with Boiling Point of Sulphitr. 523 



perature gradient along the thermoelements identical with that 

 surrounding the gas thermometer bulb itself. 



4. JB oiling Point of Sulphur. 



Finally an attempt was made to establish one temperature in 

 this region from which the intermediary thermoelement should 

 be completely eliminated. The gas thermometer bulb itself 

 was immersed in the vapor of boiling sulphur. For this deter- 

 mination the nitrate bath was replaced by an appropriate sul- 

 phur boiling-point apparatus, all other conditions remaining 

 the same. In building this apparatus, which is shown in tig. 3, 

 the experience of the Bureau of Standards was utilized for the 

 most part. To this design certain modifications suggested by 

 the unpublished work of Prof. G-. A. Hulett of Princeton were 

 added by way of rendering the determination, as far as prac- 

 ticable, independent of particular experimental conditions 

 employed. 



Heat was supplied electrically from a coil of high resistance 

 wire about the sulphur tube, the coil ending about 2 cm below the 

 level of the surface of the liquid sulphur (Bureau of Standards 

 usage). An independent coil surrounded the vapor region, sep- 

 arated from it by an annular air space of about l cm (Hulett). 

 The bulb was surrounded first by a shield of sheet aluminium 

 (Bureau of Standards) with holes near the top and bottom to 

 permit the free circulation of the sulphur vapor and a hole in 

 the center of the bottom diaphram to permit the escape of liquid 

 sulphur which chanced to condense on the shield. The shield 

 afforded protection against any direct interchange of radiation 

 with the furnace or with the boiling liquid and its steep con- 

 ical roof diverted the condensing liquid sulphur away from the 

 bulb. Subsequently with the purpose of varying these condi- 

 tions the aluminium shield was replaced by another of similar 

 form but of glass (Hulett) and of somewhat smaller diameter. 

 This was suspended from the conical aluminium roof of the 

 first shield, which now overhung the side walls by several mil- 

 limeters, w T ith the effect that liquid sulphur condensing upon 

 the cone could drip from the overhang instead of running 

 down the side wall past the bulb. The radiation conditions 

 were also radically altered by this substitution of glass for 

 aluminium both around the bulb and below it. 



Further variation was provided by changing the current in 

 the two heating coils. Variations of some 35 per cent in the 

 main coil about the boiling liquid were tried and the upper coil 

 was varied from zero (Bureau of Standards usage) to over 40 

 per cent of the current in the main coil. Or, in other terms, 

 the l cm air jacket about the vapor was varied in temperature 



