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Prospectus and further particulars on application to DIRECTOR. CHEMICAL NEWS,} April 23, 1915 Thymol: its Melting- and Solidifying-point. THE CHEMICAL NEWS. VOL. CXI., No, 2891. THERE is considerable variation in the published melting. points of thymol, as will be seen from the following figures:-44 C., Allen, Sprecker, Fownes, Cooley; 49'5° C., Bayley; 50° C., Roscoe and Schorlemmer, Thorpe, Kraugh. It would thus appear that two modifications of thymol exist, with melting-points of 44° and 50° C., or else that it undergoes a change on prolonged heating, which reduces its melting-point. The author has therefore undertaken the examination of the solidifying and melting of thymol under varied conditions, with the view of ascertaining the conditions which control variation from the normal. Unless otherwise stated, the same test tubes, 6 x 1 in., were used throughout the solidification tests, and the same thermometer, a 52° C. divided into tenths. Time to fall from sa C. to zero and I mins. 2 mins. It is evident this method also yields constant results, though solidification is 75 per cent more rapid than when cooled in air by Method A. Failure to obtain normal solidifying-point is most likely due to temporary thermometer bulb and stem effects due to rapid cooling. The main point of these experiments is that supercooling is four times as great as by Method A, though cooled three times quicker, which points to the time factor as being essential for crystal formation. We here see the speed of crystallisation is slower than the rate of cooling. The whole contents of tube do not solidify at 48.3° C., but only part of same, complete solidification taking place as the temperature is lowered. After completion of above tests the thermometer was tested against a standard one and found correct. Method C.-Solidification while Partially Melted.Melted partially at 49° to 50° C. till about three-quarters melted, and stirred up crystals with the liquid. Removed from bath and stirred with thermometer till temperature ceased to fall, and fixed thermometer for readings:— Solidifying-point + rise, °C 485 486 48.5 483 484 Rise, C... 0'0 0.6 ΟΙ 0'2 Ο Ο The As soon as thermometer is fixed all the crystals fall to bottom and attach themselves to sides. When thermometer has reached maximum and fallen to 48° C. onehalf of thymol is still fluid. Though crystallisation bas taken place under extra good conditions, and a fairly constant solidifying-point registered with minimum supercooling effect, yet the bulk of the thymol remains fluid. The time factor is here prominently brought out. amount crystallised here per unit of time must be very small, as supercooling rapidly ensues. The solidifying. point by this method varies by o'3° C., which is apparently due to small percentage crystallised, while the thermometer remains at maximum. Constant points cannot be expected when supercooling ensues so rapidly. It would appear that as the supercooling effect becomes eliminated the amount crystallised per unit of time decreases, resulting in a short period stationary-point, supercooling again commencing. Method D.-Cooled by Stirring in Hot Water Jacket.Melted thymol at 70° C. and cooled by stirring in air to 52° C., and placed tube in large hot water jacket at same temperature; stirred thymol and hot water jacket constantly, and allowed to cool at rate of cooling of water jacket: : Solidifying point, + rise, °C 489 490 49'0 48.8 What takes place here is that, when lowest temperature is reached, on cooling fine crystals form in the melt, and as stirring is continued and temperature rises a shower of crystals fall to bottom of tube, the tube at same time becoming coated on one side to a depth of 2 mm. with crystals. When solidification is complete and temperature has fallen 15° C. below solidifying-point, about 70 per cent of contents of tube is still liquid; even when tempera. ture has fallen 5° C. below maximum rise the greater part is still liquid. The remarkable feature of these experiments is the constant solidifying-point obtained and failure to attain solidification without supercooling. That During solidification tube is full of floating crystals, complete solidification of contents of tube does not con- which rapidly fall to bottom on ceasing to stir. The tinue at 48′5° C., though ideal conditions are present, shower of crystals fall from surface of thymol where superrequires explanation. As solidification will not begin till cooling must be present, due to contact of thymol with the supercooled, it is apparent the rising temperature stops air at 60° F. The rate of crystallisation is very slow, even crystallisation, and supercooling again requires to take with stirring, and apparently is slower than rate of cooling place to again start crystallisation. Thymol, therefore, of large water jacket. This again points to the slow crysbehaves on solidifying as if it were two different sub-tallising speed. What takes place here is solidification in stances, one which solidifies at 48.5° C. and the other at surface layers, which are broken up by the stirring and a much lower temperature. But there can be no doubt dispersed through the mass. We have every reason to the phenomenon is due to supercooling effect. believe these layers are supercooled. The author has already pointed out this fact as regards mutton tallow (CHEMICAL NEWS, cxi., p. 37). From this it will be seen that large surface and small volume, and vice versa, will more or less modify solidification. A noted feature of above results is high solidifying points, which will require further explanation. Method B.-Stirred while being Cooled in Cold Water. -Melted at 70° C. and cooled by stirring in air to 52° C., plunged tube into cold water at 8° C. and continued stirring till temperature ceased to fall and rose to maximum, and fixed thermometer 1 cm. from bottom of tube and in centre: |