1856.] Silt held in suspension by the Hooghly. 151 



A second series of experiments to ascertain the mean quantity of 

 Silt held in suspension hy the vjaters of the Hooghly in various 

 months of the year : as also the quantity carried out to sea. With 

 an Appendix on its sectional Area and average discharge. — By 

 Heney Piddington, Curator Museum Economic Geology. 



It will perhaps be recollected by the readers of the Journal that 

 at the close of my former notice on this highly interesting geologi- 

 cal and physical problem, (Journal, Vol. XXIII. p. 283,) I re- 

 corded there Major (now Lieut.-Col.) Baker's remark, that the 

 water at the surface would hold a less, as that at the bottom would 

 hold a greater proportion of silt in suspension than the true mean 

 amount, and I announced then that I had contrived a simple method 

 of obtaining water at small depths. 



This is, simply, a bottle attached mouth downwards to one side of a 

 double line, near the bight, at which there is a leaden sinker ; so that 

 when the bottle is lowered by that side of the line, the sinker carries 

 it down, mouth downwards, and the air within the bottle prevents 

 any great quantity of water from being forced in, while being lower- 

 ed to the required depth (in this case 3 fathoms or 18 feet). The other 

 side of the line, hitherto left slack, is then hauled upon, and the 

 bottle thus being reversed fills quickly with water and is hauled up. 

 This is of course not as strictly accurate as a more complex contri- 

 vance would be, but it is sufficiently so for all practical purposes. 

 I may add that all the water at Calcutta for the whole year was 

 taken up by myself about sunrise, on the dates which will be found 

 prefixed to each month. I am not always at liberty on any fixed 

 day, or the weather was sometimes unfavourable during the rains, 

 so that the intervals are not exactly months. As before, the time 

 of tide has been wholly disregarded to obtain a good average. In the 

 few months during which the bottles of water were kept, no deposit of 

 carbonate of lime, except slightly in one or two months, took place. 

 The following was the process followed to obtain the results. It is 

 one quite familiar in all details to chemists, but may be useful or of 

 interest to those who not being practical chemists might desire to 

 repeat our experiments on the water of other rivers. 



