and Attached Water. Ill 



cessation of loss is for both atoms sufficiently well marked and 

 abrupt, the final balance of water is retained in both cases with 

 considerable tenacity. 



In the second series of experiments the flask preserved its 

 weight exactly. The total loss on the 5*6462 grams was 0*4119 

 gram, showing a percentage loss of 7*277. 



The whole analysis now stands as follows, allowing for the 

 loss of the glass in the first series, for the salt dried over sul- 

 phuric acid : — 



Calculated. 



Ba . . . 56-56 56*14 



Cl 2 . . . 28*91 29*10 



«H 2 . . 7-44 



/3H 2 . . 7*23 (7*28 and 7*19) 

 100*14 



On mixing the bodv BaCl 2 + H 2 with water a rise from 

 21° to 27° (or 6°) was obtained. The anhydrous salt with 

 water gave from 19° to 38° (or 19°). 



§ 187. Briefly to recapitulate concerning BaCl 2 + 2H 2 0. 

 At the ordinary barometric pressure, and in a current of air 

 dried and freed from carbonic acid, one water molecule is re- 

 moved at all temperatures above 25° C, the other at all tempe- 

 ratures above 60° C. In the figure (p. 112) A shows the rates 

 of loss of the /3 molecule in tenths of milligrams, the ordinates 

 being proportional to such losses. The abscissas are the tempe- 

 ratures. B shows the losses in like manner of the a molecule. 



Chromatic Value of other Media than Water. 



§ 188. There are few media besides water which dissolve 

 metallic salts. Amongst the few glycerine stands preeminent ; 

 and this liquid is indeed comparable with water itself in its 

 solvent power. On account of this very solvent power, there 

 appears to be at present no evidence of the replacement of water 

 by glycerine in solid hydrated salts, similar to the replacement 

 in siliceous jellies. Some gly cerates (using the term homolo- 

 gously with hydrates) are well-defined bodies enough : and the 

 properties of some new ones will be described subsequently. 

 Here I shall confine myself to the description of the effect upon 

 the colours of a few salt solutions, according as the solvent is 

 water or glycerine. Being partially what is called " colour- 

 blind," I have, of course, availed myself of the services of my 

 friends in describing the appearances presented. 



§ 189. Many are entertaining the idea of the relationship 

 between the vibrating periods of the light-wave and the mass 

 of the molecule, simple or compound, of the medium. The 



