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Test-Tube Hydrometer, Shot-Loaded and Calibrated (Boy Mechanic, 1915)
A hydrometer for specific gravity made from two test tubes: the small one, weighted with shot set in plaster and corked, floats in the liquid held in the large one, and the depth it sinks is read against marks copied from a bought hydrometer.
Beginner
An hour plus calibration
Instructions
1
1
How it floats
How it floats
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2
Read the Boy Mechanic
Read the Boy Mechanic
"The specific gravity of any material is the ratio of the weights of equal volumes of the material and water."
3
3
Mount the jar
Mount the jar
Take two test tubes, one able to hold the other. Stand the large one upright in a hole bored in a small block of wood: it holds the liquid.
Materials for this step:
Test Tubes1 piece
Hardwood Board1 pieceTools needed:
Brace and Bit4
4
Load the float
Load the float
Put shot or other heavy metal in the bottom of the small tube until it floats upright: almost wholly under water if it is for liquids heavier than water, only just upright if for lighter ones. Fix the load with a little plaster of Paris.
Materials for this step:
Test Tubes1 piece
Lead Ingot1 piece
Plaster of Paris1 piece5
5
Seal it
Seal it
Push a small cork into the open end and seal it with shellac, or with resin or sealing wax melted over it with a hot soldering iron.
Materials for this step:
Corks1 piece
Shellac Varnish1 piece
Pine Resin1 pieceTools needed:
Soldering Iron6
6
Mark the water line
Mark the water line
Float it in the large tube filled with pure water (rain water will do, distilled is better) and file a small mark level with the surface. In lighter liquids the mark sinks below the surface; in heavier ones it rises above.
Materials for this step:
Distilled Water1 pieceTools needed:
Files (Hand File)7
7
Calibrate
Calibrate
Float your tube and a borrowed hydrometer in the same liquid and mark your tube to match its readings. Starting with a heavy liquid, add water little by little; both float lower each time, giving more marks.
Materials for this step:
Distilled Water1 pieceTools needed:
Files (Hand File)8
8
Troubleshooting
Troubleshooting
Hydrometer troubleshooting.
Flow
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9
History and honest limits
History and honest limits
From **The Boy Mechanic, Book 2** (Popular Mechanics, 1915), p. 456 (checked on the archive.org scan boymechanicbook200chic2). Lead ingot stands in for his shot; the float numbers are our example.
Materials
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Tools Required
3- Placeholder
- 2 vendors sell this, none ship to you yetPlaceholder
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