1890.] 



Observation* on Pure Ice. 

 FIG. l. 



The ice for the pure ice experiments was frozen from distilled water 

 contained in a sheet-iron vessel. The inner tank was surrounded 

 both at the sides and bottom by an outer jacket of iron, which was 

 provided with holes at the bottom for the waste liquids to escape. 

 The coolest freezing mixture used, No. 1, consisting of three parts 

 by weight of crystallised calcium chloride and two parts by weight of 

 snow, was placed in the compartment A, which yielded a constant 

 temperature of 35 F. There was also provided a larger outer com- 

 partment B, filled with the freezing mixture No. 2, of snow and 

 ordinary salt, giving a steady temperature of F., the latter mixture, 

 No 2, completely enclosing the inner and coolest freezing preparation, 

 No. 1. Good results were obtained by using this arrangement. 

 Previous to mixing, large quantities of the snow and calcium chloride 

 crystals were stored and maintained separately at a temperature of 

 F. in other vessels, and the respective freezing mixtures, No. 1 in 

 compartment A, and No. 2 in compartment B, surrounding the ice 

 tank were constantly renewed during the experiments from these 

 cold stores. Thermometers were inserted in the mixtures and also in 

 the ice during the experiments. The preceding description refers to 

 the maintenance of the ice block at the lower temperature of 35 F. 

 for the observations required at that temperature. 



For the observations at F. the ice block was surrounded only by 

 the freezing mixture of snow and salt placed for these experiments 

 in compartment A, and the ice block was encircled by snow only for 



