orjiltering large quantities of Liquid. 399 



-^though the greater part generally falls down again into the funnel, 

 a small quantity still afiieres to the sides of the tube. It is for 

 this reason that the tube must be wider towards F ; for when its 

 diameter is uniform, the air rushing in at E, pushes the liquid over 

 the edge F, into the flask. When constructed as in the figure this 

 does not take place. Where minute accuracy is not required, the 

 small portion adhering to the tube will be of little consequence ; 

 in analytical investigations, however, it involves the necessity of 

 carefully cleaning out the tube. 



This rude arrangement I have described chiefly for the sake of 

 those who cannot themselves work in glass, and who have no ac- 

 cess to those who can. To others I can recommend a far more 

 perfect, more elegant, and more ingenious little instrument, lately 

 invented by Berzelius, and described in a letter I received from 

 him a few days ago. It is in fact quite a beautiful little machine, 

 and will be received as a most welcome gift by every practical 

 chemist. 



a b, in the marginal figure, is a tube of about half 

 an inch internal diameter, drawn out to a fine point, 

 and bent up at the lower extremity : c is a wide 

 thermometer tube, inserted into the side of a h, 

 and bent up till parallel vnth it : a 6 is fixed into 

 the mouth of a flask of water, which is then invert- 

 ed. The air enters by the tube c, and makes its 

 way into the flask, expelling the water in a stream 

 from h. If the extremity h is now suspended over the precipitate 

 upon the filter, the air will enter, and the stream will flow till the 

 surface, d e, of the water in the funnel rise a short distance above 

 the point h. All action will then cease, till a portion have passed 

 through the filter, when it will again commence, and these alterna- 

 tions will terminate only when the flask has become emptied. It is 

 diflicult to form an idea of the utility of this little instrument, 

 without having employed it. A precipitate may be kept washing 

 all day and all night, requiring attention only when the flask i^ 

 empty. 



A flask with two necks, one drawn out to form 

 the instrument, and the other with a stopper for 

 pouring in the water, as represented in the figure, 

 would form a very elegant arrangement, and do 

 away with the necessity of removing the instm- 

 ment from the bottle every time it required fill- 

 ing up. 



The instrument may be had in great beauty, 

 and at a very trifling expense, from Mr. Conolly 

 of Lothian Street, to whom I have made known 

 the most eflicient dimensions. 



PORTOBELLOj 12/A Jtdy 1830. 

 VOL. II. 3 p 



C^T' 



