1870.] On the Heating-Powers of Arcturus and a Lyra, 159 



Hydrogen does not decompose the dry salt, even with the aid of sun- 

 light, nor does a stream of that gas decompose an aqueous solution of the 

 salt, but the dry salt is rapidly and perfectly decomposed by that gas at an 

 incipient red heat, its metal being liberated. 



Nitrogen has no chemical effect upon the salt, even at a red heat, nor 

 upon its aqueous solution. Dry ammonia gas is copiously absorbed by the 

 dry salt. In one experiment the salt absorbed about 844 times its volume 

 of the gas. The salt in a fused state is rapidly and perfectly decomposed 

 by dry ammonia gas, and its silver set free. A saturated solution of the 

 salt is also instantly and violently decomposed by strong aqueous am- 

 monia. 



Oxygen has no effect either upon the dry salt at 15° C, or at a red heat, 

 nor upon its aqueous solution. Steam perfectly and rapidly decomposes 

 the salt at an incipient red heat, setting free all its silver. No chemical 

 change took place on passing either of the oxides of nitrogen over the salt 

 in a state of fusion. 



By passing anhydrous hydrofluoric acid vapour over perfectly anhydrous 

 and previously fused fluoride of silver, at about G0° Fahr., distinct evidence 

 of the existence of an acid salt was obtained. This acid salt is decomposed 

 by a slight elevation of temperature. 



Numerous experiments were made to ascertain the behaviour of argen- 

 tic fluoride in a state of fusion with chlorine, and great difficulties were 

 encountered in consequence of the extremely corrosive action of the sub- 

 stances when brought together in a heated state. Vessels of glass, plati- 

 num, gold, charcoal, gas carbon, and purified graphite were employed*. 

 By heating the salt in chlorine, contained in closed vessels, formed partly 

 of glass and partly of platinum, more or less corrosion of the glass took 

 place, the chlorine united with the platinum and fluoride of silver to form 

 a" double salt, and a vacuum was produced. By similarly heating it in 

 vessels composed wholly of platinum, the same disappearance of chlorine, 

 the same double salt, and a similar vacuum resulted. Also, by heating it 

 in vessels composed partly of gold, an analogous double salt, the same 

 absorption of chlorine and production of rarefaction were produced. And 

 by employing vessels partly composed of purified graphite, a new com- 

 pound of fluorine and carbon was obtained. 



III. "Approximate determinations of the Heating -Powers of 

 Arcturus and a Lyrse. By E. J. Stone, F.R.S ., First Assistant 

 at the Royal Observatory, Greenwich. Received October 

 13, 1869. 



About twelve months ago I began to make observations upon the heating- 

 power of the stars. My first arrangements were simply these : I made 



* In the next communication will be described the results obtained with vessels 

 formed of other materials. 



