ESSAYS 663 



Before the water is admitted into the reservoir it must be relieved of any- 

 acid which is held in solution, this being the primary treatment to which 

 it is subjected. For this purpose it will be necessary to construct a small 

 subsidiary receptacle in which the operation can be performed. Concrete 

 can be used in this case also, and should be similarly plastered with " pudloed " 

 cement, this being entirely unaffected by acids. The dimensions of the 

 tank may be approximately 8 ft. long by 4 ft. wide and 4 ft. deep, or larger 

 as circumstances demand. The interior should be divided into two com- 

 partments of equal size by the introduction of a partition wall across the 

 centre, extending from the top of the external walls down to within 6 in. 

 of the bottom. The water is delivered directly from the well into one end 

 of the tank, and the further compartment is connected with the main reser- 

 voir by means of an outlet-pipe a few inches down from the top. This tank 

 can be constructed in one corner of the reservoir, if desired, in a similar 

 manner to, and connected with, the sand filter by the outlet-pipe, thus making 

 the whole scheme compact and self-contained ; but this will necessarily 

 entail increasing the dimensions of the main reservoir. The rising main 

 from the pump can be connected either through or over the top of the con- 

 crete wall. 



The preliminary filtration of the water for the extraction of the acid is 

 effected in the primary or small tank, both compartments of which have 

 been nearly filled with clean chalk broken to pass a 3-in. ring, and with all 

 dust carefully excluded. Chalk has a decided affinity for acids, and as the 

 water is delivered into the first compartment and is compelled to pass down 

 under the partition, and up to the outlet at the opposite end, it is subjected 

 to both downward and upward filtration, and cannot possibly obtain access 

 to the reservoir without first coming into intimate contact with the chalk. 

 The effect of this treatment is that all traces of the acid are removed from 

 the water during its passage to the sand filter, while its alkalinity is improved, 

 and it will exert little, if any, deleterious action on the metallic pipes and 

 fittings through which it circulates. As both the primary and secondary 

 tanks are partially exposed to the weather, it is imperative that suitable 

 provision should be made against the effects of frost, any valves or con- 

 necting pipes being well wrapped round with non-conducting material. 

 When the tanks are situated below the ground the open tops can be covered 

 in with reinforced concrete supported on light iron joists, entrance to the 

 tank for the purpose of cleaning or repairs being obtained through man- 

 holes formed in the concrete, and covered with a well-fitting slab. 



Although this process is simple, it is remarkably effective in eliminating 

 the corrosive properties of the water, and little cause for dissatisfaction 

 should be experienced if care and forethought are applied to the measures 

 which are taken. It is obvious that the periodic renewal of the chalk 

 will be essential, as it becomes inert owing to its absorption of the acidic 

 element in the water. The length of time which should elapse between 

 refilling the tank will depend on the composition of the water and its effects 

 on the pipes and fittings. 



A simple test for determining the purity or otherwise of the water is to 

 immerse a piece of blue litmus paper in a sample drawn from the outlet 

 of the primary rank. The least trace of acidity will cause the paper to 

 change from blue to red, and the intensity of the tint will indicate the con- 

 dition of the water, and the comparative urgency of the necessity for renewing 

 the chalk. 



Very little consideration is required to demonstrate that the only extra 

 expenditure involved by the adoption of this plan is the outlay incurred 

 in constructing the primary filter and its connections. This is really a 

 trifling matter compared with the whole system of water-supply ; and as the 

 results which accrue from the treatment are perfectly satisfactory in every 



