I 
48 PROFESSOR GRAHAM ON THE CONSTITUTION OF 
the acid to crystallize with this proportion of water in a variety of circumstances, and 
believe that it is never deposited from its aqueous solution in any other state. Of 
these three atoms of water one atom is basic, which is expressed in the formula by 
placing its symbol before that of the acid ; while the other two atoms of water are 
attached to this oxalate of water, and may be termed the constitutional water of the 
oxalate of water. These two atoms of water are found in the oxalate of magnesia, 
the oxalate of zinc, and the other oxalates of the magnesian class, as well as in the 
oxalate of water. 
It is well known that oxalic acid can likewise exist in combination with no more 
than one atom of water (its basic water), and is obtained in that state by drying it at 
a temperature a little above 212° Fahr., or on subliming the hydrated acid by a higher 
temperature. I have made many experiments in order to discover whether, in the 
case of the other two atoms of water, one is retained more strongly than the other, 
or whether an oxalate of water with one additional atom of water, instead of two, 
could be obtained. The common crystals were dried at various temperatures, both 
in air and in vacuo, but either none of the water was lost, or the entire two atomic 
proportions. There is certainly no intermediate hydrate. 
2. Oxalate of Zinc. 
Zn CC H 2 . 
In the oxalate of water we observe a contracted solubility, and all the oxalates of 
the magnesian class of oxides are very sparingly soluble in water. They may be ob- 
tained by precipitation, on mixing a solution of oxalate of potash with sulphate of 
zinc, &c. Cold solutions of the salts were always made use of in our experiments ; and 
the precipitates, which were always granular and more or less distinctly crystalline, 
were washed with cold water, and dried by exposure to the air for a week or two, 
without the application of artificial heat. 
The oxalate of zinc is admitted to possess two atoms of water, and these I find are 
retained pretty strongly, as in the case of oxalate of water. It was observed that 
24*95 grains of the salt lost only 0*44 grain by three days exposure to 212° Fahr. ; 
but by a few hours at 315° Fahr. the salt lost in all 4*87 grains of water, and appears 
to have become anhydrous. 
3. Oxalate of Magnesia. 
Mg CC II 2 . 
The oxalate of magnesia retains its two atoms of constitutional water very strongly, 
and it is doubtful whether they can be expelled without decomposing the salt ; 1374 
grains of the salt lost only 0*32 grain by an exposure to 212°, protracted for several 
days ; and by two days at 300° Fahr. the whole loss amounted only to 0’47 grain. 
22*36 grains of the same salt, ignited, left 5*94 grains of caustic magnesia, or one part 
