170 The Philippine Journal of Science laie 



following composition: Lead, 85 to 90 per cent; antimony, 10 

 to 15 per cent; tin, to 5 per cent; copper, to 1 per cent. 

 The methods of analysis which I have found most satisfactory 

 and which are intended to apply to this class of alloys in 

 particular are as follows : 



ANTIMONY 



The method of Walker and Whitman ^ for antimony, which 

 is a modification of Low's ^ method, has been closely followed 

 except for the changes which are noted. The method as given 

 by them * is as follows : 



To 1 gram alloy in a 450 cc. Erlenmeyer flask, add 10-15 cc. strong 

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

 This is generally accomplished in about 30 minutes from the time fumes 

 of SOa begin to be given off. Cool, add 200 cc. water and 20 cc. strong 

 hydrochloric acid, boil to make sure that all SOj is driven off, cool and 

 titrate rapidly with potassium permanganate which has been standardized 

 against metallic antimony. The true endpoint is when a pink color shows 

 after agitating the liquid, though this pink will very soon disappear. 



In carrying out this method, difficulty is often experienced 

 in obtaining a sharp end point, and some chemists have 

 never used it to any extent on that account. However, a 

 sharp end point can be obtained if the method is modified 

 as follows: Use a 300 cubic centimeter Jena-glass Erlen- 

 meyer flask for digestion and dilute to about 150 to 175 

 cubic centimeters. If after boiling the volume has decreased 

 materially, add sufficient water to replace that which has been 

 evaporated. Cool the solution thus obtained to about 5 or 10°C., 

 and titrate as rapidly as possible, until the end point is nearly 

 reached, then add two or three drops at a tiflie, shaking the 

 flask thoroughly. When a pink color flashes over the entire 

 solution, the end point is reached. These precautions are neces- 

 sary because the pink color at the end point is not permanent, 

 as in the case of iron titrations, and unless the solution is kept 

 cold and the permanganate added in some definite way for 

 every determination, one is very likely to obtain erroneous 

 results. 



The permanganate solution should be standardized frequently. 

 During the titration, if the hydrochloric acid solution is not 

 sufficiently dilute, sometimes the odor of chlorine will be noticed, 



= Joum Ind. & Eng. Chem. (1909), 1, 520. 

 'Journ. Am. Chem. Soc. (1907), 29, 66. 

 * Loc. cit. 



