It would be nice if the island is volcanic - you'll need it for the sulfur. Mirabilite is a "desert mineral", not likely to be found even on a desert island.
Burning sulfur gives sulfur dioxide, which reacts with lye (sodium hydroxide) solution to form sodium sulfite. Allowing that solution to react with sulfur again gives you sodium thiosulfate.
Does the desert island have a mailbox? :) I could mail my film for processing...
Sea water contains sodium, potassium, bromide, sulfate and bicarbonate ions. Therefore, in principle you could use fractional crystallization to get most of what you would need. It would be a bit like the Curies separating radium from rock, but what's time to someone marooned on a desert island?
Taking some time out to find a volcanic fumarole wouldn't be a bad idea; once you have elemental sulfur, from any source, you are on your way. Having sulfur to oxidize to the trioxide would let you make sulfuric acid, useful in extracting gallic acid and for other purposes. Reducing sea-water sulfate to free sulfur might be a challenge; is there a chemical engineer in the house? (Carbon [i.e.--charcoal] reduction of sulfate might work if the thermodynamics are right, but I don't have a convenient way to check at the moment.)
Presumably, this island has coral, shellfish, or at least carbonate rock available; burning the calcium carbonate to lime will allow you to make calcium hydroxide, which can be used along with wood ashes to produce sodium and potassium hydroxides---burn some of your sulfur (where did you get that, anyway?) to sulfur dioxide as Ole describes and you have solved the fixer problem.
If you don't want to get your carbonate from the water, you could also reserve some hydroxide; left alone, it will absorb carbon dioxide and react to form carbonate, which is (conveniently) insoluble in concentrated hydroxide.
I hope that you had the foresight to land on a largish deserted island forested by oak trees; not only would the ash provide alkali, and the galls, acorns and bark provide developers, but the fractional crystallization is not going to happen by itself by itself, so you are probably fated to spend a lot of time (and fuel) tending a fire!
Any time now some folks are bound to show up and point out that our desert-island chemistry isn't environmentally sound and that our products don't meet Kodak's quality standards; when this happens, we will hijack their ship and sail home to get our film developed there! :)
the beach sand will contain silicon...so why not just make a digital camera?
it might just be easier to draw pictures in the sand & maybe make a castle
Thankyou all for your replies to my posting. I particularly like Greybeards volcanic fumarole suggestion as it sounds very visual and the question originated from a discussion we were having regarding a short story idea.
I'll keep an eye on the thread and reply in more detail.
Many thanks again,
How are you going to go at this next ?)
- how big an island do i need to raise a herd of cattle to kill off to extract the gelatin...
- make the paper to make the prints with the cotton, and...
- are we going to try to master reversal processing with horse piss developer, and then the special staining found after we make a second devloper refined from our wastes collected only after certain meals to attain a certain granularity?
This thread facinates me but, the problems are not sequential and the solutions have not been solved step by step. Would you mind if we make a novel, well a short story, in order to go step by step and all interested will go along with the development of the story as every step is solved with real answers? When the story ends the answers are real even if the events are fiction and the process can be used by everyone in their personal photographic experience.
I volunteer to spend 6 months on a tropical island to get ground truth data
There was an episode of "Naked Science" in which the scientists had to make a photograph using watercolor paper, a silver dollar and a few other "lost island" items. They failed, mainly because they ran out of time. You might keep your eyes open to see if they rerun the episode.