In turn efforts were made to dispose of the nuisance as a fuel, the heavy proportion of oil present in the dried cake being the attractive feature prompting this application. This recommendation found scanty favour. Another brilliant mind conceived the idea of consuming the refuse in gas-producers, thus obtaining a low-grade gas for power purposes. This attempt failed to meet approbation. A third expedient was its conversion into an illuminating gas, but this likewise failed to overcome the obstacle. In so far as lighting is concerned, in many places the practice is followed of allowing the gas thrown off by the decomposing fæcal matter during its passage through the sewers, to be led to the burners of adjacent street lamps to mix with the ordinary town gas and thus be consumed. But this is merely a safety precaution; it is not followed from economical motives. Now that electricity is widely displacing gas for street illumination, even this quasi-utilitarian system is meeting with defeat. Under the Grossmann system, as practised at Oldham, the sludge is subjected to a complete scientific treatment. The process is continuous and automatic throughout. Moreover, the plant is designed and built upon the unit principle, which allows the standardization of parts and ability to meet any desired demand by merely acquiring a sufficient number of units to comply with the sewage resulting from a given population. Each unit is capable of dealing with sludge arising from the purely domestic sewage of 20,000 inhabitants. Thus a town of 100,000 inhabitants would require 5 units, a city of one million souls 50 units, and so on in arithmetical progression. Furthermore, any number of units can be worked together, so that in those centres where the population fluctuates according to season or other conditions, a certain number of units can be shut down during the off period.