44 Prof. Magnus on the Elastic Forces of 



I feel a great desire to see the rock analyses on which Sir 

 Kobert Kane has founded so important a statement, and sin- 

 cerely hope that he will before long mate them public, as I feel 

 utterly at a loss to reconcile the statement with the results I 

 have arrived at. The granite rock in question consists of quartz, 

 mica and felspar : the quartz contributes no alkali, the mica is 

 well known to contain potash in excess, the felspar I have shown 

 contains potash in excess over soda in the ratio of 9:2; how, 

 then, can a rock which is a mixture of the three be said to con- 

 tain both potash and soda ? " but the latter almost always so 

 preponderant, as to lead to the conclusion that the potash should 

 in most cases be considered to belong to the mica which the 

 granite contained ; and that the felspar was almost exclusively an 

 albitic or soda felspar, containing only in some instances a small 

 quantity of replacing potash." 



I remain, Gentlemen, 



Your obedient Servant, 



Trinity College, Dublin, Joseph A. Galbraith. 



December 12, 1854. 



VII. On the Elastic Forces of Vapours of Mixtures of two 

 Liquids. By Professor Magnus*. 



IN the communication of his interesting researches on the 

 elastic forces of the vapours of different liquids, M. Regnault 

 states, " It may be said that the law of Dal ton has been accepted 

 on sufferance, inasmuch as it seemed to be a natural consequence 

 of the notions formed regarding the constitution of gaseous fluids, 

 and which were developed by Laplace, Poisson, and other mathe- 

 maticians. Physicists have not deemed it necessary to submit 

 the law to an experimental examination." 



This statement contains a complaint which is not well founded. 

 In a memoirpublished inPoggendorfFs.^nn«/era,vol.xxxviii. p. 181, 

 in the year 1836, "On the boiling of Mixtures of two Liquids, and 

 the bumping of such mixtures," I have shown that the law of 

 Dalton is not applicable to the vapours of mixed liquids ; that is 

 to say, of liquids which mutually dissolve each other by their 

 mixture. It is there stated, — " If a liquid, aether for example, 

 be brought into the vacuum of a barometer tube, and if, 

 after the maximum tension of the vapour developed has been 

 observed, another liquid, for instance alcohol, be introduced, 

 whose vapour at the existing temperature possesses a smaller 

 tension than that of rether ; then the tension of the vapours of 

 both liquids is less than that of the aether vapour alone, and is 

 ever feebler the more alcohol is added, until finally, when a 



* From Poggendorff's Annalen ; communicated by the Author. 



