The logs, brush, and leaves from the lower bank (under the artificial bank) are carefully removed. The foundation is generally cut for the entire width of the flume. The sketch (Fig. 18) shows the method of posting along cliffs, where the foundation is occasionally narrower than the flume. Where flumes connect with the ditch, the posts of the flumes, for a distance of several boxes, are 4 to 41⁄2 feet high, allowing an additional side plank. The grade of the flume is 32 feet per mile. The planking is 2 inches thick.

CHAPTER XI.

PIPES AND NOZZLES.

Wrought-Iron Pipes.-Wrought-iron pipe is used extensively in California on account of its cheapness of construction, its adaptability for crossing depressions, the facility with which it can be moved (changes of the position of the line being often necessary), and other advantages arising from its lightness combined with great tensile strength.

It is used as

(1) A water-conduit, replacing ditches and flumes. Where large depressions are crossed it is called an "inverted siphon."

(2) A "supply or feed pipe," conveying water from the "pressure box" to the claim.

(3) A "distributing pipe," taking the water from the "distributer," or "gates," at the end of the supply pipe, and delivering it to

(4) the "discharge pipe" or "nozzle."

Large mining companies often have their pipes constructed at their own workshops, although generally the iron plates of proper size and thickness are punched and rolled before delivery, and put together on the claim.

Inverted Siphons. According to Father Secchi, there is near the town of Alatri, in Italy, an "inverted siphon" with a depression of three hundred and thirtyeight feet, supposed to have been constructed by the Romans two hundred years before Christ. The pipes

are of earthenware, embedded in concrete, and are said to be still in a good state of preservation. There is, therefore, no novelty in the construction of this kind of waterconduit; but the use of wrought-iron pipe for this purpose was very limited until adopted in California, where it has been very largely employed, and where there have been obtained valuable data of the strength of materials and methods of construction, as well as of the flow of water through long pipes, essentially modifying theories and formulas previously accepted.

Thickness of Iron.-The thickness of the iron is determined by the pressure of the water and the diameter of the pipe, allowance being made, of course, for the quality of the material and the method of riveting. The factor of safety against damage from accident is regulated by the importance of the line. On account of va riations in plates marked as being of the same size and number, it would be well, as a precautionary measure, to

TABLE XIV.

Thickness and Weight of the Principal Sizes of Iron used for Hydraulic

weigh each plate used, as thereby any essential difference in thickness could be detected. Iron plates which have been subjected to the action of salt water are undesirable.

The Spring Valley Water Company, of San Francisco, California, strain their pipes from 11,400 to 13,000 lbs. per sectional inch.

The Virginia City and Gold Hill Water Company, of Nevada, has an inverted siphon (of inferior English iron) with a maximum pressure of 1,720 feet head, equal to 746 lbs. per square inch, No. o iron, with 5%-inch rivets, being used at the lowest point of depression and subjected to a tensile strain of 13,310 lbs. The No. 9 iron is strained fully 15,000 lbs., and the No. 7 over 14,000 lbs., per sectional inch.

The Texas Creek pipe, four miles below the Bowman Dam, Nevada County, California, is an inverted siphon 4,438.7 feet long, 17 inches in diameter, made of riveted plate iron. Its inlet is 303 feet above the outlet, and with a full head it will discharge about 1,260 miner's inches. It sustains a maximum pressure of 770 feet or 334 lbs. per square inch.*

At Cherokee,† California, there is an inverted siphon of ordinary English plate, 30 inches in diameter, with a maximum pressure of 887 feet head.

The maximum strains on the several sizes of iron used in practice are given in the following tables:

* See Official Report North Bloomfield Mining Co., 1878.

+ For further description see p. 172.