, OF ARTS AND SCIENCES. 343 



advantage of being applicable to the filtration of liquitls which quickly 

 destroy woody fibre. The length of time required to dry them thor- 

 oughly, and their sensitiveness to atmospheric conditions, are their 

 great drawbacks. 



For the simple filtration of corrosive liquids without reference to a 

 subsequent estimation of the precipitate, filters of sand, broken glass, 

 garnets, and fibrous asbeslus have for a long time been used. More 

 recently, asbestus has been moulded into the shape of an ordinary fil- 

 ter : in the di-y state by Lowe,* by rubbing between hollow and a 

 solid wooden cones ; in the wet state by Gruner,t by grinding asbes- 

 tus, mixed in a mortar with water, to a pulp, transferring the mixture 

 to a funnel choked with asbestus, inserting an accurately fitting cone of 

 brass gauze, which presses the asbestus against the walls of the funnel, 

 pouring off the water, carefully removing the cone and drying the layer 

 of asbestus which adheres to the glass. Bottger| has used filters of 

 gun-cotton; and Bunsen§ has devised a filtering apparatus for corrosive 

 liquids to be attached to his pump, which consists of a disc of artificial 

 pumice fitted to a conical tube and packed around its edge with 

 fibrous asbestus. 



None of these later-mentioned methods, however, are well adapted 

 to the quantitative estimation of precipitates. 



Impressed with the desirability of further improvement in those pro- 

 cesses of quantitative analysis which involve the use of dried filters, or 

 the separation of filter and precipitate before ignition, 1 have had the 

 good fortune, in taking the matter up in turn, to succeed in devising 

 and preparing a felt of anhydrous asbestus, which is capable of filter- 

 ing liquids with a rapidity and efficiency at least as great as may be 

 obtained by the use of good filter paper; is light, compact, incombus- 

 tible at the highest temperatures used in analytical processes ; is not 

 acted upon by acids (excepting hydrofluoric acid) or alkalies ; is suf- 

 ficiently coherent to resist entirely the disintegrating action of a liquid 

 forced through it under the pressure of the Bunsen pump, and which 

 may moreover be prepared by a very simple process : in short, a fil- 

 tering material which, in my belief, makes it possible to reach a high 

 degree of accuracy in many analjnical processes which hitherto have 

 been none of the best, and to add to those already known new methods 

 which previously have been impracticable. 



My mode of preparing and using the asbestus felt is as follows': — 



* Dingl. pol. Jour, cxlviii. 444. t Jahresb. Chem. 1869, p. 990. 



} Dingl. pol. Jour. civ. p. 463. § Ann. Ch. Pharm. cxlviii. p. 290. 



