152 iSilt held in suspension by the Hooghly. [No. 2. 



1. The vrater was filtered and accurately measured, a small allow- 

 ance being made for that retained by the filters. 



2. The filters were double, both were carefully dried at about 

 100° Eakt. and that containing the solid matter weighed, the 

 other placed to counterbalance it in the opposite scale, so that the 

 weight of the silt only was taken. 



3. The deposit was tested for carbonate of lime by putting a 

 minute portion into a watch glass with acetic acid, when the effer- 

 vescence would be immediately perceptible. 



4. The filtered water was slightly alkalised by ammonia to neu- 

 tralise the superabundant carbonic acid, and the lime being preci- 

 pitated by oxalate of ammonia was obtained as an oxalate, for which 

 the equivalent quantity of carbonate of lime is set down. The 

 whole of the filters for twelve months were then burnt, and the car- 

 bonate of lime being converted into the dry sulphate, the remainder 

 was estimated as magnesia, with a trace of iron. This amounted 

 for the twelve months, at the surface, to 3.05 grs. or 0.254 of mag- 

 nesia per month ; and at the 3 fs. depth to 3.75 grs. or 0.312 of mag. 

 nesia per month ; a quantity too small to deserve notice, were it not 

 for the remarkable contrast which the estuary waters at the Gasper 

 channel will be seen to afford. The whole is set dowu as carbonate 

 of lime, and this difference is referred to in a note at the foot of the 

 tables, which are as follows : 



