How does a Fyrite work

1. What is a fyrite?/What is a fyrite used for?
2. How to use a fyrite.
3. How does a fyrite work?
4. Help improve this article.
5. Where can I get a fyrite?
6. Papers or articles about fyrite.
7. Fyrite pictures.

What is a fyrite?/What is a fyrite used for?

A fyrite is a volumetric gas analysis device.  The device is used to measure the concentration of a selected gas in a sample of gas.  The gas is “selected” by choosing the composition of the liquid inside the analyzer. A fyrite is used to make reference measurements for calibrating sensors in laboratory and medical devices, particularly incubators. A fyrite can also used to analyze combustion efficiency, for example in furnaces.

The analyzer looks like this (this one is for CO2 measurement):

The fyrite has the following functional parts

• Chamber: The chamber has a reservoir at the bottom containing the fyrite fluid.  The narrow column in the middle is where the measurement takes place. At rest, the chamber is sealed with a spring-loaded plunger and is air tight.
• Measurement Scale: The graduated scale along the narrow measurement column is used to measure the gas concentration. On the pictured device, the scale is adjustable to correct for variation in fluid volume.
• Plunger: The spring-loaded plunger on top allows for the introduction of a gas sample into the chamber and for resealing of the chamber once the sample is taken (see image below).
• Diaphragm: The bottom of the chamber where the fluid sits is made out of soft, flexible rubber (see image below). This soft, flexible property is important and will come up later.
• Fluid: The fyrite fluid is mostly water.  For the CO2 fyrite, the “active ingredient” is potassium hydroxide (KOH).  The CO2 solution is colored red for identification (The O2 solution is blue). The O2 solution has a bunch of ingredients and I have’t bothered to figure out how it works since I rarely use it (but maybe I will later).

How to use a fyrite

These instructions will describe how to use the device pictured to measure CO2 concentration. The general process should be similar for any such device.

1. Invert and right the device to absorb any CO2 that might be inside. To do this, hold the device upside down at a 45deg angle and allow all of the fluid to flow into the top chamber, then turn it right side up at a 45deg angle and let all of the fluid flow back to the bottom chamber.
2. Press the plunger several times to equalize chamber pressure with atmospheric pressure.
3. Zero the measurement scale. This means to move the zero mark on the scale to the top of the fluid.
4. Arrange the sample tube so that it can pull gas from the desired area. Some devices have a sample port with a barb where you can directly attach the tubing. Other device have a hole into which you can insert the tubing or a probe attached to the tubing.
5. Press the other end of the sample tube (with the round head) onto the plunger of the fyrite device. The piece on the end of the tubing should seal around the top of the pluger. Depress the plunger, holding the sampling device tightly to the plunger to maintain the seal.
6. With the plunger depressed, squeeze and release the bulb on the tubing 20 times to introduce a sample of the gas into the fyrite. Release the plunger on  the 20th squeeze.
7. Invert and then right the device to mix the fluid with the gas sample. Make sure to hold at a 45deg angle going both ways.
8. Read the concentration from the scale. If there was any CO2 in the gas sample, the level of the fluid in the chamber will have risen.

How does a fyrite work?

What caused the level of the liquid to rise so much?

The KOH in the solution reacts with the CO2 in the gas sample to produce K2CO3 (potassium carbonate) which is a water soluble salt. The result for our purposes is that a portion of the gas proportional to the amount of CO2 in the sample is removed from the gas and dissolved in the water. Since dissolved solids are much, much smaller and less energetic than gases, the density of the gas in the chamber decreases which creates a lower pressure inside the chamber relative to outside. The (now higher pressure) air outside the chamber pushes against that soft flexible rubber diaphragm on the bottom of the chamber, reducing the volume inside the chamber which manifests as a rise in the level of the fluid inside the chamber.

Somebody figured out how much fluid rise equates to how much % CO2 given the softness and flexibility of the rubber diaphragm and the cross-sectional area of the measurement column (or they decided how much fluid rise they wanted per % CO2 and chose the rubber properties and column cross section accordingly). We just believe they did it right and use the device.

Help improve this article

If you want to help improve this article, here are some ways you can do so:

• If you know the origin of the name “fyrite” or know who might, please let me know @jasondoolittle on twitter or comment on this post.
• If you’re good at chemistry or know somebody who is (and I don’t mean if you can google it. I can too, I just don’t believe everything I read on the Internet), I would appreciate a proper reaction equation for the aqueous KOH and the CO2 taking into account all the water and etc, and for bonus points do the O2 as well. Here is a link to the MSDS with the ingredients.
• If you have a fyrite or similar device that is different than the one pictured here, please send me a photo of it.
• If you use a fyrite as part of your work or hobby, let me know what you use it for.
• If you have or know of any papers or articles about fyrite gas analysis, please share them with me.  I will link them at the end.

Where can I get a fyrite?

If you need a fyrite, you can buy one at Amazon (This is an affiliate link which helps pay for this site. See my full affiliate disclosure and policy): Bacharach 0010-5090 Fyrite CO2 and O2 Testing Kit

Papers or articles about fyrite

Replacing liquid fyrite with digital to improve in vitro fertilization laboratory quality control procedures

Fyrite pictures