T H E J O L - K X A L O F I N D U S T R I A L A N D E-VGINEERIIVG C H E M I S T R Y
404
I n general, we secured consistent results. Once in a while anomalies would occur; t h a t is n-e would obtain results which were entirely out of harmony with t h e other values. These errors were mostly plus in character and were a t t r i b u t e d t o a n ununiform mixing of t h e sample of sewage. Rarely was a determination lost a n d t h e n only due t o carelessness or technical errors. Some samples went foul t h e third or fourth d a y when experience h a d shown t h a t t h e y contained enough nitrate t o keep t h e m sweet a t least I O days. These "freak" results were also attributed t o poor mixing of t h e sample, or t h e presence of a n undue a m o u n t of organic matter in suspension. In general, however, t h e method worked quite smoothly a n d gave consistent resu rs all through t h e work. Before t h e investigation began, some preliminary work in t h e laboratory mas done, t h e results of which strengthened t h e conclusions above noted. I n connection with other collaborators of D r . Lederer bn t h e English method, we endeavored t o find t h e best dilution a n d also a value a t j days from which t h e absolute value of oxygen demand could be calculated. This we found not t o be feasible. T h e results in Table I1 show n o agreement whatsoever in t h e carious dilutions. One would expect t h e error in a I per cent dilution n o t t o be a n y more t h a n twice as large as t h e error in a z per cent dilution. Our experience, as t h e table shox-s. has been contrary t o this supposition. X method whose results 1-ary so with each dilution employed requires. in our judgment; some further s t u d y in order t o determine t h e reason for t h e deviations. T A B L E 11-EFFECT
O F VARYING
Incubation a t 20' C.
-
P PI ..cent . . ...
nuvppn --~, ----
DILUTIONS OF S E W A G E 7 6 P P I f Oxygen a t S t a r t
Ratio
Sewage IncuAbsorbed in of Oxygen in bation Diluted Sewage Absorbed in Mixture D a y s P. P.&I. P e r cent 5 : 10 d a y s 0.4 5.55 0 36 0.00 0.0 i.90 0.6 0 6 7.90 ii Per cent 1 1 14.42 I .4 18.40 21.05 1.h 8 21 " 0 5 1.6 21 . 0 5 9 1.6 10 21 .0.i 1.6 1 21.05 1.00 1.6 21.05 1.6 21.05 .. 1.6 21.05 1.6 ?1,05 51 Per cent 1.6 28.94 2.2 2.2 28.94 .. 2.6 34.21 9 2.6 .. 34.21 .. 10 3.1 40.79 50.00 3.8 2.00 6 0 . 5 2 .. 4.6 67.10 ., 5.1 J 1 71.05 43 P e r cent 5.6 73 68 76.31 .. 5.8 76.31 .. 5.8 J 8 . 34 .. i. 8 76.94 .. 6.0 10 i8.94 6.0
Oxygen Absorbed (Basis of Sewage) P . P. Lf. P e r cent 111.1 5.25 11l.i 2,25 166.6 i .89 166.6 7.89 305.5 14.47 51 1 . 1 24.20 58'4.0 27.66 584.0 27.66 584.0 27.66 584.0 27.66 222.2 10.54 222.2 10.54 222.2 10.54 222.2 10.54 222.2 10.54 14.47 305.8 305.8 11.47 361.3 11.20 361,3 17.20 20.40 431.0 10.00 211.0 12.10 255.5 13.43 283,2 14.20 299.5 14.72 310.3 322.2 15.56 15.56 322.2 15.56 322.2 333.5 15.80 15.80 333.5
Using a known sewage, comparisons of both methods of procedure of t h e nitrate method were made. T h e results contained in Table I11 confirm those published b y Ledeyer.' Those in M e t h o d A were obtained b y adding varying quantities of SaN03 t o t h e sewage, a n d noting t h e one which just remained sweet. Those in M e t h o d B were obtained by adding a n excess of N a N 0 3 and 0.4 cc. methylene blue t o just one bottle of sewage. All determinations n-ere made after I O 1
J , Infect D i s . , 14, 485.
5'01. 8 ,
NO.j
days' incubation a t zoo C. in zjo cc. glass stoppered bottles. T A B L E 111-OXYGEN
A-By B-By Trial No. Method A , . . . . . . . . Method B . . . . . . , , ,
DEHAYD
(P. P. M.)
adding excess iYaNOs adding 10 cc. NaNOs 1 2 3 4 300 265 250 310 310 270 248 308
BY N I T R A T E M E T H O D
(26.56 g. per liter) 5 6 8 7 287 326 297 269 290 320 300 265
9
307 310
IO 278 275
T h e agreement in Table 111 shows t h a t t h e excess of S a S 0 3does not affect t h e biologic process upon which t h e loss of oxygen depends. From this we decided t h a t t h e addition of excess N a S 0 3 t o t h e sewage would give us as reliable results as t h e use of varying concentrations would. I n order t o see whether t h e two methods, t h e excess nitrate and. t h e dilution method, gave results of close agreement, t h e two were tried on a known sewage. For t h e dilutions! aerated distilled water with a temperature of 20' C. Tvas used: 2jo cc. bottles were filled t o overflowing and 3 cc. of sewage added near t h e b o t t o m of t h e bottle. After mixing t h e y were incubated for IO days a t z o o C. T h e Rideal a n d Stewart' procedure was used. Thirty-five per cent of t h e oxygen was absorbed a t t h e end of I O days. T A B L E I ~ ~ - c O M P , A R I S O N OF O X Y C B N DEXAND (P. P . 31.) BY T H E N I T R A T E AND T H E DILUTIONb 1 E r H O D S . I N C U R A T I N G AT 20'
c.
Trial h-0. 1 7 3
26 h
9 10
Dilution Method 305 298 301 310 302 285 297 289 300 294
Trial Dilution KO. Method 11 293 12 298 13 307 14 290 15 310 288 296 18 298 19 302 20 289
Nitrate Method 301 285 299 312 304 283 294 285 298 291
;$
Nitrate
Method 298 296 303 285 306 295 300 293 299 294
A%sidefrom t h e fact t h a t t h e nitrate results are consistently lower t h a n t h e dilution results, t h e t w o determinations agree fairly well. In fact, they agree well enough for all practical purposes, and strengthened us in our decision t h a t t h e nitrate method would give satisfactory results in t h e field; also they are i n strict accord viith those obtained b y Lederer.2 Furthermore, our experience has confirmed this decision, a n d after a year's trial, we conclude t h a t t h e nitrate method is far better adapted t o field work t h a n t h e modified English dilution method. WATZRAND SEWAGE LABORATORY KANSAS.L.4WRENCE
U N I V E R S I T Y OF
A COMPARISON OF THE PERMANGANATE METHODS FOR THE DETERMINATION OF REQUIRED OXYGEN By
JOHN
H. SACHS
Received December 3, 1915
As t h e determination of required oxygen is of very great3 importance i n t h e examination of waters, i t was thought t h a t it would be well t o look into t h e methods in use for t h e same a n d t o choose from among t h e m t h e one t h a t seemed t o give t h e best results. I t was realized a t t h e s t a r t t h a t the method is n o t quantitative, a n d t h a t t h e results obtained are only comparative. On t h e other hand, were a large number of waters examined in exactly t h e same way, t h e 1 Analyst,
a6 (1901), 141. czt a Fleck, Z. angew. Chem.. 1889, 580. 2 LOC
M a y , 1916
THE JO U R N A L 0F I .!IT D U S T RI A L A D E Y G I S E E RIiVG C H E M I S T R Y
results would surely show t h e relative quantities of oxidizable matter present. As early as 18j1, Forschammerl began using a dilute solution of potassium permanganate for t h e oxidation. H e proceeded b y simply adding this t o one liter of t h e water under examination until a faint pink color persisted for one-half hour. F r o m this method has sprung t h e m a n y methods now in use. These methods m a y be divided into t w o classes: ( I ) O x i d a t i o n iia acid solution; (2) O x i d a t i o f z in alkalilze solution. These methods have been further modified according t o t h e time t a k e n for t h e oxidation, t h e temperature a t which t h e oxidation is carried out a n d t h e a m o u n t of permanganate used for t h e oxidation. OXIDATION I N ACID SOLUTION
405
flask of 300 cc. capacity. One-half cc. NaOH solution ( 2 : I ) is added and from a burette I O cc. of standard permanganate. After boiling I O min. the contents of the flask are cooled to 50-60'. 50 cc. H2S04( I : 3 ) are then added and from a burette I O cc. of a standard solution of oxalic acid. The procedure from this point is similar to that of the Kuhel method. E XP E RI 11E N T.4 L
To choose from among these methods t h e following series of determinations were carried o u t , using water solutions of certain organic compounds. T h e solution of permanganate used was of such a strength t h a t I
cc. =
0.1
mg. available oxygen.
+ +
ACID SOLUTION-^^^ cc. water 15 cc. KMnOa 3 10 cc. NzS04 ( I : 3) ALKALINESOLUTION-^^^ cc. water 15 cc. KMnO: - 1 cr. S a O H ( 1 : 1)
TRBATMEXTS Alkaline I Roiled in Brlenmeyer beaker 10 minutes (Kubel) . . . , . . , . . V I1 Heated In Erlenmeyer beaker 35' for 1 h o u r . . . . , . . , . , . . VI I11 I n c u b a t e d i n closed flask 37' for 3 hours ( T h r e s h ) , . . , , , . . VI1 1V Allowed t o s t a n d in closed flask a t ordinary temperature for 3 hours ( T i d y ) . . , , . , , . . . : , , , . . . , , , , , , . . . , , , , , , . , VI11 Acid
.
The K U B E L ~method is as follows: To zoo cc. of the water to be examined there are added IO cc. of dilute HzS04 ( I : 3 ) . To this, when heated to boiling, there is added from a burette After treating as above, t h e flasks were quickly a standard dilute solution of the permanganate until a decided red color remains, The boiling is continued ten minutes with cooled t o 10-1 j '. T h e alkaline solutions were acidithe addition oi more permanganate if the color tends to fade fied with H2S04. An excess of KI was added and t h e out. Standard oxalic acid solution is then added until the iodine liberated t i t r a t e d with thiosulfate. Both t h e pink color has completely disappeared. The excess of oxalic thiosulfate a n d t h e permanganate solutions mere acid is then titrated with the standard permanganate solution. frequently standardized. T h e results, expressed in The difference between the total amount of permanganate used mg., of oxygen consumed by I O O cc. of t h e water and the permanganate equivalent to the oxalic acid added, are given in Table I. gives the amount of permanganate reduced. Correction must T.~BLE I Results in Mg. Oxygen Consumed per 10'0cc. W a t e r be made for ferrous salts, nitrites or hydrogen sulfide, if they k 1 D SOl,CTIONS AL,KALIX$ So~urioss be present. Treatment: I 11 111 117 v \'I VI1 VI11 KOBRICH~ recommends that the permanganate solution be 1 Lactose . . . . . . . , , , , , 0.547 0.592 0.110 0.033 0.505 0.473 0.309 0.272 Glucose , . . . . . . , , , 0.641 0.652 0.054 0.027 0.587 0.641 0.543 0.415 made by dissolving 0.5 g. of the salt in one liter of water; 11 Sucrose , . , . . , , , . . , , 0.783 0.739 0.096 0.020 0.620 0.636 0.488 0.317 after the addition of 150 cc. pure concentrated H2S04, the 1 Urea . . . . . , . . , . . , 0.086 0.092 0.023 0.01; 0.081 0.083 0.038 0.040 1 Dried Egg A l b . . . , , 0.400 0.483 0.156 0.173 0.415 0.461 0.161 whole is heated at 90' for 3 hrs. in a flask with a long neck. 1 S t a r c h , , . . . . ., . , . , , , 0.571 0.334 0.027 0.016 0.41.5 0.312 0.254 0.178 0.108 1 A g a r . . . . . , , . . . . . , , , 0.613 0.505 0.046 0.035 0.397 0.402 0.161 0.127 The solution is then standardized with oxalic acid. 100 cc. 1 Gelatine . , . , . . . , . . . . 0.119 0.178 0.037 0.033 0.359 0.312 0.175 0.119 of the water to be tested are then mixed with jo cc. of the per- 1 Dried M i l k . . . . . , . . , , 0.6000.537 0.072 0.028 0.524 0.520 0.236 0.212 Dried E g g Alb.. , , , , 0.908 1.100 0.577 0.484 0.923 0.953 0.496 0.358 manganate solution and 15 cc. H2S04. This is heated in the 55 Gelatine ... . , , , 0.242 0,552 0,100 0.077 0.808 0.729 0.407 0.442 5 Lactose . . . . . . .. , 1.500 1,500 0.138 0.033 1.183 1.131 1.050 0.888 same kind of flask as was used above a t 90' for 3 hrs. He points out that chlorides must be removed and corrections It is a t once seen t h a t a t t h e high temperatures made for nitrites present. t h e most oxygen is consumed. It will also be noticed TIDY'S4 process differs from the rest in that the oxidation is t h a t there is little difference in t h e results a t X j a n d carried out at ordinary temperatures. He recommends the use of 250 cc. of the water; to this is added IO cc. HzSOI and 100'. At t h e lower temperatures, especially in t h e I O cc. KMn04. After standing in a stoppered bottle for 3 acid solutions, t h e consumption of oxygen is much hrs. a t ordinary room temperature an excess of KI solution smaller. I n almost every case t h e oxygen consumed is added, and the iodine liberated titrated with 'thiosulfate. a t ordinary temperatures is less t h a n t h a t consumed A blank experiment in which recently distilled water is used is a t 37'. I n Methods VI1 a n d VI11 t h e solution usually also made. took on a green color, due t o t h e formation of K?MnO4. THRESH'S' METHOD--2jO cc. of the water to be examined are These methods were, therefore, discarded. In Methods measured in a flask fitted with a stopper. To this are added I O V and VI there was usually a larger q u a n t i t y of t h e CC. HzS04 and I O cc. of a permanganate solution, of such strength M n 0 2 separated t h a n in any other method. This' that I cc. = 0.1 m g . available oxygen. The stopper is then acts catalytically t o reduce more K,14n04. GriinhutZ inserted and the flask with its contents incubated for 3 hrs. at 37 '. If the pink color tends to face out, more of the perman- has shown t h a t t h e presence of M n in water introganate solution is added. After 3 hrs. the flask is cooled, duces quite a n error by these methods. For these reasons t h e alkaline methods were discarded. I cc. of a 5 per cent K I solution added and the iodine liberated Another set of experiments was then arranged in is titrated with thiosulfate. While the water to be tested is incubating, a blank test is run. The ferrous salts, nitrites, which t h e oxidation of I O O cc. of water was carried o u t etc., are a t first determined by finding horn much oxygen is in Erlenmeyer flasks t w o ways: ( I ) heating for I hr. consumed in j min. a t 37'. Here'the a t 8 j " , and ( 2 ) incubating for 3 hrs. a t 3 7 ' . OXIDATIOX IX ALKALINE SOLUTION amount of K?MnO4 was r a r i e d . T h e results of these SC€IULzE'S6 PROCESS-100 cc. of the water are placed in a experiments are shown in Table 11. Fresenius, Z . anal. Chem., 2 (1863), 425. F r o m these results, it can be seen t h a t a t t h e higher Braun, I b i d . , 6 (1867). 253. temperatures t h e more K I I n O a used for t h e oxidation, 'I Kobrich, Chew.-Zlg., 11, 4. t h e more oxygen is consumed. At 37' there is little Tidy, J . Chem. SOC., 35 (1879), 66. ,
, , , ,
, , , ,
,
,
, , , , , l . .
j
Thresh, "Examination of W a t e r a n d Water Supplies," 1913, 309. T r o m m s d c r f f , Z . anal. Chem.. 8 (1869). 350.
I 2
,
S c l l , Z. angew. Chem., 24 (19 I I ) , 1509. G r u n h u t , Z . anal. Chem., 62 (1913), 36
T H E J O U R N A L O F I N D U S T R I A L A N D ELVGINEERIATrGC H E M I S T R E -
406
TABLEI1 Results in Mg. Oxygen Consumed per 1013 cc. Water 1 Hour-85‘ KbfnOa Solution: 15 cc. 5 Gelatine ........................ 0.552 5 Dried Egg Alb.. . . . . . . . . . . . . . . . . 1.100 5 Dried Milk . . 1.500 Sewage No. 2. .................... Sewage No. 3 ..................... City t a p water. . . 3 Hours-37 5 G e l a t i n e . . .....
20cc. 0.697 1.293 1.850
. . 0.372
1.228 1.082
1.415 1.280 0.440
0.100 0.549
0.103 0.539
S e w a g e N o . 1 . .................... Sewage No. 2 ..................... Sewage No. 3 ........... City tap w a t e r . . . . . . . . . . . . . . . . . . . .
0.426 0.435 0.455 0.155
25 cc. 30 cc. 40 cc. 0.821 0.872 0,952 1.425 1.526 1 . 7 9 0 2.142 2.336 ‘2.706 1 . 5 8 8 1.786 2.094 1 . 5 3 0 1.655 1 . 7 3 0 1.422 1.605 1.675 0 461 0.482 0 527
0.108 0.565 0.490 0.452 0.444 0 , 4 6 0 0.440 0,633 0.490 0 . 1 6 0 0.162
0.123 0.618 0.494 0.459 0.473 0.482 0.178
0.140 0.670 0.477 0,431 0.453 0.473 0.182
difference in this respect. This makes i t quite clear t h a t in comparing results of oxygen consumed a t high temperatures, only those results can be compared t h a t are obtained by a method in which t h e same amount of permanganate is used for t h e oxidation. This is a very i m p o r t a n t point. However, a t 3 7 O , the a m o u n t of K M n 0 4 used for t h e oxidation plays n o large p a r t a n d hence such results can be compared no m a t t e r whether or not t h e same amount of permanganate is used. Although t h e presence of chlorides interferes with t h e determination of oxygen required in acid solution, t h e 37’ acid solution method of Thresh seems best. T h e chlorides can be readily removed b y AgzO a n d hence offer no great difficulty. CITY
HEALTI
