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Stirring as a Time Saver in Gravimetric Analysis. 



W. M. Blanchabd. 



While making experiments recently on the deposition of metals with a 

 rotating anode, it occurred to me that various gravimetric analyses might 

 be greatly facilitated by rapid stirring of the precipitate. That stirring 

 greatly facilitates precipitation is known to every one, but I do not know 

 that any data have been recorded to show just how efficient the stirrer may 

 be, hence these experiments. These results are very surprising. 



A stirrer was made from a small glass rod about two millimeters in 

 diameter. It had the shape of the letter T, the arms, each about eighteen 

 millimeters long, being flattened at the ends and turned so as to resemble 

 an ordinary propeller. The stem was about ten centimeters long and was 

 attached to a wheel run by a small electric motor, which in turn was con- 

 nected with an ordinary 110 volt lighting circuit. There was thrown in 

 the circuit a small lamp bank so that the speed of the motor might be 

 varied. The following analyses were carried out with the stirrer making an 

 average of 900 revolutions per minute. 



1. Estimation of barium in crystallized barium chloride. The sample 

 of the pure salt, 0.2330 gram, was weighed out in a 150 c. c. beaker, diluted 

 to about 50 c. c, acidified with hydrochloric acid, heated to the boiling 

 point, treated with slight excess of dilute sulphuric acid, stirred four min- 

 utes, immediately filtered, washed, ignited, cooled, and weighed. Found 

 for barium ,56.25% ; calculated, 56.23. 



2. Estimation of calcium in pure calcium carbonate. A small sample 

 of the purest calcium carbonate, 0.2225 gram, was transferred to a 150 c" c. 

 beaker, converted into the chloride, diluted to about 50 c. c, heated to boil- 

 ing, treated with slight excess of ammonium oxalate, made alkaline with 

 ammonia, stirred four minutes, then filtered, washed, ignited, heated over 

 the blast lamp, cooled and weighed. Found for calcium oxide 56.0-1% ; 

 calculated 56.03. 



3. Estimation of copper in citpric sulphate. A small sample of re- 

 crystallized pure sulphate, 0.2000 gram, was weighed in a 150 c. c. beaker, 



