760
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 EIVGINEERIAVG C H E M I S T R Y
t i m e during which t h e oil is kept a t a given temperat u r e capable of producing t h e "cracking" effect. It is, therefore, obvious t h a t if there is a n y cracking i n t h e course of a distillation t h e r e should be twice a s much in t h e course of two, a n d t h a t successive distillations of t h e s a m e sample of petroleum should cause a progressive increase i n t h e percentage of constituents distilling below some given temperature. On t h i s basis t h e following procedure was a d o p t e d : A sample of oil was distilled i n t h e usual manner u p t o a given t e m p e r a t u r e , all t h e distillate being collected in a single t a r e d receiver. After stopping t h e distillation a n d letting t h e condenser drain, t h e a m o u n t distilled was determined b y weighing. I t was t h e n poured back i n t o t h e cooled distilling flask a n d another distillation conducted u p t o t h e same temperature. If cracking occurred i n t h e first distillation i t should also TABLEV I - E X P E R I M E S T S
TO
TESTF O R
"CRACKING"
GLASS Large bore GLASS UnconMedium bore stricted APPARATUS ( H E M P E L ) COPPERConstricted neck neck T e m p . OF vapor a t end of distillation 289' C. 312O C. 312' C. 325' C. a 57.0 65.0 64.8 70.1 64.8 69.6 P e r cent by weight ' h 56.z 64.5 65'3 70.0 of repeated distillations: 56.' 66.1 I d .... 66.7 66.2 .... e , ... .... 66.3 .. .. Residue (per c e n t ) . . . . . . . . . , . . . . . I . . 4 2 . 0 33.0 32.5 28.6 S u m of residue a n d last distillate.. . . . 9 8 . 7 99.7 98.8 98.6 Per cent loss . . . , . . . , , , , .. , , , . . . , . , , 1 . 3 0.3 1.2 1.4
h a v e occurred i n t h e second a n d t h e cut up t o t h e given t e m p e r a t u r e would be greater i n t h e second instance. T h e results of several of these experiments are given i n Table IrI. I t is obvious t h a t even u p t o 3 2 j 0 C. (uncorrected) there is n o appreciable a m o u n t of cracking with t h e sample of Pennsylvania crude oil employed. It is proposed in a later connection t o experiment furt h e r i n t h i s direction a n d learn t h e behavior of other typical crude oils. For t h e present, however, it seems sufficiently clear t h a t t h e reflux condensation in\-olved in t h e \-arious methods of efficient fractionation is not a source of danger in t h e production of cracking. CONCLUSIOIiS
A former paper shorn-ed t h e fundamental advantages of a method of efficient fractionation for t h e analytical distillation of petroleum. T h e present series of experiments has brought o u t t h e following facts: I-Comparisons of a large number of t y p e s of distilling a p p a r a t u s showed t h a t several (Glinsky, Young a n d T h o m a s , long pear, Le Bel-Henninger, Golodetz, Hempel, long rod a n d disk a n d evaporator) produce approximately equal results. 11-Of t h e several, t h e Hempel is easily first on t h e basis of mechanical a d v a n t a g e , t h e Glinsky, Young a n d T h o m a s a n d evaporator being t h e only ones comparable t o i t . 111-With t h e moderate r a t e of distillation employed for t h e fractionation of petroleum t h e dimensions of Hempel columns may v a r y widely, b o t h i n length a n d bore, with b u t slight effect on t h e results produced. 117-With columns of equal dimensions other mechanical factors are of minor importance. T h e size, shape a n d material of t h e distilling bulb h a v e no ap-. preciable influence. Glass beads are not as good me-
T'ol. 7 , S o . 9
chanically a s aluminum b u t t h e y a t t a i n t h e same degree of fractionation. T h e size of t h e initial charge of oil is of some slight importance on account of t h e introduction of variation t h r o u g h t h e lag of t h e liquid i n t h e condenser t u b e . T-Mechanical advantages seem t o be greatest for t h e one-piece glass a p p a r a t u s with unconstricted neck of I-in. bore a n d 6-in. length f r o m bulb t o outlet. CHEJllCAL S E C T I O S O F P E T R O L E L M DIVISION
u. s
BUREAUO F h1VIIKES.
PITTSBURGH
A COMPARISON OF METHODS FOR DETERMINING
PUTRESCIBILITY OR OXYGEN DEMAND By FRANK E. HALEA N D THOMAS W. MELIA
Received April 7 , 1915
T h e experiments described in t h i s paper were carried o u t a' year ago in connection with t h e work of t h e committee, headed b y D r . A r t h u r Lederer, appointed t o establish s t a n d a r d methods for Putrescibility or Oxygen D e m a n d of Sen-age,' etc. Pressure of routine work has prevented further experiments which we hoped t o make t o sustain t h e conclusions here presented. N o results are reliable as representative of p a r t s per million of oxygen required t o prevent putrescibility unless such results can be consistently obtained a n d are supported b y t h e results of different methods. This laboratory has for several years used 'the Dilution Method as described b y Jackson a n d Horton.' T h e essential features are dilution with aerated distilled water of known oxygen c o n t e n t , employment of methylene green, zinc double salt ( t h e q u a n t i t y originally specified corresponds t o t h e a m o u n t of methylene blue recently recommended b y Ledere? a s yielding best results a n d least antiseptic power), dilutions differing b y t w o volumes sufficient t o obtain one bottle remaining colored, use of medicine droppers inserted t h r o u g h one-hole rubber stoppers, incubation for four t o five d a y s , a n d noting t h e days a t which different dilutions become colorless. T h e original oxygen of t h e distilled water multiplied b y (one plus t h e highest dilution becoming colorless) equals t h e p . p. m. oxygen required t o prevent putrescibility. Our dilutions ha\-e been made in cylinders without preventing aeration of t h e sewage. I n t h e present work comparison was made betlyeen t h e above method, using b o t h distilled water a n d Brooklyn t a p water, t h e English Excess Oxygen Dilution Method with some modifications, a n d t h e Lederer S i t r a t e Method using excess nitrate. T h e bottles used in each case were of 3 0 0 cc. capacity. For t h e English method t h e bottles were filled with aerated distilled water through a funnel, keeping t h e funnel full, a n d overflowed t o half their volume t o , displace air a n d t h e first water coming in contact with air. T h e n 3 cc. of sewage were introduced undern e a t h b y pipette forcing out some distilled water. Afedicine droppers inserted through rubber s t o p p e r s were filled with t h e distilled water a n d inserted collapsed 2 3
T H I S JOCRKIL, 6 (1914). 8 8 i . I h i d . . 1 (1909), 328. i l m . J o u r . Pub. Health, 4 (1914). 241
T H E J O C R S d L OF I N D C S T R I A L A N D ENGI,VEERING C H E M I S T R Y
Sept., 191j
for 37' C. incubation, glass stoppers for 20' C. T h e r e was n o aeration of t h e diluted sewage. Bottles were filled with t h e liquids at room t e m p e r a t u r e . Several bottles were filled, oxygen determined a t once o n one, a n d t h e n on one every d a y . F o r t h e Lederer method a solution of sodium n i t r a t e was made a n d dilutions of t h i s m a d e i n t e s t t u b e s such I -ENGLISH 2-ENGLISH
METHOD-UNCORRECTED
-
M e t h o d upon I O cc. of t h e incubated sewage mixture. Medicine droppers inserted through r u b b e r stoppers were used. T h e results of t h i s comparison of methods are given in T a b l e I . Fig. I represents graphically t h e results obtained a t 3 j O C. incubation. Lederer' s t a t e s as a result of his experiments a n d also upon a u t h o r i t y of m a n y pre-workers t h a t t h e
~ETHOD-~ORRECTEO-\o/~~O~
WATER-DILUTION M E T H W
550-3-DlSTILLED 4
!
;61
5.50
B ~ ~ WATER ~ ~ ~ -DILUTION Y ~ METHOO.(NlTRATE-40X.
5oO-oXYGEN
BASIS
So0-5-KN03-40XYGEN
DEMAND
CORRECTED
--I
45 0
z
5
a
OXYGEN
n
D E M A N D --+\OO
COMPARISON OF ENGLISH, NITRATE E X C E S S I\HD DILUTION M E T H O D S
L
2
I2 3
-I
I
[
I
i--- 50 DAYS
4--5-
COWPARISON OF RES;LTS-UNCORRECTED AND CORRECTCO FOR OXYGEN L05T IN B L A N K S
0
o
i
z 5
4
S
G
,
t3
I
a
,
IO
,
t h a t I cc. added below t h e surface t o a bottle filled with sewage gave varying excess a m o u n t s of n i t r a t e . T h e bottles were filled b y siphoning t h e sewage from a large bottle a n d overflowing t o force o u t air and sewage i n contact with air. A t t h e e n d of j days' incubation a t 3 j o C. t h e n i t r a t e a n d nitrite were determined, t h e former b y t h e Phenolsulfonic Acid
n i t r a t e yields 2.j oxygen a t o m s for I nitrogen a t o m . Several years ago we noted t h a t less high dilutions were obtained with Brooklyn t a p water t h a n with distilled water b y t h e Dilution M e t h o d a n d t h e required a m o u n t of oxygen could be obtained only b y assuming t h a t 1
Jour. Infect. Dis., 11, May, 1914.
T H E J O U R N A L OF I N D U S T R I A L A N D EiYGINEERING C H E M I S T R Y
762
n i t r a t e yielded 4 oxygen a t o m s for I nitrogen a t o m i n accordance with t h e following e q u a t i o n :
HKOs
+ HzO
r u b b e r s t o p p e r , with glass s t o p p e r , with open t u b e s a s experimented with b y Phelps i n Ohio River investigations, a n d with open bottles, a t b o t h 37' C. a i d zoo C. T h e results shown i n T a b l e I1 were astonishi n g t o s a y t h e least. One would naturally assume t h a t a n open bottle would absorb oxygen from t h e air. I n every case oxygen was lost. S a t u r a t i o n a t t h e t e m p e r a t u r e a p p a r e n t l y h a d n o direct relationship although losses were usually greater a t 37' C. t h a n a t zoo C. T h e presence of r u b b e r did n o t a p p a r e n t l y explain t h e loss since t h e open bottle a n d glass stoppers also suffered serious losses. T h e r e a r e doubtless some
+
NH3 202 It m a y be assumed t h a t carbonic acid combines during t h e reduction with t h e alkali of t h e alkaline n i t r a t e s t o f o r m nitric acid so t h a t complete reaction would be expressed b y t h e following: 2KK03 H2C03 zHzO = K2C03 + 2NH3 4O? Analyses for a m m o n i a proved sufficient a m o u n t present t o confirm t h e reaction. T h e s a m e reaction h a s been n o t e d b y one of us' i n t h e utilization of t h e
+
=
+
Vol. 7 , No. g
+
TABLEI-PUTRESCIBILITY EXPERIMENTS: COMPARISON OF DIFFERENT METHODS(EXPRESSEDAS OXYGEK D E M A A D P. , P. hl.j Dilution method Brooklyn water Distilled water (Oxygen 10.8 p . p. m.) (Oxygen 8.53 p. p . m.) ( N i t r a t e used 0.45 g.) 370 c. 37' C. Time P. p. m. Dil. Oxygen p. p. m. D a y s Dil. oxygen Basis 2'12-1 4-1 I.... 15 136 12 155 165 2 . . . 25 222 18 215 229 3 . . . . 29 247 20 252 268 4 . . . 33 290 22 275 293 5 . . . . 37 324 24 300 319
English Excess Dilution M e t h o d (1-99 dilution of u n s a t u r a t e d sewage) (Oxygen used 30-60Yc> Oxygen a t s t a r t 9.01 p. p. m. 8.85 p. p. m. 37' C. 200 C. Uncor- CorUncorCorrected rected rected rected 300 140 20 0 399 209 142 100 451 261 19.5 138 536 316 298 236 241 179 569 349
Excess n i t r a t e m e t h o d (Ledererj 37' C. 1 cc. n i t r a t e solutions t o 300 cc. sewage Original oxygen introduced p . p. m. Basis 21/2-1 612 306 275 245 211 ~~~i~ 6 1 979 490 441 392 343
. . . . . . . 212
21/?-1 { BBasis a s.i s 4 1 . . . . . . . . .
192 307 i-15
339 +30
207 331
205 328 1 3
191 306
"ii;ii"'
Probable e r r o r ( a ) . . . -5 ... 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
,301
I . . . .
,z09
...................................................................................................... ............... ................ ...... ........................... 9............................................... ...... ....................... 10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...... ........................ 8. . . . . . . . . . . . . . . . . . . . . . . . .
214 252 265 27.1 281
322 130 33s
( a ) A s based o n n i t r a t e determination a t s t a r t a n d after 5 d a y s ' incubation.
oxygen of n i t r a t e i n corrosion of iron pipe b y water. Here t h e exact equivalent of a m m o n i a was recovered b y analysis t o meet t h e equation with corresponding reduction of n i t r a t e t o zero. As Lederer has worked mainly a t z o o C. t h e reaction m a y be different a t t h a t temperature. I t will be n o t e d i n Fig. 1 t h a t a ratio of 2 . 5 oxygen t o I nitrogen g i r e s results which are altogether too low, whereas a r a t i o of 4 oxygen t o I nitrogen gives results exactly corresponding with t h e dilution results of * 3 2 0 p . p . m. T h e curve with Brooklyn t a p water agrees v e r y well upon t h e 4 t o I assumption although t h e a m o u n t of n i t r a t e used is so small t h a t t h e effect is not very different f r o m t h a t caused b y t h e 2 , j t o r a t i o which gives 300 p. p. m. i n j days. T h e English method a p p a r e n t l y gave results almost twice as great ;is t h e Dilution h l e t h o d . Investigation was m a d e a s t o t h e cause of t h i s discrepancy a n d when I
O F SEWAGE USED IX T H E EXPERIMENTS OF TABLE I M a n h a t t a n Sewage f r o m Manhole a t 3 5 t h S t r e e t 8r 7 t h A v e . , District PARTSPER MILLION PARTSPERMILLIOX Nitrogen a s free a m m o n i a . . 72.7 Fixed solids. , . , , , , , . 1224 Nitrogen , a s albuminoid ammonia. . . . . . . . . . . . . . . 2 1. 3 0.016 Xitrogen as n i t r i t e . . , , , . , , . Xitrogen a s n i t r a t e . . . . . . . . 0.25 ,20 T o t a l solids . . . . . . . . . . . . . . 1489 Iron. . . . . . . . . . . . . . . . Loss on i g n i t i o n . . . . . . . . . . 265 Oxygen consumed .... 72
TABLE II-.~NALYSIS Source:
h - e w Y o r k City-Hotel
corrections are made for blanks r u n with distilled water these results also agree with t h e Dilution M e t h o d a s shom-n i n t h e corrected curve. W h e n a e r a t e d distilled water is bottled in t h e usual w a y without t h e addition of sewage, i n c u b a t e d a t 20' C. or 37' C. and oxygen determined, t h e r e is a loss of oxygen dependent u p o n t h e time of incubation, t e m p e r a t u r e of incubation, t y p e of stopper, a n d p r o b a b l y also a m o u n t of oxygen content. Comparisons were m a d e with t h e medicine dropper, with solid 1
A m . Jour. Pub. Health, S (1913), 1338.
physical phenomena accountable. Gas always collects under t h e stoppers a n d we believe t h a t a certain a m o u n t of oxygen is carried with i t a n d not reabsotbed until t h e oxygen content is nearly exhausted. Upon removing t h e stopper t o introduce reagents for oxygen determination in t h e English m e t h o d t h i s osygen gas TABLE III-PARTS
PER
3lILLION LOSS
I n c u b a t e d a t 3 i 0 C. Jackson's Rubber bulb pipette stopper Initial nays oxygen Loss Init. Loss 1. . . . . . 8 . 1 21.55
. . . .
3 : : : ; ; ::::: : : :: . . . . i::::;: i:;; ;:$; 5- . .. .. .. .. .. 16 22 .. 22 46 7 : i 9 11 .:3i 88 8 8.16
. . . . . 8.16 I . . . . . . 8.16 2 . . . . . 8.16 2
7.19
2.24 2.14 2.08
I:c;bated kt 20d C, 1 . . . . . . 8.12 0.33
. . 8.12 1.22 . 3 . . . . . 8.12 1.32 2..
::: : 1:. . !: 1: '
3. 3.. . . . . 3 . ., . 3. . . . . .
3.
,, ,.
8.16 8.16 8.16 8.16 8 .16
t1: . 4 2
1.42 1.42 1.14 1.16
7.79 1.38 1.38 7.!9 , . 19 I . 3 8
. . . .
. . . . . . . . . . . . "
"
7:i9 7.,9 7.79 z.79 I .79
0:59 0.59 0.59 0.59 0.61
OF
~ X u c E h -xpi D ~ ~ T ~ ~ \v*.rss L E D
Glass stopper I n i t . Loss
. . . . ..
. . . . , ,
. . . . 8116 0192 8.16 0.92 8.16 0.94 8.16 0 . 9 6 8.16 0.96
. . . .
8.12 8.12 8.12 8 '. 11 22 8.14 8.14 8.14 8.14 8.14
0.41 0.41 0.57 0 '. 55 77 0.57
0.57 0.57 0.5; 0.59
Phelps open t u b e Init.
Loss
0.40 0.40 0.49 0.56 0.56 i.79 1.38 7.79 1.40
Open bottle Init.
6.49 6.49 6.49 6.49 6.49
6.49 6.49 6.49 6.49 6.49
8 : i 2 1:92 8.12 I .Yj 8.12 4 . 3 1
8 . 1 2 3.87
6.49 6.49 6.49 h6 '. 4499
6.49 6.49 6.49 6.49
0.17 0.1; 0.24 0 '. 2244 f . 7 9 1.14 7.79 1.16
s:i2 i:is 8 . 12 1 . 5 9
. . . . .
. . . . .
0.49 0.49 0.56 0.56 0.57
. . . . . . . .
0.17 0.li 0.32 0 .' 3 2
. . . . . . . . . . .
. . . .
,
under t h e stopper is lost. T h e Phelps open t u b e lost oxygen like a n open bottle since reagents for oxygen . determination were introduced t h r o u g h t h e t u b e a n d a n y t r a p p e d oxygen iyas determined. I n t h e Dilution h l e t h o d oxygen is completely removed a n d a n y oxygen under t h e stopper reabsorbed. A t least if a n y oxygen were there t h e methylene green would show i t . Consequently no correction applies t o t h e Dilution LIethod. T h i s is also t r u e of t h e n i t r a t e m e t h o d since nitrate is not reduced until oxygen is gone. Together with t h e other collaborators of Dr. Lederer we endeavored t o carry t h r o u g h determinations b y t h e .
Sept., 191:
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,VGINEERING C H E M I S T R Y
English method a t different dilutions of sewage in a n endeavor t o find t h e best dilution, also if possible a percentage value a t j days t h a t could be calculated t o a complete absolute value. It was common experience among t h e collaborators t h a t different dilutions did not agree with each other. Fig. I 1 s h o m t w o such series upon t h e same sewage with values uncorrected a n d with values corrected. There is no sane reason why t h e results of different dilutions should not agree aside from errors of multiplication, t h a t is, a n y error with I per cent dilution would be three times as great in effect as t h e same error with 3 per cent dilution. We believe loss of oxygen errors account in great measure for these discrepancies with t h e English method. T h e corrected values on Fig. I 1 sho\\T closer agreement a t I O days t h a n t h e uncorrected \-alue. Agreement is not close at j days or other intermediate points. T h e reason for this m a y be t h a t oxygen loss m a y not t a k e place in the same degree or with t h e same rapidity with t h e different dilutions as v i t h distilled xmter alone. T h e z per cent values a t j days on Fig. I1 agree quite closely with DEYAND ESGLISH3fETIIOD Ratio of oxygen P.p. m . oxygen absorbed Days C) absorbed absorbed expressed as t o sewage of incuin diluted sewage in 5 : 10 days bation P.P m. Per cent Per cent Uncorrected Corrected 1'3% sewage in mixture. 20' C . incubation, 8.13 p. p. m. 0 a t start A B A B A B A B A B I . . . 0.08 0.09 . . . . . . . 24 2; 0 0 2 . . ,. . 0.44 0 . I; .. , , ., , 132 51 0 0 3 . . . . . 0.56 0 .3 5 .. , 168 I05 0 0 4 . .... 0.60 0.55 180 165 9 0 5 . . . . . 0.70 0.65 9 'S 63 63 210 195 19 24 6 . . . . . 0 . 7 5 0 . 7 4 . . . . . . . . 225 222 54 51 i . .. . . 0 . 8 4 0.83 . . . . . . 2.52 249 81 i8 8 . . . . 0.92 0.90 . . . . . . 276 2i0 I05 99 126 9 . . . . . 1.03 0.99 . . . . . . . 309 297 138 10 . . . . . 1 . 1 1 1 03 14 12 . . . 333 309 162 138
TABLE IV-OXYGEN
--------
1 9 sem:age in mixture, 20" C incubation, 8.05 p. p . m. 0.25 l . . . . . 0 30 . . . . 2 . . .. . 0.52 0.65 .. . . . .. 3.. . . 0.93 1.12 . . . . .. 93 154 4. . . 1 . 3 8 . . . .. 138 1.81 21 22 i4 i2 166 5.. . . 1 . 6 6 1 . 9 3 .. . . . . .. 191 6 . . . . 1.91 2.11 . . . .. 205 7 . . . 2.05 2.30 8 . ... . 2 . 1 6 .. . . . , . 216 2.46 .. , . ,. 219 9 . . . , 2.19 IO.. . .. 2.25 2.50 28 30 .. .. 225 "
;:
0 a t start. 0 25 65 112
154
181 193 211 230 246 250
0 36 81 109 134 148 159 162 168
0 8 55 97 124 136 154 173 189 193
27, sewage in mixture, 20' C . incubation, 8.01 p. p. m. 0 a t s t a r t 0 1. . . . . 0.41 0.44 . . . . . . 21 22 0 I4 2 . . . . 0 83 0.86 . . . . . . . . 42 43 13 1.12 . . . . . . . . 57 56 28 27 3. . . . . 1.14 . . 1.68 1,57 . . . . . . . . 84 i9 .i5 50 61 3 . . . . . 1.92 1.80 24 22 69 56 96 YO 67 84 6 . .. . . 2.01 2.26 . . . . . . . . 101 113 72 98 7 . . . . . 2.25 2.54 . . . . . . 113 127 84 112 8 . . . . . 2.48 2.82 . . . . . . . . 124 141 05 9 . .... 2.53 3.01 . . . , , . 127 152 'I8 123 10 . . . . . 2 . 8 0 3.2'2 35 40 . . . . 140 161 111 132 1 % sewage in mixture, 37' C. incubation, 8.30 p . p . m. 0 a t s t a r t 1....2.54 . . . . . . . . . 254 ... 94 .. 2 . . . . 3.62 . . . . . . . . . . 362 . . 172 . . . .. 58 .. 93 . . 485 ... 265 3 . . . . 4.85 ... 4 . . . . 4.88 . . . . . . . . . . 488 . . . 268 5 ..... 5,24 . 63 . . . . . . 524 . . . 304 S O T E - A a n d R are duplicates. Above tests on one sample of sewage
4..
each other a n d m-ith t h e 3 per cent value on Fig. I11 a t j days. Tht.se percentages feel t h e effect of t h e loss of oxygen least and approach nearer t o t h e prcscribed conditions in t h e English test. T h e English method specifies 3 0 t o 6 0 per cent consumption of oxygen in five days. Hom-ever. little prediction can be made as t o results when starting a test. I n t h e nine sets charted in Figs. I 1 and 111, only t h e t w o starred curves on Fig. I11 met this condition. Oniy a few of t h e results turned out as expected. Although t h e results on Fig. I11 are all corrected,
763
there is no agreement between t h e different percentages. This uncertainty of result b y t h e English method militates greatly against its usefulness. It appears t o offer the simplest of technique, b u t is exceedingly disappointing. I n Fig. ITTare shown results a t 3 7 " C. a n d a t 20" C. on three different sewages b y t h e English method, I per cent dilution, corrected values. More consistent results appear t o be obtained a t 3 7 " C., a s well as quicker results, t h a n a t 2 0 ' C. K e believe t h a t t h e standard methods for oxygen demand should be made at 3 7 ' C. More reliable results a n d quicker are t h u s obtained, a n d as t h e results in a n y case are empirical, comparison between laboratories will be closer. T h e results a t 20' C. DEMANDENGLISH METHOD P. p. In. Ratio oxygen absorbed exof oxygen pressed as t o sewage 0,absorbed absorbed ------D a y s of in diluted sewage in 5 : 10 days Unincubation P. p. m . Per cent Per cent corrected Corrected 1/3Y0 sewage in mixture, 20' C . incubation, 8.05 p . p. m . 0 a t s t a r t I ........ 0,95 ... 2 . . . . . . . . 1,35 ... 3 . . . . . . . . 1.75 ... 4 . . . . . . . . 2.05 5 . . . . . . . . 2.12 26 ' 5, 6 . , . . , . , , 2.16 .. .. . . . . . . . . . 2 . 18 .. ...
TABLEV-OXYGEN
8 . .......
2 20
..
9 . . , . ,.. , 2.10 ., 1 0 . . . . . . . . 2.25 28 1 % semape in mixture, 20' C. incubation, 8.05 p. p. m. 0 a t s t a r t 1 . .. . . . . . 0.95 .. 95 54 2 . . . . . . . . 1.45 .. 145 88 205 148 3 . , . . . . . . 2.05 .. 4 . . . . . . . . 2.53 .. 5 . . . . . . . . 2.82 35 . . . . . . 3 .03 I . . ...... 3.25 8... . . . . . 3.33 .. 9.. . . . . . . 3.35 .. 1 0 . .. . . . . . 3.35 42 3 j ; sewage in mixt:ure, 20' C. incubation, 8.05 P . P . m. 0 a t * t a r t 1 . . . . . . . . 1.23 .. 41 27 58 39 2 . . . . . . . . 1.75 .. 3 . . . . . . . . 2.05 ... 68 49 .. . . . . . . 2.50 .. ,.. 83 61 3 . .. . . . . . 2 . 8 1 35 79 94 13 ... 110 91 6 . ,. . . . . . 3.31 .. 7 . . . . . . . . 3.45 ... 115 96 .. 8 . . . . . . . . 3.52 .. ... 117 98 9.. . . . . . . 3.55 , . ... 118 99 10.. . . . . . . 3 . 5 7 44 ... 1I 9 100 1 % sewage in mixture. 37" C . incubation, 8.05 p. p . m. 0 a t s t a r t 1.. , , . , , , 2.63 .. ... 263 103 ... 363 li3 2 . . . . . . . . 3.63 3 . .. . . . . . 4.42 55 100 442 222 ?,.. . . . . . 4.43 ... 443 223 3 . . . . . . 4.43 55 ... 443 223
6.
1..
should be made special as applying t o a n y particular stream, possibly, as Hoover recommends, using open bottles or otherwise striving t o approach natural conditions, b u t for comparison between laboratories 3 'j C. seems far more advantageous. S U 31 1IA R Y
I-We believe t h a t t h e Dilution Method using methylene green, or methylene blue, is a t present t h e only reliable method for determining oxygen required t o prex-ent putrcscibility. The results of other nicthods. if rightly interpreted and corrected coincide. 11-Fil-e days a t 3 j " C. are preferable t o t e n days at 20" C. 111-Ground glass stoppers are preferable L O a n y other type. IY-The English method as a t present practiced is subject t o grave and uncertain errors; among t h e m loss of oxygen, a n d is therefore exceedingly unreliable. -1pparently other unexplainable variations occur.
7 64
T H E J O U R N A L O F I N D U S T R I A L AiVD E N G I N E E R I - V G C H E M I S T R Y
V-The Nitrate Method should be thoroughly investigated in comparison with the Dilution Method in order t o determine t h e amount of oxygen available from t h e nitrate both a t 3 j 0 C. a n d a t zoo C. I t appears possible t o develop considerable accuracy and obtain comparable results b y this method under proper conditions. b I T . PROSPECT LABORATORY, BROOKLYX, NEWYORK -~ ~
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MOLYBDIC ACID RECOVERY B y C . G. XRJISPROSG Received March 16, 1915
T h e large waste of molybdic acid and t h e difficulty experienced in obtaining t h e reagent pointed out t h e great need of a process for its recovery. Numerous methods were tried a n d cast aside on account of their impracticability or t h e unnecessary consumption of expensive reagents b u t finally a method. which is herewith described, was found, which is practical a n d simple: namely, t h e precipitation of t h e acid in H N 0 3 b y concentration, a n d its solution in ",OH, whereby t h e molybdic acid is obtained in a condition t o be readily used for t h e preparation of a new stock solution for phosphorus. PROCESS
On account of t h e fact t h a t phosphomolybdate precipitates are often added t o t h e waste molybdic acid residues in steel analysis, these should be filtered before t h e recovery process is commenced. This is most conveniently accomplislied b y means of a n asbestos suction filter. T h e filtered solution is t h e n placed in a five-liter German flask a n d supported inverted over a large evaporating dish on a sand bath, allowing b u t a small
Vol. 7, NO. 9
cold water, allow t o settle and decant. Wash t h e precipitate thoroughly a couple of times with water b y decantation t o remove t h e iron salts a n d treat with enough I : I S H 4 0 H t o fill t h e dish. A dark brown precipitate will form, due t o precipitated iron. T h e whole is then washed into a large flask, warmed slightly and allowed t o s t a n d a couple of hours with a n occasional shaking t o facilitate solution. When all is in solution, or after two hours, t h e liquid may be filtered off by a siphon, sand a n d asbestos, suction filter into another flask. Arrange t h e suction t u b e so t h a t the lower portion of t h e solution, containing the precipitate, will be t h e last t o come upon t h e filter, t h u s preventing troublesome clogging of t h e filter by t h e iron precipitate. Add j per cent of t h e original amount of N H 4 0 H t o t h e solution t o make u p for t h a t used in precipitating t h e iron. This solution contains t h e N o O s as ammonium molybdate a n d when t h e specific gravity of it is taken with a hydrometer a t z j C., b y referring t o accompanying cu ve t h e per cent of 1 1 0 0 3 present may be found and then t h e proper amount of fresh 11003 added t o bring the concentration u p t o 0 . 2 8 2 j g. per cc., which is t h e concentration of t h e precipitating solution for phosphorus. T h e solution of (NH1)2r\100d may be evaporated t o dryness and t h e n roasted a t 600' C. t o hIoO3, b u t this is impractical in most cases. T h e specific gravity curve was plotted from d a t a obtained b y making up solutions of different concentrations and using a pyknometer a t 2 j ' C. Various solutions were made u p t o test t h e curve a n d in each case t h e specific gravity indicated t h e per cent of Moo3 t o within 0 . 0 0 3 g. per cc. excepting in concentrations below 0 . 0 6 g. per cc.. which concentrations are seldom met with in actual practice. T h e solution of ( X H 4 ) 2 X l o 0 ,in I : I I\"IOH when ready t o mix with H N 0 3 has a concentration of 0 . 2 8 2 5 g. per cc. with a specific gravity of I . 2 0 ( 2 j o C.). This, when mixed with HNOs a n d water, constitutes the regular phosphorus precipitating solution. T h e recovery in these tests, which were carried out on large amounts of residues and under actual working conditions, was 93 per cent and the recovered molybdic acid obtained by evaporation a n d roasting a t 600' C. tested chemically pure in all cases (hlerck's reagents and their tests). T h e cost of recovery is practically nothing except for the gas a n d time, as no reagents are used which do not go t o make u p the working solution for phosphorus determinations. O
ENGINEERING EXPERIMENT STATION IOWASTATECOLLEGE. AMES
amount of t h e solution in t h e dish. This method allows a large amount of liquid t o be evaporated with little attention. T h e flask may be refilled until t h e precipitate of h/IOO3, which forms in the bottom of t h e evaporating dish, becomes too bulky. Remove t h e flask and evaporate the solution in the dish until it begins t o foam considerably a n d there is just enough solution left t o cover t h e precipitate a n d keep t h e iron in solution. Cool, dilute with one-half volume of
THE IODIDE METHOD APPLIED TO THE DETERMINATION OF COPPER IN THE PRESENCE OF TIN By ROBERTW. COLTMAN Received May 28, 1915
I n t h e determination of copper in a copper-tin alloy, t h e usual procedures involve a separation of t h e copper and tin. The most common method is t o decompose t h e alloy with nitric acid, whereby metastannic
