924 Popular Science Monthly 



V-Block With Clamps for Small The Balanced Aquarium for the 



Drill Press Proper Care of Fish 



THE V- block shown in the accompany- 

 ing drawing and photographs is a very 

 handy tool on the drill press. It is espe- 

 cially useful 



when one has 

 small round 

 pieces to be 

 drilled. The 

 work may be 

 held securely 

 and the holes 

 drilled accu- 

 rately. 



The clamps, 

 of which there 

 are two, are de- 

 signed so that 

 a wide or nar- 

 row bearing on 

 the work may 

 be had. This 

 is shown in the 

 photographs. 

 The screw in 

 the back regu- 

 lates the level 

 of the clamp 

 and the other 

 draws the 

 clamp down into contact with the work. 



The post is turned to fit the lower table 

 bracket of the drill press. The center of 

 the V is in line then with the center line of 



The clamp and how it is 

 used in a drill press 



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Turn to fit 

 drill press 



Detailed dimensions of the V-block clamp for 

 use in a drill post for drilling round stock 



the spindle, and the holes drilled in work 

 will pass through the center. To prevent 

 small drills from running off center a guide 

 may be bolted down on the clamp. 



IT has only been made possible to produce 

 a naturally balanced aquarium since 

 science has progressed far enough to 

 establish the conditions under which aquatic 

 plants and animals live. All living things 

 require oxygen. Oxygen is breathed in and 

 carbon dioxide is given off. All aquatic 

 animals use only that oxygen which has 

 been dissolved and mixed with the water, 

 and give in return carbon dioxide. During 

 the day all green plants use carbon dioxide 

 and give oxygen off as waste matter. But 

 at night this process is reversed ; that is to 

 say, at night the plant uses the oxygen for 

 inspiration and gives off carbon dioxide. 

 This is easily proved by an interesting 

 experiment. Isolate an aquatic plant with 

 a certain amount of air. A few days later 

 the volume and composition of the inclosed 

 air will still be constant. But if carbon 

 dioxide be added to the inclosed air during 

 the day an analysis will later show that the 

 oxygen is predominant. In a balanced 

 aquarium the plants use up the carbon 

 dioxide during the day which has been 

 given off to the water, and in return they 

 give off oxygen. One plant can use only a 

 certain amount 

 of carbon di- 

 oxide during the 

 day and give off 

 a certain amount 

 of oxygen. For 

 this reason the 

 number of plants 

 in an aquarium 

 should exceed 

 the number of 

 fish it contains 

 to prevent the 

 accumulation of 

 carbon dioxide 

 in the water and 

 to assure an 

 abundant supply 

 of oxygen. 



If there are no 

 plants in an 

 aquarium the 

 water must be 



changed regularly to keep it pure and 

 healthful for the fish. A balanced aqua- 

 rium, containing both plants and fish, keeps 

 the water fresh, pure and healthful for the 

 fish and only that part of the water need 

 be replaced which has evaporated. 



Plants in an aquarium to 

 make it properly balanced 



