ON A NEW FILTER. 
219 
. with a ledge, C, from which the bottom slopes to a central spout, D. A perfo¬ 
rated plate of tin, E, strengthened at the under side by cross pieces of the same 
metal, rests upon the ledge. A ring of tin, F, a quarter of an inch thick, 
strengthened with cross pieces, is also provided. Upon this ring the filtering- 
medium, flannel, calico, felt, etc. is stretched, and the whole is placed (medium 
downwards) upon the perforated plate. The ring should be so contrived as to 
press the filtering-medium tightly against the sides of the vessel, and yet just to 
rest upon the perforated plate. A small hole, G, is drilled horizontally through 
the ledge opening into the instrument close under the perforated plate. A tube 
is then provided of any length from one foot to thirty, and at one extremity is 
reversed upon itself twice. This tube may be of various materials, but on the 
whole vulcanized india-rubber is the most convenient. In that case the bent 
piece at the end should be of some solid substance, such as glass. 
To put the apparatus into action, stretch the filtering-material over the ring, F, 
and press it into its place upon the perforated plate, E. Attach the tube to the 
spout D, and close the extremity, II, with a cork. Four in the liquid to be 
filtered. A portion soon passes through the medium and fills the tube, the air 
escaping through the small hole G. As soon as the liquid begins to escape at 
this hole, stop it with a little wax; remove the cork from H, and the action 
commences. 
The dimensions of the instrument and the material of its construction will, 
of course, vary with the purpose for which it is to be employed. That which I 
have had made for my own use is of pure tin. It is ten inches high, nine inches 
in diameter at the larger and eight inches at the smaller end. The ledge is one- 
third of an inch deep, and the tube of india-rubber is four feet long. I find this 
elastic tube very convenient, for, as the necessity for pressure is not so urgent 
at the commencement of the process as subsequently, when the filtering-medium 
has become choked, the operation can be commenced with efficient result by 
bringing the receiver to within a few inches of the bottom of the apparatus, 
and the column can be gradually lengthened and the effect proportionately in¬ 
creased by simply lowering the receiver, to each new position of which the elas¬ 
tic tube readily accommodates itself. 
With this instrument I have filtered to perfect brightness eight gallons of 
turbid solution within the hour, and have had the satisfaction of seeing the last 
ounce pass through almost as quickly as the first. 
7 , Regent Place , Clifton. 
Dr. Attfield, at the request of the President, explained the action of the filter. He 
said that the great rapidity with which, according to Mr. Schacht’s experiments, liquids 
passed through the apparatus, aud which was the most important feature in the instru¬ 
ment, was quite in accordance with the known laws relating to gravitation, and de¬ 
pended on the depth of the orifice of outflow below the surface of the liquid ; the velo¬ 
city of the current would be ten times greater if the bottom of Mr. Schacht’s tube were 
100 inches from the upper surface of the liquid than it would if the orifice were only 1 
inch below. The action of the filter was similar to an effect known to every one whose 
house was supplied with water from a cistern in the roof or upper part of the dwell¬ 
ing. The rapidity of flow from the kitchen- or basement-tap of such a system was 
so much greater than that from a bedroom or attic as to almost force a jug or basin from 
the hand of any one unaccustomed to that particular arrangement of water supply. 
That there should be any flow at all from such pipes was simply due to the law of gra¬ 
vitation. So the continued action of a siphon was also referable to gravitation, the 
velocity of action of any one siphon being dependent on the distance of the orifice of 
outflow below the level of the liquid operated on. Dr. Attfield also alluded to the effect 
produced on, and by, the atmosphere in which the operations with the filter, or a water- 
supply or siphon, might be performed. lie did this because some filtering materials 
might appreciably impede the passage of liquids, in which case the unimpeded gravita¬ 
tion of the liquid in the lower part of Mr. Schacht’s ingenious instrument would have a 
