Unusual way to melt gold.

I have seen this done in a national geographic magazine in 1972. I had forgotten all about it until I watched this video. Watch at 10:30, the rest of the video is crap. No fuel or electric power for this melter.

 

Yup.. crap video for the masses. Amazing people even click this bs. I never would have.

The only thing worth looking at here is the comments. It really shows what a shitshow world we live in these days. I weep for humanity.

 

I have one of those kind of lenses. But I never tried melting metal with it before.
Patrick

 

Ya, not too practical, I guess. But, there is no harm (maybe even some good) in some over-enthusiastic young guys rediscovering the power of sunlight and dramatizing it. Perhaps it will inspire somebody to look at some more practical use of solar energy or take a more general look at the physics involved.

Denis

 

Oh man, I wasted perhaps 60 seconds of my life on that, too much. The flashlight bit was just too much and the question of using another lens to "magnify" the effect, as though the lens produces instead of focuses the energy. Had none of them ever played with lenses or bothered to read even the slightest bit about optics?

 

I junked a 56 rear screen tv about 10years ago. The only thing I kept out of it was the giant fresnel lens. Figured, you never know when you might need to start a fire without a match. There was a weirdo sciencey kind of fruitloop in florida years ago that did goofy crap along these lines. The world is littered with "youtube stars"

 

Was the big magnifying glass used in the video come from a rear projection tv? If so I will dismantle one to get the lens.

 

I'm grateful Ironsides included the time mark in his post to make his point. I dont suffer the clown shows for long.
There are some other more watchable videos available on the topic.

Pete

 

It doesn't look like the ones I have seen, not that I have seen many; the ones I have seen were rectangular.

 

I have a small one from an overhead projector downstairs. It measures about 12" square, and is very capable of melting small amounts of lead.
One can buy fresnel lenses, even that large, but they do get spendy, and I suspect would have limited usage for foundry work.

Roger

 

They can be found on the rear ends of some motor homes too but not sure of their metal melting ability.

 

Funny experiment.
But melting a solid block of 12kg of gold will not work, even with such a large Fresnel. Even the 31g gold melted partially only. Lots of radiation heat losses.
Moreover, the high heat conductivity of gold lets the heat on the spot of the focal point move to the cooler parts of the block.

It was funny to see that the liquid gold retained its yellow luster ('yellow mercury') rather than glowing red / orange hot. I did a similar experiment with copper in a propane flame in bright sunlight. The reducing atmosphere of the flame kept the copper oxide free and even when molten. The overwhelming sunlight allowed to retain its pink luster, like 'pink mercury'.

 

I remember watching a TV documentary in the 1970's, where the French had established a solar array of mirrors in the Pyrenees, that when concentrating their light melted a hole through 1" steel plate.

My memory may be wrong about the 1", but it was impressive even in black-and-white.