Distillation of Binary Mixtures, 



531 



seem now to remove all donbt. The existence of a minimum 

 boiling-temperature for a strength of 96 per cent, shows that 

 the curve there crosses the diagonal. Between this point 

 and 100 per cent, the vapour is the weaker, and the curve 

 lies in the lower triangular half of the square. But the 

 deviation from the diagonal in this region is probably 

 extremely small. 



The following from JSToyes and Warfel's table may 

 useful : — 



be 



Strength. 



Boiling-point. 



Strength. 



Boiling-point. 



100 



78-300 



85 



78-645 



99 



78-243 



80 



79-050 



98 



78-205 



75 



79-505 



97 



78-181 



65 



80-438 



96 



78-174 



55 



81-77 



95 



78-177 



48 



82-43 



94 



78-195 



35 



83-87 



93 



78-227 



26 



85-41 



92 



78-259 



20 



87-32 



91 



78-270 



10 



91-80 



90 



78-323 







10000 



Hydrochloric Acid and Water. 



One of the ingredients of the mixture being gaseous under 

 ordinary conditions, the observations are limited to that 

 portion of the curve for which the strength of the liquid does 

 not exceed 35 per cent., unless freezing appliances are called 

 into play. No attempt was made in the present experiments 

 to pass the above limit, the object being merely to determine 

 w ith moderate accuracy that part of the curve with which 

 we are usually concerned in the laboratory. It was known 

 from the experiments of Roscoe and others that the curve 

 would cross the diagonal at the strength of about 20 per 

 cent. 



The general plan of the work was the same as in the case 

 of alcohol and water, but the strengths were usually deter- 

 mined chemically. In the case of the stronger acids it was 

 not possible to condense the vapour at atmospheric tempera- 

 ture; and I contented myself with a calculation in which the 

 strength of the vapour was inferred from observations of the 

 quantity and strength of the liquid in the retort before and 

 after the operation. Results obtained in this way are doubt- 

 less of minor accuracy. 



It may be worth while to reproduce in tabular form the 

 data relating to the weakest acid. 



