1880.] Revision of the Atomic Weight of Aluminium. 329 



The numbers given are not the result of one reading, but the mean 

 of four or five. The copper block, after being raised to the tempera • 

 ture at which the meniscus of the liquid disappeared, was allowed to 

 cool till a cloud became visible, shortly afterwards followed by a 

 reappearance of the meniscus. The temperature was again raised, and 

 so on, readings being taken each time. They never differed by more 

 than half a degree. The tubes, therefore, must have possessed the 

 temperature of the heater. 



The experiments described in a former part of this paper, relating to 

 the difference of refraction shown by a liquid above its so-called critical 

 point, and the gas evolved from it, were repeated with carbon tetra- 

 chloride and carbon disulphide, and held good in both cases. The 

 phenomena observed differed in no particular from those already 

 described. 



In conclusion a few remarks on the liquefaction of the so-called per- 

 manent gases may not be deemed out of place. If the deductions from 

 the above experiments be correct, it follows that that form of matter 

 which we call gas may be converted into liquid by pressure alone ; but the 

 meniscus will never become visible, for the process of change is a gradual 

 one. To render the meniscus visible, it is necessary to take advantage 

 of the fact that liquids under such circumstances have a much greater 

 coefficient of expansion by heat, and conversely a much greater coefficient 

 of contraction on withdrawal of heat, than gases. It, therefore, becomes 

 necessary to lower the temperature until the liquid by contraction 

 acquires a specific gravity greater than that of its gas, and then, and 

 not till then, does the phenomenon of a meniscus become observable. 



III. " Revision of the Atomic Weight of Aluminium." By 

 J. W. Mallet, F.R.S. Received March 13, 1880. 



(Abstract.) 



After remarking that there is probably no one of the so-called 

 chemical elements, equally abundant in nature with aluminium, and 

 occurring in as numerous compounds, with regard to the atomic 

 weight of which our knowledge has long rested upon so slender a 

 foundation of accurate experiment, the author gives a brief statement 

 of prior determinations, noticing in succession the researches of 

 Berzelius, Sir Humphry Davy, Thomson, Mather, himself, Dumas, 

 Charles Tissier, and Terreil, and quotes the numbers given in several 

 of the more recent chemical handbooks, reports, &c. 



He then proceeds to describe a redetermination of this atomic 



