XI. A, 4 Witt: Analysis of Babbitt Metal 171 



and the solution will become slightly yellowish. In this case it 

 is best to throw out the determination and start a new one, using 

 slightly less hydrochloric acid, because, under such conditions, 

 the true end point cannot be obtained. 



TIN 



Walker and Whitman's method for tin has been closely 

 followed, but slight modifications have been found helpful. 

 Their method is as follows: 



Treat from 0.2-1 gram of alloy (do not use an amount of alloy containing 

 more than 0.2 gram tin) in a 450 cc. Erlenmeyer flask with 10-15 cc. strong 

 sulphuric acid, heat on the hot plate until the alloy is thoroughly decomposed, 

 cool, add 200 cc. water, 30 cc. strong hydrochloric acid, and about 1 gram 

 of steel turnings, heat and when reduction appears complete, but before the 

 last particles of steel have dissolved, place a two-hole rubber stopper in the 

 neck of the Erlenmeyer flask — one hole of the stopper should carry a tube 

 reaching below the surface of the liquid, the other hole should carry the 

 short arm of a bent tube, the long arm of which reaches nearly to the bottom 

 of a 100 cc. Erlenmeyer flask containing a solution of sodium bicarbonate. 

 This small Erlenmeyer is held on the bent tube by a cork which has a notch 

 cut in it to act as a vent. Through the tube reaching below the surface of 

 the liquid in the large Erlenmeyer pass a current of carbon dioxide, heat 

 to boiling until all steel is dissolved, continue passing CO2 and cool as 

 quickly as possible; loosen stopper but let current of CO2 continue, add 

 cautiously some starch solution and titrate with N/10 iodine. It is neces- 

 sary to absolutely exclude air and to standardize the iodine solution with 

 pure tin. Eesults are accurate. 



I find this method very satisfactory up to the point where 

 the solution is boiled with 1 gram of steel turnings. 



Walker and Whitman recommend the use of steel turnings 

 for the reduction of tin, but give no details concerning the kind 

 of steel or the size of the drillings which are best suited to 

 the work. This is likely to give one the impression that any 

 steel drillings which may be around the laboratory may be used. 

 This is not true if it is desired to obtain the most rapid and 

 most accurate results. Some steels are more suitable than 

 others. For instance, a steel high in phosphorus is to be 

 avoided. In general, a mild, open-hearth steel is best suited to 

 the work. In order to complete the reduction in a comparatively 

 short time, the steel drillings should be small and uniform in 

 size. By using uniform drillings, the time of reduction is 

 known within a very few minutes, and the work can be planned 

 and carried out accordingly. The steel which I have found 

 to give the most satisfactory results contained about 0.12 per 

 cent carbon. The drillings were placed on a 40-mesh sieve, 

 and only the portion passing the sieve was preserved for use. 



