Dec.,
1912
T H E J O U R N A L OF I N D L - S T R I A L A S D E S G I - Y E E R I J Y G C H E M I S T R Y .
tend to become contaminated with any soluble materials encountered. The most striking difference between the two lies in their respective calcium content. Natural brines are comparatively rich in calcium (and magnesium), while the calcium content of the artificial brines represents but little more than the solubility of calcium sulphate in t h a t solution. I
BURE.4U O F SOILS, U . S . DEPARTMEWT O F AGRICULTURE, \VASHIXGTON.
THE DETERMINATION OF ZINC BY ELECTROANALYSIS.' BY ELLWOOD B . SPEARAND S A X J E L S . STRAHAK.
The electrolytic determination of zinc has been attended by unsatisfactory results because many of the vital conditions were not known and many of the causes of deleterious effects not clearly understood. Two years ago a n article was published2 by one of us on the causes of the high results so frequently obtained, and in another articles the statement was made t h a t our experiences with the potassium and sodium hydroxide methods were unsatisfactory. Some time later Kemmerer4 published very fair results, having used a rapid method with KOH. This method is, with the slight modifications we have introduced, one of the very best for the determination of zinc. Our modifications consist in: First, cooling the solution a few minutes before the end of the experi-
method. These causes will be considered later. The procedure itself is as follows: The zinc to be determined, preferably about 0 . 4 gram, must be in the form of sulfate. Nitrates and ammonium salts must be absent. Very little free sulphuric acid should be present, because potassium sulphate, wkiich is formed when the acid is neutralized with the hydroxide, is not very soluble in strongly alkaline solution: I O to 2 j grams KOH are dissolved in water and the total volume of the electrolyte made up to 1 2 5 cc. The solution is brought almost to the boiling point and electrolyzed with a normal current density of 3 amperes. A' rotating platinum anode and stationary nickel gauze cathode may be used, but vie strongly recommend a rotating nickel gauze cathode (see Fig. I ) and a stationary platinum plate or spiral anode. The cathode must be kept completely buried in the solution. The anode should be placed above and never a - the side of the cathode. The time required for complete precipitation varies, of course, with the size of the cathode. With a cathode area of r o o sq. cm. the time necessary was 45 minutes, using 2 5 grams KOH,and 30 minutes using only 1 2 grams. Seven to eight minutes before the end of the experiment, the anode and the inside of the beaker should be washed down with a small amount of water from a wash bottle in order to obtain any zinc t h a t may have crept up owing to frothing or stirring. This is a precaution that should always be taken in electroanalysis. Five t o six minutes before removing the electrodes the solution should be cooled, with ice if necessary, to below 2 5 ' C. The solution should be lowered from the electrodes without interrupting the current. The cathode should be quickly but thoroughly washed first with z'ater, then with alcohol, and finally with ether that h a s beeqz zery recently dried over s o d i u m a%d jreshly distilled. The ether should be immediately dried off the cathode by gentle heating and the electrode weighed after standing for one-half hour in a desiccator.
--
TABLEI .
TABLE11. Grams of zinc.
Grams of zinc.
Taken. 1 . . . . . . . . . 0.3946 2 . . . . . . . . . 0,3946 3 . . .. . . . . . 0,3946 4 . .. . . . . . . 0 . 3 9 4 6 5 . . . . . . . . . 0.3946 6 . . .. . . . . . 0 , 3 9 4 6 7 . . 0.3946 8 . . . . . . . . . 0.3946
hY0.
FIG. I .
FIG.2
ment. S e c o d , reducing the amount of the KOH employed. The reasons for these changes are discussed below. We have also carefully investigated t h e various causes of error in the employment of this 1 Paper presented at the' Eighth International Congress of Applied Chemistry. S e w York, September, 1912. 2 J . A m . C h e m . Soc., 32, 533. 3 Ibid., 32, 532. THISJOURNAL, 2, 375.
889
Found. 0.3943 0.3948 0.3949 0.3947 0.3949 0.3955 0.3945 0,3942
7
No.
A
Taken. 1 . . . . . . . . . . 0,3946 2 . . . . . . . . . . 0.3946 3.... 0.3946 0.3946 4.... 5 . . . . . . . . . . 0,3946 6 . .. . . . . . . . 0 . 3 9 4 6 7 . . . . . . . . . . 0.3946 8 . .. . . . . . . . 0.3946
Found. 0,3946 0.3948 0.3952 0.3952 0.3950 0,3943 0.3947 0.3951
The method is capable of giving very good results, but this is due to a compensation of errors. When the deposit is washed with water some zinc is always lost in the mash water, while some zinc hydroxide is formed at the same time on the electrode. These two amounts are small and very closely counterbalance each other. I n Tables I and I1 we give 16 consecutive results, using 2 5 and 1 2 grams KOH,respectively. The results were not all obtained on the same day nor by the same experimenter.
890
T H E JOGRL\-AL
OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY.
P R E P A R A T I O N OF T H E S O L U T I O N S F O R T H E I X V E S T I G A TION.
Zinc Sulphate.-About 4 grams c. P. zinc, the purity of which had been verified b y a careful analysis, were dissolved in nitric acid, slightly more than the requisite amount of concentrated sulphuric acid was added and the whole evaporated to dryness over a water bath. The resulting zinc sulphate was dissolved in water and the solution made up t o 2 5 0 cc. in a carefully calibrated flask. Potassium Hydroxide.-Two hundred and fifty grams KOH of good quality were dissolved in water and the solution made up t o one liter. Solution for Analysis.-Twenty-five cc. of the zinc sulphate solution from a carefully calibrated pipette were added t o I O O cc. of the prepared KOH in a deep 2 5 0 cc. beaker. For the analyses using a lesser amount of KOH, 50 cc. of the solution and 50 cc. water were taken. The solution was brought almost to the boiling point and at once electrolyzed. Zinc deposits from hot KOH have a much more metallic appearance than those from a cold solution a n d in the latter case the results are always too high. The solution must not contain nitrates, else all the zinc cannot be thrown down. One gram of potassium nitrate will almost completely prevent the deposition of the zinc. We have not yet investigated the cause for this. T H E ELECTRODES AND T H E I R MANIPULATION.
Cathode.-Many copper, platinum and nickel cathodes of various shapes were tried and the most satisfactory was found t o be one of our own design, a s shown in Fig. I . I t is made of nickel gauze, 30 mesh t o the inch, with a stout wire standard of the same material. The gauze should not continue t o the center t o meet the stem because the rotating motion given t o the solution sometimes causes the center t o become exposed t o the air and some of the freshly deposited zinc is oxidized t o zinc hydroxide. If zinc is deposited electrolytically and any portion of the deposit exposed, to the air a white ring of zinc hydroxide can be seen on the upper edges. Our investigation showed t h a t the deposits always weighs 2-4 mg. too much, provided t h a t the cathode protruded above the solution. This fact doubtless explains some of the high results obtained by many experimenters. The upper edge of the cathode should be turned in toward the center, dome-shaped, for, as the anode is placed above the cathode for reasons given below, most of the deposition will take place on the extreme upper edge, become bad and fall off if the cathode is shaped as shown in Fig. 2 . The cathode was rotated at the rate of 400 revolutions per minute. A rotating cathode is preferable t o a rotating anode, because in the former case a much better stirring effect on the immediate surface of the cathode is obtained. Copper cathodes are not suitable because they oxidize somewhat in hot solution and thus introduce a n error. Platinum cathodes do not give as good zinc deposits as nickel, possibly because of the difference in polarization effects on these two metals.
Dec., 1 9 1 2
Anode.-As already indicated, the anode may be a platinum plate or spiral. The object in placing the anode above the cathode is to prevent the oxidation of the deposit b y the gases liberated by the current. It was found by experiment t h a t the rate of deposition was very much slower, and t h a t i t was almost impossible to get all the zinc out if the anode were placed by the side of and close t o the cathode. This is a n excellent confirmation of the theory pointed out b y one of us in an article elsewhere on oxidation processes a t the cathode.1 The solution should be cooled for the last 5-6 minutes, with ice if necessary, in order that the temperature of the liquid may not be above 2 5 ’ C., when the cathode is removed. At the moment of lowering the solution, the cathode is covered with a layer of KOH, which rapidly attacks the deposit if the temperature is above 2 5 ’ C. Some of the zinc would be dissolved and potassium zincate be formed. When the cathode is washed, most of this comes off and zinc is thus lost in the wash water. Even when the temperature is low some zinc is found in the washings, but the amount is fortunately small. On the other hand, the solution must not be cooled too long before the end, otherwise the character of thedeposit isaffected. The cathode must be washed thoroughly b y rotating it in water to get rid of the KOH. The water should be cold and the work should be done with despatch or a n appreciable amount of zinc hydroxide will be formed, thus invalidating the determination. The deposit should next be dipped into alcohol and finally thoroughly wet with ether t h a t has been dried over sodium. Washing with alcohol and ether alone will not remove all the KOH, and the results will be high if water is not used. The deposit should be immediately dried over a heated surface or free flame. The ether must not be allowed t o evaporate off in the air nor in a desiccator, else the metal, cooled below the temperatura of the surroundings, will be covered with a film of moisture t h a t will attack the deposit, form zinc hydroxide, and therefore increase the weight. This was shown experimentally by treating the previously dried and weighed deposits with ether, allowing them to stand in a desiccator until dry, and reweighing. Each treatment caused a n increase of from 2 to 6 tenths of a milligram. I t is unwise t o heat the deposit much above the temperature of the surroundings. If the ether is not recently dried and distilled it contains water and oxides that attack the freshly deposited zinc. It is obvious that the naked cathode should be treated in precisely the same manner before the electrolysis in which the deposit is t o be made as when the precipitation is completed. The endeavor was made t o prevent the loss of zinc in the wash water first, by siphoning off the KOH solution and gradually replacing i t with water; and second, by making the wash water a conductor with a few drops of KOH and allowing the current t o pass 1 “The Coprecipitation of Copper and Carbon by Electrolysis; Oxidation a t t h e Cathode.” Original Communications Eighth International Congress of Applied Chemistry, Vol. 21, P. 9 3 .
Dee.,
1912
T H E JOCR&\-AL O F I.\-DUSTRIAL
through while the cathode was being washed. The first method proved a failure because zinc is continuously redissolved, even during the passage of the current. A portion of this zinc was unavoidably siphoned off and lost. Employing the second method, we succeeded in getting all the zinc on the electrode, but the results were invariably from 2-4 mg. too high. This increase in weight was doubtless due t o the presence of zinc hydroxide formed by the action of water on the deposit. Our investigations embraced a large number of experiments and I 80 quantitative determinations. SUM 31A RY
.
I n this article we have introduced cerrain modifications of the potassium hydroxide method and shown t h a t it is reliable for the electrolytic determination of zinc. We have shown that this method entails a compensation of errors. A new cathode has been devised and recommended for use in electroanalysis. The following sources of errors have been investiga. ted and pointed out: I. The loss of zinc in the wash water, counterbalanced b y the formation o zinc hydroxide on the cathode. 2. The effect of air on a n exposed cathode. 3. The oxidation of the deposit by anode gases. 4. The effect of temperature a t the beginning and end of the electrolysis. j. The effect of ether containing water and oxides o n the deposit. 6. The high results obtained by letting the ether evaporate off the cathode in a desiccator. 7 . The presence of nitrates. LABORATORY OF INORGANIC CHEMISTRY, INSTITUTE O F TECHNOLOGY, MASSACHUSETTS BOSTOS.
THE KAMBARA EARTH. A DECOLORIZING MATERIAL FOR MINERAL OILS, ETC. By K. KOBAYASHI. Received Sept. 18, 1912.
The production of Kambara earth in Japan has greatly increased in the last three years. The chief source of the material is in the province of Echigo, though deposits of the earth belonging t o this class have also been found in other provinces. Now the Kambara earth is largely used as the decolorizing material for mineral oils, especially for neutral oil and lubricating oil. There are massive deposits of very pure Kambara earth near Uchikura River, three miles southeast of the city of Shibata, Kambara, Echigo. I have found two other deposits of the earth, one in the province of Fukushima, and the other in the province of Ishikawa. I have investigated this earth since 1892. and found that it belongs to the class of Fuller's earth in England and Florida earth in the United States of America. The Kambara earth in these deposits is simply dug out, dried in iron pans, ground with iron stamps, and used after levigation treatment. This Kambara earth
AA'D EiYGI-YEERIA'G CHEMISTRY.
89 1
occurs usually in massive state, with white or yellowish color, sometimes bluish or sometimes greenish. P H Y S I C A L AND C H E M I C A L P R O P E R T I E S O F T H E KAhIBARA EARTH.
Owtward Appearance.-The Kambara earth resembles hard wax, in the outward appearances, is soapy to the touch and is strongly detergent, absorbing grease and oil. I t is easily dissociated b y and miscible with water. A fine powder of the earth has no soapy feeling as the powder of steatite or soapstone has. The paste of the earth made with water shows no adhesiveness between particles. The decolorizing action of the earth may be promoted by heating i t t o 1oo0-1 j o o C. But if the earth is heated t o red heat, i t loses its combined water and a t the same time its suitability as a decolorizing agent is destroyed. (2) Degree of Fivleness of the Earth.-The Kambara earth consists of very fine particles of the earth and has no crystalline particles of quartz in it. The classification by sifting shows clearly this fact. (I)
Under 0.1-0.25 0.25-0.5 Above 0.1 mm. mm. mm. 0 . 5 mm. K a m b a r a e a r t h (Echigo). . . . . . K a m b a r a earth (Fukushima) . , , K a m b a r a earth (Ishikawa). , , . . Kaolin (Owari).. . . . . . . . . . . . . . Kaolin (Owari). . . . . . . . . . . . . . . Steatite (Harima) . . . . . . . . . . . . .
29.3 25.0 24.2 14.5 7.1 0.5
69.2 73.5 73.5 36.4 21.2 38.8
1.5 1 .5 2.3 23.6 35.5 38.5
0 0 0 25.5 26.2 22.2
From these results i t will be understood t h a t there is a great difference in fineness between Kambara earth and other kaolins. I t s suitability as a decolorizing agent, as a matter of fact, depends upon the degree of fineness. (3) The Chemical Composition of the Earth.-The following analysis shows the composition of the earth: K a m b a r a earth.
Percentages.
Echigo SiOz. . . . . . . . . . . . . . . . . 60.71 Al2O3.. . . . . . . . . . . . . . . 13 18 Fe20d.. . . . . . . . . . . . . . . 3.68 CaO . . . . . . . . . . . . . . . . . 0.62 MgO . . . . . . . . . . . . . . . 0.38 NaZO K20. . . . . . . . . 1.54 Loss o n ignition., 20.04 Loss on heaiing t o 110' c . . . . . . . . . . . . . . . . . . 14.72
+
.....
Clay.
.-
Fukushima. 63,li 13.2: 2.20 1.44 1.09 0.42 17.95
IshiStea. kawa. Kaolin. Kaolin. tite. 58.11 68.60 47 20 71.94 20 86 21.23 34.61 21.41 0.45 1.04 1 .oo 1 .os 0.56 0.10 0.31 0.21 1.20 0.23 0.42 0.26 0.50 0.75 0.52 0.58 5.01 7.93 16.17 18.58
11.41
10.37
. . . . . .
...
From the above analytical point of view, we cannot distinguish the Kambara earth from kaolin or steatite, but we can do it b y the determination of the hydrates of silica in it. According to Mr. D. T. Day, the analytical results on Fuller's earth and Florida earth are as follows: Fuller's earth. Yel!owish. SiOn.. . . . . . . . . . . . . . . . 59.37 Al?Oa., . . . . . . . . . . . . . . . 11.82 Feg03.. . . . . . . . . . . . . . . 6.27 C a O . . . . . . . . . . . . . . . . . . 6.17 MgO . . . . . . . . . . . . . . . . . . 2.09 Nan0 K20 . . . . . . . . . . 0.99 Loss o n ignition.. ...... 13.19
+
Fuller's earth. Bluish. 52.81 16.92 3.78 7.40 2.27 0.79 14.29
Florida earth. 56.73 27.78 3.21 0.81 0.64
.... 19.52
Dakota earth. 58.72 16.90 4 .OO 4.06 2.56 2.11 8.10
He defines Fuller's earth in the following words: "Fuller's earth seems to be a high percentage of silica, occasionally as much as from 6 j per cent. to 7 0 per
