Saturday, 16 February 2013

08:20 – It’s spitting snow as I write this. Barbara is coming home this morning. Frances will be covering tonight at their parents, and they’ll discuss whether their parents can get along without one of them starting Sunday night. I hope so, because Barbara and Frances both need their lives back.

I labeled and capped 63 125 mL bottles of the fertilizer concentrate yesterday, to go with the dozen bottles I already had in stock. I may just go ahead and make up another 75 bottles, which’d give me enough for 150 biology kits. The solution is completely stable, so shelf life isn’t an issue. As with many of the solutions in our kits, we add 1 mL/L of 10% thymol solution as a preservative. Thymol at 100 mg/L inhibits growth of molds and bacteria.

I also discovered that the Vita Grow Part C powder (pure monopotassium phosphate) had doubled in price since I ordered it less than a year ago, from $18 for four pounds to $36. That means that for about the same cost, I can just make up the fertilizer A concentrate from reagent grade phosphoric acid and potassium hydroxide. It’s also quicker. I can just dilute 149.3 mL of concentrated phosphoric acid to about 3.5 L, dissolve 224.3 g of potassium hydroxide in that dilute acid solution, make it up to 4 L, and the solution is complete.