172 ANNUAL OF SCIENTIFIC DISCOVERY. 



wear and tear is far less. Another remarkable feature of this gas 

 is its non-condensability in the mains, none of the drips having 

 yet required to be pumped. The loss by leakage and condensi- 

 bility is therefore exceedingly small, never having exceeded 3 

 per cent. The mains in one place, particularly, are laid only 16 

 inches under the surface for a space of one-half mile, owing to 

 the difficulty of excavating a very hard unstratified rock. But 

 during last winter, with the thermometer often at and below zero, 

 no trouble of condensation was experienced. 



Other materials can be used beside naphtha, any of the prod- 

 ucts of the oil-wells, such as crude petroleum, dead oil, "still 

 foots," etc. Any oil or oily or fatty matter may be used. In fact, 

 all liquid, semi-liquid, or solid carbonaceous matter can be em- 

 ployed to make gas by this process ; and the letters patent ful- 

 ly specify and cover this ground. It is only necessary to ob- 

 serve that, where the materials used do not vaporize (like naph- 

 tha, etc.,) by the application of a steam coil, it is only necessary 

 to apply a sufficient degree of heat through the aid of a furnace, 

 that will convert the material into a vapor, in the first instance; 

 and that this vapor (which is necessarily more or less condensable) 

 shall pass into a retort heated to a temperature sufficient to con- 

 vert it all into a fixed gas. This is the great novelty of the inven- 

 tion, and gives it the great advantage over the ordinary method 

 of distilling either oils and other hydro-carbons, or coals and the 

 like materials, to produce illuminating gas. If coal is used, it 

 first distils, and oil as a condensable vapor is eliminated ; this, 

 instead of going to make coal tar in the hydraulic main as usual, 

 is passed into a red-hot retort, where it becomes a true gas, and 

 nothing else. 



This process is a great stride in the art of making gas upon 

 true chemical principles. In the old process, the charge of coal 

 is thrown into a hot retort ; a portion next the retort is distilled 

 at a proper temperature to produce a fixed gas ; but another 

 portion in the centre of the charge is distilled at a low tempera- 

 ture, which will only yield oily and condensable matter, and this 

 goes to form the tar in the hydraulic main. This is the very 

 essence, so to speak, of gas, and is a dead loss to the process in a 

 chemical sense. Again, another portion of the charge becomes 

 too highly heated, and is destructively decomposed, forming 

 either a hard incrustation on the sides of the retorts called gas 

 carbon, or clogs the mouth-piece and stand and bridge pipes, in 

 the form of a combined gummy and sooty matter. Although the 

 gas may be formed properly in one part of the retort, before it 

 escapes a portion becomes decomposed and resolved into new 

 chemical combinations, principally carbonic oxide, carbonic acid 

 gas, and free hydrogen. All this is wrong, and to the analytical 

 mind of the scientist, but more especially to the practical mind 

 that comprehends it fully, the whole process of gas-making ap- 

 pears not only absurd but even ridiculous, when compared with 

 the new process. Amer. Oas-Liglit Jour. 



The McCracken Process. By this process of gas manufacture 

 the tar condensing in the hydraulic main is allowed to overflow, 



