36 
Chemistry, however, has made of late great advances in this curious 
research, and it will soon appear that the composition of atmospherical air 
has been more rigorously determined. 
Chemistry affords two general methods of ascertaining the constituent 
principles of bodies, the method of analysis* and that of synthesis .f 
When, for instance, by combining water with alkohol, we form the spe¬ 
cies of liquor called brandy, we certainly have a right to conclude (by this 
synthesis) that brandy is composed of alkohol and water. And when, by 
distillation of brandy, we obtain, separate, water, and alkohol (by this ana¬ 
lysis), our evidence of the constituent principles of brandy is then rendered 
complete; and in general it ought to be considered as a principle in chemi¬ 
cal science, never to rest satisfied without both these species of proofs. 
THE MODERN ANALYSIS 
O F 
ATMOSPHERIC AIR; 
Or its Separation into r 1. VITAL AIR. 
Two Elastic Fluids, l 2. AZOTIC AIR. 
Lavoisier’s experiment. 
This illustrious chemist having placed 83 grain* of fluid mercury in a 
retort, adapted to a bell-glad*, which enclosed 100 cubical inched of common 
air, he kept up in his furnace a constant fire, of such force, as to keep the 
quickdilver almost always at its boiling point. 
On the second day small red particled began to appear on the surface of 
the met cury, which gradually increased in size and number for four or five 
days. 
Com meed that the calcination of the mercury after that time did not go 
on, he extinguished the fire; and when the vessel was cool, he found in his 
bell-glass, instead of 100 cubical inches of air, only 86, and therefore a loss 
of 14 cubical inched of air. 
* V™ ^ ree 5 C WOrd The separation of any compound into its several parts. 
t from the Greek word The putting together the several parts of a compound body. 
