WOOD PIPE FOR CONVEYING IRRIGATION WATER. 39 



also that decay occurs at summits of pipe lines where air accumulates 

 much sooner than at depressions. 



The practice of coating continuous stave pipe has not been common, 

 but in a considerable number of cases some treatment has been ap- 

 plied for the purpose of preserving the wood. There is wide differ- 

 ence of opinion as to the value of such treatment, and the effective- 

 ness for the purpose intended may depend also greatly on what is 

 used and upon how and when it is applied. 



On exposed portions of new pipes the United States Reclamation 

 Service has used a paint consisting of 6 pounds of red oxid mixed 

 with 1 gallon of boiled linseed oil. One gallon of the paint was suf- 

 ficient for two coats on 125 square feet of pipe. On top of the pipe 

 where exposed to the sun and where water from leaky joints runs 

 down over it this paint does not last long, much of it being gone in 

 two years. Repainting while the pipe is in use is usually not prac- 

 ticable, because oil paint will not adhere readily to wet material. 

 The use of paint on exposed pipes under ordinary conditions prob- 

 ably adds very little to their life. 



The Denver Union Water Co. on new work in 1911, used a primary 

 coat of linseed oil and lampblack, and a secondary coat consisting 

 of an asphaltum mixture. In March, 1914, the "Mabton siphon," 

 which had been uncovered the fall previous on account of decay, was 

 given two coats of coal tar tempered with creosote. The mixture 

 was applied by a machine which pumped the hot mixture through a 

 hose and nozzle, shooting it on to the pipe with considerable pressure. 

 The same machine was used in cleaning the soil and decayed material 

 from the pipe before painting. Other instances might be cited show- 

 ing the use of asphaltum or tar on old pipes after uncovering. The 

 cost of the work is considerable and its value is questionable, partic- 

 ularly where pipes are to remain exposed. 



The staves of a 50-inch pipe built at Burbank, Wash., December, 

 1912, were creosoted before construction. This pipe was buried in 

 sandy soil and operates under little or no internal pressure. The 

 cost of treating the staves was said to be $24 per thousand. Car- 

 bolineum was used as an exterior coating on part of a 48-inch pipe 

 built at Wenatchee in 1907, and on a 12-foot pipe built in Oswego 

 County, N. Y. 



Where pipes are to be placed in contact with the soil, and where 

 the internal pressure is not sufficient to insure complete saturation of 

 the staves, it is probable that their durability may be increased by 

 treating with some preservative. 



A difference in the effectiveness of materials for this purpose is 

 indicated by the following example : In 1890 a 54-inch pipe of Texas 

 pine was built for the Bessemer Ditch Co., at Pueblo, Colo. About 

 1,500 feet of this was subjected to light pressure, and at times the pipe 



