y. A. Baker 
1 18 
then a few drops of standard iodine solution were run in. At the 
first drop a heavy, dirty-white precipitate formed. It was evi- 
dent from the nature of the precipitate and the substances in solu- 
tion that cuprous iodide, stained with free iodine, was being pre- 
cipitated. However, several titrations were made, in the hope that 
the interfering action of the copper would be perfectly regular, 
and that a correction could be made after the amount of copper 
present had been determined. The addition of iodine was there- 
fore continued till the characteristic blue coloration indicated that 
the end point had been attained. Care was taken to stir the solu- 
tion thoroughly after each addition. The heavy precipitate 
present obscured the end point to some extent, but it was suffi- 
ciently well noted each time. 
Three different portions of the alloy were taken, and the fol- 
lowing results were calculated to a weight of 4 grams of the alloy. |j 
One portion required 175 cc. of the standard iodine solution, j 
another required 133 cc., and the other required 159 cc. It was 
manifest that the reaction v/as altogether too irregular to justify i 
any confidence in it. ! : 
The following method was finally used fin the determination of t 
the metals present in the alloy. Take portions of two or three ^ 
grams each and cover with nitric acid (1:1). Action takes place 
at once without heating, and soon the alloy is entirely decomposed, j 
Expel nitric fumes and add about 10 cc. of concentrated sulphuric | i 
acid. Heat till white fumes come off quickly. Cool, add 50 cc. i 
of water, filter and wash. The lead in the precipitate may be esti- * 
mated gravimetrically or volumetrically. The filtrate contains 3 
the copper, tin and zinc. ‘ 
To the filtrate add enough water to make its volume up to 150 : 
cc. Add 25 cc. of sulphuric acid. Place clean aluminum foil 1 
in the liquid and bring up to a boil. Boiling is continued till all I 
the copper is precipitated in the metallic form. Separate the 
metallic copper by decantation or filtration, wash and weigh as 
metallic copper, after drying; or dissolve and estimate volumetric- 
ally. The copper is now entirely separated from the tin, the latter 
remaining in the filtrate along with the zinc which does not inter- 
fere with the estimation of the tin by iodine. The tin is now 
reduced by metallic antimony in a current of carbon dioxide as i 
directed by Mr. Low, and titrated with the iodine solution. 
The iodine solution produces, now, no precipitate, but the oxida- ' 
