SUPPLY OF WATER. 



sand is the most eligible. Powdered charcoal has 

 long been known as a powerful filtering medium, 

 attracting and detaining especially organic matter. 

 Animal charcoal, or that derived from burning 

 bones, is still more efficacious than wood charcoal. 

 A filter of animal charcoal will render London 

 porter almost colourless. 



According to recent researches, it would seem 

 that loam and clay have similar properties, and 

 may be made available as filters. Professor Way 

 states that ' they have powers of chemical action 

 for the removal of organic and inorganic matters 

 from water to an extent never before suspected.' 

 The filthiest liquids, such as putrid urine and 

 sewer-water, when passed through clay, dropped 

 from the filter colourless and inoffensive. The 

 clay used was that known as pipe-clay. The 

 great objection to the use of clay for filtering is 

 the difficulty of getting the water to pass through 

 it, otherwise it would be an excellent substitute 

 for sand ; but, as mentioned above, dirty or coloured 

 water, when mixed with clay and shaken up, be- 

 comes pure when the particles of clay are allowed 

 to subside. 



Filters for domestic use will be noticed in the 

 number on HOUSEHOLD HINTS. 



Softening of Water rendered Hard by Chalk 

 ClarKs Process. This is one of the most beautiful 

 applications of science to the arts of life that could 

 perhaps be named. We extract the inventor's 

 own account of it, as given in a paper read before 

 a meeting of the Society of Arts : 



' In order to explain how the invention operates, 

 it will be necessary to glance at the chemical 

 composition and some of the chemical properties 

 of chalk ; for while chalk makes up the great bulk 

 of the matter to be separated, chalk also contains 

 the ingredient that brings about the separation. 

 The invention is a chemical one for expelling 

 chalk by chalk. Chalk, then, consists, for every 

 I Ib. of 16 oz., of lime, 9 oz. ; carbonic acid, 7 oz. 



' The 9 oz. of lime may be obtained apart, by 

 burning the chalk, as in a lime-kiln. The 9 oz. of 

 burnt lime may be dissolved in any quantity of 

 water not less than 40 gallons. The solution 

 would be called lime-water. During the burning 

 of the chalk to convert it into lime, the 7 oz. of 

 carbonic acid are driven off. This acid, when un- 

 combined, is naturally volatile and mild ; it is the 

 same substance that forms what has been called 

 soda-water, when dissolved in water under pres- 

 sure. 



* Now, so very sparingly soluble in water is 

 chalk by itself, that probably upwards of 5000 

 gallons would be necessary to dissolve i Ib. of 16 

 oz. ; but by combining i Ib. of chalk in water with 

 7 oz. additional of carbonic acid that is to say, 

 with as much more carbonic acid as the chalk 

 itself contains the chalk becomes readily soluble 

 in water, and when so dissolved, is called bicar- 

 bonate of lime. If the quantity of water contain- 

 ing the i Ib. of chalk with 7 oz. additional of 

 carbonic acid, were 400 gallons, the solution would 

 be a water of the same hardness as well-water 

 from the chalk strata, and not sensibly different in 

 other respects. 



' Thus it appears that i Ib. of chalk, scarcely 

 soluble at all in water, may be rendered soluble in 

 it by either of two distinct chemical changes 

 soluble by being deprived entirely of its carbonic 

 acid, when it forms lime-water, and soluble by 



combining with a second dose of carbonic acid, 

 making up bicarbonate of lime. 



' Now, if a solution of the 9 oz. of burnt lime, 

 forming lime-water, and another solution of the 



1 Ib. of chalk and the 7 oz, of carbonic acid, 

 forming bicarbonate of lime, be mixed together, 

 they will so act upon each other as to restore the 



2 Ibs. of chalk, which will, after the mixture, 

 subside, leaving a bright water above. This 

 water will be free from bicarbonate of lime, free 

 from burnt lime, and free from chalk, except a 

 very little, which we keep out of account at 

 present, for the sake of simplicity in this explana- 

 tion. The following table will shew what occurs 

 when this mutual action takes place : 



AGENTS. 



PRODUCTS. 



Bicarbonateof { Chalk 16 oz. = i6oz.of chalk \ u 



lime in 400 < with / M 



gallons ( Carbonic acid 7 oz. ) J = 



Burnt lime in 40 gallons of lime- > = i6oz.ofchalk ) .* 

 water 9 oz. ) 



' A small residuum of the chalk always remains 

 not separated by the process. Of 17 grains, for 

 instance, contained in a gallon of water, only 16 

 grains would be deposited, and i grains would 

 remain. In other words, water with 17^ of hard- 

 ness, arising from chalk, can be reduced to ij, 

 but not lower. 



' These explanations will make it easy to com- 

 prehend the successive parts of the softening 

 process. 



' Supposing it was a moderate quantity of well- 

 water from the chalk strata around the metropolis 

 that we had to soften, say 400 gallons. This 

 quantity, as has already been explained, would 

 contain i Ib. of chalk, and would fill a vessel 

 4 feet square by 4 deep. 



'We would take 9 oz. of burnt lime, made 

 from soft upper chalk ; we first slack it into a 

 hydrate, by adding a little water. When this is 

 done, we would put the slacked lime into the 

 vessel where we intend to soften ; then gradually 

 add some of the water in order to form lime-water. 

 For this purpose, at least 40 gallons are necessary, 

 but we may add water gradually till we have added 

 thrice as much as this ; afterwards, we may add 

 the water more freely, taking care to mix inti- 

 mately the water and the lime-water, or lime. Or 

 we might previously form saturated lime-water, 

 which is very easy to form, and then make use of 

 this lime-water instead of lime, putting in the 

 lime-water first, and adding the water to be soft- 

 ened. The proportion in this case would be one 

 bulk of lime-water to ten bulks of the hard water.' 



It is of importance that the lime-water that is, 

 the softening ingredient be put into the vessel 

 first, and the hard water gradually added, because 

 there is thus an excess of lime present up to the 

 very close of the process. Instead of lime-water, 

 the lime itself may be put at once into the vessel, 

 and some of the water to be softened gradually 

 added to dissolve it. The softened water thus 

 obtained has no action on lead pipes or cisterns, 

 as many soft waters have. One ton of burnt 

 lime, used for softening, will produce three and a 

 half tons of precipitate. The present water-supply 

 of the metropolis, if subjected to Clark's process, 

 would deposit about fifty tons of chalk daily. 



The process was in operation on a large scale 

 for several years (1854-1861) at Plumstead, near 



