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 -~ ~
~~
~
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
Sept., 1 9 1 5
T H E J O V R A T A L O F I A 7 D C T S T R I A LA
acid and copper nitrate are formed. The tin precipit a t e is filtered off. and the copper determined in the filtrate. This method has t h e disadrantage t h a t the metastannic acid filters with difficulty; furthermore, the tin precipitate always contains traces of other metals present in the alloy, so t h a t i t must undergo further treat nient. Tin and copper may also be separated by sodium sulfide in alkaline solution, whereby the copper separates as sulfide and the tin goes into solution as a sulfosalt. The inconvenience of this method needs no comment. Having had occasion t o investigate the behavior of mctallic copper and metallic tin when treated with concentrated sulfuric acid, t h e writer was struck b y t h e facility with which t h e tin was held in solution. The fact t h a t tin goes into solution as a stannic salt \Then treated with concentrated sulfuric acid is made use of in Low’s method for antimony in babbitt meta1;l the hydrochloric acid added after t h e decomposition of t h e alloy ensures t h e tin and antimony remaining in solution after dilution. I t m-as found t h a t the solution of tin in sulfuric acid alone was fairly stable. and with the knowledge t h a t stannic salts do not liberate iodine from a solution of potassium iddide, the question naturally arose as t o whether copper might not be determined by the iodide method in a solution containing tin. Further experiments showed t h a t this x a s quite feasible; b y proper treatment of t h e alloy a solution of stannic and cupric sulfate in sulfuric acid may be obtained t h a t may be titrated for copper with the same accuracy as a copper sulfate solution alone. Allthough hydrochloric acid holds tin in solution much more readily t h a n sulfuric, its use was not considered, as copper is not readily soluble in hydrochloric acid and t h u s would necessitate the use of aqua regia t o effect solution of the alloy. The nitric acid would then have t o be removed by repeated evaporations with hydrochloric, consuming much time, and making the method much less simple t h a n in its present form. Preliminary work showed t h a t t h e best method of preparing the solution vias t o treat the finely divided alloy with nitric acid until decomposed, and then fume with sulfuric acid over a n open flame (using a Jena Erlenmeyer), The metastannic acid dissolves to stannic sulfate, and t h e copper nitratc is converted into copper sulfate. On taking the cold residue up with water, a clear solution is obtained t h a t may be titrated directly for copper by the iodide method. The use of sulfuric acid alone t o decompose the alloy is not satisfactory, as a small residue of copper remains even after repeated fuming. -4 large excess of acid must be used, otherwise the pasty mass will spatter. I t is practically impossible t o control the amount of free sulfuric acid present, and this is important, as in using a mineral acid in t h e copper iodide method, the acidity must be low. The allowable amount of tin present under given conditions of acidity was determined as follows: 1
J . Am. Ckem. SOL.,29 (19071, 66.
D E S G I N E E RI N G C H E M I S T R Y
765
T h e volume of the solution t o be titrated having been chosen as 7 j cc., and the amount of concentrated sulfuric acid as 3 cc., increasing quantities of metallic tin were dissolved in nitric acid, evaporated with 3 cc. of concentrated sulfuric,’ diluted t o 7 j cc., and the stabilities of the different solutions compared. Tin Gram
1-01,
0.05 0.1 0.2
i5
Cc. 75 75
Conc. HzSOi Cc. REMARKS i No change in one hour i Slight turbidity in 15 minutes 3 Tl-ould not dissolye t o clear solution
I t is evident t h a t not more t h a n 0.1gram of t i n may be present, otherwise hydrolysis and precipitation of stannic hydrate take place in a short time. The weight of copper titrated may be a s high as 0 . 2 j gram (=s = 3 9 . 3 cc. N / I O Xa2SzO3). This weight of copper in the preseflce of 0 . I gram tin would be equivalent t o 71.43 per cent Cu. There vould then be 28. j 7 per cent Sn. As t h e amount of tin in a bronze is seldom so high as this, there is no danger t h a t the sample taken for analysis \\ill contain more t h a n the allowable weight of tin, provided the amount of copper present is not much over 0 . z j gram. EXPGRILIESTAL DATA STAND A R D I Z A T 1 0 Ii 0 F T H I 0 S C L F AT E S 0 L U T I 0 N A G AI S S T C O P P E R FOIL-The sample v a s dissolved in nitric, fumed with 3 cc. conc. H,S04, allowed t o cool, 2 5 cc. TTater added, and el-aporated again t o fuming. The solution mas allowed t o cool, diluted t o 7j C C . , I O cc. of 40 per cent K I solution added: and titrated with the thiosulfate solution. Grams couuer
NO.
i... .,,,. 2...,.. , ,
~~
I .
.... .. , , . , . . . . 3 . .,. .. , , . . . , , .
0.2655 0.2648 0.2684 AVERAGEVALUE 1 cc. Na:S203.. , ,,
Cc. XatSIOs 42.37 42.24 41,83
. ,.. . . ....
1 cc. = Grams Cu 0 006266 0,006269 0.006267 0.006267
.., . , .
O F Trs--The solution was prepared as before, but metallic tin was added t o the copper samples:
TITRATION
OF
COPPER
IN
PRESENCE
CU
So. 1 2 3
\\‘eight-Grams Cu Sn 0.2526 0 250i 0.2455
0.0311 0.0504 0.0799
Per cent Cu Sn 89.04 8.26 ,3.45
10.96 16.74 24 5 5
cc XazSzOa Gram ~~
40.31 40.02 39.i5
0.2526 0.2508 0.2454
UIFFhK-
FOUXD ENCE Per cent
Per cent
89.04
F33.30
+0.’04 ,3.41 -0.04
These differences lie entirely within t h e limits of error. A S A L Y T I C A L P R 0C E D U R E
Weigh out a sample containing not over 0 . 2 j gram copper and boil with I j cc. of z : I nitric in a 5 0 0 cc. Jena Erlenmeyer pro\-ided with a small funnel t o prevent loss. When t h e alloy is thoroughly decomposed, add dilute sulfuric acid equivalent t o 3 cc. of concentrated acid, remove and rinse t h e funnel, and ex-aporate over an open flame. As the eraporntion progresses: the solution becomes more and more clear. After t h e nitric acid is all driven off, a n d the sulfuric begins t o fume, the stannic and cupric sulfates suddenly separate out, forming a very characteristic crystalline mass of pearly scales some\\-hat resembling manganese ammonium phosphate. The flask must be removed from the flame immediately after this 1 Three cubic centimeters of concentrated sulfuric acid is the maximum amount which may he present in t h e copper iodide method, according t o Gooch and Heath, Z . anorg. Chem., 66 (1907), 129.
5
T H E J O U R N A L OF I N D L - S T R I A L A N D ENGINEERING C H E M I S T R Y
766
crystallization takes place or t h e mass will spatter. After cooling, take u p with about 2 j cc. water, shake until dissolved, a n d again evaporate just t o fuming in order t o remove the last traces of lower oxides of nitrogen. Allow t o cool, takk u p with j o cc. cold water (the stannic sulfate dissolves more quickly b y using less water at first) and when all is in solution, a d d z j cc. more water, I O cc. of 40 per cent K I , and titrate immediately with t h e N / I O thiosulfate. If the alloy contains a small amount of lead, some lead sulfate remains undissolved, and t h e solution a t the e n d point is yellowish (owing t o t h e lead iodide) instead of the creamy white of cuprous iodide, b u t the presence of lead has n o effect upon t h e titration. a t least in moderate amounts A copper-tin alloy containing about I O per cent of tin a n d 8 per cent lead analyzed as follows: N O
1.. . .. . . . ..... 2.. , , .., ..... 3.. , , . . , , , , ., . . 4 . , . . . . .., . . . .. 5,....,,.......
Sample Gram 0.3127 0.3227 0.3303 0,3108 0.3327
Cc. NazS%Os 39.49 40.79 41.70 39.21 42.02
Cu FOUND Gram Per cent 0.2474(8) 7 9 . 1 4 ; 0.2556(3) 79.22 0.2613 (4) 79 12,: 0.2457 (4) 0.2633(4)
I:?;
-4verage Per cent Cu 79.16 i9'11
I n the analyses indicated as 4 and j above, the alloy was decomposed with nitric, t h e metastannic acid filtered off, a n d t h e copper determined in t h e filtrate after evaporation with sulfuric. Too much stress cannot be laid upon the fact t h a t a second fuming of t h e solution is necessary: 0 . 0 5 gram of metallic tin, treated with nitric, fumed once with sulfuric, a n d diluted t o 7 j cc., gave a blue color with K I a n d starch requiring 0 . jj cc. t o discharge it. When this same amount of tin was fumed twice, potassium iodide and starch gave no color in the diluted solution. As regards t h e time necessary, determinations I , z and 3 , cited above, were r u n in one hour. T h e filtering, washing and evaporating necessary when t h e ordinary method was used, made t h e time about five hours. ( I n this, no correction was made for a n y copper remaining with the metastannic acid.) The method proposed is simple, accurate. and rapid; the a d r a n t a g e s of carrying out t h e analysis in t h e same container are obvious. I n conclusion. it must be remembered t h a t no metals which separate iodine from potassium iodide m a y be present, such as antimonic or ferric salts; t h e method has naturally t h e limitations of t h e iodide method in this respect. It is simply the desire of the writer t o show a n extended use of this excellent method, t h u s making i t available under apparently adverse conditions. 614
EAST1 l i T H
STREET, CLEVELAND, OHIO
TlTRATION OF NITRATES WITH FERROUS SULFATE B y FREDC. BOWMAN A N D \\-. W. SCOTT Received M a y 29, 1915
T h e great variety of methods of determining nitrates found in chemical literature shows t h e need felt b y chemists for simpler ways of making this important analysis. Most methods now in use involve distillation or evaporation or the'use of special appara-
V O ~7. , NO. 9
tus, all of which t a k e a good deal of time and attention. The method proposed b y the authors is as easy and quick as a n y ordinary titration, has a , w i d e range of usefulness and is accurate enough for most purposes. BIBLIOGRAPHY
The first mention of t h e method was made b y Grossart1 in 1847. He titrated nitrates in boiling 60 per cent sulfuric acid with a ferrous sulfate solution, using ferricyanide as an outside indicator. He gives no details or test analyses. K O doubt his results were less accurate t h a n he thought. Mohr2 announced t h e discovery of t h e method in 1861. He dissolved t h e sample in sulfuric acid (diluted I t o 9) and titrated a t 70" t o 80" C. with a ferrous sulfate solution containing zoo grams of t h e salt per liter, using as t h e end point t h e appearance of a brownish color. He declared t h a t it was a good technical method, b u t Fresenius3 and E d e r , 4 who examined it later, condemned it strongly. I n 1899 van Deventerj carried out the reaction over mercury in a Crum tube with exclusion of air, using fairly strong sulfuric acid as a medium and a weak ferrous sulfate solution as reagent. T h e process was awkward t o handle. S o comment on these methods was found in the journals, a n d evidently they failed of acceptance. T h e y were all based on t h e reduction of t h e nitrate t o K O and not t o N203, as in t h e method given below, for estimations in presence of sulfuric acid. N o mention of acids other t h a n sulfuric was found in t h e literature. ESTIU.4TIOX
O F SITRIC ACID IX P R E S E K C E O F A R S E N I C ACID
The writers devised t h e method given below, originally, for t h e purpose of estimating nitric acid in arsenic acid. T h e original form of t h e method was as follows: Dilute t h e sample t o be tested t o I O O cc. with nitrefree arsenic acid of such strength t h a t there is not more t h a n 20 per cent water in the mixture. Then titrate with a ferrous sulfate solution, containing 264.7 grams FeSO4.7HsO and jo cc. strong sulfuric acid per liter ( I cc. = 0 . 0 2 g. "03). Standardize t h e solution on a known amount of nitric acid. The following reaction occurs: 6FeS04 zHN03 3HzSO4 = 2NO 3Fe2(S04)3 4HsO The ferrous sulfate forms a dark brown color, which disappears on stirring as long as a n y nitric acid remains. T h e end point is t h e first permanent brown and is readable t o 0 . 0 3 cc. During the first t w o thirds of t h e titration, t h e ferrous sulfate is taken u p very quickly; then a lively evolution of N O commences a n d continues t o the end. It would be thought t h a t t h e oxygen of t h e air might reoxidize the N O
+
1
+
+
"Sur un nouveau dosage de l'acide azotique e t des azotates," Grossart.
Comfit. rend., 1 ( 1 8 4 i ) , 21. 2 3 4 5
+
Dingler's Polytechnisches Journal. 160 (1861), 219. ZeilschvifC f u e r anal. Chemie. 1 (1862), 32. I b i d . , 16 (1877), 267. Zeilschrift fuev p h y s i k . Chemie, 31 (1899), 50.
