As well, some metals we think of as strong become very brittle at cryogenic temperatures. Brittle = prone to shattering or cracking under even tiny stress.
Breaking that mirror would be very expensive very bad luck
The main thing is that it has very low thermal expansion when it’s that cold. Note that this is about the rate of expansion, not the absolute amount. The telescope is always kept cold, but there are still small thermal variations. So having a small rate (coefficient) is valuable to keep the mirrors from distorting. And beryllium has the unusual property that its rate of expansion is very small at that temperature.
Thank you. This is an example of the clear scientific explanations I get on these boards. I appreciate it.
Wood ash is not the primary donor of potassium. It’s function is essentially as an alkaline moderator of Ph, reducing the acidic environment created by bacterial activity in the ammonia/nitrogen/nitrite/nitrate conversion of urine and manure, the PRIMARY source(s) of potassium and nitrogen in niter beds. Yes, wood ash contributes, but its mass effect is minimal compared to urine and manure and possesses NO nitrogen.
However, wood ash is also used when extracting (leaching) the final mass of nitrates with water at the end of the procedure that takes 1-2 years for completion. At this point it acts as a potassium donor for any un-attached nitrites, but the bulk of KNO3 has already been produced.
But reliance on wood ash to provide all the necessary potassium in this entire process would require such a huge amount it would prove toxic to the bacteria, due to the extreme alkalinity it would create…not to mention your stated scarcity of such.
“old rotting timbers” would provide nothing to this process except un-necessary carbon and anerobic bacteria.
Of course, potassium nitrate is used…as is charcoal. But one would not say that trees (the precursor of charcoal) are used in the manufacture of gunpowder
For an interesting read, goto: . Joseph Leconte, 1823-1901. Instructions for the Manufacture of Saltpetre A Civil War era rebel’s guide (published in 1862) for producing KNO3.
My balderdash definition for “potash” would be medical marijuana for hemorrhoids
I shudder to think how it would be administered.
Old rotting timbers provide a source of nitrates, not potassium. Dung and urine beds are used because of the plentiful supply of those materials but rotting timbers alone can be used
Right, no one would say that because it doesn’t make sense. Gunpowder is made from three primary ingredients, and trees isn’t one of them while potassium nitrate is.
The rotting of timber (essentially carbon) has a net consumption of nitrates, it doesn’t produce them, and the biological process involved in rotting timbers primarily involves anerobic bacteria. Niter bed production of nitrates (KNO3) require aerobic bacterial action. Rotting logs are a lose-lose proposition so, no, they definitely could not be used exclusively as a replacement for urine and manure. Best to keep them out of the equation altogether. I certainly never said rotting logs provided potassium.
Likewise, it doesn’t make sense to say, as you did, that wood ash (potash) is used for such. Potash is not one of the three primary ingredients of gunpowder either. Remember my “nitpick” way upthread? I stated that wood ash wasn’t used in the manufacture of gunpowder per se, but rather, it was used in the production of KNO3. That was the inception of this whole conversation!
And I never said rotting logs were used. Do you know what timbers are?
Exactly what I said.
It’s obvious that we’ve not been on the same page here, and apparently you really have a need for the last word, so here’s your chance.
Please enlighten me as to the difference between rotten log and rotten timber.
I accept your apology and since your plea for information sounds desperate I’ll provide it.
Rotting logs are trees that fall over in the forest. Timbers are made from logs but are used as components in structures like houses and barns. They aren’t lying on the wet forest floor like a log where they slowly decay. Instead they’re use in structure keeps them off the ground and provides plenty of exposure to air. There they become infested with insect larva and bacteria that use aerobic action to produce nitrates. The cellars of timber frame structures are often full of decaying wood and larva bodies which are full of nitrates.
The need for potassium nitrate in France during their endless wars with England became so great they enacted a law allowing the government to seize peoples homes and farm structures to be used to make nitrate for gunpowder. Since these timbers have been rotting for years already, possibly a century or more they are immediately ready to use instead of waiting nearly a year for nitrates to form in dung piles.
Yeah, pot-ass-ium is a lousy name.
Interesting.
Here is a video. FWIW I am not posting it to be political but it seems to answer the OP.
Driven past it many a time.