152 



Dr. J. Monckmaru The Specific 



I have calculated tlie specific resistance from the experiments, more 

 as an indication of the magnitude of the resistance at the boiling 

 point, and of the changes that take place as the temperature varies, 

 than as an accurate determination of specific resistance. 



There are several circumstances which prevent the great accuracy 

 usually expected in such cases. First the extreme difficulty of obtain- 

 ing a steady temperature without exposing the electrodes to chemical 

 action. Thus if the readings be taken at 350° C, by using a bath of boil- 

 ing mercury it requires a considerable time to get the whole mass of 

 sulphur to this temperature, the sulphur being a very bad conductor 

 of heat and there being no agitation to assist. When the whole is 

 steady and the electrodes are introduced, they cool the portion in 

 contact with them, and it is necessary to wait until the temperature 

 rises again. Hence arises an uncertainty, we may take it before the 

 temperature is fully recovered, or we may delay too long and allow 

 chemical action to commence. The same objection applies, in some 

 measure, to boiling sulphur, but as the whole is in motion the recovery 

 is quick. 



Great care is necessary to prevent bubbles of gas rising up between 

 the electrodes and so increasing the resistance. 



Some error might also arise from the size of the electrodes, 

 3'35 cm. x 0*45 cm., distance 0'2 cm. They were as large as the quan- 

 tities of pure sulphur obtained by nearly three months' work enabled 

 me to use them. 



With these reservations I give the specific resistance of melted 

 sulphur, calculated from experiments with the three specimens men- 

 tioned. 



Specific Resistances. 



No. 1. At 440° C 7-8 megohms. 



2. „ 8-0 



3. „ 7-3 



2&3. At 350° C ... .. 56-5 



300° C 282-5 



Boiling Point. 



An objection has been raised to the curve found in the experi- 

 ment on the boiling point of sulphur under varying pressures, on 

 the ground that the vapour-pressure rises in a straight line, and 

 that, therefore, the boiling point would give a straight line also. 



It is usually stated in text-books that when the vapour-pressure of 

 a liquid becomes equal to the pressure on the surface of that liquid 

 it immediately begins to boil. If this is a scientific fact, the objec- 



