Intelligence and Miscellaneous Articles. 443 



by the barometer, that of the pure solvent by a table prepared iu 



advance. 



It follows, from the researches of Von Babo, "VViillner, and 



f 

 others, that the ratio •'— between the vapour-tension of a salt in 



aqueous solution and the tension / of pure water is sensibly inde- 

 pendent of the temperature; the exceptions to this rule are pro- 

 bably due to an incipient dissociation of the salts dissolved. 



The author has investigated whether this holds also for other 

 solvents, and has found that it does with sufficient nearness. 



The experiments of Von Babo and of Wiilluer have shov^n that 

 if a number N of molecules of a salt be dissolved in 100 grammes 

 of water, the vapour-tension uudergoes a diminution \\hich, for 

 the same temperature, is proportional to the number of molecules 

 dissolved. This is expressed by the formuhi 



where K is a constant depending on the nature of the salt. 



This law only holds if the solutions are very dilute ; for stronger 

 solutions the formula should be replaced by the following one : 



•tZ = K- 



where N' is the number of molecules of the fixed substance con- 

 tained in 100 molecules of the mi.rture. The value of N' is given 

 by the formula 



lOON 



X' = 



100 -hn 



f—f. 

 The ratio '^^,;i being what is called the relative diminution of 



f N ■' 



vapour-tension of the substance in question, the latter formula may 

 be thus expressed in ordinary language. For all solutions of the 

 same icind the relative diminution of vapotir- tension is proportional 

 to the number of molecules of the solid dissolved in 100 molecules of 

 the mixture. 



The author cites a series of experiments made with benzoate of 

 ethyl, dissolved in ether in proportions varying from 9 to 97 per 

 cent., the results of which closely agree with those calculated by 

 the modified formula. 



The author further found that there is a relation between the 

 lowering of the freezing-point and the diminution of the vapour- 

 tension of the same solution. For dilute aqueous solutions of the 

 same nature and the same concentration, the number ivJiich expresses 

 the relativet ension of the vapour is always near the -j-Q-y part of that 

 luhich eapresses the loivering of the freezing-point. 



This holds also for other solvents than water ; thus, with ben- 

 zine the ratio appears to be about 63. 



