In oceanography it is of importance to take in-situ water samples. This tutorial will explain how to make a Niskin bottle. A Niskin bottle allows us take a water sample from a specific depth.

One practical use for the Niskin bottle could be finding the thermocline. In order to do this we would take various water samples from different depths, measure their temperature and hence find the approximate depth at which we have a (relatively speaking) high drop in temperature.

The way the Niskin bottle works had to be adapted a little in order to make it at a low cost and high viability. The here presented bottle uses two ropes: one holds on to the actual bottle and the other activates it at the wanted depth. Once the activation rope is pulled the bottle closes and the water is trapped inside.

Also check out this video. Here you can see professional Niskin bottles in action.

Supplies

Necessary Tools

power drill
drill bit 4mm
drill bit 3mm
sand paper 100 - 200
file
cutter (utility knife)
scissors

Material

PVC tube approximately 33cm long (inner diameter: 85mm, outer: 90mm)
2 gummy plungers (max diameter 105mm)
400mm chain that weighs around 300g or more
50 cm of latex tubing
plastic splint 5mm in diameter
about 60m of rope to take water samples of up to 30m of depth

Step 1: Cutting and Polishing of PVC Tube

polish thoroughly the cut borders of primary tube. The uniformity of the surface defines later the quality of the closing mechanism

Step 2: Slot

At one end of the primary tube create a slot. This will serve as a fixed point for the cable tie. (This end of the primary tube is the part pointing downwards)

Step 3: Plug Preparation

Cut a 45º angle in the ends of the plugs. (This is done in order to facilitate the closing process of the bottle, see also Step 13)

Step 4: Drill the Plugs

With a power drill place a hole in both plugs. Use a 4mm drill bit.

Step 5: Inserting Latex Rubber Tubing

Put the latex tubing in one of the plugs as indicated in the photo. The piece of rope is merely a way of helping to get the tubing threaded through the small hole.

Step 6: Locked Off First Plug

This is how the plug should look like after the latex tubing was pulled through and tied off with a knot. In the photo we can see only one side. The other side will be done after having passed the latex tubing through the PVC tube. See also photo 10.

Step 7: Drill Two Holes for the Upper Holding Loop

Drill two holes (in the opposite end as shown in Step 2) using a 4mm drill bit. Insert the rope that will be used to attach the bottle. The here shown slot is not necessary.