496 THE POPULAR SCIENCE MONTHLY. 



the operations performed by the early chemists : some state in a gen- 

 eral way their acquaintance with the processes of distillation, sublima- 

 tion, filtration, etc. ; others are more explicit. Hermann Kopp, in his 

 exhaustive " Geschichte der Chemie," * states that " filtration as a 

 chemical process was first accurately described by Geber, who calls it 

 by a special name, destillatio per Jiltrum, ' trickling through a filter,' 

 in contrast to the collection of a liquid by ordinary distillation," Fer- 

 dinand Hoef er, in his " Histoire de Chimie " f writing of Geber, men- 

 tions that he recognizes two kinds of distillation — with and without 

 fire — the former being " per alembicum," and the latter consisting of 

 " une simple filtration." 



Now, we propose to show that the ancients carried on the operation 

 of filtration in two ways, essentially distinct in principle and in the 

 manner of execution, and that these methods were characterized by 

 two different expressions which have been confounded by the authors 

 named. Moreover, we shall establish this by quotations from writings 

 covering a period of more than two thousand years. 



In the first place, an examination of the very passage in Geber's 

 Works, referred to by Kopp and by Hoefer, shows that the method 

 therein described differs radically from filtration as ordinarily con- 

 ducted at the present time. We quote the passage as found in the 

 works of Geber, " the most famous Arabian Prince and Philosopher,'' 

 " faithfully englished by R[ichard] Il[ussell]," and printed at London 

 in 1678. In the thirteenth chapter of the fourth part of the fii'st book 

 of the "Summe of Perfection," Geber treats of the three kinds of 

 distillation : by an "Alembeck," by a "Decensory," and "by Filter." 

 After describing in quaint language the well-known method of using 

 the alembic and the decensory (which differs chiefly in the application 

 of heat on the top of the apparatus), Geber writes thus of filtration : 

 " The Disposition of that which is made by Filter is, that the Liquor 

 to be Distilled be put into a Stone Concha, and the wider part of the 

 Filter put into the said Liquor, even to the Bottom of the Concha, 

 but the narrower part of it hang out over the Orifice of the said Yes- 

 sel. And under that end of the Filter must be set another Vessel for 

 receiving the Distillation. Therefore when the Filter begins to Dis- 

 till, the Water with which it was moistened will first Distill off ; which 

 ceasing, the Liquor to be Distilled succeeds. Which Liquor, if it 

 be not as yet serene, it must so often be 'put into the Concha again 

 and redistilled, as until it be Distilled most serene." 



This dates from the eighth century, and evidently describes a sort 

 of capillary siphoning. The expressions ''placing the wider part of 

 the filter " into the liquid and allowing the " narrower part of it to 

 hang out over" the vessel admit of no other interpretation. For 

 convenience of distinguishing this method of filtration from that in 

 which porous sacs are employed, we propose to name the former 

 * Vol. ii., p. 26. t Vol. i., p. S35. 



