j00
T H E J O C R N A L O F I N D C S T R I A L A N D EAVGIIZIEERIAVGC H E M I S T R Y
i j per cent): made u p t o jo cc.! and a portion nesslerizea at o n c e . The Columbus Sewage Testing Station' published a modification of the Rideal and 11cGowan methods which is as follows: Measure out a n amount of sewage t h a t will contain 0 . o O o j t o 0.001g. of nitrogen. Add j cc. of H?S04. digest until colorless, and rinse the digestate into a 50 cc. flask. Cool and fill to t h e mark, and pipette 2 j cc. into a T O O cc. flask. Add N a O H ( 2 j 0 g. per liter) until a precipitate forms, then add 2 cc. of Ka2COi (100 g. per liter). Mix and make u p t o J-olume and allow t o stand 6 hrs. Nesslerize I O cc. made up t o j o cc. in a Nessler tube, reading after I j min. L. Khipple* tried t o use the Columbus modification on Boston sewage but found t h a t he could not get accurate results. so recommended the following: j o cc. of the sample are digested with j cc. of concentrated sulfuric acid, and a small amount of CuSOd until colorless. The digestion is completed by t h e addition of a fen. crystals of permanganate t o t h e hot acid. After cooling, t h e digestate is diluted t o 2 j 0 cc., mixed, and a portion ( 2 j cc.) is pipetted out and mixed ii-ith a n equal portion of j per cent N a O H , and filtered through a filter paper which has been washed previously with I O O cc. or so of ammonia-free water: 2 0 cc. of the filtrate are pipetted into a Nessler tube and made u p t o j o cc. with water. M i x by pouring one tube into another, and nesslerize. Read after 10 min. -4 blank should be run on t h e entire process. Because of its rapidity, this latter method n-as tried on Kansas sewages, b u t with no success, the results obtained always being too low. As we h a d - n o trouble due t o turbidity in the tubes, we started a n investigation t o see under what conditions exact results could be secured. For this purpose the effect of large and small amounts of copper sulfate and potassium permanganate were ascertained, as well as t h e effect of the length of time the samples stood before nesslerizing. T h e results of our work TTere finally embodied in the following method which we have found t o give accurate results on Kansas sewages a t ieast.
METHOD A D O P T E D F O R K A X S A S S E W A G E S
T o IOO cc. of sewage add j cc. concentrated HzSO?, z cc. C u S 0 4 ( I O per cent) and digest ti!l clear, and then a half hour longer. X small crystal of K h l n 0 4 is added, and. after cooling, t h e whole is made u p t o z j o cc.:. 2 j cc. are pipetted out into a IOO cc. Sessler tube, 2 j cc. of N a O H ( j per cent) added, and the volume made u p with ammonia-free water: t h e tube is then stoppered and allowed t o stand 24 hrs.: I O cc. are nesslerized after making u p t o j o CC. The reading on standard X I O = parts per million of nitrogen.
Yol. 8,
KO.6
IOO cc. of sewage a d d 5 cc. of concentrated HYSOl and I O cc. C u S 0 4 ( I O per cent), digest until clear, and then a half hour longer. Add 0 . j g. KbTnO4, make u p t o j o o cc.. and pipette 5 0 cc. into a steam distillation flask. -4dd j o cc. Xa2COs ( I O per cent) and distil over 2 5 0 cc. Make u p t o j o o cc. and nesslerize j o cc. Reading X I O = parts per million of nitrogen. E F F E C T O F TIME-In t h e method a t first employed, t h e samples were nesslerized as soon as they had settled clear, or immediately after filtering. A fentypical results are given in Table I. Since the results b y direct nesslerization were a!ways too low, it occurred t o us t h a t a n increase of time for t h e reaction in alkaline solution might increase t h e amount of nitrogen found. A series of samples of raw sewage were r u n , allowing t h e digestates t o stand 24 hrs. before nesslerizing. X shorter period did not give good results. -4 few of t h e results are found in Table I.
TABLEI - N I T E O G E h
IN P A R T S PER
IMXEDIATE XESSLERIZATION Distillation . . . . . . 25 25 10 85 35 Direct., . . , , . . , 17 10 15 14 17 EFFECTOF TIME: Distillation . , . . . , . . . . . . . . 50 30 40 once . . . . . . . . , 15 10 20 Direct At After 24 hrs . . . . . . , 50 20 35
{
MILLIOPR A W
SEWACE
40 20
25 14
35 20
54 52
48 34
25 40 3 5 30 10 22 18 18 20 38 30 25
5'0
30
25 10 22
35 20 35
30 10
35 I
50 20
15 50
I4 26
EFFECT O F KMn0,-The fact t h a t in the distillation method we added 0 . j g. K M n 0 4 while in t h e direct n-e added only a small crystal, suggested t o us t h a t in t h e latter case we might not be adding enough K M n 0 4 in order t o bring about a n equivalent amount of oxidation. Experiments with varying amounts of KAln04 in both methods showed t h a t the concentration of t h e K l l n O i did not influence the results at all. E F F E C T O F CuS04--TTarying concentrations of CuSOz were tried, and. equally as good results were obtained with 2 cc. as with I O cc. of I O per cent solution of
cuso4. CosCLcSIoKS
I--The direct method for determining organic nitrogen in sewages proposed by Whipple has been slightly modified. 2-The length of time the digestates are alkaline influences the accuracy of the results. We found t h a t the best results could be obtained b y allowing t h e samples t o stand 2 4 hrs. before nesslerizing. 3--Increase in concentration of potassium permanganate has no influence on t h e results obtained. q-Increase in concentration of copper sulfate has no effect. \VATER
APD
SEWAGE LABORATORY
UXIYERSITY OF KANSAS,
L.4U'REXCE
ON THE VOLUMETRIC DETERMINATION OF TIN BY POTASSIUM IODATE By GEORGES JAMICSON Received December 29, 1915
The iodine and ferric chloride methods are t h e ones most commonly employed for the volumetric estimaIn all t h e work t h e following distillation method tion of tin. The iodine method is based upon t h e as recommended b y t h e Standard Methods of Water titration of stannous chloride in hydrochloric acid Analysis was used t o check t h e direct results: TO solution with iodine, using starch as indicator, while 1 Public Healih, 31, 116, Part 2. the ferric chloride method in general use is based 2 Sun. Research Lab., 4, 162. EXPE R I U E NTA L
T H E J O C R N A L O F I N D G S T R I A L A N D ENGINEERI-\TG C H E M I S T R Y
J u n e , 1916
upon adding an excess of ferric chloride t o a hydrochloric acid solution of stannous chloride a n d titrating t h e resultant ferrous chloride with potassium permanganate. T h e iodine method has b y far t h e widest application, as it can be used t o titrate stannous chloride in t h e presence of ferrous salts as well as metallic antimony, which would react readily with ferric. chloride. T h e iodate method has t h e advantage over both of these methods in t h a t t h e end-point is exceedingly sharp. Furthermore, there is far less danger of overtitrating t h e solutions. Another advantage is t h a t extreme precautions t o prevent outside oxidation of t h e tin during t h e titration are not necessary because t h e potassium iodate may be added very rapidly t o t h e appearance of iodine i n t h e solution, t h e n without further precaution t h e titration can be completed as slowly as desired. I t should be observed t h a t t h e iodate method cannot be employed t o t i t r a t e tin or stannous chloride in t h e presence of cuprous, ferrous, antimonious salts or precipitated metals. However, in t h e majority of cases, it is a simple matter t o avoid or eliminate these interfering substances a n d apply t h e method with satisfactory results. T h e method t o be described is based upon t h e t i t r a tion of precipitated tin or stannous chloride with potassium iodate i n t h e presence of strong hydrochloric acid, according t o t h e general method of L. W. Andrews' which has not been previously applied t o t h e estimation of tin. I n order t o test t h e method, a solution containing 3. j67 grams of normal potassium iodate in 1000 cc. was prepared. According t o t h e equations of t h e reactions,
j0I
t h e oxidation of t h e stannous chloride solution a n d i t was observed t h a t t h e more solution removed from t h e liter flask, t h e faster t h e stannous chloride was oxidized b y t h e oxygen of t h e air admitted t o t h e flask, as would naturally be expected. TABLEI-TITRATIONOF STANNOUS CHLORIDESOLUTION Expt.
Date Mav 1 . . . . . . . . . . . . . 14 2 . . . . . . . . . . . . . 17 3 . . . . . . . . . . . . . 17 4 . . . . . . . . . . . . . 18 NO.
SnClz Solution Cc. 10.0 10.0 10.0 10.0
KIOs Used Cc 16.0 14.9
15.0 14.8
Sn(As SnClz) PRESENT Iodine Iodate Error Method Method Gram 0,0636 0,0635 -0.0001 0.0595 0,0591 -0.0004 0.0595 0.0595 0.0000 0.0587 0.0587 0.0000
From these experiments it will be seen t h a t t h e iodate titrations checked t h e iodine titrations closely. T h e iodate method will be found very convenient t o determine t h e amount of stannous chloride present in solutions. I n cases where it is necessary t o t i t r a t e considerable amounts of stannous chloride, it is recommended t h a t a much stronger solution of potassium iodate be employed, as i t is very important t o have t h e solution a t t h e end of t h e titration contain a t least I O per cent of actual hydrochloric acid t o prevent t h e hydrolysis of t h e iodine monochloride. For t h e next series of experiments, a standard solution was prepared b y dissolving exactly 3 grams of pure tin in about I jo cc. of concentrated hydrochloric acid, with enough nitric acid t o oxidize t h e tin t o stannic chloride. Three grams of tartaric acid were added a n d t h e solution was diluted t o one liter. Measured portions of this solution were placed in t h e t i t r a tion bottles, in each of which was placed z grams of high-grade 30 mesh zinc. After t h e reaction had proceeded for 2 0 minutes or longer, 40 cc. of I : 2 hydrochloric acid were added. As soon as t h e zinc KIOB Sn 6HC1 = SnC14 KC1 IC1 3 H z 0 , had completely dissolved, leaving metallic tin, several cubic centimeters of potassium iodate were added, zSnC12 6HC1 = KI08 2SnC14 KCl IC1 3 H 2 0 , followed b y I O cc. of concentrated hydrochloric acid a n d a piece of platinum foil t o facilitate t h e solution of t h e equivalents of this solution are respectively I cc. = t h e tin. T h e titration was continued with very thor0.001983 g. Sn a n d 0.003966 g. Sn. T h e titrations were carried out in 2 5 0 cc. glass stoppered bottles ough shaking until t h e tin was practically all dissolved. i n t h e presence of a cooled mixture of 30 cc. concen- Then 6 cc. of chloroform were added a n d t h e titration t r a t e d hydrochloric acid, 2 0 cc. of water, a n d 6 cc. of finished in t h e usual manner. I t is very important chloroform. During t h e first part of t h e titration, during t h e titration t o a d d sufficient potassium iodate t h e potassium iodate was added rapidly while shaking so t h a t there is free iodine or iodine monochloride t h e bottle so as t o give t h e contents a gentle circular present in t h e solution a t all times, otherwise some of motion until t h e iodine color, which gradually appeared, t h e t i n might dissolve, forming stannous chloride a n d had increased t o t h e maximum amount, t h e n t h e hydrogen a n d t h u s cause a serious error. ,4 blank stopper was inserted a n d t h e solution was thoroughly determination using 2 g. of zinc a n d t h e same a m o u n t shaken. T h e titration was continued with thorough of hydrochloric acid as in t h e actual titrations required shaking of t h e closed bottle after each addition of 0.20 cc. of potassium iodate solution, which has been potassium iodate until t h e end-point (the disappear- detected from t h e amounts of solution (KIOp used), ance of t h e violet color of t h e chloroform) was ob- given in Table 11. tained. TABLE11-REDUCTION BY ZIKC A N D TITRATIONOF T I N BY IODATE
+
+
+
+
+ +
+ +
+ +
The first experiments were made using a solution of stannous chloride which was prepared b y diluting jo cc. of t h e laboratory reagent t o a liter. T h e solution contained 2 2 j cc. of I : I hydrochloric acid per liter which was sufficient t o maintain a perfectly clear solution. This solution was standardized b y t h e iodine method on three different days as indicated in Table I. No precautions were t a k e n t o prevent 1
J . 4 m . Chem. Soc., 26 (1903), 675.
KIOa used
cc.
i:::::: : : : : : : : : : : : :
3 .................... 4 ....................
5.. . . . . . . . . . . . . . . . . . . $;:I: 1 : : : : : : : : : : : : : :
7.6 30.2 24.0
i;:?
Tin present Gram 0.0300 0.0600 0.0150 0.0600 0.0476 0.0420 0.0900
Tin found Gram 0,0297 0.0601
Error Gram -0.0003 i o . 0001 +0.0001
0.0151 0,0599
-0,0001
0.0416 0.0902
-0.0004 4-0.0002
0.0478
'0.0002
These results show excellent agreement with t h e amounts present, t h u s confirming t h e equation given in t h e first part of this paper. The solution of tin
502
T E E 3OURNAL OF Ih'DUSTRIAL A N D ENGINEERING CHEilNSTRY
even in t h e presence of platinum was slow and it was found t h a t a titration required from to of an hour for completion. An a t t e m p t was made t o reduce stannic solutions t o t h e stannous condition with nickel powder which was made by reducing t h e oxide with hydrogen a t a red heat, T h e nickel powder was found so reactive t h a t unless large amounts were used, i t dissolved so quickly t h a t only a partial reduction of the tin was obtained. Since it appeared t h a t nickel would be the most suitable reducing agent for general use with the iodate method, t h e next series of experiments was made using strips ( I X j.j X 0.1cm.) of sheet nickel for the reduction. which was found satisfactory. The reduction was made in 2 j o cc. Erlenmeyer flasks provided with a 2-hole rubber stopper which carried a glass t u b e extending t o within I cm. of t h e surface of t h e liquid. T h e other hole was provided with a short tube which extended a short distance below t h e stopper. Several experiments were made using measured portions of t h e stannic chloride solution described above. T o each portion of this solution 1 5 cc. of concentrated hydrochloric acid and 2 nickel strips were added. The stopper was inserted a n d the flask was heated on the steam b a t h for 45 minutes t o ensure t h e complete reduction of the tin. Then a current of carbon dioxide gas was passed through the longer t u b e and t h e flask was placed in ice water. When the solution had reached approximately t h e temperature of the bath it was filtered b y suction into a titration bottle (containing 6 cc. of chloroform) t o remove the finely divided nickel which had separated from the edge of the strips. T h e filter used was a calcium chloride prolong tube ( I O X 1.8 cm.), provided with a perforated platinum disk upon which was placed a thin layer of absorbent cotton, a layer ( 2 . j cm.) of purified sea sand, and another thin layer of cotton on top. Other filter mediums were tried b u t were not found satisfactory. Before pouring the solution into the filter, a moderate stream of carbon dioxide gas was led in b y means of a bent glass t u b e which extended t o within I cm. of t h e filter bed for a minute after starting the suction. T h e flask and filter were washed with small amounts of I : I hydrochloric acid and t h e solution was titrated a t once as described above. I t was found necessary t o make blank determinations under the very same conditions as in t h e actual experiments with each new lot of sheet nickel and apply t h e corrections (due t o t h e iron content of t h e nickel) t o the subsequent titrations. The results in Table 111 111-REDUCTION B Y S H E E T NICEE% AND T I T R A T I O N OF S T A N N O I J S S A L 1 Error Tin present Tin found SnCh taken KIOs used Gram Gram Gram cc. 1" cc. 0,0000 0.0900 22 7 7 0.0900 1 . . . . . . . . 30.0 -0.0003 0.0627 0.0630 15.80 2. , , , , , , . 21.0 -0.0001 0.0539 0,0540 13 60 3 . . . . , . . . . 18.0 -0.0001 0.0299 0.0300 7.55 4 . . , . . , , , , . 10.0 -0.0003 0.0294 7 40 0,0297 5 . , . . .,,., . 9.9 -0.0002 0.0298 0,0300 7 50 . . . . , . . , , , 10.0 -0.0002 0.0298 0.0300 i . , . . . ., ., . 1 0 . 0 i.50
TABLE
Erpt.
6
include this correction, amounting to 0 . j cc. of t h e potassium iodate solution. Several blank determinations were made upon t h e nickel used in this investigation with concordant results. I n order t o apply this method t o the determination
Vol. 8, KO. 6
of tin in solder and type metals, a sample of 0 . 2 - 0 . j g., depending upon tin content, was heated in a 2 5 0 cc. Erlenmeyer flask with I j cc. of concentrated sulfuric acid. It is very important t o boil t h e solution gently until all t h e sulfur dioxide is expelled, otherwise, it would be titrated along with the tin.' After cooling, 20 cc. of water a n d I j cc. of concentrated hydrochloric acid were added, after which t h e tin was reduced and titrated as described a b o i e . The following results mere obtained: TABLEIT-ANALYSIS
TIN ALLOYS KIOa used Grav. Det Tin found G. Cc. Per cent Per cent 0,5000 6.30 5.04 4.99 0.5000 6.25 5.04 4.96 3.5000 3.90 3.20 3.09 0.5000 4.00 3.20 3.1, 0.2000 19.60 38.761al 38.86 OF
4110y
Expt. NO.
I ......., . . 2... .. . . . . 3..... .. , . . 4 . . . . . .. . . . 5.. ., . . . . , ( a ) Iodine
.
.
NAXE Type Metal Type Metal Type Metal Type Metal Solder method.
I t is recommended'that a n iodate solution containing 8.994 g. of KIOBper liter ( I cc. = O . O I O O O g. Sn) should be used for t h e analysis of solders, using 0.5 gram sample. I t should be observed in t h e analysis of t y p e metals, etc., t h a t when t h e filter becomes clogged with precipitated antimony, it should be heated with warm nitric and tartaric acids and washed thoroughly with water and hydrochloric acid until all of t h e antimony is removed. Also it is advisable t o keep the nickel strips free from deposited metals by frequent cleaning. Since bronze contains so much copper it was found best t o decompose t h e m in the usual manner with nitric acid and filter t h e metastannic acid in a Gooch crucible. After washing t h e precipitate, i t was transferred along with t h e asbestos mat t o a 2 5 0 cc. Erlenmeyer flask, a n y metastannic acid adhering t o t h e sides of the crucible being wiped off with a pinch of slightly d a m p asbestos and added t o t h e main precipitate. About 1 5 cc. of concentrated sulfuric acid were added a n d the flask was heated until the acid had boiled gently for z or 3 minutes. After cooling thoroughly 2 0 cc. of mater and 1 5 cc. of concentrated hydrochloric acid TTere added. The asbestos was filtered off o n a Gooch crucible and washed with I : I hydrochloric acid, using as little as possible. Then the solution was reduced with nickel and titrated in the usual manner. T A B L E \'-QNALYSIS
i\lloy G. 0.5000 0.5000 0.5000
KIOs used cc. 10.95 10.93 11.05
OF BRONZE Tin by Grav. Det. Per cent 8.75 8.75 8.75
Tin found Per cent 8.68 8.66 8.76
T h e results of this investigation show t h a t tin may be estimated with accuracy b y the iodate method and t h a t i t is applicable t o the analysis of alloys a s well as solutions. With this titration i t is important t o maintain a n acidity of a t least 1 0 - 1 2 per cent of actual hydrochloric acid in order t o obtain t h e correct reaction. Furthermore, i t should be remembered t h a t cuprous, ferrous: and antimonious salts, as well as any precipitated metal, will react with potassium iodate. SHEFFISLD CHEMICAL LABORATORY Y A L E UNIVERSITY,
1
NEW
HAVEN
A m . J . Sci., 38 (1914), 166.
