|MadSci Network: Chemistry|
Dear User, The main principle behind making rock candy is called crystallization. What is crystallization ? Matter can be found in several states, including gas liquid and solid forms. (You can include plasma, but physics is a bit unclear as to consider it a separate form of matter). We are now interested in solids - which can be amorphous or crystalline. Amorphous solids are often really very viscous liquids, for example, most glass will "flow" given time, which can be easily observed in windows, which get thicker at the bottom with passing of time (glass "flows" down). Other amorphous solids can be liquid/crystalline arrays and all sorts of intermediates between liquid anc crystalline phase. Now, what is a crystal ? Crystal is formed when molecules of the substance arrange themselves in infinite repetitive arrays. A good example of two-dimensional crystal can be created by putting small spheres (such as round candy or better, balls from ball-bearings) into a shallow tray. As you add more and more balls, you will reach the point when the bottom of the tray is more or less covered and the balls will start to aggregate into ordered patterns. This is very much like what happens during crystallization. The patterns which emerge when enough balls are put together will represent the lattices of the growing crystals. If you use objects of different shape, as long as they are all of the same size and shape, will form "crystalline" arrays too - you can easily arrange say gummy bears in an ordered pattern on a sheet of paper. Now imagine that the patterns are not two dimensional, but three dimensional and you will get a basic picture of what a crystal really is. From the point of view of everyday life, these patterns are infinite, or close to being infinite, simply because the size of the actual crystal is so much larger than the size of individual molecule. There are a couple of primer books, some of which are quite old, dealing with crystals and crystallization. You would have to do a search in your local library, using the words "crystal" or "crystallization". Often the "science kits" sold in many toy and novelty stores will contain some references too, but of course, these kits are often costly and silly - most of the experiments which are offered in them can be performed at home with household ingredients and at a fraction of the cost. Having dealt with crystals in general, I will try to elaborate on rock candy in particular: Sucrose is not at all easy to crystallize, due to its "evil" properties, as can be seen from my older post. To grow crystals, namely, rock candy, one often has to use "seed crystals" i.e. tiny nuclei which will give rise to large, pretty crystals. Rock candy is grown around a stick or a piece of cord, which has been rolled around in crushed sugar crystals. Small bits stick to the stick or cord, and these, when in contact with supersaturated sugar solution or melt, result in large crystals which form rock candy. This is the reason why rock candy is not one large crystal - there are many hundreds of starting seeds, resulting in formation of many hundreds of individual crystals in each piece of the treat. http://www.beakman.com/rock-candy/rock-candy.html http://www.rockcandy.com/1what.html http://inst.augie.edu/~klbuysma/crystal/sld001.htm I hope that this provides some generalized information. Feel free to contact me if you require further details. I have included a couple of links - much more information can be gathered by searching with altavista or northern light using keywords "crystal growing" "rock candy" "crystal growth" etc. Hope it helps, A.G.E.
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