Gooch — Precipitates for Solution and Peprecipitation. 11 



Art. II. — The Handling of Precipitates for Solution and 

 Peprecipitation ,/ by F. A. Gooch. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — cxxxv.] 



In many processes of analytical chemistry, the preparation 

 of substances in pure condition is brought about by precipita- 

 tion, solution, and reprecipitation ; and sometimes this cycle of 

 operations must be repeated. When a precipitate, gathered 

 upon a filter, is easily acted upon by the appropriate solvent, 

 the process of dissolving the precipitate from the filter is 

 simple ; but when the precipitate is refractory toward solvents 

 or difficult to attack on account of its physical condition, as is 

 the case with many gelatinous precipitates, the proper hand- 

 ling of the precipitate involves some inconvenience and delay. 



In meeting such difficulties, I have found it advantageous 

 to place within the ordinary paper filter, before filtering, a 

 movable lining of platinum gauze upon which the precipitate 

 rests for the most part and with which it may be removed. 

 The simplest form of this device is easily made : ■ 



by cutting platinum gauze to the shape shown jfA ^m 

 in the accompanying figure. In ordinary use, a mm 



this piece of gauze, folded to make a cone of Jjj 

 angle a little less than 60°, and held by pincers |j| 

 at the point of overlapping, is placed within this II 

 filter and allowed to fit itself closely by the lj[ 

 natural spring of the gauze when released. ^Sj Wk 



Upon filters so prepared a precipitate may be 

 collected and washed as usual ; and, at the end 

 of the operation, the cone with nearly all the precipitate may be 

 transferred, by means of ivory-pointed pincers, to dish or 

 beaker for suitable treatment. The small amounts of the pre- 

 cipitate which have passed through the gauze, being somewhat 

 protected by the gauze against the compacting action of filtra- 

 tion and washing, are generally removable with ease from the 

 filter by a jet of the washing-liquid. After washing, the gauze 

 may be replaced within the same filter and serve for a second col- 

 lection of the precipitate to be subsequently dissolved, in case 

 double precipitation and solution are desirable. The final col- 

 lection of the precipitate is, of course, made upon paper with- 

 out the gauze lining, when precipitate and filter are to be 

 ignited. 



This device has proved very serviceable in the handling of 

 such precipitates as ferric hydroxide, aluminium hydroxide, and 

 basic acetate precipitations. 



