128 Mr. Dalton on Sulphuric Ether. [Feb, 



This is used from temperature 80° to 110° or 120°. The third is 

 to have its short leg filled with mercury, and a drop of ether as 

 the other, and its long leg filled to various heights with mercury, 

 according to the temperature. It may be advantageously used 

 from 120° to 140°. For temperatures between 140° and 212°, I 

 have always used a tube similar to the last mentioned, but hav- 

 ing its upper extremity sealed, and containing air of common den- 

 sity over the mercurial column, and nearly equal in volume to 

 the capacity of the other leg. When the ether vapour is formed 

 in force, it condenses the said air, and from the condensation, 

 the force is inferred by a well-known law. Having had some 

 reason to suspect my former results by this instrument were 

 somewhat too high ; I have been induced to examine the 

 defects to which this instrument is liable. The end of the tube 

 must be drawn out to a point before sealing, and suffered to cool 

 to the temperature of the air ; after this, the end must be closed 

 by the point of a flame, otherwise the. air in the tube may be 

 rarefied by the heat, in which case the force of the steam will be 

 overrated. Another cause of similar error is the existence of 

 ether vapour in the air at the moment of sealing ; this will 

 happen if the tube is not carefully dried inside after the instru- 

 ment is filled with mercury. In this case, the air in the tube is 

 rarefied by the steam, and consequently is of an unknown but 

 reduced density. The opposite error is liable to be induced, by 

 the frequent use of the instrument. By the motion of the 

 mercury, the small remains of ether mechanically mixed with it 

 rises to the top, and a visible stratum of ether is thereby exposed 

 to the air. In this case an addition of force is given to the air ; 

 but as the quantity of this force is known for any temperature, it 

 may be allowed for accordingly. I prefer, however, sealing the 

 tube when well dried, and the air of atmospheric density at the 

 time ; and if the ether appear to rise to the surface afterwards, 

 the correction must be applied. In order to have a complete 

 check upon this instrument, it should be adapted so as to be 

 applicable at some temperature (as 140°), where the force is 

 known by other direct means. The error, if any, will thus be 

 shown, and may be calculated for other temperatures. 



I have lately made, for the first time, various experiments on 

 the force of steam from water, in temperatures from 212° to 

 300° ; the results which convince me that the theoretic forces 

 which I gave in the fifth volume of the Memoirs, as also those 

 subsequently in my Chemistry, are both erroneous ; the former 

 being about as much too small as the latter are too large, so that 

 the mean of the two series is a near approximation to the truth. 



Experiments on the force of aqueous steam in high tempera- 

 tures have been lately made by Mr. Southern, of the Soho, 

 Birmingham,* and by Dr. Ure, of Glasgow,t the results of 



• Dr. Robison's Works by Dr. Brewster. 



f It would bavegiveD me great pl< asure to liave been able to adduce Dr. lire's 



