1825.] 



Mr, Donovan* s Jilt ering Appamtus. 



115 



Article VI. 



Description of an Apparatus for filtering out of Contact with the 

 Atmosphere, By Si. Donovan, Esq.^' 



Wk promised in our last to give a description of Mr. Dono- 

 van's apparatus for filtering substances liable to be affected by 

 t'le contact of the atmosphere, as solutions of caustic alkali, &.c. 



An inspection of the wood-cut annexed 

 will at once explain the nature of the in- 

 strument. It consists of tv*'0 glass vessels, 

 the upper one A has a neck at /;, which 

 contains a tight cork, perforated to admit 

 one end of the glass tube c. The other end 

 of the vessel A terminates in a funnel pipe, 

 which fits into one of the necks of the 

 under vessel D, by grinding or luting, or 

 by a tight cork. The vessel D has also 

 another neck e, which receives the other 

 end of the tube c, the junction being 

 secured by a perforated cork, or by luting. 

 The throat of the funnel pipe is obstructed 

 by a bit of coarse linen loosely rolled up, 

 and not pressed down into the pipe. The 

 solution is then to be poured in through 

 the mouth at /;, the cork and tube having 

 been removed, and the first droppings are 

 to be allowed to run to waste, and not 

 received into the under vessel D. The 

 parts of the apparatus are now to be joined 



together, and the filtration may proceed at the slowest rate, 

 without the possibility of any absorption of carbonic acid by the 

 alkali. 



The mode of action of this simple but ingenious apparatus is 

 too obvious to require any explanation ; but Mr. Donovan 

 observes, that it should be made of green glass in preference to 

 white,the former being much less acted onbyfixed alkalies than the 

 latter. He states that a white glass bottle containing a solution 

 of caustic potash will often be cracked by it in every direction, 

 and in a singular manner. 



This apparatus is useful for filtering liquids, to which access 

 of the carbonic acid, or moisture of the atmosphere, would be 

 injurious, as well as for the filtration of volatile substances, as 

 alcohol, ethers, ammoniacal fluids, &c. If a stratum of coarsely 

 pulverised glass or flint be substituted for the roll of linen, it 

 may be employed for filtering corrosive acids, which would b^ 

 weakened by absorbing water from the atmosphere. 



? Abridged from the Dublin Philosophieal Journal. 



1 2 • ■-'o^; ■■"■•% ■- 



