The later trials were mainly concerned with the breaking up of the paraffin oils into permanent illuminating gas.  Experiments were made at low heats, medium heats, and high heats, which proved that, according to the respective qualities of the paraffin oils employed in the trials, there was more or less tendency at the lower heats to distill oil instead of permanent gas, while at the high heats there was a liability to decarbonize the oil and gas, and to obtain a thin gas of comparatively small illuminating power.  When, however, a good cherry red heat was maintained, the oils split up in large proportion into permanent gas of high illuminating quality, accompanied by little tarry matter, and with only a slight amount of separated carbon or deposited soot.

The best mode of splitting up the paraffin oils, and the special arrangements of the retort or distilling apparatus, also formed, he said, an extensive inquiry by itself.  In one set of trials the oil was distilled into gaseous vapor, and then passed through the retort.  In another set of experiments, the oil was run into or allowed to trickle into the retorts, while both modes of introducing the oil were tried in retorts charged with red hot coke and in retorts free from coke.

Ultimately, it was found that the best results were obtained by the more simple arrangement of employing iron retorts at a good cherry red heat, and running in the oil as a thin stream direct into the retort, so that it quickly impinged upon the red hot metal, and without the intervention of any coke or other matter in the retorts.  The paraffin oils employed in the investigations were principally:  (1) Crude paraffin oil, being the oil obtained direct from the destructive distillation of shale in retorts; (2) green paraffin oil, which is yielded by distilling or re-running the crude paraffin oil, and removing the lighter or more inflammable portion by fractional distillation; and (3) blue paraffin oil, which is obtained by rectifying the twice run oil with sulphuric acid and soda, and distilling off the paraffin spirit, burning oil, and intermediate oil, and freezing out the solid paraffin as paraffin scale.  The best practical trials were obtained in Pintsch’s apparatus and in Keith’s apparatus.

After describing both of these, Dr. Macadam went on to give in great detail the results obtained in splitting up blue paraffin oil into gas in each apparatus.  He then said that these experimental results demonstrated that Pintsch’s apparatus yielded from the gallon of oil in one case 90.70 cubic feet of gas of 62.50 candle power, and in the second case 103.36 cubic feet of 59.15 candle gas, or an average of 97.03 cubic feet of 60.82 candle power gas.