172 The Philippine Journal of Science isis 



The fine particles passing an 80-mesh sieve were rejected. A 

 considerable quantity of these drillings was prepared and after 

 thorough mixing was preserved for use in babbitt analyses. 

 The uniformity of the drillings, both in size and composition, 

 was a very helpful factor. 



The troublesome part of this method for tin is in making 

 the titration. The antimony compounds present have been 

 reduced to metallic antimony, which is present as a black, 

 flocculent precipitate. This is most troublesome with a sample 

 which is high in antimony and low in tin, in which event it is 

 usually necessary to allow the precipitate to settle after each 

 addition of iodine before the presence of the blue color of the 

 end point can be distinctly seen. Another disadvantage is that 

 the precipitate is likely to conceal small pieces of undissolved' 

 steel, which would, of course, cause high results. 



To avoid this remove the antimony by filtering the boiling-hot 

 solution through a coarse filter paper and wash several times 

 with hot water. If the solution is not filtered while very hot, 

 lead chloride will crystallize out and interfere with the operation. 

 Receive the filtrate in a 300 cubic centimeter Erlenmeyer 

 flask, add 0.5 gram of steel drillings, and proceed with the 

 method in the regular way. Cool the flask by placing it in 

 a beaker of cold water, being careful to have a vigorous stream 

 of carbon dioxide passing in order to compensate for the vacuum 

 caused by the condensation of the steam in the flask. If a few 

 flakes of antimony appear during the second reduction, they 

 may be disregarded, since by removing the bulk of the anti- 

 mony the object has been attained. 



LEAD 



Considerable difficulty was encountered in finding a method 

 for the determination of lead which was accurate and at the same 

 time sufficiently rapid for routine babbitt analysis. Most of 

 the methods which I have tried from time to time failed in one 

 of these two respects. A modification of the method used by 

 Alexander^ in the analysis of lead ores has given very satis- 

 factory results. The following solutions are needed : 

 Ammonium molybdate, 4.25 grams per liter. 

 Acid ammonium acetate: 

 Ammonia, 400 cc. 

 Water, 450 cc. 



Concentrated acetic acid, 400 cc. 

 Tannic acid; one part of solid to 300 parts of hot water.' 



• This solution should be made fresh whenever used. 



'Eng. & Min. Joum. (1893), 55, 293. 



