68 DEPOSITS OF PHOSPHATE OF LIME. [bull. 46. 
through an iron pipe. After passing through the washers the nodules 
fall on an iron screen, which separates the large masses from the smaller 
pieces. Sometimes two or three screens haviug different-sized meshes 
are used. The small-sized product is of lower grade than the large, as 
it is mixed with numerous siliceous pebbles which have gone through 
the screen with it. 
The next step is to dry the nodules. This is done either by burning 
them with wood in large sheds, which sometimes hold several thousand 
tons, or by passing hot air. through the mass. Sometimes the nodules 
are treated with fire and hot air combined. In this way they are freed 
from the 12 to 18 per cent, of moisture which they contained after be- 
ing washed and are ready for shipment. On cooling, the nodules ab- 
sorb about 1 per cent, of moisture, and such is their porosity that they 
can be made to absorb 5 to 15 per cent, of water. 1 The drying of the 
nodules takes 35 to 40 cords of wood for 1,000 tons of nodules, and the 
process lasts thirty-six to forty hours. The drying and burning of the 
phosphate not only save the freight on the water which it originally 
contained, but also make it better fitted for manufacturing purposes. 
The nodules in the river bottoms are now obtained by dredging 
boats, though, a few years ago, large quantities were obtained by ne- 
gro divers and with oyster tongs. The dredging scoops have to be 
very strongly built in order to break through the nodular stratum. 
The boats are held in position at the four corners by what are called 
(i spuds." These are strong square poles with iron points. They are 
dropped into the water before dredging is begun, and go through the 
nodule stratum and down into the bed below, thus affording a firm sup- 
port to the boat. The nodules are thrown from the scoop into the 
washer, which is on a lighter alongside the dredging boat. The washer, 
in some cases, is the same as those used by the land-mining companies ; 
but often it consists of a truncated cone, with perforated sides, revolv- 
ing on a horizontal axis. It is supplied on the inside with steel spirals, 
arranged around the side like the grooves in a rifle. Into both ends of 
the cone heavy streams of water flow. The nodules are dumped by the 
dredge into the small end of the cone and come out at the large end. 
They are then removed by a derrick to another lighter and towed to 
shore. 
Besides the ordinary dredging machine, several other contrivances 
are used for raising phosphate from river bottoms. The owners of 
the Sea Island Chemical Works, instead of using the ordinary dredg- 
ing scoop, have a contrivance consisting of six large claws which open 
when they descend, and close, forming a kind of bucket, when they rise. 
It is said that one of the machines which this company owns can 
dredge in 50 to 60 feet of water, while the ordinary dredging boat can- 
not raise the phosphate in over 20 feet of water. Another dredge has 
been lately introduced by Mr. Brotherhood and is known as the Broth- 
er. C. U. Shepard, jr.: South Carolina Phosphates, 1880. 
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