353 



one-tenth milligram. Although the particles of CuSCN are much smaller 

 than those of AgCl, they were retained by the pores of the crucible. 



III. Determination of Al in A1 2 (S0 4 ) 3 as A1 2 3 . 



The effect of high temperature upon the Alundum crucible as well as 

 its applicability for filtration of gelatinous precipitates, were discovered by 

 this analysis. Chemically pure Al2(S0 4 )3.18H 2 was dehydrated by gentle 

 dessication and final heating for 4^ hours at 140°. A solution was prepared 

 such that each 50 c. c. contained .2154 grams of A1 2 (S0 4 ) 3 . Al(OH) 3 was 

 precipitated from the hot solution in the presence of NH 4 C1 by just a sufficient 

 amount of NH 4 OH. After boiling, stirring and allowing to stand, the pre- 

 cipitate was filtered through the crucible previously heated in the flame of a 

 blast lamp for several minutes, and washed with water containing small 

 amounts of NH 4 C1 and NH 4 OH. In seven attempts however in spite of all 

 precautions and lengthened time of treating the precipitate, part was drawn 

 through the crucible with the filtrate. The last three determinations were 

 made with an entirely new solution of A1 2 (S0 4 ) 3 , each 50 c. c. containing 

 .2001 grams. 



EFFECT OF HEATING ON THE CRUCIBIE. 



Except in one case where the change was negligible, the crucible lost 

 in weight consistently from one analysis to the next. The first crucible was 

 pulled apart by suction while cleaning with water following the third analy- 

 sis, and the second in exactly similar fashion after the fourth analysis in 

 which it was employed, showing that the material becomes extremely brittle 

 after heating several times in the blast lamp. 



IV. The determination of Ba in BaCl 2 as BaS0 4 . 



The extremely small size of the particles of BaS0 4 under ordinary con- 

 ditions recommended a further test of the crucible. The pure BaCl 2 was 

 thoroughly dried by heating three hours at 140° and a solution made such 

 that 50 c. c. contained .2007 grams. The hot solution slightly acidified with 

 HC1 was treated with pure dilute H 2 S0 4 while vigorous stirring was main- 

 tained for five minutes, after which the BaS0 4 was allowed to settle for five 

 minutes. 



Percent Ba in BaCl 2 calc. 65.96 found (1) 65.86 



(2) 65.98 



(3) 65.79 



The crucible was washed with water under suction and maintained 



23— 406G 



