The second method of manipulation depends on the fact that, while above or below the transition point transformation of one form into the other can take place, at the transition point the two forms undergo no change. The bulb of the dilatometer is, therefore, charged with a mixture of the stable and metastable forms and a suitable liquid, and is then immersed in a bath at constant temperature. After the temperature of the bath has been acquired, readings of the height of the meniscus are made from time to time to ascertain whether expansion or contraction occurs. If expansion is found, the temperature of the thermostat is altered until a temperature is obtained at which a gradual contraction takes place. The transition point must then lie between these two temperatures; and by repeating the determinations it will be possible to reduce the difference between the temperatures at which expansion and contraction take place to, say, 1°, and to fix the temperature of the transition point, therefore, to within half a degree. By this method the transition point, for example, of sulphur was found to be 95.6° under a pressure of 4 atm.[400] The following are the figures obtained by Reicher, who used a mixture {333} of 1 part of carbon disulphide (solvent for sulphur) and 5 parts of turpentine as the measuring liquid. TEMPERATURE 95.1°. ----------------------------------- Time in minutes. | Level of liquid. ----------------------------------- 5 | 343.5 30 | 340.5 55 | 335.75 65 | 333 ----------------------------------- TEMPERATURE 96.1°. ----------------------------------- Time in minutes. | Level of liquid. ----------------------------------- 5 | 342.75 30 | 354.75 55 | 360.5 60 | 361.5 ----------------------------------- TEMPERATURE 95.6°. ----------------------------------- Time in minutes. | Level of liquid. ----------------------------------- 5 | 368.75 100 | 368 110 | 368.75 ----------------------------------- At a temperature of 95.1° there is a contraction, _i.e._ monoclinic sulphur passes into the rhombic, the specific volume of the former being greater than that of the latter. At 96.1°, however, there is expansion, showing that at this temperature rhombic sulphur passes into monoclinic; while at 95.6° there is neither expansion nor contraction. This is, therefore, the transition temperature; and since the dilatometer was sealed up to prevent evaporation of the liquid, the pressure within it was 4 atm.