May. 1944
349
ANALYTICAL EDITION
Determination of Sulfur in Brass and Bronze by the Combustion M e t h o d ALBERT C. HOLLER AND J A M E S P. YEAGER, United Stater Metal Producb Co., Erie, Pa.
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H E authors have successfully applied the well-known hightemperature combustion method of Hale and Muehlherg (1,s) to the determination of sulfur in braan and bronze.
Figure 1 shows the absorption end of the combustion train. A Dietert Varitemp c o r L tion furnsce used for tht alyses. The gen was pur16 passage th concentrated furie mid, 401 tassium hydru.-vu, and a n A s w r i t e calcium chloride tube, in order. The exit end of the Ziroofrax combustion tube was packed
was complete (5 or 10 minutes) the mid was titrated with the standard sodium hydroxide solution with the oxygen still on. The combustion was continued for another 5 minutes and if the acid color of the indicator returned, alkali wa8 added until the end point was again reached. The method was tested on Bureau of Standards samples 124 of ounce metal and 63s.of nhosohnr hronee hearin. mdal (Tahlo I).
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found to be the only suitsble bedding material for use in the combustion boats. Because of the presenoe of paphite in some of tlre sarnplpa, bromocresol grccn ( p H ranee 3.8 to .i, 1) was u r d as indicator in the titration of It.? acid. T h P d l u m hgdrnxide d u t i o o was standardized a~!ainsts O.d-rram snmol.: oi Uunau oi Standards l9~-&1, h.O.H.ywliich rmt&ins0.U40b; sulfur. A 0.1- to 1.0-gram sample of drillinga wlirh remam on a No. 00 hut pass through a KO. 20 siew was tykrn for ana1)ais. Thp s m p l e was burned a t 2100' F. i n R stwnm of d x y ~ e nw h k h pamrd at the rate of 2 liwr.3 per minute. \!'hen the rombu6tion
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The authors wish to express their deepest appreciation to T. S. Woodward, Carnegie-Illinois Steel Corporation, Youngstown, Ohio, for his helpful comments in connection with this paper.
The (Predictable) Concentrating of Standard Solutions Owing to Evaporation H E R M A N A. LIEBHAFSKY, Research Laboratory, General Electric Company, Sshmeebdy, N. Y.
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H E suthor has seen no evaluation of the (predictable) increase m normality caused by the evaporation of water that oooum in a carboy from whioh a standard solution is being withdrawn 8nd replaced by dry air under the simplest experh31Ital conditione. The problem a m e in this 1a.boratory in oonnection with routine titratione of high precision. In carrying out these titrations, about 40 ml. a t a time of carhonate-free sodium hydroxide are forced by meam of dry, carbon dioxide-free air from a 15liter carboy into the buret. h u m e (1) that a carboy of any Bhape whatever is initially filled with VJ litem of?tandard Frnormal solution, (2) that each portion of solmt.inn mt.hdmwn 1s.~~ renlaeed bv drv air. and (3) =~ that the w soace in the carboy becomes &tu&d dith waier wpor becweezi withdrswals. Consider the system when the carbay contains an arbitrarily chosen volume, V , of N-normal solution, the solute being nonvolatile. Let 0.024 gram per liter be the water content of satujated air under labomtory conditions. Then, if dV liter of solution has just been anthdrawn, 0.024 ~
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dV grsm (or ml.) of liquid water will bo vaporirid, nnd 0.024 dlr.\r, I000 equivalertr t,f aulute will be left behind to ~ncreasethe narmalitv of the remainiim solution. Rut t1.k amount of solute i s ~ e q kilo VdN equivaleth, where dN is the resulting increase in normlity. UgOn considering the sign of dV, equating, transposing and integrating, one now ObtaiSs In N d N i = 2.4(1O1;)X In V,/V2, or log N*/N, = 2.4(10-6)10g V,/V,. (The rubscripts refer to arbitrarily chosen initial and h a 1 states; N must inorease as V decreases.) If the volum~of solution in a 15-liter carboy is redneed in the manner prescribed to 1.5 ml., log Nz log NI = O.OM)l, or the normality of the residuum will increase by 0.02%. which is negligible for most volumetric work. ~~~~~~
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If the simplest experimental conditione do not obtain-if, for example, the room temperature varies markedly, or if there is loss of water vapor from the carboy, &s to a drying agent-then unpredictable changes larger than 0.02% may occur in the normality of a standard solution.
