504 
BATII CHEMISTS’ ASSOCIATION. 
very appreciable degree; whether this was a constant result that could be relied upon 
for jurisprudencial purposes, or merely the result of digestive inequalities, his experi¬ 
ments had not been sufficiently numerous to determine ; it was nevertheless an interest¬ 
ing fact to note. The paper was profusely illustrated by diagrams and spectra of the 
various bodies alluded to in the paper, thrown on the screen with very fine effect by 
means of Mr. Highley’s pneumatic electric lamp. 
The President, in the name of the meeting, thanked Mr. Evans for his very able paper, 
and the manner in which he brought the abstruse subject so plainly before their intel¬ 
ligence ; he expressed the pleasure he had in moving a vote of thanks to Mr. Evans. 
Carried by acclamation. 
BATH CHEMISTS’ ASSOCIATION. 
The usual monthly meeting of the above Association was held at the Commercial 
Boom on Friday evening, the 2nd of March. A large number of members and their 
assistants attended. Mr. Comma* s, President, in the chair. Mr. Schacht, of Clifton, 
read the following paper on his method of filtration. A discussion ensued, in which 
several members took part. 
Mr. Tylee proposed, and Mr. Pooley seconded a cordial vote of thanks to Mr. Schacht 
for his valuable paper, and for his kindness in coming to Bath. 
“On certain Physical Aids to Filtration,” by G. F. Schacht. The lecturer, after 
alluding in high terms of admiration to Dr. Attfield’s lecture upon the “ Physics of Fil¬ 
tration,” and to several thoughtful communications he had privately received from that 
gentleman, begged his audience to follow him while he briefly referred to some of the 
general properties of matter, and its behaviour when under the influence of those forces 
which he thought were concerned in the process of filtration. He then hastilv treated 
upon the subjects—Gravitation, Cohesion, Adhesion, Elasticity, Statics, and Dynamics. 
The explanations upon these points were necessarily abrupt, but beside their general 
bearings upon the matter, attention was especially drawn to the different behaviour of 
masses of matter under the influence of these forces when in the solid form, and when 
in the form of liquids and gases, chiefly in the respect of the pressure resulting from 
their gravity operating in the former case in masses, and consequently downwards only, 
that is towards the earth’s mass, and in the latter case—particle by particle; and hence, 
the particles being infinitely mobile, not only downwards, but laterally and upwards 
also. He showed this fact to be at the root of hydrostatic and aerostatic phenomena, 
and in illustration, referred to the enormous accumulation of statical force that was 
obtainable within a confined space by the application from without, to a small area of 
that space of a comparatively small amount of force. He stated this impulse, whatever 
its amount, to be felt by every portion of the confined space of the same area as that 
originally influenced, and, in illustration, asserted that if a cubical box, measuring twelve 
inches every way, were filled with water, and into one square inch of its wall a tube 
were inserted through which might be applied some force equal to one pound weight; 
that weight would be felt by every square inch column within the box, and would 
result in a pressure upon its inner v r alls equal to one pound multiplied by the number 
of square inches contained upon those walls, viz. 864,—that is, 6 sides of 144 square 
inches each. He added, the same phenomena would occur were the box filled with air, 
provided the same conditions of pressure were brought about, and he begged his audience 
to get this fact clearly before them—that the amount of pressure upon the inner walls 
of a vessel, communicating with the outside by means of an aperture, w^ould always be 
equal to the pressure upon that aperture (be it great or small) multiplied by the number 
of times the area of the inner walls exceeded the area of the aperture. For example, in 
the case of a vessel of air, if the pressure upon the aperture be increased beyond the 
ordinary pressure of the atmosphere, the strain upon the containing walls might be so 
great as to risk disruption from within; and, on the other hand, if a portion of the ordi¬ 
nary pressure of the air be withdrawn from the aperture, the w r alls might be driven in¬ 
wards by the inadequately-opposed pressure of the air from without. 
He then drew attention to some of the dynamical results of the employment of statical 
force. Torricelli had long ago announced a law which bore upon the relation of the 
rate of efflux of liquids to the height of the column of liquid above the aperture from 
which it is flowing. The statical pressure upon any spot in the containing vessel, it 
