KR i-:kz IXC. :\i I xTr r es . 



93 



Secondly, tlie volume of the resulting^ solution niusl l)e kepi 

 as small as possible or much of the cooling effect will be 

 wasted upon the solution itself. 



Thirdly, since salts that are mixed dissolve into liquids (all 

 being chemically inert), each one as if it alone were present, 

 it is quite feasible to increase the absorption of heat very 

 greatly by making mixtures of considerable complexity. 



Fourthly, that while water is the most commonly used 

 solvent, increased effect may follow the addition of an acid to 

 the water in case of salts that are more soluble in dilute acids 

 than in water alone. 



Lastly, that when solvent and salt can be mixed in the 

 solid form, as in the case of ice and salt, or that of ice and 

 calcium chloride, absorption of heat is brought about, not 

 only by the solution of the salt, but also by the liquefaction of 

 the solvent. 



A few typical freezing mixtures, illustrating some of the 

 principles to which reference has been made, are noted below. 

 The table sets forth the materials, the parts by weight and the 

 degrees Fahrenheit (above zero unless otherwise marked) that 

 can be attained. 



WATSON 'S LIST : 



Aininoiiiinii nitrate i 



Water i 



40 to 4 



Aiimioninm nitrate i 



Sodium carlionale i 



Water i 



5u to — 3 



Anmioninni chloride... 5 



Potassium uilrate 5 



Water 16 



50 to 10 



Sodium sulphate 6 



Ammouiuui nitrate 5 



Dilute nitric acid 4 



50 to— 40 



Ammonium chloride... 5 



Potassium nitrate 5 



Sodium sulphate 8 



Water 16 



50 to 4 



Sodium sulphate 6 



Ammonimn chloride. . . .4 



Potassium nitrate 2 



Dilute nitric acid 4 



50 to — 10 



Snow 24 



Sodimu chloride 10 



Ammonium chloride... 5 



Potassiiun nitrate 5 



To — 18 



