neutral paraffinoid resins in three nearly equal portions. The viscous oils deposit, on standing, scales of paraffin wax amounting to about 1.5 per cent of the total tar. The detailed composition of the hydrocarbons, phenols and bases will be discussed later on. In primary tar from a Saxon carbonising coal, as shown in Fig. 8, crude paraffin wax amounts to about 32 per cent. instead of 1.5 per cent as in the case of gas flame coal. On the other hand, the phenols amount to only about a quarter or one-fifth of those from gas flame coal. The proportion of the limpid neutral oils is roughly doubled; that of the viscous neutral oils is approximately the same. The percentage of bases is in both cases equally small.

Figure 8

The Temperatures Required for the Production of Primary Tar

Various statements have been made on the behaviour of coal when gradually heated. Bornstein describes the behaviour of gas flame coal from the Graf Bismarck Colliery as follows:

About 200 degrees Water first split off
200-225 degrees First oily distillate
300 degrees Copious evolution of water
310 degrees First evolution of volatile sulphur compounds
390-400 degrees Main distillation commences
410 degrees First combustible gas
420 degrees Strong evolution of gas.
Fritsche reports on the yield of primary tar at different minimum temperatures. He heated the aluminium retort (Figs. 3 to 5) charged with 20 grams of coal at a constant rate of 10 degrees per minute to the desired temperature,

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