Tuesday, 30 August 2011

08:00 – The Pentax K-r DSLR showed up yesterday, along with its kit lens, a spare battery, and a memory card. When I opened the battery and charger, I plugged in the charger and plunked in the battery, only to see the indicator light green. I assumed that meant the battery was fully charged, so I installed it in the camera. It had a very low charge, so I resorted to reading the manual. As it turns out, the charger light is green as long as the battery is charging and goes out when the charge is complete. One interesting thing. The manual recommends not storing the battery completely charged, because that reduces its service life. That’s a new one on me. I thought storing a partially-charged battery was bad, but at least for the Pentax battery that’s the recommended procedure.


I’m still working on the biology book and kit. One thing I want to include is several different antibiotic resistance samples–amoxicillin, cephalexin, erythromycin, penicillin, tetracycline or doxycycline, metronidazole, and so on. The problem is, the things are ridiculous expensive to buy.

For example, Home Science Tools sells a set of eight antibiotic test discs–two each of penicillin, ampicillin, neomycin, and erythromycin–for $3.95. These discs are tiny. They appear to be about 3/16″ (4.8 mm) in diameter, about the size of the discs produced by a notebook 3-hole punch. And you only get two of each for $4.

I could buy antibiotic discs from a wholesaler for maybe $10 per hundred, but that’s still $0.10 each. That starts to add up if I include multiple discs of several different antibiotics. So I decided to make my own and supply them in the biology kit as 2X2″ (5X5 cm) squares, which the user can trim or punch to the desired size. With half-centimeter squares, for example, a 5X5 cm sheet would provide 100 test pieces, each 5X5 mm, or 5 mm circular pieces if they used a hole punch. (Sterility is not a major issue; even bacteria that are resistant to a particular antibiotic are typically resistant only to the levels found in blood plasma, not to the levels present in these test papers.)

I can buy filter paper in 8.5X11″ (21.6X28 cm) sheets, each of which will provide 20 squares, each about 5 cm square. I’ll run each sheet through the laser printer and print the type and concentration of antibiotic in small print repeated at frequent intervals. I’ll then sterilize the sheets with dry heat and absorb an aqueous solution of the relevant antibiotic into each sheet. Of course, the issue then becomes how to determine the concentration. To do that. I’ll weigh a sheet of the filter paper dry, soak it in water, allow it to drain, and reweigh it. Knowing how much water each sheet absorbs will allow me to calculate how concentrated to make the solution to reach a given concentration of antibiotic in a specified area of the filter paper. I love devising cunning plans.


09:35 – Well, no more site traffic stats for me. When I clicked on the site stats link, WordPress told me that the stats plugin now required installing and enabling something called Jet Pack and setting up an account on WordPress so that I could get to my stats in the WordPress cloud. I hate clouds. And site traffic doesn’t matter to me. I don’t care if I average 100 visitors a day or 10,000. I write this journal for myself, not for anyone else.


12:17 – I just assembled enough chemistry kits to fill the orders that have been outstanding since I ran out of kits on Saturday. While I was at it, I built a dozen extra kits and put them on the shelf. Final kit assembly goes much faster now that I have all the components organized and ready to hand. Assembling a dozen kits from subassemblies and individual components now takes less than an hour.