722 Agricultural Journal of Victoria. 



THE WATER SUPPLY AND DRAINAGE OF BUTTER 



FACTORIES. 



By T. Cherry, M.D. 



Filtering the Water- 



Tb-e importance of a pure water supply at every stage in the 

 preparation of butter is well known. In order that food products 

 of all kinds may keep well it is essential that as little dirt as possible 

 should be mixed with them. Care needs to be exercised at every 

 stage of the process from the beginning to the end, for neglect at 

 any point is fatal to the whole result. Pure water is therefore a 

 necessity. The smaller the amount of organic matter and the fewer 

 the micro-organisms the better. Water may be purified either by 

 gravity filtration, by pressure filters, or by heat. Each method has 

 its special advantages ; but taking the average conditions and 

 requirements of our factories I think the best plan is the old-fashioned 

 method of sand filtration. The filter bed consists of approximately 

 one foot of gravel at the bottom, then two feet of sand, the finest 

 being placed on the top. The finer and sharper it is the better. 

 There is from 12 to 18 inches of water on top of the sand, so that the 

 pressure is very slight. The average rate of filtration is found to be 

 about 50 gallons per square foot of surface in 24 hours. Nearly all 

 the filtered water supplied to towns in all parts of the world is 

 subjected to this method. In London, where over 160 million gallons 

 of river water are filtered daily, this method is invariably used. 

 There is no question, therefore, of its efficiency. The remarkable 

 thing about it is that the number of micro-organisms per cubic 

 centimeter is reduced to less than 100, whatever may have been the 

 number to begin with. The number in the unfiltered Thames water 

 last October and November averaged about 17,000 per c.c. Filtration 

 reduced them to 60. The water from the Lea contained 540 before 

 and 26 after filtration. To give local comparisons, the unfiltered 

 Thames water is about the same as the Yarra at Princes Bridge ; the 

 Lea is about as pure as the Yarra above Studley Park. The London 

 sand filtei's cover more than 100 acres. The average amount filtered 

 is from 20 to 70 gallons per square foot of surface per 24 hours. The 

 thickness of sand varies from 1'75 to 4"3 feet. 



The construction of these sand filters is very simple. The area is 

 determined by the quantity of water required per day, on the basis 

 before stated. The retaining walls are four or five feet high, and the 

 bottom is graded to slope to the outlet. The walls may be made of 

 brick, concrete, or wood. Good, clean, sharp sand and gravel are all 

 that is required ; a number of large pebbles are arranged round the 

 outlet so that the water has free earress. The feed water is run in at 



