I 



1873.] D. Waldie— 0;i the Muddy Water of the Ilugli. 210 



way as it does in the valley and the source of the Ganp^es ; in England the 

 rainfall and hardness both rise and fall repeatedly during the year. The 

 case is entirely different from the state of matters here in which we have a 

 very soft water from the commencement of the regular rains gradually be- 

 coming harder in NoTember and December and continuing so till the rains 

 set in again in the following year. There is no reason, therefore, to expect 

 any noticeable disturbance in the conditions of filtration in England from 

 change in the condition or nature of the water, but every reason to expect 

 it here, if we can only suppose or admit that such a change in the water 

 may affect the filtration. And I would ask, why we should not admit that 

 it should do so ? My experience convinced me that it did so affect the fil- 

 tration, and though I could not satisfactorily account for it or explain how 

 it did so, I continued firml}^ to maintain that it did so, that this was the 

 true cause of the difficulties, and that consequently other explanations were 

 fallacious and baseless. 



I should have been glad to have found other corroborative evidence of 

 the correctness of my opinions, but had no means of obtaining it. Fortu- 

 nately the discovery of the nature of the peculiarity rendered this of com- 

 paratively small importance. I return now to the consideration of this 

 subject a little more in detail. 



IV. — After ascertaining that such a very small quantity of lime salts 

 or rather of chloride of calcium, for that was the salt experimented with at 

 first, was sufficient for the purpose required, I proceeded to compare the 

 efficiency of different neutral salts. For this purpose I had to choose a 

 standard of comparison, and as the enquiry related at present to tlie Hugli 

 water, I chose it with refei-ence to the composition of this. Chloride of 

 Sodium or common salt might have been taken, but I found its effect com- 

 paratively so small that I gave that up. The really influential constituents 

 in the river water were the salts of lime and magnesia, particularly the car- 

 bonates, and as I found that these were of nearly equal power, I decided to 

 take that which existed in largest quantity, namely carbonate of lime, as the 

 standard of comparison. But as a solution of carbonate of lime in excess of 

 carbonic acid is troublesome to prepare, its strength somewhat troublesome 

 to ascertain, the solution itself weak, consequently involving the addition of 

 a notable quantity of water, besides being liable to change, I chose for my 

 working standard a solution of chloride of calcium equivalent in strength to 

 1 grain carbonate of lime in 50 cubic centimetres of solution, equal to I'll 

 gm. chloride of calcium in 50 c. c. This formed a convenient strength for 

 measuring by a pipette. For the composition of the water, I assumed that 

 during the rain}- season it contained salts of Lime and Magnesia equivalent 

 altogether to 7 grains of carbonate of lime in 100,000 flgn. or "07 gramme 

 in 1 litre. This is equal to 49 grains in 1 gallon. Perhaps it is rather too 



