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T H E J O U R M A L O F I N D C ' S T R I A L ALVD E N G I N E E R I N G C H E N I S T R Y
second fusion of such oxides gave no further carbon dioxide t o a freshly filled and clear barium hydroxide tube. Great care was taken a t all stages of t h e work t o eliminate extraneous carbon dioxide or other substances t h a t would cause a blank, so t h a t , as already stated, t h e blank was always negligible. The frequent blanks which were made during this work myere carried out ( I ) without any steel in t h e furnace; ( 2 ) when burning B. of S. Standard Steel No. 2 3 , which, as shown in t h e table of results in this paper, gives identical values when burned in the ordinary way and by our modified method. The fused oxides were readily remo1Ted from the boats, in preparation for t h e next combustion, by digesting in strong hydrochloric acid for a few hours. The results in t h e table show t h a t some steels give higher results by the new method t h a n are shown on t h e certificates, others yield only slightly higher figures a n d still others give the same results by both methods. We find it impossible to relate these three classes with t h e size of drillings used, with t h e carbon content of t h e sample, or especially, with t h e presence or absence of t h e usual alloying elements. In only two cases were t h e results by the modified method as much as 0 . 0 2 per cent higher t h a n the certificate value; with most of t h e other samples t h e difference was of t h e order of 0.01per cent. Our work does not cover the Bureau's complete series of standard analyzed steels and irons, but t h e results are deemed quite representative, and we believe they are complete enough t o justify us in t h e conclusion t h a t t h e certificate values for these steels cannot be affected with a n error greater t h a n 0.01j per cent (probably minus), and in most cases t h e error is much less. I t is believed t h a t such errors are negligible, considering t h e uses to which these standards are a t present being put. The experimental difficulties and t h e inconvenience of this method of determining carbon place it beyond t h e reach of most industrial and works laboratories, and we do not, therefore, recommend its use t o such, except in t h e case of products for which it may be found better adapted t h a n other methods. BCREAUOF STANDARDS, WASHINGTON
AN ACCURATE END-POINT IN THE VOLUMETRIC DETERMINATION OF SULFUR IN STEEL By HERBERTZSCHIEGNER Received November 26, 1915
The following method was devised with the object of eliminating the inaccuracies due t o t h e varying shades of t h e blue color of t h e starch iodide formed in t h e titration of hydrogen sulfide with iodine. While it depends primarily on t h e production of starch iodide, as does t h e former method, the actual blue color is disregarded. In t h e experimental evolution of this end-point a standard solution of potassium iodide and iodate was used, together with a n ammoniacal solution of cadmium chloride as a n absorption medium and a solution of wheat starch as indicator. The iodine or iodate solution is made slightly stronger t h a n usual and is standardized against a steel of known sulfur content.
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This deviation from the usual method is in use in our laboratory and yields very good results. The starch solution found to give t h e best results is made by rubbing t o a paste with water, 1 2 g. of wheat starch and pouring the mixture into z liters of boiling water in which is dissolved 3 g. of potassium or sodium hydroxide. Two cc. of this solution are measured from a pipette or burette for each titration. Starch solution thus prepared will keep indefinitely and is not subject t o t h e salting out of t h e colloidal starch which is t h e case when zinc chloride is added as a preservatire. To obtain uniform results a standard m o d u s o p e r a n d i must be adhered t o . The volume of the HC1 used t o decompose the CdsS, t h e volume of t h e indicator, and t h e volume of the final solution must equal t h e volumes of t h e solutions used in standardizing t h e iodine or iodate solution. A special titrating vessel is required, consisting of a white porcelain beaker, about 7 cm. in diameter and 16 cm. in depth. On the bottom of this beaker (inside) is cemented a thin, black disc of hard rubber or celluloid about 2 cm. in diameter. ( A substitute for this vessel may be made by painting t h e black spot on the outside of a glass beaker, then covering the whole outside of the beaker with white enamel; t h e black spot should then appear sharply defined against the white of t h e beaker.) The determination is carried out as usual until t h e titration is commenced, then t h e black spot is carefully observed, and as the solution darkens t h e iodine is added carefully with agitation. Finally a point will be reached when one drop of iodine will render t h e 'spot invisible on allowing t h e solution t o come to rest. This is t h e end-point and t h e burette reading may now be taken. Owing to the milkiness of t h e solution when high sulfur iron or steel is being analyzed the black spot may not a t first be apparent b u t will become plainly visible when t h e titration is about four-fifths completed and will remain so until t h e last drop of iodine renders it invisible. The end-point is sharp and the results in terms of per cent do not vary more t h a n 0,001. An incandescent lamp may be placed a t such a distance from t h e titrating vessel t h a t t h e same results will be obtained with artificial light as with daylight. The light should not be situated directly over t h e beaker b u t t o one side of it. AMERICANLOCOWOTWE COMPANY SCRBNECTADY,N. Y.
THE DETERMINATION' OF BARIUM CARBONATE AND BARIUM SULFATE IN VULCANIZED RUBBER GOODS' By JOHN B. TUTTLE Received November 17, 1915
With t h e advent of buying rubber goods on specifications i t became necessary t o develop methods which would accurately determine the various constituents. One of the most important determinations is t h a t of total sulfur. I n a recent publication of this Bureau,2 the sulfur-bearing constituents of vulcanized rubber 1 2
Published by permission of the Director of the Bureau of Standards. Bureau of Standards, Technologic Paper, 46; THIS J O U R N A L , 7
(1915). 6 5 8 .
