Hello, Mike, Yes, clock gearwork can accomplish the necessary movement in a variety of ways, some quite simple. Herington gives a number of line drawings. The points he stresses is that, unlike inorganic and metallic specimens, organic specimens should be in vertical tubes for a variety of reasons. Not least of which is the ease of up and down movement by wind up or winding down a cord or chain from pulleys, axles or even cams.
Unlike water, most organic compounds become denser when they freeze. I assume DMSO is like this, but if anybody knows for sure, I would appreciate confirmation on this. If this is correct, then a tube of DMSO will freeze from the bottom up if it is lowered into the ice-water. There are a range of suitable diameters for the container. It has to be more than 2 millimeters, otherwise there can blockage by bubbles. It has to be less than 4 centimeters, otherwise the zone's core may not melt. In any case, a batch of more than 2 kilograms is too much. A long thin vessel is preferable to a short stubby vessel. Glass is convenient for it tranparency but is prone to shatter when crystal cling to the inside surface. Herington seems to recommend stainless steel or other inert metal. He also notes that a coating of silver helps keeps reactive specimens pure, but this shouldn't be a problem with DMSO. Herington states a key principle on page 12: "If an impurity depresses the freezing point of the main component, it travels in the same direction as the zone. But if it raises the freezing point, it travels in the opposite direction to the zone." I suppose one could look up the freezing points of the odiferous compounds and make a good guess as to whether these impurities raise or lower the freezing point from that of absolutely pure DMSO. This may have a bearing on whether to let the container ascend or descend in the ice-water. Herington mentions that those who use this method usually prefer a focused lamp to melt the zone. Nichrome wire can be be formed in a ring to do the heating, too. Even a meat skewer can be bent into a ring-and-handle that can be heated by a Bunsen burner to melt the zone. I envision using an ice-water reservoir on the bottom and cold ambient air on the top, with a heating ring just above the surface of the ice-water, with a perforated piece of cardboard acting as a shield between the heater and the ice-water. Depending on which way the impurities move, it might not even be necessary for the melt to freeze at the top. The interface of liquid and solid DMSO may just push the impurities up and up, until upper liquid can be decanted with its load of impurities. Matthew
