A P . 7 1919
T H E J O U R N A L OF I N D U S T R I A L A N D E X G I J E E R I N G C H E M I S T R Y
for t h e mixture with no sodium was raised t o t h e same value as was obtained with t h e first ore. By this time, however, t h e mixes had been rotated for many hours in t h e kilns and had, therefore, become thoroughly pulverized. When we, therefore, ground t h e ore very fine before using it t h e results were likewise improved. T h e state of division is not, however, t h e sole factor in t h e difference between the two ores for we have worked with ore coarser t h a n t h e second and obtained excellent results. A more important factor appears t o be t h e ease with which t h e ore becomes pulverized in t h e kilns (hardness). I n view of t h e facts stated, we therefore made another set of experiments in which we used recovered and residual manganese dioxide with new potassium hydroxide. T h e former was obtained from t h e same manufacturer who had furnished US with t h e recovered alkali described in t h e second section. The ratio of alkali t o manganese dioxide was again 2 . 2 8 moles of t h e former t o one of t h e latter. When t h e old manganese dioxide, as we may call t h e material for brevity, was used just as it was received, it gave uniformly low yields-from 2 j per cent t o 3 5 per cent of t h e theoretical-while we should have obtained about 8; per cent. Since it is well known t h a t manganese dioxide absorbs (or perhaps combines with) relatively large amounts of caustic alkalies, we suspected t h a t t h e old dioxide might be contaminated with considerable sodium hydroxide. We therefore washed it very thoroughly with water and in some cases boiled it with dilute nitric acid. When t h e recovered and residual dioxide was fresh i t responded very well t o this treatment; material which had been kept for some time, and especially material which had dried out, was not much improved. These results point t o the conclusion t h a t i t was t h e absorbed sodium hydroxide which was responsible for t h e deteriorating of t h e dioxide and which becomes more difficult t o remove as the material dries out. Since the first section of the paper shows how large amounts of residual dioxide can be avoided and as it is not necessary to convert the manganate into permanganate by processes in which large amounts of dioxide are reprecipitated, it did not Seem necessary f o r us to follow up this point further. SUMMARY
I-It is found t h a t when manganese dioxide is heated with potassium hydroxide in a current of air t o produce potassium manganate, t h e reaction frequently stops before t h e maximum oxidation stage has been reached. This can be avoided by remoistening and reheating t h e mix; t h e use of moistened air also is helpful. 2-The yield of potassium manganate varies greatly with t h e proportion of potassi11m hydroxide in t h e mixes. At t h e temperatures a t which these exPeriments were carried out and with t h e pyrolusite used, practically all of t h e manganese dioxide is converted into manganate when 2 . 5 moles 'of potassium hydroxide are used for each mole of manganese dioxide. gPThe conclusions Of that in this mangani-manganates and not manganates are obtained
3 23
and t h a t t h e maximum yield attainable is, therefore, only 6 0 per cent is thus proved t o be incorrect. 4-Larger amounts of alkali, however, cause t h e manganate t o decompose into a mangani-manganate, similar to, if not identical with, t h a t postulated by Sackur. j-The substitution of sodium hydroxide for potassium hydroxide greatly lowers t h e yield if t h e proportions between alkali and manganese dioxide iiamed are employed. What t h e effect of other proportions would be is as yet undetermined. Care must be taken, therefore, not t o allow sodium t o accumulate in t h e recovered caustic when t h e operation is carried out continuously. 6-It is very important t o pulverize t h e ores very finely and t o keep them finely divided in t h e kilns in order t o obtain t h e highest possible yields. Some ores are more difficult t o handle in this respect t h a n are others. 7-The residual manganese dioxide sometimes deteriorates on repeated use. This may be caused b y absorption of impurities from t h e solution. If t h e dioxide before it has had time t o d r y out is thoroughly washed with water or boiled with dilute nitric acid, its effectiveness for t h e process may be restored. This work is t o be continued along the lines suggested. A number of similar problems connected with t h e preparation of barium manganate remain t o be solved and work on these has also been begun. KENT CHeMrCAL
UNIVERSITY OF CHICAGO CHICAGO, ILLINOIS
THE DETERMINATION OF ZINC AND COPPER IN GELATIN1 B y GEORGES. JAMIESON
Received October 2, 1918
One method used for t h e determination of zinc and copper in gelatin is based upon the destruction of t h e organic matter b y digestion with nitric and sulfuric acids.2 After t h e digestion is completed, water is added, and the is made 'lightly alkaline with ammonium hydroxide. Then a measured quantity of hydrochloric acid is added. T h e copper is precipitated as sulfide and filtered. T h e filter containing t h e copper sulfide is digested with nitric and sulfuric acids until a colorless solution is obtained. T h e copper is finally titrated by t h e well known iodide-thiosulfate method. When t h e hydrogen sulfide has been removed from t h e filtrate containing t h e zinc, ammonium chloride is added along with ammonium hydroxide t o make t h e solution alkaline. Enough hydrochloric acid is added t o render t h e solution acid t o methyl orange. After adding a large excess of sodium or ammonium acetate, t h e zinc is precipitated with hydrogen sulfide and filtered. T h e zinc sulfide is dissolved in hydroch~oric acid and the resulting filtrate is boiled to t h e hydrogen sulfide. A small amount of ferric chloride is added and a basic acetate precipitation is made in t h e usual manner in by permission of the Secretary of Agriculture. Methods of analysis, A . 0.A . C.,1916, 175.
1 Published 2
3 24
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
order t o separate any phosphates present from t h e zinc. The zinc is precipitated from the filtrate as sulfide and after filtration is ignited t o t h e oxide. It is well known t h a t t h e digestion of gelatin with nitric and sulfuric acids requires almost constant attention during t h e entire process which generally takes 2 hrs. and sometimes longer for completion. I n addition t o t h e digestion, t h e long analytical procedure makes the method unsatisfactory. Several years ago C. R. Smith decomposed gelatin with hydrochloric acid in connection with t h e determination of arsenic1 and suggested t h a t this method of decomposing gelatin could be used t o advantage for t h e determination of t h e other metals in place of t h e tedious digestion process. Mr. Smith and a number of other chemists have employed t h e hydrolysis method for t h e determination of zinc and copper in gelatin. Since t h e method of separating t h e zinc and copper from t h e hydrolyzed solution is somewhat different from t h a t employed in t h e digestion method, it will be briefly described. A small amount of magnesia mixture and a n excess of sodium phosphate solution are added along with enough ammonium hydroxide to make t h e hydrolyzed gelatin solution alkaline. Then the zinc and copper are precipitated together as sulfides and filtered. The crystalline precipitate of ammonium magnesium phosphate serves t o collect t h e metallic sulfides so t h a t they can be readily filtered. The precipitate is treated with a cold solution of I : I O hydrochloric acid which has been saturated with hydrogen sulfide in order t o dissolve t h e zinc sulfide and leave t h e copper sulfide on t h e filter. The zinc and t h e copper are determined as described above. It is believed t h a t t h e following method will be found much simpler t h a n those now used. The size of t h e sample taken for analysis varies from 2 0 t o 50 g., according t o t h e amount of zinc and copper present. The samples are weighed into 500 cc. beakers and treated with I O O cc. of water and 1 5 t o 3 0 cc. of hydrochloric acid, depending upon t h e amount of gelatin taken for analysis. The covered beakers are heated for a n hour or two on t h e steam bath. During t h e first part of t h e heating, t h e solutions are agitated several times in order t o loosen any lumps adhering t o t h e bottom of t h e beakers. After hydrolysis t h e solutions are made very slightly alkaline with ammonium hydroxide and allowed t o cool t o about 40' C. Then hydrogen sulfide is passed into t h e solutions for 2 min. While passing in t h e hydrogen sulfide, t h e solutions should be stirred several times with t h e delivery tube in order t o facilitate t h e separation of t h e sulfides in t h e form most suitable for filtration. When t h e sulfides have settled for about I O rnin., they are filtered on a 9 cm. filter and washed several times with a very dilute solution of colorless ammonium sulfide. The wash solution is prepared b y passing hydrogen sulfide for several minutes into 2 5 0 cc. of water which contains 0.5 cc. of I : I ammonium hydroxide. I n t h e case of high-grade gelatin it is recommended t h a t about 2.5 mg. of iron should be added t o t h e hydrolyzed gelatin before making t h e solution alkaline. 1
J . Assoc. Oficial Agr. Chemists, 121 1 (1915), 244.
Vol.
11,
No. 4
It is found t h a t t h e ferrous sulfide greatly facilitates t h e precipitation and t h e filtration of small quantities of zinc and copper sulfides. The iron is conveniently added in the form of a standard solution which contains 2.49 g. of ferrous sulfate in 1000 cc. (I cc. = 0.5 mg. of iron). If t h e directions given above are closely followed in making t h e hydrolyzed gelatin solution very slightly ammoniacal, there is no danger of leaving any weighable amount of copper sulfide dissolved in t h e ammonium sulfide in t h e filtrate. The sulfides are dissolved b y pouring a small quantity of very hot I : I nitric acid around t h e upper edge of t h e filters. The filters are washed very thoroughly with water a t room temperature. The filtrate is evaporated with I O cc. of I : 3 sulfuric acid until all t h e nitric acid is expelled. When the sulfuric acid is cool. 30 cc. of water are added, and t h e solution is filtered t o remove t h e silica. The filtrate, which should have a volume of' about I O O cc., is warmed t o about 50' C. and hydrogen sulfide is passed into t h e solution for a t least 5 min. in order t o precipitate t h e copper completely. The copper sulfide is filtered on a Gooch crucible and washed with hot water saturated with hydrogen sulfide. During t h e filtration and washing of t h e precipitate a very gentle suction is employed, otherwise there is t h e danger of having some of t h e copper sulfide pass through t h e crucible. When t h e washings have thoroughly drained, t h e Gooch crucible is placed inside of a porcelain crucible and dried over a small flame for a few minutes. Then t h e flame is gradually increased t o its capacity. At this point t h e outer crucible is removed and t h e Gooch crucible heated directly in t h e oxidizing part of t h e flame for 1 5 min. After cooling and weighing, t h e crucible is heated again as hot as possible for 5 min. more in order t o be certain t h a t all t h e copper is converted into t h e oxide. The filtrate containing t h e zinc is heated until t h e hydrogen sulfide is expelled. After adding about 5 cc. of ammonia in excess of t h a t required t o neutralize t h e sulfuric acid in t h e solution, 15 cc. of 50 per cent formic acid are added and a rapid stream of hydrogen sulfide is passed into t h e solution for 5 min. t o precipitate t h e zinc sulfide. It is important t o stir the solution with t h e delivery tube while passing in t h e hydrogen sulfide until t h e larger part of t h e zinc is precipitated. The solution containing t h e zinc sulfide is heated on t h e steam bath for about half an hour. The zinc sulfide is filtered on a Gooch crucible and washed with a 2 per cent solution of ammonium thiocyanate. During t h e filtration and washing of t h e precipitate, it is best t o use either no suction or at most a very slight suction. When all of the precipitate is in t h e crucible and t h e wash solution has largely run through, t h e suction is increased until i t is sufficient t o drain t h e crucible properly. The zinc sulfide is dried and ignited t o convert it into t h e oxide in t h e same manner as t h e copper sulfide is treated. After weighing, t h e crucibles containing t h e oxides of zinc and copper-are treated with hydrochloric acid, thoroughly washed with water, and ignited in order t o prepare t h e m for subsequent analyses. Several samples of commercial gelatins of various
Apr., 1919
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
grades were analyzed b y t h e hydrolysis method described above as well as by t h e digestion method for t h e sake of comparison. I n t h e digestion analyses i t should be noted t h a t t h e copper was determined b y weighing t h e oxide in place of t h e volumetric method given above. Also t h e zinc was precipitated as sulfide in the presence of ammonium Eormate and formic acid instead of ammonium acetate and acetic acid. I n confnrmity to t h e usual custom, the results of t h e analyses are stated in terms of milligrams of metal per kilo of gelatin or parts per million. HYDROLYSIS METHOD DIGESTION METHOD
cu p.m. NO. 1................ 1................ 1................ 2 2 3 3i:O 3.. 26.6 4 .............. 20.0 4 .............. 24.0 5 24.0 5.. 22.4 5 20.0
............... ............... .............. ............ .............. ............ ..............
Zn P.p.m. 1341.0 1341 .O 1341.0 126.0 128.0 96.4 104.0 64.0 56.0 77.9 80.3 80.3
cu Zn P . P . ~ . P . P . ~ . 1341 .O 1340.0
,. .. .. ..
3i:O 32.0 20.0 20.0 24.0 24.0
..
lii.0 3.4 96.4 68.0 56.0
80.3 80.3 76.0
The copper was separated b u t was not determined in Samples I a n d 2 because a t first it was intended only t o investigate the determination of zinc. I n order t o test the method further, measured quantities of standard solutions of zinc and copper were added t o weighed amounts of Sample 5 . T h e hydrolysis and analyses were made as described above with t h e following results: SAMPLP, TAKENCu Added
Grams
Mg.
Zn Added
Cu Found
Mg.
Mg.
Zn Found Mg.
It should be observed t h a t t h e amount of zinc and copper in 2 0 g. of Sample 5 gelatin as determined by averaging the results obtained by previous analysis. has been deducted from t h e results given above. The results obtained with these trial analyses show t h a t t h e method is accurate. I n order t o obtain satisfactory results, i t is most important t h a t the directions be followed in every detail. Furthermore, great care must be taken t o eliminate by filtration any non-volatile matter which may separate during t h e course of t h e analyses, before proceeding t o make t h e final precipitation of the zinc or copper sulfides. Also, t h e Gooch crucibles used must be prepared so t h a t they will not lose weight during the filtration and ignition of t h e sulfides. BUREAUOB CHGMISTRY DEPARTMENT OF AGRICUGTURE WASHINGTON, D. C.
THE DEOXYGENATING EFFECT OF THE EFFLUENT FROM THE MILES ACID PROCESS OF SEWAGE TREATMENT By F. W. MOHLMAN Received July 12, 1918
Experiments with t h e Miles acid process of sewage treatment were conducted a t t h e New Haven Sewage Experiment Station under t h e direction of Prof. C. E, A. Winslow, from June I, 1917, until May I, 1918,in comparison with three other processes which have been considered for New Haven conditions.’ 1
Eng. News Record, 79 (1917), 18.
325
Some very interesting facts were established during this work regarding t h e Miles acid process. The Miles patent, No. 1,134,280claims t h a t the Miles process “ ( I ) consists in introducing-an inorganic acid as the sole effective agent” and “(3) consists in introducing sulfurous acid into the sewage.” Sulfurous acid seems t o have a selective toxic action on bacteria which is more intense t h a n is obtained by the same hydrogen-ion concentration of sulfuric acid. The effect of the sulfurous acid is augmented by t h e germicidal power of the bisulfites formed from the bicarbonates. Therefore, from the standpoint of effective disinfection, sulfurous acid is preferable t o sulfuric. It also has the decided advantage of being cheaper, when made as needed, by burning sulfur or pyrites and conducting the gas into a part of the sewage, which can then be used for acidifying the remaining sewage. We have applied compressed sulfur dioxide t o t h e sewage as i t flowed into a settling t a n k through a galvanized iron pipe about 2 0 f t . long. The settling t a n k was 16 f t . long, 4 f t . wide, and 4 ft. deep. T h e detention period was 4 hrs. when treating 10,000 gal. of sewage per day. After acidification the sewage contains bisulfites a n d some free sulfurous acid. It also contains lime and magnesium soaps, which are attacked by the acid, liberating the free f a t t y acids. As the sewage passes through t h e tank, part of t h e bisulfites a n d sulfurous acid is oxidized t o bisulfates and sulfuric acid. I n t h e effluent there is a mixture of sulfurous acid, sulfuric acid, bisulfites, RHSO3 (R indicating S a , K, Ca, Mg, or Fe), and bisulfates, R H S 0 4 . T h e oxidation takes place a t t h e expense of t h e dissolved oxygen in t h e sewage, and some oxygen is also supplied by absorption of atmospheric oxygen from t h e surface of t h e liquid. The oxidation may easily be followed by determining total sulfur dioxide in both bisulfites and sulfurous acid by titration, using an excess of iodine solution. By titration with standard sodium hydroxide, using methyl orange as indicator, all of the sulfuric acid b u t only half of the sulfurous acid is determined. This is due t o t h e fact t h a t t h e reaction H z S 0 3 NaOH = N a H S 0 3 HzO takes place, and N a H S 0 3 reacts neutral t o methyl orange. T o get accurate results as t o the total acidity, all sulfurous acid should first be oxidized t o sulfuric acid or else the sulfur dioxide in the sulfurous acid must be determined. Titration with standard sodium hydroxide using phenolphthalein as indicator includes t h e acidity due t o bisulfites a s well as t h a t due t o sulfurous acid a n d sulfuric acid, as N a H S 0 3 reacts acid t o phenolphthalein. By a combination of the three titrations t h e exact state of oxidation of t h e sulfur dioxide may be followed. These facts must be remembered in determining t h e acidity of t h e Miles effluent, as erroneous results may be reported when titrating with methyl orange when the effluent contains unoxidized sulfur dioxide. We have usually attempted t o carry the free acidity t o 50 p. p. m. (as CaC03). Preliminary tests made on February 14, 1918, showed a total content of 118 p. p. m. of sulfur dioxide
+
+
