COMPARISON OF PLATINUM AND GAS THKI.'VH >MK ! 



65 



The interior trough, which is 112 centime, long, 17 centims. wide, and 14 oentims. 

 deep, is provided at one end with a system of screw blades for stirring. Resting 

 11 1 M. n its bottom is the metal i'mmework on which the thermometers are arranged. 

 Tliis thermometer support is so contrived that all the thermometers can, without risk 

 of straining them, be simultaneously clami>ed jmrallel to one another, and in the same 

 hiiri/ontal plane. 



During the comparisons the platinum thermometer was fixed horizontally, with its 

 spiral in the same plane as the mercury thermometers, and close to them. To 

 prevent the water from penetrating to the portions of it which were exposed, the head 



Fig. 11. 



llitth fur <'ni>ij*ii'i*H!t in Wntfr. 



.1, xtfin, and r, haul, of platinum thermometer; /, brans box surrounding the head of 

 platinum thermometer ; />, heater for water in outer tank ; r, plate of milk glass. 



was placed in a square brass box open above and provided with a side tube, through 

 which the greater part of the length of the thermometer stem projected, the joint 

 being made by an india-rubber stopper. 



The internal tank is provided with a rim, on which rests a piece of plate glass 

 s millims. thick, covering the whole surface of the water, with which it is just in 

 contact. 



By tliis arrangement the cooling by evaporation is almost entirely prevented, and 

 the attainment of a very constant temperature much facilitated. When operating at 

 temperatures below that of the room, it is advisable to cover the glass with a thin 

 layer nf \\ater, in order to avoid the deposition of dew upon it. 



fOL, ' \riv. A. K 



