Originally from fix.com, in a blog post titled Sifting Through Soil

The important parts:

Most state extension services will perform a detailed soil analysis for a small fee, but you have to wait for the results. Many people take a soil sample in spring, but you can home-test the soil at any time during the year. There are soil test kits for sale at most home improvement stores, but a no-cost, at-home soil test is simple, can be done in any spot in your garden, and takes just a glass jar. Once you complete the test, you can use the results to figure out what to add to your soil to improve it.

Step-by-Step Soil Test

• Clean a pint or quart mason jar and lid
• Fill the jar about halfway with soil. I like to do several different tests, isolating spots in the garden—a jar from each flower bed, for example. That’s because the soil may differ from spot to spot
• Fill up the rest of the jar with water, leaving a bit of headspace in order to shake up the contents
• Tighten the lid and give the jar a good shake for two to three minutes
• Put the jar down and let it rest for four to five hours. As the jar is resting, you might notice the soil doing something interesting: It’s separating into distinct layers: sand at the bottom, silt in the middle, and clay at the top.

Analyze Your Soil

After completing the soil test, you need to determine the percentages in your mason jar. Measure each of the three layers and calculate approximately how much space each takes up in the jar. That’s the approximate makeup of your soil, and indicates what soil type you have