Mr. Faraday on the Limits of Vaporisation. 73 



the bottles, were prepared. Then selected substances were 

 put into the tubes, and solutions of other selected substances 

 into the bottles : the tubes were placed in the bottles so that 

 nothing could pass from the one substance to the other, except 

 by way of vaporisation. The stoppers were introduced, the 

 bottles tied over carefully and put away in a dark safe cupboard, 

 where, except for an occasional examination, they have been 

 left for nearly four years, during which time such portion of 

 the substances as could vaporise have been free to act and 

 produce accumulation of their specific effects. 



No. 1. The bottle contained a clear solution of sulphate of 

 soda with a drop of nitric acid, the tube, crystals of muriate of 

 baryta. One half or more of the water has passed by evapo- 

 ration into the tube, and formed a solution of muriate of baryta 

 above crystals, but both that and the remaining solution of 

 sulphate of soda is perfectly clear ; there is not the slightest 

 trace of sulphate of baryta in either the one or the other, so 

 that neither muriate of baryta nor sulphate of soda appear to 

 have volatilised with the water. 



No. 2. Bottle, solution of nitrate of silver; tube, fused chlo- 

 ride of sodium. All the water has passed from the nitrate of 

 silver to the salt ; but there is no trace of chloride of silver 

 either in one or the other. No nitrate of silver has sublimed 

 with the water, nor has any chloride of sodium passed over to 

 the nitrate. 



No. 3. Bottle, solution of muriate of lime ; tube, crystals of 

 oxalic acid. The water here remained with the muriate of 

 lime. In the tube, the oxalic acid when put in had formed a 

 loose aggregation, with numerous vacancies, and with a very 

 irregular upper surface about an inch below the upper edge of 

 the tube. No particular appearances occur in the vacancies; 

 but at the top there has evidently been a sublimation of the 

 oxalic acid, for upon the crystals and glass new crystals in 

 exceedingly thin plates and reflecting colour have been formed ; 

 these rise no higher in the tube than to the level of the most 

 projecting part of the original portion of oxalic acid ; no 

 appearance of sublimation is evident above this, and it seems 

 as if the most elevated parts of the salt have given off vapour, 

 which has sunk and formed crystals on the neighbouring 



