| Date of Experiment. | Height of River above Low Water. | Temperature. | Grains of Sediment in a Pint of Water. | |||
|---|---|---|---|---|---|---|
| 1846. | ft. | in. | ° | A. | B. | |
| May | 21 | 10 | 11 | 72 | 6.66 | 7.00 |
| " | 25 | 10 | 11 | 73 | 9.08 | 9.12 |
| " | 27 | 10 | 10 | 78 | 7.80 | 9.00 |
| " | 29 | 11 | 0 | 74 | 7.30 | 8.10 |
| June | 2 | 11 | 1 | 75 | 4.80 | 5.45 |
| " | 4 | 11 | 1 | 75 | 7.87 | 6.10 |
| " | 6 | 11 | 4 | 75 | 4.60 | 4.90 |
| " | 8 | 11 | 4 | 75.5 | 5.48 | 5.60 |
| " | 10 | 10 | 4 | 76 | 6.70 | 6.80 |
| " | 12 | 10 | 8 | 76 | 6.50 | 6.30 |
| " | 14 | 10 | 5 | 76.5 | 6.00 | 6.00 |
| " | 16 | 10 | 4 | 76.5 | 6.47 | 6.15 |
| " | 20 | 10 | 4 | 77 | 7.08 | 7.40 |
| " | 22 | 10 | 2 | 77 | 9.88 | 9.00 |
| " | 24 | 9 | 8 | 77 | 8.40 | 8.48 |
| " | 26 | 8 | 9 | 77.5 | 8.25 | 8.78 |
| " | 28 | 8 | 0 | 79 | 9.10 | 9.58 |
| July | 1 | 7 | 2 | 79.5 | 9.15 | 9.25 |
| " | 3 | 7 | 2 | 79.5 | 9.63 | 10.00 |
| " | 6 | 6 | 2 | 81 | 8.20 | 7.57 |
| " | 8 | 6 | 0 | 81 | 7.30 | 6.96 |
| " | 10 | 6 | 1 | 81 | 6.12 | 6.28 |
| " | 13 | 5 | 9 | 82 | 7.72 | 7.30 |
| " | 15 | 5 | 10 | 82 | 6.67 | 6.60 |
| " | 17 | 5 | 10 | 82 | 4.45 | 4.57 |
| " | 20 | 5 | 4 | 82 | 6.07 | 5.75 |
| " | 24 | 3 | 10 | 84 | 5.76 | 5.72 |
| " | 27 | 3 | 1 | 84 | 4.77 | 4.60 |
| " | 29 | 3 | 11 | 84.5 | 4.28 | 4.13 |
| Aug. | 1 | 2 | 6 | 85 | 4.40 | 4.44 |
| " | 3 | 2 | 0 | 84 | 3.18 | 3.34 |
| " | 5 | 1 | 9 | 83 | 3.56 | 3.40 |
| " | 7 | 1 | 5 | 83 | 2.85 | 2.85 |
| " | 10 | 1 | 6 | 83 | 3.03 | 2.92 |
| " | 13 | 2 | 8 | 84 | 2.97 | 3.00 |
The mean average of column A. is 6.32.
The mean average of column B. is 6.30.
Transcriber's Note: Data in the above table is as in the original.
'By comparison with distilled water,' says the same, 'the specific gravity of the filtered river water we found to be 1.823; pint of such water at 60° weighs 7,297.40.' Engineer Forehay says the sediment is 1 to 1,800 by weight, or 1 in 3,000 by volume.
Professor Riddell also comes to the following conclusions, after an analytic investigation of the sediment. He took one hundred grains from the river margin, dried it at 212° Fahrenheit, before weighing, and found it to contain:
| Grains. | |
|---|---|
| Silica, | 74.15 |
| Alumina, | 9.14 |
| Oxide of iron, | 4.56 |
| Lime, | 2.08 |
| Magnesia, | 1.52 |
| Manganese, | 0.04 |
| Potassa, | not determined |
| Soda, | not determined |
| Phosphoric acid, | 0.44 |
| Sulphuric acid, | 0.07 |
| Carbonic acid, | 0.74 |
| Chlorine, | 0.01 |
| Water, | 3.12 |
| Organic matter, | 3.10 |
| —— | |
| Total, | 98.97 |
The existence of so large a quantity of sediment in the water of the Mississippi, leads to divers formations in its bed. These formations are principally 'bars' and 'battures.' The banks are also much affected.
When the water of the river, aided by the current, has attained its full capacity of buoyant earth, as we have already said, the excess falls to the bottom. Instead, however, of remaining permanently where it first lodged, which would soon fill up the channel and cause the river to overflow, the scouring of the water on the bottom forces a large portion along with the current, though it be not suspended. Pursuing its course for a while, some irregularity or obstruction falls in the way—a sunken log, perhaps. This obstacle checks the progress of the moving earth—it accumulates; the next wave brings down more—the accumulation becomes greater; until, in the course of a few years, there is a vast field of deposit, and a 'bar' is formed. These 'bars' often divert the channel, and occasion the immense washings before alluded to.
Bars are generally found close to the banks, though there are examples in which they extend in a transverse direction to the current. Bars of this kind very much embarrass and endanger navigation in low water. At Helena, Arkansas, there is an instance of a transverse bar, upon which, in October, the water is less than six feet. These bars are formed of sand, which seems to have been the heavier and less buoyant of the components of the earth thrown into the current by abrasion, the lighter portions having been separated by the water and carried off.