7 6 Dr. Thomson on Oxalic Acid. 
entering the tube. The experiment was repeated three- 
times. 
4. A hundred grains of oxalate of lime, when thus heated, 
yield above sixty cubic inches of a gas, which is always a 
mixture of carbonic acid and inflammable air, nearly in the 
proportion of one part of the former to three and a half of the 
latter, reckoning by bulk. The specific gravity of the inflam- 
mable gas was 0.908, common air being 1.000 ; it burns with 
a blue flame, and when mixed with oxygen, may be kindled 
by the electric spark. The loudness of the report depends 
upon the proportion of oxygen. 
The smallest quantity of oxygen, with which it can be 
mixed, so as to burn by the electric spark, is l-gth ; the com- 
bustion is very feeble, and is attended with no perceptible 
report. If the residue be washed in lime water and mixed 
with i-9th of its bulk of oxygen, it may be kindled a second 
time : this may be repeated five times, after which the residue 
cannot be made to burn. 
The combustion becomes more violent, and the report 
louder, as we increase the proportion of oxygen, and both 
are greatest when the oxygen is double the bulk of the gas. 
As we increase the dose of oxygen, the combustion becomes 
more and more feeble ; and five parts of oxygen and one of 
gas is the limit of combustion on this side : for a mixture of 
six parts of oxygen and one of the inflammable air will not 
burn. 
In these experiments the results differ materially from each 
other, when the proportion of oxygen used is small and when 
it is great. I am not able at present to account for this dif- 
ference, which holds not only with respect to this gas, but 
