Intelligence and Miscellaneous Articles. 471 



ON THE FREEZING-POINT OF WATER CONTAINING DISSOLVED 

 GASES, AND ON THE REGELATION OF WATER. BY C. SCHULTZ. 



Gases, like solids or liquids, dissolved in water lower its freezing- 

 point. This is well known in the case of hydrochloric acid and of 

 ammonia, which, from the exception they present to the law of the 

 absorption of gases, are not considered to form mere solutions in water. 

 The same effect is very distinct in the case of sulphurous and car- 

 bonic acids ; and by adopting certain precautions it may also be ob- 

 served in the case of the permanent gases oxygen, hydrogen, and 

 nitrogen. 



The following experiment shows that pure water solidifies at a 

 temperature at which water containing dissolved air remains liquid. 

 In a glass bulb provided with a U-tube, water, freed from air by 

 boiling for a sufficient length of time, was introduced, and was shut 

 off from communication with the atmosphere by mercury in the 

 bend. This vessel was surrounded by melting ice obtained from 

 distilled water. Over this melting ice a current of air washed with 

 water was passed. The water in the bulb had, by strong cooling, 

 been made to freeze, and the ice formed melted, except a very small 

 piece. If the vessel is then surrounded by the mixture of aerated 

 water and ice, large crystals of ice are gradually formed on it. 



Helmholtz has given an experiment the method of which has 

 been applied in the foregoing one. In a vacuous vessel containing 

 water, ice is formed when it is surrounded with ice melting in the 

 air, This experiment is designed to show that ice melting in the 

 air has, owing to the external pressure, a lower melting-point than 

 that which has been freed from this pressure. But it has been shown 

 above that ice melting in the air has a lower melting-point than 

 that which melts under the same pressure without contact with air. 



By comparison with the known lowering of the melting-point of 

 pure water produced by pressure, we are in a condition to determine 

 the small value of the depression of the melting-point produced by 

 absorbed air. If the open end of the U-tube in the above apparatus 

 be connected with a column of mercury under an excess of pressure 

 of two atmospheres, the renewed formation of ice almost ceases ; and 

 with an excess of pressure of 3J atmospheres the ice in the vessel 

 gradually melts. According to Thomson, the lowering of the melt- 

 ing-point of pure water by a pressure of 3 atmospheres amounts to 

 o, 02 ; so that ice in contact with water which is saturated with air 

 under the pressure of 1 atmosphere, melts at about this much lower 

 temperature than it does under the same pressure, air being excluded. 

 If we define the temperature 0° as that of the melting-point of pure 

 water under a pressure of 760 millims. mercury, the zero-point of the 

 thermometer may, on the ordinary determination in melting ice, lie 

 between and — ^j°. 



The alteration in the melting-point of water by absorbed hydrogen 

 is far smaller. Water which is saturated with hydrogen under the 

 ordinary atmospheric pressure freezes in a mixture of ice and water 

 saturated with air. 



