Optical studies on the growth of sucrose crystals in solution

The growth of sucrose crystals from aqueous solution has been investigated. A Review of the previous work on the growth of crystals from solution has been made.A new interference technique has been applied to the problem in the employment of the Mach-Zehnder interferometer. This has the advantage over any other type of interferometer for two reasons. One is that the fringes can be localized in any desired plane. (In the present case this was the plane of the growing crystal). The second is that in an interferometer such as the Michelson type the light beam traverses the object in two directions i.e. in going from the beam splitter and returning to it. If the object has considerable local variations in refractive index there can be some displacement of the beam, which on its return journey does not pass exactly along the same path that it did initially. This might lead to fringe confusion. In the Mach-Zehnder system the beam passes through the object in one direction only and this difficulty does not arise. The changes in refractive index of the solution were measured for a number of crystals growing from solution and hence the concentration along a face was determined. This was in many cases a maximum at the corners of the crystal but faces were observed which had a uniform concentration along their length for quite a long period of time. The value in all cases was greater than solubility concentration. The effect of convection on growth was investigated.When a crystal grows a stream of depleted solution can be seen rising from the crystal. This was observed to become established at a corner of the crystal. The concentration of the solution at the centre of this stream has been measured and was approximately 1% less than that in the bulk of the solution. The streaming effect would also appear to affect the rate of growth, which increases when the effect is established and fluctuates when the streaming undergoes variations.