26
DETERJlI.Y.lTIOS O F Z l S C
PYROPHOSPHATE.
VII. DETER3IINATIOK O F ZIXC AS PYROPHOSPHATE GY
CfSO.
0.STONE, 1’11. 13,
Sometime since I Iiad occasioii to aiialyze a sample of water said t o contaiii tlie tailings from a n aninlgamatirig mill. T h e analysis of the srisl~cndctlmatter only nrldccl u p about eighty-eight per cent. I tried lmiliiig the filtrate from tlie magnesia with KOII, this threw tIow11 :1 f i l l C , c ,t:illinr. white pi ipitate; on making a qnalitativct cl?;:tniiiiatioii of 11iis I foiincl it c:oiitaincd ZnO, and P,O,. 011wcighiiig t h r ~ ) r w i p i t n tand e cslcnlatiiig thc amount of ZuO. it coiit:iiiictl, sii~~1)osiiig it t o 1~ Zn, PzO,, I found it eleven and a fraction per c(iiit., which niade niy aiialysis a d d t i p very close t o one huntlrc!(l p i . (wit. ‘l’liis led nit! to cxperimerit with phosphate of zinc yit.h tlic foliowiiig results. If :I mixtiire of an avid solrition of a zinc salt :tncl nn alltalitie ortlio-l)liospliate is e x i c t l y iicutralized with aninionin, the zinc iS prcuipitntcd as a bulky, flocculent, t~oublephosphate of ziiic and ammorii:i, casily so1iiI)le in aritl:: or :iminonia, aiid sliglitly soluble in potassic hydrate. If t,lic: soliitioii i i i xminonia is boilrd, tliedouble. pliosplintc re1)rwipitates a s a f i i i v , crystnlliiie white precipitate, very sliglitlj~soliible i n ~inirnoiiia,a ~ t almost l n l ~ o l u t e l yirisoluble in water. I f tlie boiling is corititinecl till the frce aninionia is all driven off, tlie precipitntion is complete. 0 1 1 dryiiig aiid igniting this precipitate the zitic is obtained as pyrophosphate Zn, P, 0,. This mc>tliotl o f dvtcmiining ziiic lins several advantages over t h e one coninionly ettiployd, of precipitating as sulphide, dissolving in hydrocli101,ic acid, rispreciipitating as basic carbonate, igniting and weighing as oxide. First.--It is rnucli quicker, as it is not necessary to let the precipitntiori st:titd, and there is only one precipitation. Second.-‘l’lie preoipit,ate scttlcs rnl)idly, filters quickly, does not run tliro1igli the filter, washes easily, dries quickly, brushes off the paper cnsily m i d conipletely when dry, :ind is ~ r r ydificalt to i’edU(!C. ,, J 1iirtl.--The presence of ammonia salts docs not, interfere with the conipletctiess of t h e precipitation. I n all of wliicli part,iculars its behavior is quite tlie reverse of that of either the sulphide or basic carbonate. Fourth.-The pyropliosphate contains only 42.16 cent. of zinc, while the oxide contpins 80.25 per cent. so that an error i n weighing makes much less difference in the result, ~ ( 3 ‘ .
DETERMINATIOX O F ZINC AS PYROPHOSFIIATE.
27
Fifth.-The phosphate does not need any purification, whereas the oxide frequently contains silica. On the other hand the phosphate bumps badly while boiling out the ammonia ; and the piecipitate sticks pretty tightly to the beaker. If the solution is kept rather dilute and only just enough ammonia is added to redissolve the precipitate first formed, and the solution is frequently stirred, the bumping will not give much trouble. The precipitate that sticks to the beaker is best removed by dissolving in a few drops of HCI, adding a little NaNB, HPO,, making just alkaline with X€I,OH and boiling till the free ammonia is expelled. Ezreriment I--Was made more to test the behavior of the phosphate of zinc and to see if the results agreed, than to test the absolute accuracy of the method. 0. 2 grms. of zinc,coated with oxide, were dissolved in H 2 S 0 4 and a few drops of ENO,, the solution was diluted t o about 300 cc., an excess of NaNH,HPO, addto re-dissolve the precipitate first ed, and just enough ",OH formed. The solution was then boiled till there was no longer any smell of N H,, filtered, washed thoroughly with hot water, dried, ignited and weighed. Gave : A Z n , P 2 0 , 0.4627 grms.=Zn 0.1979 grms. B Z n 2 P 2 0 , 0.4624 grms.=Zn 0. 1977 grms. A was filtered as soon as the NH, was expelled. B was allowed to stand in a warm place for three hours after boiling. Ezperriment 17.-0.2 grms. of zinc ore, mainly oxide, was dissolved in HCl, HNO, and II,SO,, evaporated till the HC1 and HNO, were expelled, diluted, filtered, the iron separated as basic acetate, dissolved and reprecipitated by a large excess of N H,OH, the filtrates combined and evaporated to about 300 cc., an excess of N a N H 4 H P 0 , added and the zinc determined as in I. I n a second portion of 1. 0 grm. the iron was separated as above,the zinc precipitated by H 2 8 in a boiling acetic acid solution, let stand, filtered, washedl dissolved in HC1, reprecipitated as basic carbonate by Na, CO,, ignited and weighed as oxide. Gave : A Zn,P,O, 0.3441 grms. Zn 0.1471 grms.=73.55 per cent B Zn,P,O, 0. 9149 grms. Zn 0.7341 grms.=73.41 " " Experiment 11%--0.2
I1 and gave : A Zn,P,O, €3
Grms. ferruginous blende treated as in
0.2721 grms.=Zn ZnaP,O, 0.2716 grms.=Zn
58.17 per cent 58.07 " ''
28
DETERJZINATION O F Z I N C AS PYROPMOSPHATK.
The analysis was afterwards completed and gave : Zn (average of 2 determinations‘ 58.12 per cent L L Fe T.61 (‘ “ Inso1til)le siliciour matter 1. i.? (‘ 8 calciihtcd t o give F e S and Zn s 32.96 “ “ ‘j
Total,
100.1?
13zprimeiit IV-1.0 grxn. Zn ,C,TI,O,), I H,O dissolved in water, excess of 2\‘aNI-1411P0, and NIi,OII added, the NII, expelled by boiling and the zinc determined as before. Gave : iZ Z i i e P 2 0 , 0.6953 grms..=Zn 211.78 per cent 13 Z i i 2 P 2 0 q 0.6974 grins.=Zri 20.62 ( I The theoretical pcrckntage is I 9 68. Erperinrcizt T’--‘l’o test tlic intliient e of alkaline and ammonia ‘I
salts :
0.5 grins Zn ‘ C 2 1 1 3 0 g ) , 2 H20,2.0 5’”s. Na, C O , , 2.0 grms. NH4C1, and 5.0 q n i i Na C,II,O, the Yinc detc3rmiried n i b c . f o i ~gal c : A %n21’,0, 0 3484 grins. = Zn 29.78 per cent 13 %nzl’,O, 0 3Ui9 grmr. = Zn 29 66 per cent.
Erpeviiizent W.--8~ tlic pliospliate of zinc is soluble in NH,OH, while the pliosplintcs of lime, magnesia, and manganese are insoluble in it, it seemed prob;il~lcthat thc h c could be separated by means of this reaction. The follon ing cxperirnents were tried to 01 test thiq : 0 5 grm. Zn (C’21130z)t’2 1 1 2 0 , 0 1 grm. Nn304, grm. CaCO, and 0.1 grin. MgSO, ; I 1 2 0 were dissolved in HCi excess of h’a SlI,IIPO, an(1 NII,OH added ant1 let stand cold for eighteen hours, t h e clear soltitioil filtciwl off, the precipitate dissolved in IICI, rcprecipitatetl by NII,OII and a f e w drops of Na NH4111’04, filtered, u aslied \\zitti cold dilntck SI14011, the NH, boiled out, niitl t h e zinc deteriiiiirc~tlas before, ga\ e . A Zn2PzC), 3-4-14. grin. = Zri 20.40 per cent. 13 Zn,PBO, 0.3451 grms. = Zn 29 t52 1wr cent T h e phosphate5 of mangancsr and lime clogged the filter arid showed a tendency to run tlirough it. To get good results the solution must be rather dilute (400 t o 300 cc.) Expriinent 1711-0 5 grin
