d.YdLYTIC'dL EDITIOAY
190 Table 111-Results T~KEV Gram
Obtained with Mercury Cathode Using a Standard Solution FUUND ERRUR FREE H.SOI Gram Gram p e r c< Gram AiUhlISL~T\l
0 0805 n 0808 n 0808 0 0808
0 0 0 0
0803 0802 080i 0806
+0 0001
0 0 0 0
0 0 0 0
002: 0025 0026 0025
0 0000
0025 0025 0023 0025
-0
-n -0
0 0 0 0
0006 0001 0002
0.14 044
o
Acknowledgment
044
01-1
0 044
The results ohtained with Bureau of Standard> zinc-ha+ die-casting alloys are recorded in Table IT'. Equally concordant results have been found in the case of other zinc-l1a.e alloys (about sixty in number) of knon 11composition olitaiiietl from other sources. Table IV-Results
Obtained with Bureau of Standards Zinc-Base Die-Casting Alloys B L R EOF~ S ~T A S D A R D S H g CATHODE METHOD
A
4 04 0 11
AI Mg
B 1 04 0 10
c
0 58 N o t detected
A 4 03 0 12
B 4 00 0 11
so. 2
fer this solution containing tlie undissolved copper to tlie electrolytic beaker. The copper will alloy with the mercury. Electrolyze the solution for 5 hours and complete the analysis a i described under Espeririiental Work.
044
0 044 0 04-1
0 0000 o on00 0 0000
Vol. 2,
c
0 jii 0 00
Recommended Procedure
The following method was adopted for the separation of aluminum and magnesium in zinc-base alloys: Dissolve a 2-gram sample of alloy with 20 cc. of 1:l sulfuric acid and 100 cc. of water. K h e n all action has ceased. trans-
The author wishes to thank H. T'. Cliurchill, chief clieiiti>t, ;Iluminum Company of America, for permissioii to use the data. R. ST. Bridges for valuable suggestions and criticism duriiig the course of the work, and the S e w Jersey Zinc Conipany for a sample of high-purity zinc. Literature Cited 1 1 ) Ardagh a n d Bongard. ISD. Esc,. CNEM , 16, 297 I19241 121 Blum, J . .lm Chem S a c , 38, 1282 119161. ( 3 ' Brophy, ISD E s c C l i E v , 16, 963 (191'43 . 4 1 Cain l b i d , 3, 476 (1911). '.j) Demorest. Zbid.. 5, 302 (1913). ( 6 1 Drown a n d McKenna, J .Inal C h r m , 5 , 657 11891, ( 7 ) Gibhs, .lrn Chpm. J , 13, 371 (18911: C h e m . Sr-,..i. 42, 291 l 8 6 f i i 181 Gooch and Havens. . I m .I, .Sciencr, [ 4 ] 2, 416 (1896, IS) Hillehrand and Lundell, "Applied Inorganic Anal 1919. 10) Kimley, J . .am Chem. Snc , 32, 6 3 i (1910). 111 Lundell, Bright. and Hoffman. ISD. E s c . CHEM 15, 11164 lQ2:3, 4\12 hIeyers. J . . l m . Chem S O C , 26, 1124 (19041. 113) Price, J . Sot. Chem. I n d , 26, 345 (1907). ( 1 4 ) S m i t h , "Electro-Chemical Analysis," p . ,55, Blakiiton', I W 7 (1.5) Smith. J . ' l m Chem. Soc.. 25, 883 (19031. ( 1 6 ) Smith. l b i d , 27, 1 2 3 3 119091
-
Confirmatory Test for Zinc' J. Stanton Pierce and Ethyl D. Nave T R . A s S u 1 . ~ . 4 s l .C ~ ~LLEGE LE , XIYGTON KY. ,
HE ferrocyanide titration of zinc, with uranyl acetate
T
as inside indicator, can be used as a confirniatory test for zinc in qualitative analysis, if interfering ions are remoyed previous t o the test. This method has the advantage orer most confirmatory tests that it affords a means of estimating fairly accurately the amount of zinc in the unknown. Zinc may be separated satisfactorily from small amounts of all members of group I11 cations except iron, by precipitation with hydrogen sulfide in 1S acetic acid solution containing aniinonium acetate, by filtration, and solution in 1 S hydrochloric acid. A trace of iron, particularly if in the ferric stat,e, interferes with tlie test. The separation of zinc aiid rnangaiiese by the above method is not sharp, so the test is not satisfactory in the presence of large amounts of manganese. Standard procedure is used for tlie precipitation of group 111, solution of all members except cobalt and nickel, aut1 precipitation of iron and manganese Jvith sodium hydroxide aiid sodium peroxide. Thus, the cations which interfere arc removed. Iluininiim also is removed by standard procediuc. hut, should it not be, it does not interfere in the slightest n-it11 the test. Tril-alent chromium interferes only by its color, aiitl this only slightly, even when present in high coiicentratioii. Either oxidizing or reducing substances interfere with tlie test. By saturation with hydrogen sulfide, all oxidizing st11~stances are removed. Hydrogen sulfide, formed by the actioii of hydrochloric acid on zinc sulfide, is remoi-ed hy evaporation to dryness. The residue is dissolved in a small wlunie uf 1 A' acetic acid. The titration may be carried out with sufficient accuracy 1
1930.
Received September 16, 1929.
Revised paper received J a n u a r y 4.
11)- the follon-iiig iiietiiod: To the acetic acid solutiim atid an equal volume of 0.01 -1-uranyl acetate antl add 0.5 -V potassium ferrocyanide from a medicine dropper (15 to I i drops per cubic centimeter), iiotiiig the number of drops r ~ quired to produce a distinct reddish 1jrowi color. If over 15 drops are required, or if the precipitate is colored due to iiiipurities. add more uranyl acetate. The nuinher of d r o p iiiiinis 1) of ferrocyanide rcpresentx the approxiniatc n i i i n tier of iiiilligrams of zinc in tlie unknowi. .\-ole-The dropper used gave 17 drops per cc. Actually. 1 d r o p corresponds t o 0 98 mg. of zinc, b u t t h e method is not accurate enough t o warrant making a correction for this. By using a standard zinc solution and titrating directly (nithout precipitating as iulfide etc 1, the iollowinx d a t a JT-ere ohtained lIil!igrams of zinc Llropi oi ferrocy,inide
0 1
2 , i 4
3
10
23
ij
I:!
28
60 34
Test of Method
Soliitioiis coiitaiiiing 5 mg. each of alLiniiiiuiii. cobalt. manganese. and nickel. and 100 mg. of chromium as chrornatp. aiiti yaryiiig aniouiits of zinc. were made 1 in aretic acid, 0.2 in amnioriiurn acetate, ailti hydrogen sulfide was introduced. The precipitate was filtered) v-aslied with dilute aniiiioniuin chloride solution. antl dissolved in 1 A\- hydrochloric acid. Tlie hydrochloric acid solution wab cvapciratetl to drylieis and the residue was t l i . ; i o l d in 2 cc. ~f 1 S acrtic acid. Titration was carried out as indicated al~oye. Zinc, mg. Ferrocyanide, drops
I)
1
, 1
10
w
2 ;i
30
23
30
As is evident from the amount uf ferrocyanide u 4 for the lower concentrations of zinc, a little zinc is lost, probahly as
the sulfide.
