Page:Popular Science Monthly Volume 91.djvu/940

 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

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