WHAT IS A CLEAN FILTER?

Lyttelton Times, Volume LXXXI, Issue 10236, 3 January 1894, Page 6

WHAT IS A CLEAN FILTER?

(British Medical Journal.) Among the various recommendations—good, bad and indifferent—which are being offered to the readers of newspapersas appropriate to cholera times is one culled from Hygiene, a ,, sanitary, paper, .advising that . water;, should. be boiled and then passed: thibugh a clean fiiter. What is a clean filter,‘and how Tong can it retain its cleanliness ? 1 Theoretically, no doubt, a filter does clean itself. That is to fay, the organic matters extracted from , the water become so changed and oxydised that they pass away in the form of carbonates and nitrates. This ia what happens in natural filtration through the living crust of the earth, the sod of field, or the organic layer which soon coats over and fills up the interstices of any sand through which water naturally flows; and, if a domestic filter were used sufficiently slowly and with intermissions frequent enough and long enough to charge it again and again with oxygen, or to keen in activity its nitrifying organisms, which is possibly only the same expression in another form, the same process might take place in it; but, as ordinarily used, ho would indeed be a man of faith who would trust himself to drink a cholera-infected water purified only by passing through u domestic filler. Their email size, the thinness of ■ the layer of filtering medium which they provide, and the rapidity with which the water must traverse it to get the quantity through, make it a matter of constant surprise that they are as efficacious as, on the average, they seem to be; But whether any given filter is at any given moment ia working order ia purely a matter of faith, and in the matter of a block filter, when the water which is used is bright to begin with, the ordinary householder has out little means of knowing that it ia not grossly out of order. How few people take the trouble to have their filters pulled to pieces and boiled, or have the filtering medium renewed at frequent intervals, and yet if the housemaid were caught using a dirty duster to the drawing-room ornaments what a disturbance there would be!