Saturday, 24 August 2013

09:04 – It was brought home again to me yesterday that different people use the same word to mean different things. The first time I remember particularly noticing this was when I worked summers during college on a road crew. We were using a high-lift (front-end loader) to fill a 10-ton dump truck with aggregate for road fill. These were chunks of rock that averaged bigger than your fist, and the foreman referred to them as “gravel”. I’d always thought of gravel as pea-size pieces, but as it turned out the foreman was using the word correctly.

One of the items I need for the AP chemistry kits I’m doing for the state virtual school distance-learning program was spec’d as “calcium carbonate (marble chips), 2 g vial”. I decided to provide a full 30 mL wide-mouth bottle because they’re much quicker to fill than a vial and the material is cheap, so I ordered 2.5 kilos of “marble chips” from one of my regular vendors. But those “chips” are actually what I’d call “chunks”, averaging maybe 3 cm. I’m not about to stand there with a sledge-hammer breaking rocks so I’ll just buy some smaller marble chips locally, which is what I should have done in the first place.

I also made up a batch of pH 7.0 buffer yesterday, for calibrating pH meters. A 100 mL bottle of this is another of the items I need for the virtual school order. This stuff is available commercially, but a small bottle typically costs $7 to $15. That’s because the commercial stuff is intended for calibrating high-end pH meters, those with accuracy of 0.01 pH or even 0.001 pH. It’s made with extreme precision and each batch is assayed to give precise pH values at various temperatures. The students will be using inexpensive pH meters with accuracy of 0.2 pH. I haven’t calibrated the batch I made up, but I’ll shoot for something in the pH 6.98 to 7.02 range at 21C.