July, 1916
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
protuberances on a hypha as if it had started t o branch a t various places: these are very irregular in shape b u t usually quite short and broad a t some places and narrower in others: there is little protoplasmic content in t h e hyphae where t h e growth is considerably stunted. il number of scattered oil globules may be all t h a t can be seen. There is no slimy protoplasm in many of t h e hyphae and the branches often appear t o be merely e m p t y cell walls. I n other hyphae there is evident plasmolysis resulting in a shrunken protoplast. I t has not been determined whether the morphology of t h e bacteria is changed when these are grown on or near a spiced medium. B . prodigiosus fails t o produce a n y pigment if t h e amount of spice is large. Although several transfers of this colorless growth are grown on spice, when the organism is transferred again t o a medium without spice, t h e pigment is produced as before. It does not appear from the extent of t h e present s t u d y t h a t spices, as used in t h e kitchen, in t h e usual amounts for flavoring purposes in spiced cakes, exert a very considerable preservative effect. Where cinnamon, cloves, and allspice are used in large amounts, t h e growth of molds may be retarded. I n spiced fruit where a large amount of t h e spice is used, the preservative effect may be much greater. This effect may be greater too when t h e spice is combined with vinegar. I t seems entirely possible, as suggested b y Hoffman and Evans, t h a t t h e active principles, a t least cinnamic aldehyde, could be used in such dilutions as t o prevent t h e growth of many microorganisms and yet in small enough quantities not t o spoil t h e flavor of .the product. Further studies on t h e action of spices on microorganisms are necessary before very positive a n d general statements of t h e practical value of t h e m as preservatives can be made. Pepper a n d nutmeg have little effect on t h e growth of microorganisms. A mixture of nutmeg and water boiled for a half hour and left exposed t o t h e air for chance inoculation was covered with various molds in less t h a n a week. Cloves and allspice in large amounts are quite effective in preventing t h e growth of molds and bacteria, a n d cinnamon is the most effective of t h e spices; this is true of t h e ground spices, their essential oils, a n d t h e alcoholic extracts. T h e bacteria used in this s t u d y are less sensitive for t h e most part t h a n t h e molds, b u t there is evidently considerable difference in t h e sensitiveness of various species of bacteria just as there is a difference in t h e sensitive,ness of molds. BACTERIOLOGY LABORATORY, AGRICULTURAL COLLEGE MADISON,WISCONSIN
SEPARATION AND ESTIMATION OF POLYSULFIDES AND THIOSULFATE I N LIME-SULFUR SOLUTIONS B y S. D. AVERITT Received March 27, 1916
I n recent years there have been quite a number of articles written on t h e composition and analysis of lime-sulfur solution. The writer first became interested in t h e problem in 1 9 1 1 when he was Associate Referee on Insecticides for t h e Association of Official
623
Agricultural Chemists. Methods for t h e analysis of lime-sulfur solution were then being considered a n d cooperative work being done. The methods' proposed b y t h e Referee a t t h a t time have since become known as the Zinc Chloride Methods. I n January of t h a t year there was issued by t h e Michigan Agricultural Experiment Station a bullet i n b y J . E. Harris in which were published methods for the analysis of lime-sulfur solution since become known as t h e Iodine Methods.2 After having worked t h e two samples of lime-sulfur submitted for cooperative work b y both methods it was found t h a t there was a marked discrepancy between t h e thiosulfate figures b y t h e t w o methods. One of t h e samples submitted was a straight limesulfur solution made with pure chemicals and the calcium calculated from the iodine titrations checked t h e determined calcium. The other sample had sodium thiosulfate added a n d the calculated a n d determined calcium would not check until t h e added sodium thiosulfate had been deducted from t h e thiosulfate figure. I n the case of the straight lime-sulfur solution, using the thiosulfate as determined b y t h e proposed methods (zinc chloride) the calculated calcium would not check t h e determined calcium. The proposed methods gave concordant results, however, and it was recommended t h a t they be made official. This recommendation was approved for final action b y t h e Association the following year. T h e next year (1912), as Referee, t h e writer in his report3 brought out t h e facts in regard t o t h e t w o methods, having first satisfied himself t h a t t h e iodine titration methods gave accurate results for thiosulfate. The Association instructed t h e Referee t o compare t h e two methods in 1913. This was done, and in his next report4 more evidence was submitted in favor of t h e iodine titration methods. There was strong opposition5 t o t h e iodine methods, however, with t h e result t h a t there are a t this time no official methods for t h e analysis of commercial lime-sulfur solutions. Taking t h e position t h a t it is desirable t h a t methods of analysis should not only be accurate b u t t h a t t h e y should possess in addition, workableness, freedom from tediousness, and as far as possible give a t least a measure of insight into the character of the substance under examination, t h e writer in this paper hopes t o make a contribution t h a t will a t least tend t o sol~7et h e problems in the analysis of commercial lime-sulfur solutions. The direct iodine titration of a lime-sulfur solution meets all of the above requirements, and while t h e zinc chloride methods may be so modified as t o give accurate results, they can never be freed from tediousness and t o the busy analyst this is a n objection t h a t 1 f
3
4
3
p. 76.
Bureau of Chemistry, Bull. 152, p. 68. Michigan Experiment Station, Tech. Bull. 6. Bureau of Chemistry, Bull. 162, p. 27. Jour. A . 0 . A . C., 1, h'o. 1, p . 59. Bureau of Chemistry, Bul!. 162, p. 38; Jour. A . 0. A . C . , I, So. I,
T H E J O C R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
624
weighs heavily against them. Consequently he will invariably resort t o rapid methods even if their use inirolves a reasonably negligible loss of accuracy. Without reviewing t h e substances t h a t may possibly occur on boiling lime and sulfur of different degrees of purity in widely varying proportions with different kinds and amounts of water, it is sufficient t o state t h a t in commercial concentrates as sold upon t h e market t h e main constituents are calcium polysulfides and calcium thiosulfate. The other things are present in traces or very small quantities. The total sulfur is easily and accurately determined, thus leaving the accurate determination of polysulfide and thiosulfate sulfur as the main problems. Of these, t h e determination of thiosulfate sulfur is t h e more important since with a n accurate determination of total sulfur the polysulfide b y difference is sufficiently accurate for all practical purposes. A quick method for t h e determination of polysulfide is gi\.-en and if t h e total sulfur is taken as the s u m of polysulfide and thiosulfate, t h e analysis of a commercial lime-sulfur solution becomes a matter of two hours or less with a surprisingly small amount of manipulation. T h e wrjter believes from his experience t h a t more accurate or at least just as accurate analyses are obtained as by the ionger methods. SEPARATIOK O F POLYSULFIDE AKD THIOSULFATE SULFUR
A K D THEIR
DETERNIXATION IS
LIIIE-SULFUR
I n this investigation several interesting and important facts were developed. The one of prime importance is t h a t hydrogen sulfide may be boiled off from a very slightly acid solutior, without decomposing t h e thiosulfate, thereby rendering its subsequent titration n-ith iodine possible. Kexi in importance is t h e fact t h a t an excess of soluble sulfide (,3!a2S) will convert tetrathionate into thiosulfate as follows: CaS4O6 Xa,S = CaS203 I\ja2S203-k S This is a me11 known reaction and affords a means of determining t h c tctrathionate formed in the titration of a. thiosulfate as t h e excess of added sulfide may bc deconiposed with r e a k hydrochloric acid using methyl orange o r methyl red as indicator. The hydrogcn sulfide is then boiled off the solution cooled and titratcd with iodine. Chapinl makes use of tetrathionate t o determine sulfides. The n1,ov-e reaction is just the reverse. Standard S a 2 S could be used b u t the x-riter foslnd some difficulty with the end-point and thou-ght it best i o add a n excess and decompose it n-ith HCi, as already described, and boil off the hydrogen sulfide. *knother observation of considerabie importance was t h a t with certain limitations sodium nitroprusside could be used as an internal indicator for sulfides with a remarkable degree of accuracy.
+
+
~
D E T E R RII N
TI0 N 0 F T H I O SU I,E A T E S U L P U R
AXALYSIS-From j to g. of the lime-sulfur solution, depending upon concentration, are accuratcly weighed and made t o P R E P A R A T I O X O F SALIPLE F O R
20
1
Twis
JOWRKAL,
8 (191h), 151.
Vol. 8, No. 7
2 0 0 cc. in a graduated flask with freshly boiled and cooled distilled water well mixed and transferred t o small bottles, filling t h e m full and sealing. These may be kept as long as necessary, opening t h e m when needed for analysis. Aliquots of I O cc. are used for the determinations.
DESCRIPTION
OF X E T H O D S
Four methods were employed in this investigation, two of which have not heretofore been used, so far as the writer is able t o learn from the literature upon t h e subject. These methods will be designated as A, B, C and D. METHOD A--This was essentially the method of Harris by direct titration with iodine. Ten cc. of the sample prepared for analysis are run into a wide-neck Erlenmeyer flask of about zoo cc. capacity having a bottom 7 to 8 cm. in diameter, about I j cc. of freshly boiled and cooled distilled water added and titrated immediately with LV/ I O Iodine, the addition of which should be fairly rapid a t first with constant shaking. When the yellow color due to the polysulfide becomes very faint, or better when the solution becomes barely white, a very small crystal of sodium nitroprusside is added and the solution vigorously shaken until the purple color develops distinctly. The color is then discharged with a few more drops of standard iodine, added quickly but carefully. This is the moiao-sdJCur eqwhuIcnt titration. The burette reading is then taken and the tifration continued until a small drop produces a faint coloration in the liquid. This is the end of the thiosulfate titration and the difference between the total amount of iodine used and that used for the mono-sulfur equivalent represents the i hiosulfate present in the solution. ( I cc. N/IO I = 0,0016 S as monosulfur equivalent and 0,0064 S in thiosulfate.) METHOD B-The procedure was the same as in ( A ) except that S i 1 0 HC1 is used instead of iodine for the mono-sulfur equivalent titration, using one drop of methyl orange or methyl red as the indicator, which should not he added until near the end-point or until the solution becomes white. T h e titration is carried to a faint but distinct end-point. A little freshly boiled and cooled distilled water is now added, the hydrogen suifide boiled off until no test is given with moistened lead acetate paper, the solution cooled, and titrated vi3h standard iodine either with or without starch as indicator. XETHOD C--The procedure was as in (A), no attention being paid t o the mono-sulfur equivalent titration, corisequcntly 110 sodium nitroprusside added. Care should he taken n o t 10 go over the end-point for thiosulfate more than a small drop of standard iodine. To the solution is then added one drop of ammonium hydroxide and a solution of sodium sulfide of approximately X / s strength added until a drop of the solution gives a test for sulfides when applied to a drop of nickel sulfate solution on a touch plate. One drop of methyl orange is now added and the solution brought to very faintly acid with xeak HCI, the H 2 S boiled off, the solution cooled and titrated as in (B). The sodium sulfide should be added from a measuring pipette and a blank run for thiosulfate on the amount used (usually- not over 1-3 cc.). METHOD D (Thompson and Whittier')-Here the procedure 11-a~as follows: A I O cc. aliquot (as in the other mcthods) is run into a 2 0 0 cc. beaker, 1 5 t o 20 cc. water added, then a slight excess of approximately S/'I O ammoniacal cadmium chloride to precipitate the sulfide. The solution is then diluted t o 100-~zjcc with freshly boiled and cooled distilled water and allowed t o stand about one hour with frequent stirring. The solution is then filtered and the precipitate washed with water, the filtrate neutralized with weak sulfuric acid, using a 1
Delan-are College Experiment Station, Bull. 105, June, 19 14.
July, 1916
T H E J O U R N A L 0 F I N D U S T RI A L A N D E AV?iGIN E E RI N G C H E M I S T R Y
drop of methyl orange or methyl red as indicator and titrated with standard iodine with starch as indicator. E X P E R I 31E i YT A L
Four samples were used in this work: Nos. I and 2 were made in this laboratory, using pure lime and sulfur and distilled water; S o . I was about half t h e strength of t h e usual commercial lime-sulfur solution, No. 2 being somewhat weaker. Nos. 3 and 4 are commercial concentrates, bought upon t h e market a n d representing the product of t w o prominent manufacturers located in different sections of the country; t h e guaranteed specific gravity was 33’ B. Table I shows t h e accuracy of t h e thiosulfate titrations after boiling off H2S from t h e very slightly acid solution. TABLEI-EFFECT OF BOILINGA SDLUTION OF THIOSULFATE 10 cc. S t a n d a r d Sodium Thiosulfate Used in Each Case ADDITIONS TREATMEXT Cc. S t I Required Not boiled 9 82 - 4 83
None 1 drop N / 1 0 HCl Bailed 1 drop N / 1 0 HCI a n d HzS HzS boiled off 1 d r o p &’/IO HC1. HzS a n d CaClz HzS boiled off
9.83 9.83 9.83
....
9.83 9.83
T h e addition of calcium carbonate and barium chloride were without effect upon t h e titration. T h e standard thiosulfate was diluted t o j o cc. with freshly boiled and cooled distilled water in all cases, and t h e boiling was continued until tests for H2S with moistened lead acetate paper were negative. The solutions were then cooled and titrated. T h e fact t h a t a very slightly acid solution of thiosulfate is not decomposed b y boiling is t h e basal feature of Method B and one of t h e main points in Method C. T h e other feature of Method C is t h e conversion of tetrathionate t o thiosulfate b y a soluble sulfide. I n order t o test this point, 5 cc. of standard Na2S203 were titrated with standard I, requiring 4 . 7 3 cc. After conversion as outlined in Method C, 4 . 7 5 cc. of standard I were required. This was repeated: j cc. standard Na2S203 required 4 . 7 0 cc. standard I, and after conversion 4 . 7 2 cc. standard I were required. From these results it would seem t h a t the accuracy of Method C could not be questioned. All figures in t h e remaining tables are given in percentages as calculated in t h e records of t h e work T A B L E 11-COMPARISDN
SAMPLE
OF
THIOSULFATE SULFUR DETERMINED BY
DIFFERENT METHODS
METHOD -DETERMINATIONS-AVERAGE 1. . . . . . . . . . . . . A 2 . 3 0 2 . 3 0 2 . 2 4 2.30 2 . 3 7 2.30 B 2.24 2.24 2.30 . . . . . . . . . . . . 2.26 C 2.30 2.28 2.31 2.30 2.30 . . . . 2.30 D 2.28 2.22 2.26 . . . . . . . . . . . . 2.25 2............. A 1 . 9 1 1 . 9 7 1 . 9 1 1.97 . . . . . . . . 1 . 9 4 B 1 . 9 7 1 . 9 7 1 . 9 7 1.91 . . . . . . . . 1.95 C 1.91 1.97 1.91 . . . . . . . . . . . . 1.93 D 1.97 1 . 9 7 1.91 . . . . . . . . . . . . 1 . 9 5 3.............A 0.84 0.86 0.94 0.86 0.84 0.84 0.86 B 0 . 8 4 0.84 0 . 8 4 0 . 8 4 0.84 C 0.84 0.84 0.86 0.85 0.94 0.94 0.94 4. . . . . . . . . . . . . A 0.87 0.87 0.91 0.87 0.88 B 0.86 0.84 0.86 0.84 0.85 0.87 C 0 . 8 4 0.89 0.89 D 0.31 0.84 0.87
....
........ ............ ................ ........ ........ ............ ................
I t would seem from an inspection of Table I1 t h a t from t h e standpoint of accuracy alone there could scarcely be a choice of methods, although in Sample I , Methods B and D give slightly lower averages. If, however, individual determinations are considered, it will be seen t h a t no figure is mithout exact or at
625
least very close duplicates in one or more of t h e other methods. The agreement in t h e other samples, with the single exception of the seemingly high figures b y Method D in Sample 3 is all t h a t could be expected or desired. I n regard t o t h e apparently high figures b y Method D on Sample 3 j it should be stated t h a t all of the first weighing was exhausted and considerable decomposition had occurred in the original sample on account of a defective stopper so t h a t no more work on it was attempted. When factors other t h a n accuracy are considered, a choice of methods is not only easy b u t highly desirable. Method A requires b u t one titration and t h a t with one reagent (Standard Iodine). Method B requires t w o titrations with two reagents (Standard H C l and Standard Iodine). Methods C and D each require three titrations with t w o and three different reagents. I n point of ease of manipulation and time required, Method A stands in a class apart from t h e others. From an experience extending over several years in its use, t h e writer unhesitatingly states t h a t four or five determinations may be made b y Method A in t h e time required t o make one determination b y any of t h e other methods. Method D is t h e most tedious and time-consuming of all the methods. As stated above, there has been strong objection t o Method A. Just recently in T I ~ I JSO U R K A L ~it was stated t h a t this method “cannot be regarded as trustworthy.” The writer of t h a t article produced no original d a t a in support of this statement a n d had evidently overlooked t h e collaborative work of a dozen chemists presented t o the Association of Official Agricultural Chemists In the Report on Insecticides in 1 9 1 3 , ~in which also, as a part of the report, was a discussion of his r e f e r e n ~ e . ~T h a t this criticism does not apply t o a straight lime-sulfur concentrate is clearly demonstrated not only in t h a t report b u t also in the present paper. I n this connection it should be stated t h a t , in Method B, after titrating with standard HC1, the precipitated sulfur was filtered off in one or two cases with each sample and BaCls added before boiling off H2S. I n no case was there a n y perceptible precipitate of B a S 0 4 until after the titration with iodine: a very slight precipitation was then noticeable in all cases and since it is extremely doubtful if any sulfite could exist in a lime-sulfur solution, certainly no more t h a n a trace, this precipitate is probably due t o a very slight oxidation of tetrathionate t o sulfate b y an excess of iodine and for this reason it is recommended, in Method A , t o prevent a regional excess of iodine b y titration just moderately fast with constant shaking. T h a t this oxidation is negligible in the analysis, however, is shown b y the closeness of t h e agreement betweeen Method B and Method -4, and t h a t within t h e experimental error all t h e methods agree in t h e amount of thiosulfate indicated. The use of ;V/zo iodine solution would probably be conducive t o somewhat closer end-points. 1
THISJ O U R Y A L 8 (1916), 151.
2Jour.A 0 A C , l , N o . l , p . 5 9 . 3 Bureau of Chemistry, Bull. 162, p. 38.
T H E J O l ' R l V A L O F I S D C 7 S T R I A L A N D ELTGIXEERIXG C H E M I S T R Y
626
D E T E R ;I11N AT1 0 N O F P 0 I, Y S U L F I D E S E L F U R
I n the longer methods of analysis t h e precipitated zinc sulfide, cadmium sulfide or precipitated sulfur from t h e iodine titrations is digested in caustic soda, oxidized and precipitated as barium sulfate. This is a long tedious process and often unsatisfactory results are obtained. I t has been known for several years t h a t the precipitated sulfur in Methods A and B may be filtered, washed and 1%-eighed directly. I n the iodine titration (Method A) the total sulfide sulfur is precipitated as folloll-s: Cas, I? = CaI, XS I n the hydrochloric acid titration it is necessary t o add t h e mono-sulfur equivalent sulfur t o t h e precipitated sulfur in order to get the total. I n t h a t titration it is very probable t h a t t h e following reactions occur:
+
+ +
+
+ +
Cas, 2HCl = CaClz HzS -f ( % - - ) S i Cas, H2S = Ca(SH)Z (~-1)s; 2HC1 = CaCl? zH2S. (3) Ca(SH)* As a n indication of the occurrence of these reactions it n-as noted t h a t until the solution becomes white therc is no very strong odor of HyS. After this point in t h e titration is reached, however, the odor of B2S becomes very strong, showing t h a t it is being formed rapidly as indicated by Equation ( 3 ) . A method of weighing t h e precipitated sulfur! which the writer has found. t o give accurate and quick resulx. is as follows: Wash a 7 cm. ashless filter several times with suction, p v t in drying oven for half an hour a t 94 t o 96' C.. place in wide mouth weighing bottle and weigh a t once. Filter t h e precipitated sulfur on the weighed filter, Tyashing well with suction, Dry in o v m for 45 minutes t o one hour and weigh as before. The difi'erence is the weight of sulfide sulfur. This has been found t o give constant weight when the amount of sulfur is not too large. I n a previous article' attention was called t o this nieihod of weighing t h e precipitated sulfur from t h e iodine titration and a comparison of t h e results with those obtained b?; oxidation and weighing as barium sulfate m-as shown. .%fter the titrations, if the solutions are allowed t o stani? n fev; hours, the sulfur collects a n d is readily filtered. I f , however, it is desired t o filter a t once, (I)
(2)
~ A B L T : TI1
1
+
-+
sulfate and polysulfide figures, in Table 11: is shown t h e total sulfur as determined b y oxidation and precipitation as B a S 0 4 and as the s u m of polysulfide and thiosulfate sulfurs. The determined total sulfur is t h e mean of t w o determinations. The s u m of t h e polysulfide and thiosulfate sulfurs consists of t h e average of all thiosulfate determinations b y t h e four methods as shown in Table 11; the polysulfide sulfur is the average of all figures b y both methods, as shown in Table 111. SANPLE NO.
TABLEIV-TOTAL SULFUR DCTERMINEDSULFUR THIOSULFATE AND Duplicates Av. POLYSULFIDE SULFUR
1 . . . . . . . . . . . . . 11.96 2 . , . , . . , . . ~. . , 1 0 . 2 8 3 . .. . . . . . . . . . . 25.03 4 . . . . . . . . . . . . . 25.48
11.94 10.26 25.14 25.42
11.95 10.27 25.08 25.45
11.89 10.22 25.02 75.43
When a straight lime-sulfur solution is titrated with iodine (Method A ) it is quite easy: when desirable, t o use.as a check upon t h e work the determined lime (CaO) and t h e lime as calculated from t h e titrations since t h e iodine is reacting with the calcium (Ca). T h e mono-sulfur equivalent multiplied by I 3 / 4 is equivalent t o the lime (CaO) in combination as polysulfide; t h e thiosulfate sulfur multiplied b y i / R is equivalent t o the lime (CaO) in combination as thiosulfate: the s u m is equivalent t o total lime (CaO). The aTerage of t h e mono-sulfur equivalent b y Method X and the average of the thiosulfate b y t h e same method as shown in Table 11 are used in t h e calculations: t h e determined lime (CaO) is the mean of t w o determinations. TABLEV-SHOWXXG
THE VALUE FOR I,IME (CAO) AS ACTCALLYDETERXINED A h D A S CALCULATED F R O M THE IODINE TITRATIONS
(METHOD A) PERCENTAGE LIXC THIO- CalcuDETERMIXED Sample &fOXOSULFUR EQUIVALENT SULFATE l a t e d ------No. Determinations Av. SULFUR ( a ) Duplicates AV. 1 2.01 1.99 2.01 1.96 1.95 1.98 2.30 5.47 5.39 5.42 5 . 4 1 2 1.71 1.71 1.72 1.71 . . . . 1.71 1.94 4.70 4.64 4.81 4 . 7 2 3 5.02 5.02 5.06 4.99 4.99 5.02 0.86 9.53 9.52 9.62 9 . 5 7 10.04 10.11 10.08 1 0 . 1 0 4 5.32 5.29 5.29 5.29 , , . . 5.30 0.88 ( a j Ca!culated from two preceding columns a s n o t e d in text
-
Acknowledgments are due Dr. A. AI. Peter. of this Station, for having called attention t o t h e fact t h a t an excess of iodine oxidizes tetrathionate t o sulfate,l and t o t h e possibility of titrating tetrathionnte directly with a soluble sulfide, as well as for helpful suggestions and criticisms in the preparation of t h e manuscript. The suggestion t h a t t h e reactions between tetrathionate and soluble sulfides is quantitative, as noted -I'OLYSITLFIDB SULFCR A S DETERMINED B Y TTEIGHIXG SCLFCR DIRECTLY in the larger works on chemistry, is due t o Chapin's HYnROCHLORIC DI?OC~ILORICSAXPLE IODINE ACID TITRATIOX paper. D TITRATIONN o . TITRATION
9.58
9.64
8 6
2.01 = 9.59
+ 2.01 = 0.6; J .
3
-~
24.16 24.01 2 4 . 16
18.96 5.12 = 24.08 19.08 5.12 = 24.20 19.12 -r 5.12 = 24.24
24.12 24.56 24.52
24.17 19.20 -k 5.40 = 24.60 19.16 5.40 = 24.56 24.58
.~
Average 9 . 5 9 2 8.28 8.26
9 63 6.58 + 1 . i 2 = 8.30 6.56 -- 1 . i 2 = 8.28
-
_-
Average 8 . 1 ;
2.20
24.54
--
4
-
.+
__
add 2 or 3 drops of weak hydrochloric acid and warm on watcr b a t h until the sulfur collects. Care must be taken t h a t no sullur is lost in t h e 11-ashing. N o more care is necessary, however, t h a n a good analyst would naturally bestow upon it. I n order t o illustrate the accuracy of both the thio1
1'01. 8, NO. 7
Jour. A . 0. A . C.. 1, No 1,
p. 95.
SU M N A R Y
I-The experiments described and d a t a presented in this paper afford new proof t h a t calcium polysulfide in solution can be quantitatively decomposed b y iodine -solutions and thus eliminated from a solution containing thiosulfate, preparatory t o the accurate determination of t h e latter. 11-It is shown t h a t t h e same end may be accomplished by means of dilute HC1 a n d elimination of the H2S formed b y boiling. 1
Ber., 48, 2088; Chem.-Ztg.. 1908, 1203.
*THISJOURNAL. 8 (1916), 151
July, 1916
T H E J O U R N A L O F I N D r S T R I A L A IV D E N G I N E E R I N G C H E M I S T R Y
111-It is shown t h a t sodium nitroprusside can be used as a n internal indicator t o show t h e end-point of the disappearance of t h e sulfide in t h e titration with iodine. IS’-This work affords further evidence of t h e interesting fact t h a t when an iodine solution or a dilute acid is carefully added t o a solution containing calcium polysulfide and thiosulfate, t h e polysulfide can be quantitatively decomposed before t h e thiosulfate is attacked. S‘-A rapid accurate method of weighing t h e pre-
627
cipitated sulfur in t h e iodine and hydrochloric acid titrations of a lime sulfur solution is proposed. VI-Two methods ( B and C ) , not heretofore used for t h e determination of thiosulfate in lime-sulfur solutions, are described, both being theoretically and practically sound and accurate. VII-The accuracy of t h e iodine titration method (or Harris method) for t h e analysis of such solutions is confirmed. EXPERIMENT STATION LEXINGTON, KENTUCKY
A%GRICULTURAL
LABORATORY AND PLANT THE FLOW OF VISCOUS LIQUIDS THROUGH PlPES
I
By W. K. LEWIS Received May 2, 1916
Y p
The carrying capacity of pipes for water under various pressure drops has been experimentally studied b y many engineers and while the results are not very concordant on account of the extreme sensitiveness t o varying conditions, none the less our knowledge of t h e resistance t o flow o€ k a t e r through pipe lines is relatively satisfactory and complete. On the other hand, practically no work has been published on t h e resistance t o flow through pipes of liquids other t h a n water despite the fact t h a t information of this sort is of vital importance t o the chemical engineer, Davis, in his “Handbook of Chemical Engineering, ” points out t h e extremely small carrying capacity of pipes for viscous liquids such as sulfuric acid a n d glycerin as compared with their capacity for water, b u t he gives no suggestions as t o methods of estimating t h e size of pipes required for specific cases. There are in this country thousands of miles of pipe lines transmitting mineral oils as well as t h e piping systems of chemical plants handling acids, solvents, a n d all sorts of liquids in large quantities. While a wealth of information along this line is undoubtedly available t o t h e engineers of individual corporations, t h e lack of a n y published figures a n d t h e importance of t h e whole problem led this laboratory t o undertake a n investigation along these lines which has extended over t h e last four years. After certain preliminary work, a series of tests was made studying t h e flow of mineral oils of varying viscosity a t relatively low velocities. T h e results of this work are reported as Series A. Later, in order t o supplement the results of these first experiments b y s t u d y of flow a t higher velocities, another separate investigation was carried out which is reported as Series B. While t h e results are limited t o relatively small pipes and low viscosities, certain generalizations can be drawn which are so well confirmed t h a t their use, even beyond the scope of t h e present experimental range, seems justified, especially as a working basis upon which t o develop further investigation. N0M E N C L A T E R E
P
’
pressure drop in grams/cm2. or lbs./sq. f t . coefficient of absolute viscosity in = sec. dynes/cm2. or sec. poundals/’sq. f t . =
1 1
= = =
length of the pipe in cm. or ft. radius of pipe in cm. or ft. density of the fluid. mean velocity a t point where sinuous flow changes t o parallel flow,cm./sec. or ft./sec. mean velocity in cm.,’sec. or ft./sec. hydraulic frictional coefficient.
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v,
=
V,
=
f
=
G E NE R A L DISC US S I 0S
It has long been known t h a t , for t h e flow of fluids through capillary tubes u p t o 4 or j mm. in diameter, 8 pzv the formula of Poiseuille, P = ---?, holds quantitaRY2
tively. Though for t h e flow o f liquids other t h a n water through large tubes or pipes, quahtitative d a t a have not been published, t h e paths along which t h e particles of liquid travel have been studied qualitatively b y introducing air or dyes into t h e fluids and photographing the effects produced by forcing t h e m , through glass containers of various shapes and sizes.‘ These observations show t h a t a t low velocities liquids move in straight lines parallel t o t h e axis of the tube, b u t when t h e velocity is sufficiently increased, t h e lines of flow become distorted, the filament forming violent eddies of constantly changing form and position. A t t h e walls of t h e container there is always a film of liquid which is retarded b y t h e friction of t h e solid surface, so t h a t it continues t o move in straight lines. The mean velocity of the fluid, a t t h e point where t h e change in type of motion takes place, is commonly known as the critical velocity and all flow below this point is called parallel, direct, or viscous motion, while t h a t above is known as turbulent, indirect, or sinuous flow. From this i t is obvious t h a t a t least two different laws must govern t h e flow of fluids, the one above and t h e other below t h e critical velocity, with the possibility of a third for an intermediate state. Poiseuille’s law would be t h e one t o use below the critical point, since his formula applies entirely t o straight line motion. For flow above t h e critical point, we have but one suggestion as t o t h e manner in which flow may t a k e place, from observation of the formulae for t h e flow of steam, air, and water above the critical rate. 1
These equations may all be written P =
H. S.Hele-Shaw, Engineering, 66 (1898), 420, 444, 477, 510.
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