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R O B E R T SPCRR TT'ESTOS
THE DETERMINATION OF MANGANESE IN WATER. BY
ROBERT SPI-RR LVESTOS.
Received A p r i l zn. 190:.
T h e need for a convenient nietl?od of determining manganese in water has been recognized by many analysts. I n t h e ordinary practice of t h e water analyst either t h e deterniinatioti is made gravimetrically or it is oirii t ted. Manganese together with iron occurs i n many ground waters, and very often its presence complicates or vitiates the processes used for t h e rei
This Journal,
25,
899.
MANGANESE I N WATER
I075
mooal of iron from water supplies. A t Breslau, in 1904, t h e sudden ~ for presence of maiiganese in t h e ground water made the s u p p l ~useless a time, notwithstanding t h e fact that t h e water was treated by aeration a n d filtration for t h e purpose of removing t h e iron from it. Extremely valuable data are x i s s i n g because of t h e inconveniences of t h e present time-consuming methods for the determination of manganese. S u c h d a t a will be collected only i f the methods be as facile as other methods used in water analysis. Waters rarely contain more than I O milligrams of manganese in a liter. Gravimetric methods are often beyond consideration, a n d t h e only ones which seem generally practicable a r e those in which t h e manganese is oxidized to permanganic acid. Of these latter t h e lead oxide methods of Chatard and others’ and t h e sodium bisniuthate method seemed to be t h e most promising. T h e sodium bismuthate method was used because of t h e greater ease with which t h e solution could be freed from the precipitate. T h i s niethod has been used far the determination of manganese in ores and steels and is described by Blair2. I t was proposed by Schneider” a n d modified first by Reddrop a n d Raniage‘ and then by Bearley and Ibbotson.’ T h e method i s based upon t h e fact that in t h e presence of an excess of nitric acid a manganous salt is oxidized to permanganic acid by bism u t h tetroxide. Rlair states that :“ T h e permanganic acid formed is very stable in nitric acid of I . 135 sp. gr. when t h e solution i s cold, but in hot solutions the excess of bism u t h tetroxide is rapidly decomposed and then t h e nitric acid reacts with t h e permanganic acid and as soon as a small amount of manganous salt is formed t h e remainder of t h e permanganic acid is decomposed, mangatious nitrate dissolves and manganese dioxide precipitates.” Reddrop and Ramage showed t h a t it was difficult to get bismuth tetroxide free from chlorides, t h e presence of which would vitiate results, so they proposed t h e use of sodium bismuthate. T h e manganese in t h e permanganic acid produced b y oxidation may be determined in two ways. After filtering off t h e excess of bisniuthate Blair adds a n excess of ferrous sulphate to the filtrate and by titration w i t h permanganate solution determines the amount necessary to deoxidize t h e permanganic acid. F o r waters containing less than I milligram of manganese, however, comparison of t h e filtrate colorimetrically with permanganate r u n froni a burette i n t o an equal volume of dilute sulphuric acid free from organic matter contained in a Kessler tube, proved to be simpler and more precise ; for larger quantities, however, the titration method should be used.
’ Sutton’s Volumetric Ana!ysis. This Journal, 26, j93. ’ Dingler. pol. J.. 269, 224.
J. Chem. SOC,,1895, 26% The Analysis of Steel Works Materials,
Method. Evaporate with about 2 j cc. of nitric acid i’sp. gr. 1.13.i) enough of t h e saniple of water to give from 0.01 to I nig. of manganese. Gently ignite t h e residue or bake it for 3 4 h0u.r a t 130’. Add j o cc. of nitric acid (sp. gr. I . 135) and when t h e solution iscool add about 0.5 gram of sodium bismuthate. H e a t until t h e pink color disappears. A t this point Blair, i i i his deterniinatioii of manganese in iron, adds sulphurous acid, ferrous sulphate or sodium tliiosulphate, to clear t h e solution if manganese dioxide is precipitated, and heats i t to dispel all oxides of nitrogen. IT‘ith waters this step was usually unnecessary, b u t whenever so, thiosulphate was the reagent used. T o tlie coo1 solution add sodium bisniuthate i r i excess. stir a few minutes, and filter through tliorougli‘!- n-aslied asbestos i n a Goocli filter. IYash with dilute nitric acid, transfer filtrate to a large Kessler tube, and m a k e up to I O O cc. lyitli diliite nitric acid. In another tube put I O O cc. of dilute suiphuric acid and add stanc!a:d potassium permanganate solution i i i i i i ! the color of tlie sample is inatclicd. T h e volume of potassium perninnganate in cc. x O.OOOI gives the Iveigiit of tiiangatiese in grasiic;. r~sp!-~sc: niillirt3111:5 as parts per million, :.rani.: per liter. Reagents. Po‘ota~sz’uv~ Po-ii/aiy.a,ic2:c So/ii!ic~z. Dissolve 0 . 2 S 8 graix of potai;-iuxn permanga:iate i n water and make u p to I lite:. I cc. is equivaleiit to c). I m g . man gane se , X i f ~ i c.Ic-id (sp. gr. 1 , 1 3 5 ) . A iiiixture of 3 parts of water and I part of strong nitric acid (sp. g r . 1.42 is used. Dz’liiic Arif7ic A c i d . jo cc. of strong nitric acid to the liter. Szi&/ziwic A c i d . 2 j cc. of pure concentrated sulphuiic acid to the liter. -Add enough permanganate to color the r;olution slightly but 1)erceptibly pink. Asbestos. Yrepare asbestos i n the usual n a y by wa-hing Isitli acid and igniting. I t should be free froin organic matter. ~~
Notes and Precautions. T h e first experiments ivith this method gave unsatisfactory, erroi:eous results. E a c h reagent was tested to ascertain the cause of the error. I t was found that t h e “C.P.” nitric acid used was impure ; it contained oxides of nitrogen. Several methods of purification were tried. T h e most efficient process proved to be that of passing a current of air through t h e concentrated acid for about half an hour T h e presence of organic matter also vitiates results ; when i n large amounts t h e color of permanganic acid does not appear in the filtrate. T h i s difficulty is overcome by ignition of the residue or by baking it for
1077
TER
MANGANESE
% hour a t 130’. T h e asbestos must be free from organic matter ; otherwise the permanganic acid will be reduced. T h e presence of chlorides also interferes with t h e determination. Samples which contain large amounts of chlorine should be treated before evaporation with a slight excess of silver nitrate and then filtered. Experiments were made iii which the bismuthate was added but once, t h e excess filtered off immediately, and the permanganic acid determined. Satisfactory results, however, were not obtained by this shorter method. T h e oxidation is complete only after the second addition of bismuthate. T h e method is very delicate. I t will detect o.ooooz gram of manganese. Experiments. T h e first experiments were made with distilled water and known solutions of manganese sulphate and potassium permanganate. T h e results were as follows :A.
WITH ~ I A X G A S H SSIY,PHATE X Grains Manganese G r a m s Manganese Added Recovered
K O
................. ................. j.................................... 4 .......... ................. I
.c.oooIo
0.00009
2
.0.00010
0.000IO
.O.OooIO
0.00010
13. so.
.......................................
j
0.000~0
\f’ITH POTASSICII PERJI.XNGhNATE G r a m s Manganese Added
.........................................
I 2
o.00050
.........................................
G r a m s Manganese Recovered
.0.00010
0.00009~
.O.ooO20
0.00020
.0.00050
0.00045
C. Efect of Ovgaizic Maffer.-Experiments were made like the above, except with t h e addition of varying volumes of leaf iufusion, this being considered typical of the organic matter contained in water. T h e results were as follows :( a ) WITHOUTIGXITIOS OF RESIDUE KO.
............................ ............................ j ............................. 4 , . .............................
G r a m s of Manganese Added
cc. Leaf Infusion
G r a m s of Xanganese Recovered 0.00010
I..
. O . O ~ I O
I
2..
.0.~010
2
0.00008
.o. 000 I O
IO
0.m007
.0.00010
25
Color faded in 5 min.
( h ) RESIDUEIGKITED KO.
I
..............................
2..
............................
G r a m s of Manganese Added
cc. Leaf Infusion
.0.0~10
25
.0.000IO
25
G r a m s of Manganese hecovered 0.OooIU 0.000 I O
D. T w o trials of the method were made, first with Boston water, a surface supply, and second with Reading water, a ground water supply containing about 2 parts per million of iron. T h e Boston water contains no appreciable amount of manganese, but manganese is presetit in the
Reading water. Beside.5 determining the manganese in the water, deterininations mere made with t h e mater containing varying ainounts of added manganese. I3osmx ~YA'I'EH
( aj
Gr:inis of Zla~ipa~icse Added
CC.
t ' I k en io$,
?,'.,
.................................
1
......
. . . . . . . 2..
'1
...............................
0.1~0000
0.00000
,
0.:,cJC I i l
0.00009
IC13
0.c00 I0
0 .O M 10
0.000I O
0.0000y
IC;,
................................. .
!. $.: , i ) : S I ; -$\..a T E K
-\
31ail ga ii ese
I/I,
il.OC100'.!
0.000065
:oo
0.~!OOC~O
0.0000;0
I I3
P. 0000;.j
j i b 1
0, r u i I '..I
0.0001 7 0
:,IC
0,030 I O
