Monday, February 15, 2016

Sugar Crystals Experiment - Rock Candy

There is a plethora of recipes for rock candy which can be found online. I used a recipe from which can be found here. I wound up using 1.5 cups of water and 3.5 cups of sugar instead of the suggested 1 cup of water and 2-3 cups of sugar. I probably could have dissolved more sugar, but I ran out. I ended up with enough solution to fill two separate glasses.

I added 1tsp of vanilla extract to the solution. I attempted to add "seed crystals" to the first skewer, but unfortunately I didn't wait long enough for the sugar to dry completely and it fell off when put in the solution. I left the second skewer plain. The skewers were set at 5pm on 2/8/16.

the setup

After 28 hours I checked on the sugar crystals. At this point, crystals were beginning to form on the bamboo skewers. Unfortunately sugar was also solidifying on the edges, top, and bottom of the glass. In the first glass the crystals were smaller on the skewer and there were larger blocks of sugar on the bottom of the glass when compared to the second glass. This is likely because with the first skewer the sugar grains that fell off the skewer provided seed crystals on the bottom of the glass where I didn't want them and lead to fewer crystals growing on the skewer.

For each glass, I cracked the sugar on the surface and gently removed the skewer. Then I poured the solution into a bowl using a spoon to filter out the larger pieces of sugar crystals floating in the solution. Then I rinsed the glass and soaked for a few minutes in hot water and a little dish detergent. This dissolved the blocks of sugar on the bottom. I poured the solution back into the clean glass and replaced the skewer. Some solution was lost during this process.

blocks of sugar forming in the glass
one of the skewers after 28 hours in the solution

The next day, about 48 hours after the start of the experiment, the glasses had again filled with blocks of sugar, even more than the previous day. I decided to end the crystal growth at this point as there wasn't much solution left after again filtering out the excess crystals. I gently removed the skewers and hung them over empty glasses to let the excess solution drip off. The second skewer grew significantly larger crystals than the first one. Another reason for this may be that the first glass was thinner, which may have contributed to the sugar blocks clogging it up faster.

first skewer after 48 hours
second skewer after 48 hours

Close ups of the crystals:

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