412 Dr. W. A. Tilden. Influence of Temperature [June 18, 



Experiments published in 1873 by Winkelmann,* on the solution of 

 the potassium, sodium, and ammonium chlorides and nitrates in water 

 at different temperatures lead to similar conclusions. Thus taking 

 Winkelmann's figure representing the heat of dissolution of nitrate 

 of sodium, 1 gram of salt in 20'80 grams of water, which is very 

 nearly 1 mol. of salt to 100 mols. of water — 



At 2 — 3° gives as a mean —60*30 cal. 

 At 50— 51° „ „ „ -4870 „ 



For a molecule of salt, or 85 grams — 



60-3x85=5125-5 

 48-7x85=4139-5. 



By the formula — 



Q T = Q, + [ (18» + C) - (18» + K)] (T - 1), 

 and using the values already given for sodium nitrate, 



Q T = -3646-6, 



and this is very nearly identical with the number calculated from my 

 own experiment at 16°. 



I have made a few determinations of heat of solution of the crystal- 

 lised sulphate and carbonate of sodium. Whilst these salts dissolve 

 at common temperatures, with great absorption of heat, the absorp- 

 tion at the melting point is very feeble, and at a few degrees higher 

 is changed into evolution of heat. This last-named effect is probably 

 due to the fact that when heated beyond their melting point, 34° 

 (circa), these salts are partly deposited in a solid dehydrated state. 



* " Pogg. Annalen," cxlix, 1. Winkelmann s experiments were directed towards 

 the object of determining the specific heat of the solutions of these six salts. One 

 difficulty in the way of the general application of this method is the uncertainty 

 attaching to the specific heats of the salts in the solid state, by reason of the varia- 

 bility of their properties according to the manner in which they have been prepared. 



