10 
figures furnished by my fifth experiment show, that if this 
supposed NH 4 gas had the normal molecular volume, and 
existed in. the amalgam from the beginning, a force of two 
atmospheres would be required to compress it within the 
amalgam. The decomposition therefore is progressive, and 
points to the existence of a real compound of NH 4 with the 
mercury. We may therefore admit, that such a compound 
is originally formed, and decomposes rapidly into mercury, 
ammonia, and hydrogen, while the gases becoming entangled 
in the mass impart to it that remarkable turgescence, which 
is not however a property of the original compound (or 
ammonium amalgam), but merely an accidental result of its 
decomposition. 
As to the cause of the retention of the gases, I am not 
prepared to offer an opinion, further than that its explana- 
tion would probably involve physical rather than chemical 
considerations. 
I have to express my obligation to the kindness of Dr. 
ftoscoe for the use of the appliances of the laboratory at 
Owens College, where the experiments were carried out, 
and I am also indebted to him for valuable suggestions. 
