“ 
eg 
<— 
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 6 will be wanting, 
and that actually developed will be a + c, c being the chemi- 
eal heat determined by Andrews. The difference of these, 
therefore, ora +c — (a+), willbec—d. But this dif- 
ference we have actually found to be greater than c. 5 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 Rey. 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 
