VOLATILITY OF AMMONIUM NITRATE. 



243 



2. HEAT OF FORMATION OF AMMONIACAL SALTS FROM THEIR 



ELEMENTS. 



1. The table of the heat of formation of the principal 

 ammoniacal salts from their elements follows : 



2. The heat of formation of the same salts in .a solid form, 

 from ammoniacal gas and anhydrous or hydrated acids, taken 

 in the gaseous form and in the solid form, has been given 

 (p. 127). 



3. We may also observe that the difference between the heats 

 of formation from the elements, of anhydrous salts of potash 

 and ammonia formed by strong acids, such as the nitrates, 

 sulphates, perchlorates, is almost constant, being about + 30 

 Cal. But this difference decreases for weaker acids ; it falls to 

 25 Cal. with the formates, oxalates, acetates, bicarbonates, etc. 



3. ON THE VOLATILITY OF AMMONIUM NITRATE. 



1. It has been shown how ammonium nitrate may be decom- 

 posed in seven different ways, according to the process of heat- 

 ing (p. 5). Here certain experiments may be mentioned that 

 indicate an eighth mode of action of heat, viz. the volatilization 

 pure and simple of this salt. 



2. Ammonium nitrate melts at about 152, a temperature 

 which the water, previously existing or formed by the decom- 

 position of the salt, does not allow us to fix very accurately. 

 It is only at 210 that it begins to decompose, that is, sufficiently 

 to furnish an appreciable volume of gas in a few minutes, for 

 the decomposition begins really at a lower temperature. This 

 decomposition becomes more and more active, in proportion as 



R2 



