maintaining it until the evolution of gas ceased. Table V shows his results with Lobberg gas flame coal.
The bulk of the tar has come over at 450 degrees, and the maximum yield is reached at 500 degrees. Broche,experimenting recently with a coal of the same origin, but less rich in tar, determined the periods required for securing the maximum tar yield at different temperatures. He heated the coal in the aluminium retort to a definite temperature and maintained it for a definite time. The experiment was then interrupted, and the tar yield determined,. The figures of Table VI were thus obtained.
The table shows that down to 430 degrees nearly the full tar yield is obtained, although the time required is ten times longer than at 500 degrees. Nothing is known of the quality of these low-temperature tars, especially as regards their content of lubricating oils. Owing to the protracted heating they are not necessarily better than those obtained at 500 degrees.
It should be pointed out that the heating periods at different temperatures relate only to the particular coal used, and that temperatures and duration of heating will vary for other coals, lignites and peats, according to their chemical composition. The examples show, at any rate, the course of tar formation at rising temperature and the minimum temperatures required for the highest
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