146 
DETERMINATION OF NITROGEN. 
ed in a porcelain mortar, with an unpolished bottom, which 
has been previously heated, carrying the pestle with great 
lightness in a circular direction. If these directions be strict- 
ly observed, we avoid completely any loss from adherence of 
the matter to the sides of the mortar, or the pestle. When 
the mixture is strongly compressed, or reduced at once to 
fine powder in the mortar, or if it is not dry, a loss is sustain- 
ed by the attachment of the substance to the sides of the mor- 
tar and the pestle. Having in the usual manner introduced 
the mixture into the tube of combustion, the mortar is to be 
several times cleaned with a portion of the mixture of soda 
and lime ; the tube is to be filled to within O' n ,0271 (one inch 
and one-eighth,) of its mouth, and on top of all is placed a 
loose plug of asbestus, previously calcined. The asbestus 
plug prevents the gas developed by the combustion from car- 
rying over fine particles of the powder, an accident which 
would, especially when the potassa mixture is used, lead to 
very inexact results, inasmuch as chloride of potassium and 
platinum react with solvents in the same way as hydrochlorate 
of ammonia and platinum. This circumstance would also 
render it more expedient to operate with the soda mixture, 
because the soluble chloride of sodium and platinum would 
be removed by the subsequent washings. 
The tube of combustion and the hydrochloric acid appara- 
tus are to be closely connected by means of soft cork ; the 
former is to be placed in a common furnace of combustion, 
and the air is to be expelled by heating with a hot coal, the 
ball a with the view of ascertaining whether the apparatus be 
hermetically closed; in which case the tube of combustion is 
to be heated to red heat by burning charcoal, precisely as in 
the method for carbon. The cork should be maintained as 
hot as possible so as not to absorb moisture; as also to pre- 
vent a loss of azote by absorption of ammonia. 
As soon as the tube is red hot, the fire is to be with- 
drawn to a distance. Carbonic acid is formed by the combi- 
nation of the oxygen of the water with the carbon of the 
substance; the hydrogen set free, at the moment of its libe- 
