Improvised filtration devices

I knew I had encountered a list of filtration efficiencies for a number of materials. The point was that in a contamination episode, you had access to any number of improvised filters that were better than nothing. I finally found a book of the handouts for my Physics 468-B class decades ago, and lo and behold!

Respiratory protection provided by common household and personal items against aerosols of 1 to 5 µ particle size

Item# of thicknessesResistance: mm H2O# of ObservationsEfficiency, Geometric mean99% confidence, lower99% confidence, upper
Handkerchief, man’s cotton16363294.292.6395.5
Toilet paper3133291.489.892.8
Handkerchief, man’s cotton8183288.985.591.6
Handkerchief, man’s cottoncrumpled3288.185.190.5
Bath towel, Turkish2113285.183.386.8
Bath towel, Turkish153073.970.778.8
Bed sheet, muslin122327268.874.9
Bath towel, Turkish1 (wet)33170.26872.3
Shirt, cotton1 (wet)>150 (a)1565.957.972.3
Shirt, cotton273065.560.869.6
Handkerchief, woman’s cotton4 (wet)84 (a)326357.358.7
Handkerchief, man’s cotton1 (wet)98 (a)3062.65767.5
Dress material, cotton1 (wet)180 (a)3156.349.662
Handkerchief, woman’s cotton4 (wet)23255.552.258.7
Slip, rayon16325046.253.6
Dress material, cotton153147.641.453.2
Shirt, cotton133234.62939.9
Handkerchief, man’s cotton123227.52232.5

(a) Resistance obtained when checked immediately after hand wringing. This resistance began to decrease after about one minute when the material started to dry.

I’m not sure of the original source. It may be an old version of an OSSHA handbook.

Heartland launches 22 climate science “gatebreakers”

The Heartland Institute has just published a whopping 22 gatebreakers, with more promised. This is a true wealth of important skeptical material, unlike anything we have seen before. My dream is coming true.

A gatebreaker is something a skeptical student can send around to the class when the teacher insists on alarmism. Or something short and simple to send to a journalist in response to an alarmist article, or to a politician making alarmist speeches, or the local blowhard alarmist. It’s power lies in its specificity and its simplicity.

The Heartland website is called “Climate at a Glance” ( which makes it sound softer than it really is, sort of like a pink pistol which you can actually buy. These are not glances; they are hard hitting rebuttals.

Homemade filters

In college, I encountered a list of improvised filters that could be used to guard against inhaling radioactive contamination. I haven’t been able to find that list, but here’s something from the Wall Street Journal: Will homemade filters protect against the coronavirus?

A coronavirus particle is about 0.12 microns, or an eight millionth of a meter. Different materials have been tested for their ability to screen out virus particles.

  • Furnace filters — 98%
  • Automotive filter — 95%
  • Vacuum bag — 90%
  • Swiffer dry sweeping cloth (five layers) 60%
  • T-shirt fabric (five layers) 60%
  • Bed sheets (five layers) 50%
  • Paper towels (five layers) 40%
  • Coffee filters (two layers) 10%

Source: Do DIY Masks Help Stop Coronavirus?

It’s Too Darn Hot

I’ve been slowly collecting notes on the science that science fiction writers get wrong. I have this idea of using them for the basis of a high school level science class. In fairness, I don’t count things like the swamps of Venus or the notion that Mercury’s dark side never faced the sun and was perhaps colder than Pluto. I intend to focus on things that were known at the time a story was written. For example, the notion that gravity would hold structures and an atmosphere against the inside surface of a Dyson sphere.

One thing that crops up from time to time in science fiction stories is helium-II on very cold planets. Pluto is one target. Or imagine a planet that’s tide-locked with its sun, with the dark side near absolute zero. You could imagine streams of superfluid helium flowing uphill because that’s what superfluids do.

Well, it occurred to me to look up the temperature at which liquid helium transitions to superfluid helium-II. This temperature, the so-called lambda point, is 2.1768K, or 2.1768 Celsius degrees above absolute zero.

The cosmic microwave background corresponds to a temperature of 2.7255K, or nearly half a degree above the lambda point for liquid helium. That means a body floating in interstellar space will exchange heat with the surrounding sky by radiation until its temperature is equal to the microwave background temperature. As a result, the planet will remain too hot for superfluid liquid helium to exist.

So good-by superfluid helium based life forms.

Since then, I’ve read that the temperature can be lower inside dust clouds, where the energy from the microwave background hasn’t had time to penetrate into its depths. And that could be the basis for an interesting story.


It’s too darn hot.

It’s too darn hot.

I’d like to go superfluid tonight,

And flow against gravitation tonight,

I’d like to be superfluid tonight,

And flow uphill over walls in the night,

But I ain’t down to transition tonight,

‘Cause it’s too darn hot

The Riot Act

The Riot Act

Ever wanted to read someone the Riot Act? Apparently all you need to do is find a group of 12 or more people “tumultuously assembled” and declare the following (preferably with a British accent, of course):

Our Sovereign Lord the King chargeth and commandeth all persons being assembled immediately to disperse themselves, and peaceably to depart to their habitations or to their lawful business, upon the pains contained in the act made in the first year of King George for preventing tumultuous and riotous assemblies. God save the King.

(A bit of Westlaw research suggests that this isn’t the entire act as passed in 1715, but it’s the part that had to be read to disperse the crowd; anyone who hadn’t dispersed in one hour after this was read was guilty of “felony riot.”)


Source: Watcher of Weasels

Bookworm is cleaning out her closet, and came across, among other things, some pithy sayings from her Contracts law class….

“Watch out for chameleon words. They change with the context.”

“The absolute best defense is a counter-claim.”

“Stay with something simple . . . like logic.”

“Always look to see what the reason for the rule is. If the reason isn’t applicable, then maybe the rule isn’t applicable.”

“It’s tooth fairy time. You are departing from reality.”

“Common sense says that’s crazy.”

“The peasants are restless. Let’s promise them a circus.”

“It’s not the village idiot you have to be worried about. It’s his attorney.”

“Put yourself where you were the day before you entered law school: intelligent and common sensible.”

“It’s like shopping for drapes to match the towels.”

“Article 9 comments [I assume it was the Restatement of Contracts, 2nd] were written by some cockroach flinging itself at the typewriter.”

“You can’t legislate common sense, but you can legislate lunacy.”

“To a litigator, perjury is just emphasis of different facts.”