﻿THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



JANUARY 1869. 



I. On the Washing of Precipitates. By R. Bunsen*. 



[With a Plate.] 



A PRECIPITATE is washed either by filtration or by decan- 

 tation : in the former case the portion of liquid not mecha- 

 nically retained is allowed to drain from the precipitate ; in the 

 latter it is separated by simply pouring it away, the foreign sub- 

 stances contained in the precipitate being then removed by the 

 repeated addition of some washing-fluid, in each successive por- 

 tion of which the pre ipitate is, as far as possible, uniformly sus- 

 pended, this process being continued until the amount of im- 

 purity becomes so minute that its presence may be entirely 

 disregarded. 



Supposing v to represent the volume of the moist precipitate 

 remaining at the bottom of the vessel after decantation, or upon 

 the filtrate after filtration, V the volume of wash-water employed 

 at each successive decantation, n the number of decantatious, and 



- the fraction expressing the proportion of the original amount 



of impurity still remaining in the precipitate after n decantations, 

 then 



I (i) 



Wv) : 



Calling W the total volume of wash-water resulting from n de- 



* Translated from the Ann. der Chem. und Pharm. vol. cxlviii. [3], by- 

 Mr. T. E. Thorpe, from the proof-sheets kindly furnished by the Author. 

 Phil. Mag. S. 4. Vol 37. No. 246. Jan. 1869. B 



