After a one-day break, it's back to Chuini. This time Kate has set me the challenge of improving the illumination of a lighthouse that we're going to build on Bawe Island, one of the coral islets a few miles due west of Stonetown. As Ellen's planning to use oil lamps for the lighthouse's light source, the easiest way I can think of to improve their brightness is to devise some way of increasing the oxygen levels in the atmosphere surrounding the lamps. I can easily produce oxygen by passing an electric current through water containing a few drops of car-battery acid. It's a process called electrolysis, and what's more, I've actually been given some graphite electrodes to build the electrochemical cell.
I try the system out on a small scale, and sure enough, pure oxygen comes off at one electrode, and pure hydrogen at the other. I'm not interested in the hydrogen though; for this challenge I just want the oxygen. All I have to do for the rest of today and tomorrow is scale up the process, to produce the gas in sufficient quantities. Again, this is a comparatively easy challenge for me. The four of us will need to work together closely though, to ensure that each of our individual contributions to the challenge can be brought together on Day 3.
By now, I've formed a few friends among the nine-strong team of security guards and drivers based at Chuini. We have a great laugh together, and their company is a welcome break from the intensity of filming. 'Dullah is into music and borrows my portable juke box every day, Tino enjoys an opportunity to polish his English, which is already very good - much, much better than my Swahili. Mao, Zaccariah and Armani are still reticent, but we're warming to each other. For this second challenge it's another guard, Ali, who offers me his help. It's gratefully received, and besides, it's important to involve these guys as much as possible, not only to satisfy their interest, but also to help them feel more widely involved in the overall project.
The time has flown today, and by late afternoon, all I've done is a short piece to camera explaining the electrolysis process. I'm going to have to get my skates on, as one of the Directors tells me that the local tides dictate that we'll have to leave for Bawe Island at 11.45 in the morning of Day 3. That's a whole half-day 'lost'. I can appreciate that life on Zanzibar is predicated on the tides, but it comes as a shock to hear that my contribution to this challenge will effectively have to be completed in little more than two days - even less time than I had in Programme 1.
Scaling the process up, I build an electrolytic cell with twenty graphite electrodes rather than yesterday's two. I use two car batteries wired up in series, rather than the small battery I used yesterday. As a result, oxygen streams off the electrodes, and I've little doubt that this larger cell will produce enough oxygen to make the oil lamps burn more brightly. I'll only need to increase the oxygen concentration in the lamp housing by a few percent in order to do the trick. At the moment though, I have a small problem; I'm losing a lot of the oxygen through leaking seals around the electrodes.
I can easily fix the leaks using epoxy resin (although the available resin will take up to 17 hours to be fully waterproof). I spend the rest of the day ensuring that the scaled-up cell is producing as much oxygen as possible, and that all of the highly flammable hydrogen gas generated at the other electrodes is vented off at a safe distance from the cell and Ellen's lamps.
With a strict deadline of 11.45 for setting off in the boats to Bawe Island, I've got my work cut out this morning. The resin has set, and I'm confident that the scaled up cell will do the job. My only remaining problem is that I can't, for some reason, get a positive test for the oxygen that streams off the electrodes. The gas I collect should re-light a glowing splint, but I just can't get it to work. I know for sure that it's oxygen - what else could it be? - but I can't prove it. What on Earth is going on?
These challenges must all seem pretty easy from the comfort of an armchair; in practice, however, in the midday heat, under pressure, and working to an immovable tidal deadline, a simple thing like showing that the gas is oxygen isn't so straightforward. With hindsight, it boils down to the fact that I'm collecting the gas in the wrong way - a trivial mistake that will be picked up by anyone who knows a bit of Chemistry. I know that oxygen is slightly heavier than air, which is composed of 78% nitrogen, a lighter gas than oxygen. The method I actually used to collect the gas on camera was wrong. What a dingbat! I comfort myself by saying that anyone can make a mistake in such circumstances, but this is going to be such a public mistake. Best just to put the whole episode behind me.
Without being able to prove to Kate, on camera, that the gas I'm collecting is oxygen, there's no way I'll be allowed to take the scaled-up cell to Bawe Island, because my part of the challenge will, unfairly to my mind, be deemed to have failed. The decision is made more difficult because we're going to have to carry the lighthouse, my part of it as well as everyone else's, the length of the island (some 2 km) - as well as when, the tides dictate where we'll actually be able to land. By 1145, Kate and I agree to leave to the other scientists the final decision on whether my huge electrolytic cell goes to Bawe or not. We decide that we have enough to carry (and so it proves), and we should go without my oxygen generator. It's a tough decision, and one that I'm still not altogether happy about, but it's my mistake that's brought it about and I have to pay for it, however unfair I consider the outcome to be. Ellen's lamps will just have to do without my help. Despite this setback, the lighthouse works a treat - my oxygen wasn't really needed after all.