Intelligence and Miscellaneous Articles. 553 



room at a temperature of 12°, the thermometer rose to the tempera- 

 ture of the freezing-point, and remained almost constant until the 

 whole of the ice was melted. 



The salts suitable for these experiments ought to be very soluble 

 at low temperatures, and to exert a marked influence on the freezing- 

 point ; they are hence few in number, and in fact are almost 

 confined to the alkaline chlorides and nitrates. In most cases, 

 M. Rudorff found that the lowering of the freezing-point below 

 zero was proportional to the quantity of anhydrous salt dissolved in 

 100 parts of water. The following numbers give the lowering pro- 

 duced by the addition of 1 part of salt to 100 parts of water : — 



o 



Sal-ammoniac 0*653 



Common salt 0*600 



Chloride of potassium 0*443 



Nitrate of ammonia 0*384 



Nitrate of soda 0*370 



Carbonate of potash 0*317 



Nitrate of lime 0*277 



Nitrate of potash 0*267 



For chloride of calcium, the lowering of temperature appeared to 

 be proportional to the quantity of salt crystallized with six equiva- 

 lents of water, and not to the quantity of anhydrous salt which the 

 solution contains. Designating by M the quantity of anhydrous 

 salt, by M, the quantity of hydrated salt dissolved in 100 parts of 

 water, by T the lowering of temperature, the experiments gave the 

 following results : — 



M. 



Mi. 



T. 



T 



M' 



T 



2 



402 



0°90 



0-450 



0-224 



4 



8*21 



1-85 



0-462 



0-225 



8 



17*20 



3*90 



0-487 



0-225 



14 



31-89 



740 



0-528 



0-232 



18 



43*05 



1000 



0555 



0-232 



We thus see that the value of — increases somewhat rapidly with 



rp JV1 



M, while that of — - is pretty constant. 



M l r J 



At a temperature of —10°, crystals separate from a concentrated 

 solution of common salt, which contain four equivalents of water 

 for one of salt, and are rapidly destroyed by increase of temperature. 

 This circumstance explains a remarkable result following from 

 M. Rudorff's experiments. So long as the lowering of the freez- 

 ing-point of a solution of common salt does not exceed 9°, it is 

 proportional to the quantity of anhydrous salt dissolved. When it 

 exceeds 9°, it becomes proportional to the quantity of salt crystal- 

 lized with four equivalents of water. This will be seen from the 



Phil. Mag. S. 4. No. 150. Suppl. Vol. 22. 2 O 



