. Summary
Individual analyses of 300 apples from 4 trees showed for individual apples ranges in arsenical residue of from 0.001 t o 0.031 grain arsenic per apple, the mean being 0.011. The
Collapsing Temperatures of Various Kinds of Laboratory Glass Tubing‘ A. W. Laubengayer CORNBLL UNIVERSITY, ITHACA, N. Y.
I Ntemperatures, designing glass apparatus that is to be used a t elevated it is desirable and oftentimes necessary to know beforehand the temperature to which the glass may be heated without becoming soft enough to collapse. The following experiments were made to secure this information, the tests being so carried out as t o duplicate, as nearly as possible, the conditions under which the glass is ordinarily used. The glasses tested were: an easily fusible soda-lime glass made by Greiner and Friedrichs, the “ R ’ glass (resistance glass) made by the same firm, Pyrex glass, Jena combustion tubing, Bohemian combustion tubing, and Moncrieff combustion tubing. Tubes with a bore of 13 mm. and a wall thickness of 1.8 mm. were used. Each glass was subjected to two tests. In the first, a tube, 1
Received December 10, 1928.
ratios for weight were from 0.004 grain to 0.095 grain arsenic per pound of fruit, with a mean of 0.031 grain. The range in area was from 0.05 grain to 1.30 grains per 1000 square inches of area of fruit, the mean being 0.43 grain. A formula is given for calculating the area of an apple from its weight which yields results differing not over 5 per cent from the best mechanical measurements. A statistical study of the data indicates that, in order to obtain a result with a probable error of 5 per cent in the value for mean arsenical residue per pound of fruit, it is necessary to analyze a sample of approximately 50 apples picked a t random. Acknowledgment
This investigation was undertaken a t the suggestion of R. C. Roark, Chief, Insecticide Division, Bureau of Chemistry and Soils. Acknowledgment is made to C. hl. Smith and G. L. Bidwell of the Food, Drug, and Insecticide Administration, U.S. Department of Agriculture, for helpful criticism. The apples used in this investigation were furnished by E. J. Newcomer (Yakima, Wash.) of the Bureau of Entomology, U. S. Department of Agriculture.
open at both ends, was heated in a n ordinary electric tube resistance furnace, and the temperature was noted by means of a chromel-alumel thermocouple which was placed in the furnace beside the tube. The temperature was quickly raised to 300 a C. and then uniformly a t the rate of 3 degrees per minute until the tube collapsed. The temperature a t which the first signs of collapse were observed was recorded. In the second test the tube was sealed a t one end, evacuated t o 3 mm. pressure, and then heated under this diminished pressure, the collapsing temperature being noted as in the first test. The results are tabulated below. GLASS Soft “R”soda lime Pyrex Jena Bohemian Moncrieff This glass devitrified readily.
COLLAPSING TEMPERATURE Open tube Evacuated tube
c.
700 760
820
860 860 820
c. 585
635 670
720 740 7700
I t should be noted that in these tests the tubes were heated for a comparatively short time. If the glass were subjected to longer periods of heating, the temperature of collapse would probably be somewhat lower. To avoid collapse of a tube, it should not be heated higher than 50” below temperatures given in the table.
