Chemical Science. 367 



2. Analysis of Mixtures of the Chlorides of Potassium and 

 Sodium. — This process is founded on the unequal diminution of 

 temperature which these chlorides produce by their solution in 

 water; 50 grammes, (772.2 gr.) of chloride of potassium, when 

 dissolved in 200 grammes (3088.8 gr.) of water, contained in a 

 glass vessel of the capacity of 320 grammes (4942 gr.) of 

 water, and of the weight of 185 grammes (2875.1 gr.,) produce a 

 diminution of 11°.4 centigrade (20.52 Fahrenheit.) The same 

 quantity of chloride of sodium gives, in the same circumstances, 

 a depression of 1°.9, (3.42 Fahrenheit.) 



Now, if a mixture of the two chlorides be made, and 50 

 grammes (772.2 gr.) be dissolved in 200 grammes (3,088.8 gr.) 

 of water, the cold produced will be proportional to the quan- 

 tities of each of the chlorides ; and it is always possible to de- 

 duce the one from the other. A table may be made, indicating 

 the diminution of temperature corresponding to known mixtures 

 of the two clorides, but it is sufficient to calculate their propor- 

 tion by _a simple rule of alligation, taking the diminution of 

 temperature produced by the solution of each chloride in water. 

 Making d this diminution, the rule by which to calculate the 

 chloride of potassium in 100 parts of a mixture, with the de- 

 gree of cold given, is 



Chloride of potassium zz loo rf-iao 

 In operating on known mixtures, the proportions calculated 

 by this rule do not differ from the true proportions by more than 

 one-hundredth. The only precautions required for this pre- 

 cision are, 1 st , to have a very sensible thermometer, on which 

 the tenths of degrees may be read with ease : 2d, to reduce the 

 mixture to a fine powder, that it may dissolve as rapidly as 

 possible in the water : 3d., to hold the vessel by the neck, only 

 so that the heat of the hand may not influence the temperature 

 of the water. The manner of operating is as fellows :— 



Having weighed 200 grammes (3088.8 grs.) of water into the 

 glass vase, in which the solution is to be made, the thermometer 

 IS to be introduced to ascertain its temperature, which may be 

 supposed 20°.4 (G8.72 Fahrenheit ;) 50 grammes (772.2 gr,) 

 of the mixture are then quickly introduced, and whilst the 

 2 B 2 



