Analysis of the compound inflammable Gases . 299 
same either in quantity or quality. The gas from Coalbrooke- 
dale tar, and that from Caoutchouc, have a larger proportion 
of olefiant gas, which in them amounts to about one-sixth 
their bulk. 
2. Sulphureted hydrogen gas is, also, most abundantly 
produced at the early stages of the distillation. Its proportion 
then varies from 1 to 5 per cent ; and towards the close of the 
process it disappears entirely. It increases the illuminating 
power of the coal gas ; but is by no means a desirable pro- 
duct ; since it yields by combustion, a gas (the sulphurous 
acid) which is extremely offensive and irritating to the lungs. 
By the distillation of coal, more sulphureted hydrogen is pro- 
produced, than is discovered among the aeriform products ; 
for a part, uniting with the ammonia which is generated at the 
same moment, forms sulphuret of ammonia, a compound 
which I have found among the condensed products. 
3. Carbonic acid gas, like the two preceding ones, appears 
only at an early stage of the process, and in small proportion, 
never amounting to 5 per cent. A portion of this gas, also, 
unites with ammonia, and hence carbonate of ammonia is 
found in the condensed fluid. 
4. The gas from coal undergoes a gradual diminution of 
specific gravity and combustibility, from the commencement 
to the close of the process. This is best shewn by inspecting 
the results of the experiments on the Black-Mine and Merthyr 
coal gas in Table II. because they were reserved in a greater 
number of separate portions than usual. The progression 
would, perhaps, have been more regular, in these as well as 
in the other instances, if much of the gas had not been al- 
lowed to escape, in consequence of the immense quantity 
Oq 2 
