58 
PROFESSOR GRAHAM ON THE CONSTITUTION OF 
3. Subnitrate of Copper. 
HNCu 3 . 
It is well known that when the nitrate of copper is heated to the temperature of 
400° or 500° Fahr., it is decomposed, nitric acid and water being expelled, and a sub- 
nitrate remaining, which consists of one atom of nitric acid, one atom of water, and 
three atoms of oxide of copper. This decomposition I find to take place and be com- 
pleted at a very moderate temperature, not exceeding 150° Fahr. ; and it appears, be- 
sides, that none of the three constitutional atoms of water of the nitrate of copper can 
be expelled without a certain corresponding loss of acid : that on heating the salt in 
question, nitric acid and water go off together, in the form of nitrate of water with 
its three atoms water. Thus, three atoms of crystallized nitrate of copper, containing 
three atoms acid, three atoms oxide, and nine atoms of water, are resolved into two 
atoms nitrate of water, each containing one atom acid and four water ; and one atom 
of subnitrate of copper, which contains one atom acid, one water, and three oxide 
of copper. 
Experiment. — In a stove of which the temperature never exceeded 150° Fahr., 
27'54 grains crystallized nitrate of copper, containing three atoms of water, exposed on 
a capsule, suffered the following gradual reduction of weight : a loss of 2*59 grains in 
one day, of 9*62 in six days, of 1 IT in seven days, of 13*35 in eleven days, of 13*47 in 
twelve days, of 13*58 in sixteen days, of 13*60 in eighteen days, and nothing more 
afterwards by a heat of 300° Fahr., continued for several hours. Of the crystallized 
nitrate, 27'54 grains have left 13*94 grains subnitrate; or we have 0*5062 subnitrate 
from 1 nitrate. By calculation the residuary subnitrate should be 0*5026, with which 
the experimental result closely corresponds. 
Another portion of the same nitrate of copper, dried exactly in the same way, lost 
1 per cent, of its weight when afterwards heated to 400° Fahr. ; and thereafter, being- 
ignited, was found to consist of 
Experiment. Theory. 
Oxide of copper .... 100* 100* 
Volatile matter .... 53*19 53*1 
153*19 153T 
I am satisfied that no other subnitrate except the preceding, which contains three 
atoms of oxide of copper, can be obtained by the decomposition of the neutral nitrate 
by means of heat. For a quantity of the subnitrate of copper of the first experiment 
narrated above being gradually exposed in a platinum crucible to a heat above the 
melting point of lead, by means of a sand-bath, so as actually to reduce a portion of 
the subsalt in contact with the bottom of the crucible to the state of black oxide, yet 
the major portion of the subsalt, which still retained its green colour, was found to 
be little altered in composition. After this extreme heating the subsalt consisted of 
