HOWIETOUN PLANK PONDS. 



157 



charred with a red-hot iron rod ; this prevents the wood rotting 

 from contact with the iron. The bolts were driven through from 

 the upper side, and the nuts screwed tight against the oak-runners, 

 and the ends held firmly in their place by four long bolts, passing 

 through four pieces of oak, laid on the sides, just outside the 

 ends. The oak distributed the strain, and the ends were held so 

 as to keep absolutely water-tight. The inside of the pond was 

 next charred, the charring-irons being rectangular blocks of iron 

 weighing 28 Ibs. These are heated at a moveable forge, and once 

 a day they are dressed and squared at the smithy. The weight of 

 these irons holds them closely to the wood, and no air reaches the 

 surface. The result is that the wood is charred without being 

 burned. Fig. 119 is a section of the 20-feet plank pond. 



FIG. 119 scale 



fc S - 6 



Charring has many advantages over painting; it is cheaper, 

 lasts longer, preserves the wood better, offers no solum to fungus, 

 and perhaps the most important of all it is easily cleaned : a hard 

 brush passed once over it is sufficient. All the plank ponds are 

 now furnished with safety-screens. The screens are fitted in 

 shallow checks, cut in the sides a little more than a foot above 

 the outlet. The screen facilitates the cleaning of the ponds, as a 

 plug in the bottom, close to the outlet, 

 can be drawn without any danger of the 

 fish escaping (Fig. 120). In practice, nearly 

 all the dirt rests between the safety- 

 screen and the outlet. If the pond is suffi- 

 ciently stocked, and if the current is strong enough, the fish work 

 all fcecal matter, and the refuse of their food, and any sediment 

 brought down by the water, through the safety-screen into the 

 still water below the outlet. Here all dirt rests, and, if stirred up 

 after the plug is drawn, is quickly carried through the plug-hole. 

 There is an art in balancing the current and the quantity of fish 



-6 - O' 



FIG. 120 scale ^. 



