SfX WILLIAM SIEMENS, F.R.S. 169 



apparatus deserved the first place, because it contained all the 

 dements of continuous, equal, and systematic feeding ; whereas 

 in Mr. Garrett's much depended upon the skill with which the 

 operation was can-led on. Mr. Garrett had stated that each time 

 the dried straw was introduced into the furnace an explosion took 

 place. That surely meant that, at the moment when the straw 

 entered the furnace, the combustible matter met an excessive 

 aniuimt of oxygen which had previously accumulated there. No 

 doubt, however, a skilled workman could produce excellent results 

 with Mr. Garrett's apparatus. With reference to the figures 

 brought forward by Mr. Head, which had been contested by 

 Mr. Garrett, he had just made a calculation which might throw 

 some light on the subject. Mr. Head had stated that 1 Ib. of 

 coal was equal in heating power to 3| Ibs. of dried straw ; and he 

 had given analyses of the coal and of the straw. From this it 

 appeared that the combustible constituents of Newcastle coal 

 were, carbon 80, and hydrogen 5 ; and of straw, carbon 35, and 

 hydrogen 5 ; making a total of combustible matter in the one 

 case of 85, and in the other 40 : but the hydrogen had a greater 

 calorific power than the carbon, and for comparison might be 

 doubled ; so that the figures would be 90 and 45. According to 

 that analysis, straw ought to possess, roughly speaking, half the 

 calorific effect of coal, and it would have that effect if the com- 

 bustion of both materials were perfect. In the case of straw 

 there was one deduction to be made which did not apply equally 

 to coal ; it contained a greater amount of ash in the form of 

 silica ; and that ash was the real difficulty to be contended with. 

 There was also a greater amount of water in the straw than in the 

 coal, but that was a matter of less difficulty. In the case of straw 

 15 per cent, of water had to be evaporated, and in the case of coal 

 only 1*3 per cent. Taking those elements at their utmost value, 

 he considered that Mr. Head's estimate, that 3| Ibs. of straw 

 were equal in calorific effect to 1 Ib. of coal, was not excessive ; it 

 appeared to him a reasonable amount, provided that something 

 like perfect combustion were obtained. The apparatus, so ad- 

 mirably explained and illustrated, showed that the question had 

 been thoroughly gone into, and the assumption that complete 

 combustion wap obtained had been verified. When straw and other 

 similar vegetable matter were consumed, the important point was 



