150 
DETERMINATION OF NITROGEN. 
tinum is totally insoluble, while the hydrochlorate of plati- 
num is very soluble; hence the color of the liquid will indi- 
cate whether this latter has been added in excess, it not being 
in excess if the liquid remains uncolored. 
The precipitate is then to be placed upon a filter which 
has been dried at 100° C, and weighed in a covered crucible, 
or in a tube. The most simple and prompt manner to perform 
this operation consists in placing the capsule vertically over the 
filter, and by means of the washing bottle detaching the pre- 
cipitate. It is then to be completely washed on the filter 
with the mixture of alcohol and ether, until the liquid which 
passes is colorless, leaves no residue, or ha6 not an acid re- 
action. The precipitate perfectly washed, is then dried with care 
at 100° C, and weighed in a covered crucible, or a tube; from 
its weight may be calculated the quantity of nitrogen. It is 
advantageous to prove this weight by calcining with care the 
hydrochlorate of ammonia and platinum, and from the plati- 
num obtain the amount of nitrogen. The hydrochlorate of 
ammonia and platinum was pure, if by a decomposition care- 
fully conducted, the quantity of nitrogen deduced from the 
platinum does not sensibly differ from the former. 
In this calcination of the hydrochlorate of ammonia and 
platinum, it is best, as recommended by M. Rose, to decom- 
pose the precipitate enveloped by its filter, in a covered cru- 
cible, commencing the heating with great precaution. If 
this precaution be neglected it is very easy to experience a 
loss of platinum, and consequently of nitrogen, for this metal 
is readily carried off mechanically, by the vapors of sal am- 
monia and the chlorine. 
It is especially necessary in this mode of determining the 
nitrogen, to use a perfectly pure chloride of platinum. It 
should not contain any hydrochlorate of ammonia and plati- 
num in solution, since this latter would form, on evaporation, 
a residue insoluble in alcohol and ether, and thus augment the 
weight of hydrochlorate of ammonia and platinum. It is 
difficult, by the simple application of heat, to separate the 
