Canned air - what is it? Why does it kill ants?

I was using some canned air on a computer today and discovered something odd. It seems quite toxic to ants.

There is a small ant nest somewhere by my back porch which results in a handfull of tiny ants wandering around. As I was spraying out the computer fan I managed to release some air away from the computer with the can tilted down (if you haven’t played with canned air, this results in a very cold white mist). I noticed the ants stopped moving as the mist settled down on them. I played around a bit more and sure enough, it kills them dead in their tracks.

At first I thought I just froze them, but I’m not sure if this is the case. It takes very little amount of the mist to stop them. I managed to take a few out from a light spray about 1 meter away from the can. As a test, I lightly sprayed my hand and except for a few cold droplets, it wasn’t that cold.

I also found just lightly spraying them with the air with the can upright didn’t effect them. Only when I used the can upside down did it have any effect.

What’s the deal?

Turning the can upside down is spraying microscopic droplets of the propellant (refrigerant) directly on them and killing them.

And the propellant is a hydrocarbon, not sure which, but most of them are toxic.

meaning that canned air isn’t merely compressed air. Ok. But why not?

It is probably a lot colder to the ants. If you sprayed it on your hand you have the entire blood supply of your body to warm that area back up. For the ants, they have to contend with droplets the size of apples using their insect metabolism.

Because air doesn’t compress well. It stays a gas at room temperature. Many chlorhydrocarbons and chlorofluorocarbons compress into a liquid very easily, therefore more can be put into a can than if plain air were used. CFCs are no longer used for this purpose, though.

ah, I see. and as the internal pressure was reduced by spraying, more propellant would evalporate and create new pressure? I never thought about how propellants in aerosols worked.

Propane in tanks wors the same way. Most of it is liquid and boils off as some gas is let out. At a given temperature the pressure in the bottle is constant. That is why you cannot measure how much propane is left in the bottle with a pressure gauge.

Compressed natural gas (CNG) does not liquify and the pressures in the bottles are in the order of thousands PSI. A prassure gauge will tell you how much gas is left.

You are making the assumption that canned “air” in fact contains air. It does not. :smack:

In the old days canned “air” was freon or another CFC.
I’m not sure just what is in the can I have here (no statement of ingredients) but the label does have the following on it
[li]never spary into an encolsed space[/li][li]DELIBERATELY INHALING CONTENTS MAY BE FATAL[/li][li]THIS PR0DUCT CAN BE IGNITED UNDER CERTAIN CIRCUMSTANCES[/li][li]First aid: Innhalation Immediately remove to fresh air[/li][/ul]
Oh here I did find one ingredient listed
Contains difluroethane

Not air at all.

Rick - it seems that those statements are in reference to the propellant. It could be that inside the can is some liquefied difluoroethane AND some air. But why wouldn’t they say that? I mean, it seems hard to believe that someone could sell a can of compressed difluoroethane and call it air. I’d think some governmental agency would require that it at least be labeled Canned “Air.”

Despite what people call it, I’ve never seen a can of dust spray labelled “canned air”.

The cans usually contain 1,1,1,2-tetrafluoroethane, C[sub]2[/sub]H[sub]2[/sub]F[sub]4[/sub]. The boiling point is -26 degrees C, -15 degrees F. One little drop of it will make a little bit of your skin slightly colder, but there’s a lot of heat in your hand and it quickly gets back to normal temperature. On the other hand, one little drop will take most of the heat out of an ant, killing it.

Also cooling natural gas to about -260°F at normal pressure results in the condensation of the gas into liquid form, known as Liquefied Natural Gas (LNG).

CC My can says Dust Off, not canned air. I doubt very much if it contains any air. Shaking the can leads me to believe that it is mostly liquid in the can when full. Compressed air does not liquify at room temp.

The boiling point changes with the pressure so your phrase is meaningless. The boiling point of any fluid is any temperature you want if the pressure is right. Well, not “anything” but you kow what I mean.

The boiling point is not -26C if it is at room temperature. If it is at room temperature then the temperature is a given and the boiling pressure will depend on that. Conversely, if you fix the pressure then it is the temperature which will be maintained constant by the constant pressure.

No shit, sailor. When spraying a liquid out of a can on earth, it can be safely assumed that the boiling point is given at atmospheric pressure. It’s not meanigless, it’s the only temperature that is meaningful given the situation.

Mine says “Compressed Gas” not"air." It also says “Liquid contents may cause severe burns (frostbite) on contact with skin.” In addition, it has all the warnings about pressure, not exposing to heat and keeping out of reach of children.

It seems to me that if it can give big ol’ me frostbite, it’s probably cold enough to kill an ant. Just guessin’ though.

Wikkit, sorry if I sounded rude which was not my intention. I did not understand what you meant and now I think I understand it and I thnk you are mistaken (if you mean what I think you mean). The liquid boiling in tha can is not at atn=mospheric pressure, it is at whatever pressure that liquid boils at room temperature. The gas coming out of the can is not liquid boiling, it is gas expanding from the pressure inside the can to the pressure outside the can.

If you are implying the gas comes out at -26C, I think you are mistaken. If you are not implying that then. . . I am still confused.

Inverting the can (creating a “very cold white mist” in the OP) will release liquid from the can. Some of the liquid will quickly boil, dropping the remaining liquid to -26C. Then the remainder will boil as it can remove heat from the environment. The liquid component of the mist hitting the ants is at -26.

If used upright, the gas coming out of the can will approach -26C if it is sprayed long enough. At some point you end up with a can of liquid at its boiling point with no appreciable pressure; the same thing will happen if you use propane gas from a tank too quickly.

Now I understand what you meant. Thanks for the explanation.