441 



" Let a + b = heat given out by ammoniacal gas when 

 absorbed by water, a representing the heat of compression, and 

 b that of the chemical action between compressed or liquid 

 ammonia and water. When ammoniacal gas is passed into 

 liquid muriatic acid, the heat represented by b will be wanting, 

 and that actually developed will be « + c, c being the chemi- 

 cal heat determined by Andrews. The difference of these, 

 therefore, or a + c — (a + 6), will he c — b. But this dif- 

 ference we have actually found to be greater than c. b must, 

 therefore, have a negative sign ; or, in other words, when com- 

 pressed ammonia is brought into contact with water, cold, not 

 heat, is the result. 



" This may appear a very paradoxical supposition, but I 

 am not aware of any fact which would prevent us from enter- 

 taining it; and the great expansion which water experiences 

 when absorbing ammoniacal gas, even confers upon it some 

 degree of probability. I may add, that this view of the mat- 

 ter gives us 239° as the value of b, and suggests an experi- 

 ment, which, though difficult, it would not be impossible to 

 perform, and the result of which would at once elucidate com- 

 pletely the subject under consideration." 



The Rev. Dr. Todd exhibited an ancient Irish brooch, be- 

 longing to the Rev. Richard Butler, of Trim. 



Mr. Petrie having been called on for his opinion respect- 

 ing the style, workmanship, and age of this beautiful relic 

 of antiquity, stated, that he considered it as the most elegant 

 specimen of Irish workmanship in silver which he had hi- 

 therto seen, but believed its age to be not so great as that of 

 most, or perhaps any, of the brooches in the Museum of the 

 Academy, or the other collections in Dublin ; its minor orna- 

 ments being peculiarly those characteristic of the early portion 

 of the twelfth century, to which period he referred it ; though 



