Early morning and droplets of dew hang off the leave of plants - except this is not dew but water of gutattion. What's the difference? It sure looks like dew.
Let's take a closer look at one of these 'dew' drops.
Notice that the droplet is at the end of a leaf. Plants take water out of the soil and release it into the atmosphere as a vapor through openings in their leaves called stomata. This process is termed transpiration. Sometimes transpiration is inadequate to remove excess water and instead of vapor, droplets of mineral laden water are released through openings similar to the stomata. This process is termed guttation and it occurs mostly in the morning when the humidity is high. It also occurs if the plant has been recently watered.
These shots were taken early in the morning, but it's also possible I'm over watering my tomato plants! For more information on guttation and plant physiology see http://en.wikipedia.org/wiki/Xylem.
Wednesday, June 23, 2010
Tuesday, June 15, 2010
Fifty years ago electronic balances were the great new technological addition to analytical chemistry. The instructor for my quantitative analysis class did not inform his students that these were available until after we had been given the gratifying experience of using double pan balances requiring that we 'count the swings' for highly precise and accurate weighings. At the end of the second week we found out just how marvelous the new balances were but not until our notebooks had been filled with many pages of weighings. I still have that notebook and so will share a lab exercise.
The lessons learned from this exercise in 1962 remain with me as a way of conceptualizing the measurement process. All measurements can be represented numerically but also possess a physical reality. Counting the swings on a balance to estimate the last significant figure in the measurement gives a feel to the measurement process that a readout on a display cannot match.
The 3 minute video 'Classic Chemistry - The Way it Was' is based on the notebook entries for one afternoon in the Chemistry 131, Quantitative Analysis, laboratory in 1962. The sixteen pages of entries are mostly weighings with some calculations and notes. That was the way it was.
Posted by ken osborn at 11:09 PM