Calcium by the Acetate and Bromine Methods. 137 



tate too vigorously nor too long and as a result there was in no 

 case any appreciable reduction. 



The filtrates from iron, being united, were evaporated to 

 400-500°-% 10 cc - of ammonia, followed by 250-350°- c - of bro- 

 mine water, were added to the hot solution, which was then 

 heated on the water bath until the precipitate gathered leaving 

 a clear colorless supernatant liquid. If digested over a direct 

 flame the separation may be hastened. 



The success of this precipitation depends largely on treating 

 the solution hot. If bromine be added to a cold solution the 

 oxidation is slow and often less complete. The addition of 

 bromine to the solution already made ammoniacal seems pre- 

 ferable to a reversal of the order as it insures a more uniform 

 oxidation. 



Three bromine separations were made, the manganese pre- 

 cipitate being dissolved in hydrochloric and sulphurous acids. 

 In no case did the third filtrate show calcium. The first and 

 second filtrates from manganese were united. The volume 

 was reduced to 300-400°'' and the calcium was thrown down 

 as oxalate and weighed as oxide. 



The manganese was weighed as pyrophosphate. The iron 

 was determined by the standard solution of permanganate. 



The following are the results. 





Weight of 



Weight of 



Weight of Weight of 



Weight of Weight of 





Fe 



Fe 



CaO CaO 



MnO MnO 





taken. 



found. 



taken. found. 



taken. found. 





grm. 



grm. 



grm. grm. 



grm. grm. 



( 9-) 



0-2254 



0-2251 



0-1699 0-1690 



0-0341 0-0355 



(10.) 



0-2248 



0-2251 



0-1700 0-1687 



0-0680 0-0689 



(11.) 



0-2252 



0-2248 



0-1700 0-1696 



0-1092 0-1094 



(12.) 



0-2251 



0-2251 



0-1700 0-1705 



0-1500 0-1501 



(13.) 



0-2254 



0-2253 



0-1702 0-1697 



0-2043 0-2053 



Error in weight of . Fe 



CaO 



MnO 







grm. 



grm. 



grm. 





( 9.) 



0-0003 



- 0-0009 — 



0-0014 + 





(10.) 



0-0003 



+ 0-0013 — 



0-0009 + 





(11.) 



0-0004 



0-0004 — 



0-0002 + 





(12.) 



0-0000 



0-0005 + 



0-0001 + 





(13.) 



o-oooi 



— 0-0005 — 



0-0010 + 



Experience tells us, that in dealing with such precipitates as 

 those of iron and manganese, repeated precipitation is neces- 

 sary. In analyzing this necessity and determining its limita- 

 tions a series of partial separations was made, and the quanti- 

 ties of manganese and calcium in each of the several respective 

 filtrates was determined. The iron, of which about - 22 

 grams was added in each case, was undetermined. 



