FLUMES AND THEIR STRUCTURE. ( .<~> 



built in this way there would necessarily be a contraction 

 that would cheek the free flow of water. This leads to 

 the question of velocity. The best flumes arc built wMi 

 a vertical drop of from two to four feet at the upper end 

 of the structure and these drops have come to take the 

 place of the inclined aprons, which were formerly much 

 in vogue. There should also be a similar drop at the 

 lower end of the flume to make a water cushion by which 

 the velocity is broken and washing out is prevented. 

 Most engineers agree that the more velocity a flume has 

 without dropping the grade the better it will be, provided 

 arrangements are made to take care of the water at the 

 discharge. If a flume is narrowed in toward its discharge 

 the sides should be raised proportionately, in order to pro- 

 vide the proper carrying capacity and at the same time 

 prevent slopping over. 



Construction. There are wooden and iron flumes, 

 each built in various forms. In building wooden flumes 

 they are so superficial at best that they should be well 

 made and no expense should be spared in their construc- 

 tion. The best material only should be used, and the 

 writer has found seasoned and surfaced lumber prefer- 

 able to unseasoned stuff. It is best to tar or creosote 

 well-seasoned lumber, and painting or tarring green mate- 

 rial is to be discouraged, as it only induces decay and 

 brings on disappointing results. Tarring may be done 

 in vats before construction, or it may be done afterwards 

 by using mops or brushes. We would advise in the lat- 

 ter case the application of boiling hot tar on the inside 

 only and after all joints, seams and crevices had been 

 carefully calked with oakum. The boxing of flumes is 

 generally of three different forms. In the first the floor 

 is built directly on stringers and the planking floor placed 

 at right angles with the longitudinal axis of the flume or 

 the flow of the water. The second style is to lay floor 

 beams on the stringers, bracing them at intervals so as 



