C H E M I S T R Y O F THALLIURI
1011
age \vas held constant when at bvork by ineaiis of the volt meter and rheostat. T h e bar hvas of nwod and carefully graduated to sisteenths of an inch. Its base served as a track for the Luiiimer-Rrotlliun sighting box to run on. T h e bar was 8 feet long with the electric lanip a t zero. T h e distance from the other end of the bar to the street light was measured by means of a light stick, with a pointer at one end of it and a fork at the other, large enough to span the lamp. Each prong of the fork terminated with a ring with a wire cross-hair stretched across it. This afforded an easy and accurate means of getting the distance from the center of the mantle t o the end of the bar, which of course, varied with the different lamps. The instrument required two inen to operate i t ; one to adjust the bar and take the reading and the other to line up the cross hairs rvith the mantle and get the distance from the bar. T h e time required to back up t o a lamp, adjust the bar, take the readings and measurements and get away was about seven minutes. The candle power of the lamps for each night's work was figured out afterwards by means of logarithms and a table of squares. Erie, Pa.
CONTRIBUTIONS TO THE CHEMISTRY OF THALLIUM, 11. BY L. F. HAWLEY. Received hloy 2, 19;.
.4 :Vex! Jfctlzod f o r f h c Grwiiiictric Detcrrriiiiation of Tlzaiiiriiii. By precipitating and weighing the thallium as thallium sulphostannate, T1,SnS,l, a very accurate and easy determination of thallium can be made. T h e thallium sulphostannate can readily be prepared in pure condition ; it is practically insoluble in water so that it can be washed very thoroughly without loss, and it can be dried at 105' without decomposition. 'l'he thallium may be in either the thallous or thallic condition at the time of precipitation since the precipitants will also act as reducing agents. All t h e elements precipitated by sodium sulphide, including those which are soluble in excess. will interfere with t h e formation of pure thallium sulphostannate. T h e reagents rtquired are a solution of primary sodium sulphide with a concentration of about I jo grains per liter, and a solution of sodium sulphostannate containing only a slight excess of sodium sulphide. This latter solution need not be free from the sodium salts formed in its preparation and can therefore readily be made by adding sodium sulphide solution to a solution of stannic chloride until the precipitate first formed is just dissolved. The procedure for the preparation of the pure thallium sulphostannate is as follo\vs : To the hot and very slightly acid solution of the thallium salt add an excess of the sodium sulphostannate solution, i. c.. more than enough to form Hawley, J . Physic. Chem., 10, 6j4 (1906).
I,. F. HAWLEI'
I012
'rI,SnS, with all of the thalliuiii present. The precipitate iiu\v consists of TI,SnS, and the solid solutio~iIvitIi excess of stannic sulphide' : if the solution is still acid there is also soixe thallium unprecipitated. =Idd the primary sodium sulphide wlutioii drop 1)y drop Jvith constant stirring until the solution is neutralized. then atltl at once 25 cc. more and heat to boiliiig. Eoil sIo\vl!. ior fi\-e minutes. stirring xvitli ;1 rot1 held against the bottoin of tlie beaker to prevent bumping. This lioiliiig in tlie prcseiicc ( i f the priiiiary sodium sulphitle solution dissolves any stannic sulphide i i i excess of the forinula TI,SnS,. : I slight decoiiipositioii of the tlialliuiii sulphostaniiate into thalliuiii sulphide aiid solublc stannic sulpliitle,amounting t o a loss n f from tivci to three iiiilligrams a 5 stannic sulphide ma!- take place on boiIiiig as aliove. Init ciii i1;Iuting the solution \\it11 \ v a t u aiitl allo\viiig i t to stand for t\vo o r three lioiir>. stannic sulphide i,s again take11 1111 and the precipitate finall!- coiisibts o f pure thallium sulpliostaniiate. This precipitate is filtered in a Goocli crucilile, is \vaslictl \\.it11 water. tlrietl at IO^". ani1 \veighed. Determinations of t!ic thalliiiiii in p i r e fiisetl tliallous sulpliati. 1)repai-ctl as in the prcyiouh article gave 80.96,S O . C )8~0, . ~ 0 , 80.96, 80.!)3. ant1 80.
