SIR WILLIAM SIEMENS, F.K.S. 185 



water at the lower extremity, in order to get a very active distilla- 

 tinn, irrespective of the illuminating quality of the gas produced. 

 P.iu the (lill'uulty which presented itself was one rather of estab- 

 lishment. It was proposed to build works simply for the purpose 

 of supplying heating gas ; and although the Town Council of 

 Birmingham went to Parliament for a Bill to empower them to 

 carry out this suggestion, they lost their Bill in the Committee of 

 tin ilouse of Lords. Since then the public desire for the use of 

 heating gas has been gradually increasing, and another mode of 

 supplying it has suggested itself to me. It may have been thought 

 of by others, and it is one that recommends itself, I think, by its 

 simplicity to your consideration. It consists in separating the 

 produce of the distillation of coal in the gas retorts into two parts : 

 one to be set aside for heating, and the other for illuminating pur- 

 poses. The result of such a separation is illustrated by the diagram, 

 Plate :;i, which is based on some experiments made many years 

 ago by M. Ellissen, the Chemist of the Paris Gas Works, working 

 in connection with M. Regnault, the great physicist. They wanted 

 to determine by accurate observation and experiment what was 

 the least time to be allowed for each distillation. Instead of 

 carrying on the operation through six hours, they came to the 

 conclusion that it should be hastened, and completed in four hours, 

 and for this purpose the Paris Gas Works first adopted the 

 regenerative gas furnace as a means of heating retorts, and they 

 have used it very largely ever since. Through the kindness of 

 M. Ellissen I have been able to construct this diagram, showing 

 the quantity and the illuminating quality of the gas leaving the 

 retorts at each portion of the four hours during which the opera- 

 tion is carried on. The cross line shows the illuminating power 

 of the gas at the different portions. The abscissae give the time, 

 and each line represents a quarter of an hour, and the ordinates 

 give the illuminating power on the curve and the quantity on the 

 other curve. The diagram shows at once that during the first 

 twenty-five minutes or half-an-hour, the gas coming from the 

 retorts has a very low illuminating power. They are chiefly 

 occluded gases, consisting in a great measure of marsh gas. At 

 the end of the first half-hour, the maximum illuminating power is 

 reached, and for about an hour and a half this high illuminating 

 power is pretty w r ell maintained. It then gradually diminishes, 



