INDUSTRIAL AND ENGINEERING CHEiMlXTRY
1288
A very strong filter paper is necessary to withstand the treatment with boiling hot 10 per cent potassium hydroxide solution. The treatment of the slag and oxide residue with caustic should be regulated, of course, by the conditions mentioned earlier in this paper. SILICAIN SLaG-Treat the ignited residue of slag and oxides obtained from the modified iodine method with about 25 cc. of 2:l hydrochloric acid in a 100-cc. beaker. Evaporate the solution just to dryness and add 5 to 10 cc. of concentrated sulfuric acid. Heat for 15 minutes t o heavy fumes of sulfuric acid, cool, dilute to 40 cc., and add 10 cc. of concentrated nitric acid. Boil until all salts are in solution, filter, and wash the paper and residue free of iron with hot dilute nitric acid and hot water. Keep the filtrate for the determination of manganese. Wash the paper free of acid with hot water, catching the washings in a different receiver. Dry the paper and residue, ignite, and rreigh. Moisten the
Vol. 19, No. 11
ignited residue with a few drops of concentrated sulfuric acid and then add 10 cc. of hydrofluoric acid. Evaporate carefully to dryness, then ignite and weigh the residue. The difference in the two weights is the weight of silica in the slag. The percentage of silicon in the slag, calculated from this determination, subtracted from the percentage of total silicon gives the percentage of silicon in the base metal. ~IAXGASESE IN SLAG-COO~ the filtrate from the silica determination to 15" C., add a slight excess of sodium bismuthate (about 0.5 gram), and agitate for about a minute. Filter by suction through an asbestos pad, washing the flask and pad with 3 per cent dilute nitric acid, making sure that the last washings are colorless. Titrate immediately with a standard solution of sodium arsenite to the disappearance of the pink color. From this titration the percentage of manganese in the slag may be calculated and the figure thus obtained is subtracted from the total manganese to get the amount of manganese in the base metal.
Estimation of Copper Oxide and Metallic Copper in Mixtures Containing Both' By W. D. Bonner and Bal Dev Kaura UNIVERSITY OB U T A H , S A L T
DIRECT method for the quantitative determination of cuprous oxide and copper in a sample containing both has not been known, although one can determine cuprous oxide indirectly by reducing with hydrogen and finding the amount of water formed. The work here reported gives a simple and fairly accurate method for determining these two when both are present. It may be especially useful in the cement copper industry, where, owing both to oxidation during drying and to direct precipitation as cuprous oxide, the cement copper always contains oxide and it is often desirable to know the amount.
A
Experimental
'
RATE OF SoLuTIow-This method is based on the fact that copper dissolves much more slowly in an alkali cyanide solution than does cuprous oxide. It has long been known that metallic copper dissolves in an alkali cyanide solution with the evolution of hydrogen, but neither the rate of solution nor the extent to which copper is soluble has been determined. Therefore the rate of solution of copper in molar sodium cyanide solution was first determined. It was found that copper free from oxygen dissolved only to the extent of about 0.2 gram per liter of cyanide solution in 3 hours, when allowed to stand a t room temperature with an occasional shaking. I n the same length of time molar sodium cyanide solution would dissolve enough cuprous oxide from an excess of the solid to form a saturated solution-i. e., about 30 grams per liter-while cupric oxide, exposing the same surface area as the metallic copper, would dissolve to the extent of 3.5 grams per liter. Pure copper was prepared by passing hydrogen over heated cupric oxide wires One portion of this copper was kept under hydrogen, another under nitrogen, and a third was exposed to air. Equal weights (5.325 grams) of these different samples of copper with 150 cc. of 1.04 M sodium cyanide solution were placed in 250-cc. Erlenmeyer flasks and stoppered with rubber stoppers each having a long glass tube to let out the gas evolved. They were then placed in the 1 Received
June 14, 1927.
LAKECITY,
UTAH
thermostat a t 25" C. and samples of the solution taken a t intervals to be analyzed for copper content. Table I-Rate of S o l u t i o n of Copper in Molar Sodium Cyanide COPPER SAMPLE 3 5 9 12 24 5 HOURS HOURS HOURS HOURS HOURS DAYS I n hydrogen 0.20 0.26 0.70 0.85 3.00 9.87 I n nitrogen 0.20 0.30 0.75 0.99 3.25 11.00 I n air 0.40 1.10 1.75 5.50 12.70 0.66
The results (Table I) show a wide difference in the initial rate of solution of the different coppers. Copper exposed to air dissolves about twice as fast initially as that kept under hydrogen or nitrogen, but the rates become more and more uniform with lapse of time. The copper kept under nitrogen dissolves a little faster than that kept under hydrogen, probably because the nitrogen, having been prepared from liquid air, contained some oxygen. The reaction between (Ch-)- and copper may be written as suggested by Kunschert :2
+ 4(CN)- + HzO C U ( C N ) ~ - - -+ (OH)- + CU~O + 8(CN)- + HzO = 2Cu(CN)* ---+ 2(OH)-
CU
'/2H2
That between Cu!O and (CN)- may be written similarly: The greater reaction rate of the cuprous oxide (or of the copper exposed to air) is therefore probably due to its greater solubility in water. Table 11-Seuaration
NO.OF
DETNS. Mean Deviation
__
of Couuer f r o m Cuurous Oxide
COPPERI N RESIDUE Mg. 249.95 4-0.04 to -0.09
CunO I N FILTRATC Mg. 250.01 t O . 1 9 t o -0.06
CORIPLETEXESS OF SEPARATION OF CUPROUS OXIDE FROM COPPER-Pure cuprous oxide was prepared by reducing Fehling's solution with sugar. This cuprous oxide readily dissolves in sodium cyanide solution. A mixture of pure copper and pure cuprous oxide (250 mg. of each) was added to 50 cc. of 0.5 M sodium cyanide solution and the whole allowed to stand for about 2 hours with occasional shaking. It was then filtered and copper determined, by the iodide method, in both residue and filtrate. 9
2. anorg. Chcm., 41, 359 (1904).
November, 1927
I,VDUSTRIAL A N D ENGI.C’EERING CHEMISTRY M e t h o d of Analysis
’
To 0.5-gram samples add 50 cc. of 0.5 -11sodium cyanide solution. Allow to stand for 1.5 to 2 hours with occasional shaking. The completion of the reaction is generally readily detected, as the particles of copper metal settle, after shaking, much more quickly than does copper oxide. Filter and to the filtrate, which contains the cuprous and cupric oxides, as well as some or a11 of the iron, add enough nitric acid to destroy the ryanide. Boil the solution to dryness and continue heating to convert the residue entirely into oxides. Add water and enough nitric or hydrochloric acid to dissolve the residue and strong ammonia to precipitate ferric hydroxide. Filter and to the filtrate add enough acetic acid t o make the solution distinctly acid. Add an excess of potaqsium iodide and determine the copper in the utjual manner. Dissolve the residue from the first filtering in nitric acid. Remove any iron by means of ammonia and determine copper in the same manner as aboye. Analyses of C e m e n t Copper a n d C u p r o u s Oxides
d large number of samples of cement copper furnished by various producers have been analyzed by this method (Table 111),as well as samples of cuprous oxide from four different manufacturers (Table IV). In analyzing a cement copper, a large part of the iron present will dissolve in the cyanide solution along with the cuprous oxide This iron doubtless forms ferrocyanide ion, and necessitates very careful treatment when destroying the cyanide in the filtrate. It is essential that, after evaporating to dryness, the residue ‘be heated until all nitrates are converted into oxides. If this is not done, some ferrocyanide seems always to escape decomposition, with the result that when the residue is taken into solution some cupric ferrocyanide is precipitated.
1289
T a b l e 111-Analyses of C e m e n t Copper COPPER CUPROUSOXIDE N O . OF Deviations Deviations SAMPLE DETNS. Mean to Mean to Per cent Per cent Per cent Per cent 6 78.39 0.13 to 0.13 16.62 0.21 to 0.26 3 39.69 0 . 0 9 to 0 . 0 4 47.44 0 . 0 4 t o 0.02 10 46.66 0.27 to 0 . 3 8 46.07 0 . 5 7 to 0 . 4 3 4 29.65 0.25 to 0.27 58.80 0.32 to 0 . 2 6 4 12.38 0 . 1 0 to 0 . 0 3 0 . 2 8 t o 0.26 66.72 3 0.17 to 0.09 8.67 59.28 0 14 to 0.14 3 40.93 0.17 to 0 . 0 9 50.89 0.11 to 0.09 0 . 1 6 to 0.20 31.06 3 57.79 0 . 0 7 to 0.07
+ -
+ -
T a b l e IV-Analyses of C u p r o u s Oxides CUPROUSOXIDE COPPIIR h-0. O R Deviations Deviations SAMPLE DETXS. Mean to Mean 4-t o Per cent Per cent Per cerit Per cenl 1 2 83.48 0 . 0 1 to 0 . 0 1 0.?8 0.28 to 0 . 1 4 88.00 2 4 0 . 2 9 to 0.24 0.87 1 . 7 2 to 0.87 3 4 98.13 0.14to0.24 0.33 0.28t00.33 0.19to0.22 0.79 0,53tto0.17 .f 4 96.60 J 4 96.58 1.59 O.45to0.98 0.10t00.12 6 3 83.61 0.13 t o 0 . 2 5 2.59 0.60toO.i8
+ -
-
The wide and erratic deviations in the copper content of the samples of cuprous oxide are due to the fact that the copper occurred in rather large granules, and it was a matter of chance how many of these might be found in any given 0.5-gram sample. Furthermore, these samples include “pure,” “c. P.,” and “analyzed” materials, and the best preparation found (No. 3) is not an analyzed reagent. Acknowledgment
During the progress of this work 51r. Kaura acquired chronic cyanide poisoning, and had to give over all cyanide work. The writers are therefore indebted to Sol F. Ravitz, of this laboratory, for the analyses of the cuprous oxides.
Measurement of Color in Stammer Units on a Kober-Klett Colorimeter’ By K e n n e t h S. R i t c h i e 2 S‘CANRORD
UNIVBRSITY,
CCASIONALLY a laboratory not equipped with a Stammer colorimeter has the problem of reporting the color of sugar and molasses liquors in the usual Stammer units. This paper describes a simple method for rnaking the desired readings in the ordinary laboratory colorimeter of the Duboscq type. The instrument used was the Kober-Klett nephelometer colorimeter which is essentially an improved Duboscq niodcl. The requirement for all colorimeters using the Duboscq priiiciple is a suitable reproducible standard color solution.
0
Ferric Chloride as a S t a n d a r d Color S o l u t i o n
The search for a desirable solution ended with r,he development of an improved procedure for preparing a standard color solution of ferric chloride. One of the ‘D7est Coast sugar refineries had been using a series of ferric chloride solutions prepared from crystals. The color tints of these solutions were not exactly reproducible, owing largely to variations in the quality of the commercial ferric chloride crystals. After some experimentation, a stock solution of ferric chloride with a reproducible color tint was prepared according to the following procedure: 1 f
*
Received October 5 , 1926. Present address, Ponca City, Okla. Lamb, Carleton, and Meldrum, J. A m . Chem.
5’06..
42, 251 (1920).
CALIFORNIA
Clean iron standardization wire is used by dissolving 62.00 grams in 100 cc. of aqua regia, made by heating the wire and two parts of concentrated c. P. hydrochloric acid in an evaporating dish on a water bath and then adding one part of concentrated c. P. nitric acid slowly, about 5 cc. a t a time. Troubles caused by excessive overheating from the rapid generation of the reaction heat of solution can be avoided by placing the iron wire in the correct quantity of HCl acid and cautiously adding the desired quantity of Hh-Ot acid in l-cc. lots. The solution is evaporated to a sirupy consistency and is then. diluted with concentrated c. P. hydrochloric acid. The evaporation and dilution are repeated three times before finally evaporating to crystallization. Care is taken not to overheat as chemical changes might occur that would affect the color tint. The crystalline residue in its mother liquor is then dissolved in 2:1 hydrochloric acid and the volume is then brought up to exactly 300 cc. This constitutes the stock solution, which is kept in a bottle wrapped with black glazed paper.
Colorimetric measurements n-ere made on different lots of the stock ferric chloride solution prepared a t various times during a period of 2 years. The intensity of t’he color tint was always the same when measured at; identical depths in the Kober-Klett colorimeter. The color tint was reproducible and permanent, exact matching of tints being obtained for solutions 2 years old and those freshly prepared. It was recognized that the stock ferric chloride solution could be made more useful by preparing dilute solutions which would have color tints of lighter intensity. M a n y
INDUSTRIAL AND ENGINEERING CHEMISTRY
1290
dilute solutions were prepared with definite ratios of concentration to that of the stock solution. Previous experimental work on caramel solutions had shown that the caramel dilution curve followed Beer’s law4 exactly-i. e., the color intensities of two caramel solutions are equal when the product of the columnar depth times the concentration of each solution is equal. Horton6 reported later that, within the accuracy of the Klett colorimeter, the dilution of caramel solutions follows Beer’s law. A comprehensive series of systematic measurements was made against the known caramel solutions and also against known depths of ferric chloride solutions. The data proved that dilutions of the stock ferric chloride solution do not follow Beer’s law. Another series of measurements to determine the depth a t which the color tint of the stock ferric chloride solution matched the color tints of various dilute caramel solutions showed that this depth was 3.0 mm. in the Klett colorimeter. Further measurements on dilute ferric chloride solutions showed that a t some definite depth for each solution there k a perfect match in tints for all the dilute caramel solutions tested. The ratios of the depths for the ferric chloride solution did not agree with the dilution ratios of these solutions, codinning the preceding study of Beer’s law. It was found that these solutions should not be continuously exposed to the colorimeter’s light for more than 5 minutes a t a time and that fresh solutions of the stock solution should be used with each new solution being measured. Evaluation of Ferric Chloride D a t a in S t a m m e r Values The next step was the determination of the Stammer “depth constant” for the stock ferric chloride solution. A series of dilute caramel solutions was carefully prepared. Portions of the first few dilutions were measured in the colorimeter and the depths a t which exact matching of tints with that of the stock ferric chloride were recorded in Table I. The ratio of ratios shows that this change in depth between succeeding dilutions is practically constant a t a ratio of 2.0. Table I-Relation FeCh a t 3.0 mm. Ratio k a t i o of ratios
of Caramel t o Ferric Chloride CONCENTRATIONS OF CARAMEL SOLUTIONS 18 1.1 12 14 1 2 . 6 mm. 2 6 . 3 mm. 3 . 1 mm. 6 . 3 mm. 1.033 2.10 4.20 8.44 2.03 2.00 2 01
The dilutions of the caramel solutions were continued to a point where very accurate measurements of the lighter color tints of the more dilute solutions could be made in the Stammer colorimeter. Carefully checked measurements were made by three observers on the same series of solutions in January, 1923. As a further check, this work was repeated in May, 1923, on freshly prepared solutions. Table I1 contains the resultant data. Table 11-Stammer
Readings on Caramel
CARAMEL SOLUTION 1
2 3 .\VER40Ea Mm. Mm. Mm. 12.3 12.5 12.4 12.4 24.7 24.8 24 7 24.8 49.6 49.2 49 3 49.6 averages are within the limits of accuracy for reading
Mm.
1:32 1:64 1:128 a The acceuted the scale and h t s .
With these data only a very simple computation was necessary to find the corresponding depth for the color tint of the stock ferric chloride solution at the 3.0 mm. depth in the Kober-Klett colorimeter. A column of the dilution ratios for the caramel solutions was made as shown in Table 111. The corresponding depth reading in the Stammer instrument was placed in the next column. The depth of 6.2 mm. for the 1:16 caramel solution was obtained by dividing 12.4 mm. by 2. These computations were continued for the depths of the remaining solutions. Since the tints of the 4
Lewis, “A System of Physical Chemistry,” Vol. 11, p. 408.
6
THISJOURNAL,15, 519 (1923).
Vol. 19, No. 11
1:2, 1:4, and 1:s caramel solutions matched the color tint of the stock ferric chloride solution a t 3.0 mm. a t depths which were 2.1, 4.2, and 8.44 times as large (see Table I), simple division gave the Stammer depth for the color tint of the ferric chloride solution as 0.369 mm. This value of 0.369 mm. may be considered the Stammer “depth constant” for the stock ferric chloride solution whenever it is used as a color standard a t the 3.0 mm. depth in the Kober-Klett colorimeter. Table 111-Stammer
“Depth Constant” of Ferric Chloride
DILUTIONRATIO CARAMEL RATIO^ 1:64 24.8 1 :32 12.4 1:16 6.2 1 8 3 1 + 8.44 1:4 1.55 i 4.2 l:2 0.775 i 2.1 1:l 0,3875 ... a Ratios for 3.0 mm. depth from Table I.
STOCKFeCll
= = =
0.359 0.369 0.358
...
M e t h o d of Using S t a m m e r “Depth C o n s t a n t ”
I n spite of the current trend in the sugar industry for more precise color measurements with spectrophotometers, the established method of measuring color in Stammer units will continue for many years. One usually reads the Stammer number as “color in 100” Brix per 100” Stammer” and computes the value from the formula: Color (Stammer) =
100 Mm. depth (instrument)
O
100 Brix of solution
The method for using the Kober-Klett colorimeter is as follows : The color tint of the stock ferric chloride solution a t the 3 . V The corresponding depth reading is obtained for the sugar liquor by matching its tint in the colorimeter with the ferric chloride tint. The Brix reading of the sugar liquor is determined. The depth readings of this liquor in the Klett colorimeter are translated to the corresponding depth readings for the Stammer instrument. The usual computation is then followed to obtain the degrees color (Stammer) of the sugar liquor.
mm. depth is used as the standard comparison tint.
To illustrate, suppose that in the Klett instrument a sugar liquor of 52” Brix density read 11.1 mm. against the stock ferric chloride solution a t 3.0 mm. Then the depth-ratio factor is 11.1 +- 3.0 = 3.7. The corresponding Stammer instrument depth would be 3.7 times 0.369 = 1.365 mm. Substituting in the Stammer formula, Degrees color (Stammer) =
100 loo X = 141 1.365 mm. 52 Brix
In case measurements have to be made on sugar liquors of very pale COlOrB, one can prepare a graduated series of caramel solutions whose concentrations of the adjacent solutions in the series have the definite ratio of 1:2. The color value of each of these solutions can be measured in terms of the ferric chloride color. It is a simple matter to select the caramel solution of approximately the same color intensity as that of the sugar liquor. Measurements can be made in the Klett colorimeter and the necessary computations made from the known relations between the caramel and the stock ferric chloride solutions. Likewise, for any instrument of the Duboscq type, it is possible t o find the Stammer depth constant for ferric chloride when used in that instrument for measuring the Stammer values of sugar liquors. Acknowledgment
This work was done in the Physical Chemistry Laboratory a t Stanford University under Prof. S. W. Young. The writer is grateful for the friendly and thoughtful encouragement of both Professor Young and R. D. Elliott, a t that time a member of the laboratory staff of the California and Hawaiian Sugar Refining Corporation.
