36 § 39. ANALYTICAL MANIPULATION. 



Moreover, tlie precipitate is so completely deprived of its 

 water, that it may be easily removed from the filter, or 

 can be ignited at once without further drying. 



To ignite the precipitate at once, Bunsen directs to wrap 

 the filter around it, put the whole in the crucible, set the 

 latter on its side as usual, apply the heat at the top of 

 the crucible first, and gradually carry it towards the bot- 

 tom as the filter is burned. 



The rarefaction of the air may be produced in various 

 ways. The flask may be connected with the upper end 

 of a water-pipe 30 feet high in such a manner as to make' 

 a Sprengel's air-pump. Desaga, of Heidelberg, furnish- 

 es a complete apparatus for this purpose. 



Or, an air-tight connection may be made between two 

 large glass bottles, or demijohns, by means of a long piece 

 of thick walled rubber tubing ; then put one bottle filled 

 , with water on a high shelf, while the other is put on the 

 floor, connect the filtering-flask with a tube leading just 

 through the cork of the upper bottle, allow the water to 

 flow from the upper bottle to the lower one, while pro- 

 vision is made for the escape of the air from this lower 

 bottle ; the rarefaction of the air in the filtering-flask will 

 follow. When all the water has flowed from the upper 

 to the lower bottle, their relative positions may be re- 

 versed, the proper connection made between the filtering- 

 flask and the upper bottle, and the filtration continued. 



Or, a small demijohn may be closed by a rubber cork 

 through which passes a glass tube, connected with a 

 small brass stop-cock; connect the demijohn with an air- 

 pump, exhaust the air, close the stop-cock, connect the 

 demijohn with the filtering-flask, and open the stop-cock 

 when all is ready for the filtration. In order to j^revent 

 acid fumes or ammonia coming from the filtered liquid 

 from injuring the stop-cock, a wasli-bottle, containing 

 sodic hydrate or sulphuric acid, may be interposed. (J 

 M. Crafts.) 



