228 ANNUAL EECORD OF SCIENCE AND INDUSTRY. 



completed, and the bell rings. The temperature observed 

 on the coated thermometer at this instant is the melting:- 

 point desired. 



Pictet has sought to determine experimentally the cause 

 of the difference between transparent and opaque ice, and 

 finds that it is due to the temperature at which the ice is 

 formed. When frozen at temperatures between and 1.5 

 C. it is as clear as crystal, but when frozen below 3 it is 

 whitish and of less density, its cohesion being also dimin- 

 ished. The causes of this whitish opacity are two in num- 

 ber first, the presence of air bubbles in the ice, and, sec- 

 ond, the irregularity of the ice crystals, which destroys its 

 optical homogeneousness. If a current of air be passed 

 through the water while freezing, the ice is clear and trans- 

 parent, no matter how low the temperature at which it is 

 frozen. 



Gernez has studied the phenomenon of supersaturation in 

 salt solutions, and finds that other liquids besides water 

 such as carbon disnlphide, the hydrocarbons, phenols, and es- 

 pecially the alcohols show this property. A salt which 

 does not give supersaturated solutions with one solvent nev- 

 er yields them with another; nor is the result attained by 

 adding a substance such as dextrin to increase the viscosity. 

 Sodium carbonate, calcium nitrate, magnesium sulphate, lead 

 acetate, and alum yield supersaturated solutions most easily. 

 In the case of all five, however, crystallization ensues only on 

 the introduction of crystals of an isomorphous substance, and 

 the latter lose this property if heated above a certain tem- 

 perature, 98, for example, for alum. Gernez gives a list of 

 120 substances which possess the property of yielding super- 

 saturated solutions. 



Mallet has examined the liquid contained in a cavity in a 

 specimen of green fluorite from Alston Moor, in Cumberland, 

 Eng., the cavity being irregular, 6 mm. long, 2.5 wide, and 1 

 deep, and filled with liquid in which was a readily mobile 

 bubble. From the experiments which he made upon this 

 liquid at different temperatures he concludes that it is sim- 

 ply water. 



Handl and Pribram have described, in the Proceedings of 

 the Vienna Academy, a new method for determining boiling:- 

 points, depending on the well-known law that the temperature 



