238 Transactions of the Royal Microscopical Society. 
drinking”; my opinion, therefore, was confirmed and acted upon, 
but, as a matter more of chance than of fact, as will he readily 
admitted. 
Much of this incertitude, if not, in time, the whole of it might, 
in my opinion, be removed, if hydro-microscopists could agree in 
the adoption of one uniform plan to which every sample of water 
examined by them for health purposes were submitted, a certain 
elasticity in detail being, of course, admissible. As some slight 
contribution towards the end I have in view (and which I hope to 
be permitted to touch upon more fully hereafter), I venture now to 
submit to your criticism a brief outline of the method adopted in 
my laboratory for all hydro- microscopical inquiries. 
In addition to the usual appliances, the following simple pieces 
of apparatus, &c., are required ; the first four articles may advan- 
tageously be in duplicate. 
1 Filter-stand, with 2 rings. 
1 Glass beaker, about 25 ounces. 
2 „ pear-shaped decigallon flask. 
1 Centignllon bottle. 
2 or more funnels (without nicks). 
2 Small pipettes. 
Filter-papers. 
Collodion (special). 
Ozo-vaseliue. 
2 Zinc or boxwood circular stencils. 
The water intended for examination is first subjected to pro- 
longed (but not too violent) agitation, which is continued whilst, 
either by pouring, or with the aid of a siphon, the pear-shaped 
decigallon flask is filled up to the mark on the neck. This flask is 
furnished either with a lateral aperture of about • 2 of an inch 
near the mouth, or with an external tube of about the same bore, 
extending nearly from the mouth to the bottom, where it com- 
municates with the interior ; the beaker being placed upon the 
stand, and a funnel, with a special filter therein, arranged above 
it in one of the rings, a little of the water is poured into the 
filter from the pear-shaped flask, which is quickly inverted therein 
in such a manner that the lateral aperture before mentioned is just 
below the surface of the liquid when the filter is about two-thirds 
full. 
Under these conditions, as will be readily seen, filtration will 
proceed quietly and continuously until the flask is emptied, for as 
soon as the level of the liquid in the filter sinks below the little 
aperture (or tube), ah' is thereby admitted to the flask, the filter is 
again filled up to the original level, and the operation proceeds 
as before. 
The filters employed, however, are of a particular kind, the 
centre of each circular paper having been rendered impervious to 
