Problem: Article: Make up three to four concentrations of one solution. Using a spectrophotometer, measure the absorbance of one concentration of solution at a given wavelength. Start with the lowest concentration of solution and move to the highest. The order isn't important, but keep track of which absorbance goes with which calculation. Using the values obtained from the spectrophotometer, plot each point on a line graph. For each individual value, plot the concentration on the X-axis and absorbance on the Y-axis. Draw a line between each of the points. If the measurements are correct, the points should form a straight line indicating absorbance and concentration are proportional to Beer's Law. To calculate the slope of the line you take rise divided by run. Using two of your data points, subtract the X- and Y-values from each other, then divide Y/X. The equation for the slope of a line is (Y2 - Y1)/(X2 - X1). The point higher on the line is given the subscript 2, while the lower point is given the subscript 1. For example: The absorbance at a .2 molar concentration is 0.27 and at 0.3 molar is 0.41. The absorbance values are Y-values, while concentrations are X-values. Using the equation for a line (Y2 - Y1)/(X2 - X1) = (0.41-0.27)/(0.3-0.2) = 0.14/0.1 = 1.4 is the slope of the line. The final step to calculating molar absorptivity with data points is to divide by the path length. The path length is the depth of the cuvette used in the spectrophotometer. Continuing our example: If 1.4 is the slope of the line and the path length is 0.5 cm, then the molar absorptivity is 1.4/0.5 = 2.8 L mol-1 cm-1.
Summary: Measure the intensity of transmitted light through varying concentrations of solution. Plot the concentration versus absorbance on a graph. Determine the slope of the line-of-best-fit through the data points. Divide the slope of the line by the path length (depth of the cuvette) to calculate molar absorptivity.

In one sentence, describe what the following article is about: Storing shoes that have dirt, dust and other residues on them could cause the material the shoes are made from to degrade over time. This is especially true for shoes made of leather or suede, but all shoes benefit from being cleaned up before you store them. Even if you're just storing your shoes for the night, and you're planning on wearing them again tomorrow, it's a good idea to clean them before you put them away. Let them dry before storing. Clean leather and suede shoes by brushing off dirt and dust with a soft, non-scratchy brush. Use a special leather or suede cleaner to remove stains. Clean canvas shoes by brushing them off, then using soapy water to clean stains. Wash plastic shoes with soap and water. If you've previously been throwing all your boots, heels, and running shoes in one big pile, picking out pairs as you need them, it's time to sort your shoes. Sorting them by season and purpose will help your closet stay organized and keep your shoes in better condition than if you just toss them all together. Group your heels and other dress shoes together. Plan to store your winter boots and other winter shoes in the same place. Group flip flops, sandals and other summer shoes together. Group your exercise shoes and casual shoes together. Shoes remain in their best condition when they're not exposed to lots of sunlight or hot or cold temperatures. The best place to store shoes is in a cool, dark closet that doesn't get excessively warm and stuffy. If you don't have enough room in your closet, you could store them under your bed or on your bedroom wall. Don't store shoes in the basement, garage or other places that might get cold in the winter and hot in the summer. The fibers the shoes are made out of could break down over time under these conditions. If you're going to be storing shoes for a month or longer before you next wear them, stuffing shoes with paper helps them retain their shape. Just make sure it's acid-free paper, since paper that contains acid can damage shoe materials. Avoid using newsprint, since it could discolor your shoes. Cut up toilet paper rolls also work well. Use shoe trees for your best shoes. If you have a pair of nice leather shoes, store them with shoe trees so they stay in tip-top condition. Shoe trees made out of cedar keep shoes smelling fresh, and they also repel moths and other bugs. Shoe trees are available at shoe stores or online. If you have a nice pair of boots you want to store, use boot stands to keep them upright. If the tops flop over, they could end up with a permanent crease after a few months of storage. If you don't want to invest in boot stands, try this clever trick: use empty, dry wine bottles to keep your boots upright.
Summary:
Clean the shoes. Sort them by season and purpose. Find a dark and temperature-controlled storage space. Stuff them with balled acid-free paper. Store boots upright.