hence a grab sample is rarely taken. If the ore is being unloaded from cars, the first sample is generally taken by fractional selection and then reduced by the same method or by quartering or channeling.

10. Fractional Selection.-When this method is used for sampling fairly large lots of ore, the first sample is taken in wheelbarrows or cars and dumped in a pile. When this pile is completed, it is removed by shoveling and a certain proportion of the material thrown into a new pile, care being taken to throw all the ore on the top of the pile, so as to thoroughly mix the sample. It is not often that the second sample is so large that it has to be taken in wheelbarrows or cars and piled in another place. When shoveling the ore, care must be taken to see that the place where the sample is piled is swept clean and that each shovelful of ore is taken from the bottom of the pile. Fractional selection is probably the most accurate method for obtaining a sample of 100 or 200 pounds from a lot of ore in which the values are not regularly distributed through the ore. The more irregularly the values are distributed through the ore, the larger should be the sample taken at each handling of the ore and the finer should the ore be crushed. After the sample has been reduced to 100 or 200 pounds by fractional selection, it is generally still further reduced by quartering or channeling.

11. Channeling. For channeling, the ore is spread out in a flat heap or layer a few inches thick and the sample taken by shoveling out two or more parallel channels, like paths through a snow bank. All or a part of the ore from these channels constitutes the sample. Sometimes two sets of channels are made, one set at right angles to the other. Channeling is fairly accurate if carefully done, but is little used, since it requires a large floor space. In channeling, the ore does not require as much mixing as in quartering, but there is sometimes considerable difficulty experienced in making the channels without knocking down some ore, either coarse or fine, from the sides of the channels.

12. Quartering. When ore is sampled by quartering, also called the Cornish method of sampling, the ore is first thoroughly mixed and then divided into four parts or quarters and two of these parts taken as a sample, while two are discarded. In order to thoroughly mix the ore, the work may be done as follows:

The ore is dumped in a large circle, as shown at a, Fig. 1, and the samplers move slowly round the ring, shoveling the

ore into a pile in its center. It is common for two men to work together, always keeping diametrically opposite each other. They drop each shovelful exactly on the apex of the resulting cone, as shown at b. This is done by holding the shovelful of ore above the apex of the cone and then suddenly pulling the shovel away from the ore in the direction of the arrow. This distributes the ore on all sides of the cone and gives a pretty thorough mixture. As another aid to complete mixing, the samplers do not shovel all the ore in walking once round the circle, but make at least two trips. Care must be taken to sweep up all the fine ore and place it on the top of the pile. It will not do to simply sweep the fine ore up to the edge of the pile, as this is apt to be the richest part of the ore.

In some cases, to insure thorough mixing, the ore is shoveled from a ring to a pile and back to a ring again several times or it may be shoveled from one pile to another. After the ore has been thoroughly mixed and piled up in a cone, the samplers walk round the cone continuously in one direction and with their shovels draw the ore into a wide, flat pile or heap. The manner of doing this is illustrated in Fig. 2, which shows the cone partly spread out. It may sometimes be necessary to shovel the ore from this flattened cone into a second cone in order to make the mixing more complete.

a

13. It is hard to get thorough mixture when very coarse and very fine material occur together, but this difficulty is lessened by moistening the ore a little.

FIG. 2

Water should not be added in

sufficient quantities, however, to make the ore cake. Very wet ore cannot be properly sampled by quartering, because the water washes the fine material away from the coarse and so prevents satisfactory mixing.

Having spread out the ore flat, it is divided into four quarters, as shown in Fig. 3. This may be done by pressing the edge of a board down through the heap on two lines that

When shoveling these channels, the ore removed is thrown.

alternately to the right and left.

After the quarters have

been marked off for separating, two opposite quarters, as, for instance, I and III, are shoveled away, taking care to remove all the fine particles belonging to them. The remaining two quarters are shoveled into a new cone and the process repeated. This time, quarters II and II' are shoveled away instead of I and II. The object of this is to overcome any possible tendency of the shovelers to make one side of the heap richer than the other. The reduction of quantity must not proceed too far before the ore is crushed to a smaller size. Even after fine crushing the sample is seldom reduced in size below 8 pounds by quartering.

14. Sampling Floor.-The floor on which the quartering is done should be smooth and free from cracks, and for this reason it is best to have it covered with iron. It

FIG. 4

should be carefully swept before it is used, to prevent rich dust from previous samplings being mixed with the ore in hand. When a good floor is not available, a large piece of strong canvas may be spread out.

15. Split Shovel.-With lots weighing not more than half a ton and when the largest lumps are not more than about 4 inch in diameter, the split shovel, Fig. 4, is sometimes used. This shovel consists of several long scoops a, with open spaces b between them, the spaces being the same width as the scoops. The sampler takes the ore on an ordinary shovel and spreads it over the split shovel, moving his shovel back and forth across the scoops as the ore slides off. When the scoops are full, the split shovel is lifted and the ore in the scoops is put one side as the sample, the rest of the ore remaining on the floor. The action of the split shovel is very much like that of the sample riffle or the Jones ore sampler, both of which are described under

the head of "Finishing the Sample,"

SAMPLING TAILINGS

16. A slotted-pipe sampler is sometimes used to sample fine material that is of fairly uniform grade, such as concentrates. The best form of this tool is shown in Fig. 5. A 1-inch iron pipe a has a slot b cut lengthwise in it from one end to

within 3 or 4 inches of the other. AT is

screwed to the unslotted end, for the insertion of a handle c. A second pipe d, just large enough for the first to easily slip inside, is also slotted, but this slote does not extend quite to either end of the pipe. The lower end of this larger pipe is forged to a point, so that it can be easily pushed into a pile of

a

FIG. 5

fine ore. The tool, while held in the position shown by the cross-section f, is forced into the material to be sampled; the inner pipe is then turned into the position g and is twisted back and forth until it fills with ore. It is then returned to the position f and the sampler is withdrawn. To pull out the driven pipe d, a cast- or wrought-iron cross h is screwed to the pipe and a lifting handle i inserted through h

17. Dipper or Bucket Sample.-To sample any running stream of material, such as the different products in a concentrating mill, a dipper or bucket may be passed through the stream at regular intervals, once an hour, for example. The dipper must pass across the whole stream, because one side may be richer than the other. It must not