DILUTION OF CONCENTRATED SOLUTIONS. 



349 



Column IV. shows the calculated value, which it may be noted compares most 

 favourably with Column III. 



The equation for heat of dilution is 



ai 



1172 



~N" 





and applies most accurately for concentrations from NH 4 NO :! . 3H 2 O and 

 NH 4 N0 3 . 10H a O, after which it shows a similar divergence to that exhibited by 

 the other concentrated solutions. 



Here we have a case of a solution giving negative heats of dilution ; yet the same 

 relation may still be applied. The extrapolated value of dQ/dN vanishes when 

 N = 24'01, suggesting a solution of limiting concentration NH 4 N0 3 . 24H 2 0. This 

 may be interpreted in a similar manner suggesting that the first effect of adding 

 water is to produce this solution, and that we are really diluting solutions, with 

 another weak solution, not water, of strength NH 4 N0 3 . 24H 2 O. 



(10) CONCLUSION AND SUMMARY. 



To sum up, the following equations can be quoted for heats of dilution for strong 

 solutions. 



(1) Hydrochloric acid (N < 10) 



(2) Nitric acid (THOMSEN) (N < 6) 



_ 4082 

 ~ ~ 



2020 



N 



(3) Sulphuric acid (THOMSEN) (N < 15) 



dQ _ 4666 



dN '- ~W 



