1 68 THE SCIENTIFIC PAPERS OF 



with one complication of the condensing engine, namely, the air- 

 pump ; but whether that advantage was not purchased at too 

 great a price was a question which he should like to see more fully 

 elucidated than was done in the paper at present. 



He should also like to know what vacuum could be regularly 

 maintained by this condenser ; there seemed to him a difficulty in 

 that respect. When the vacuum was produced in the auxiliary 

 condenser no doubt the water in the upper chamber by its own 

 gravity fell readily into the lower chamber ; but only a small 

 portion of the air that was accumulated in the upper chamber 

 would follow it ; and in proportion as the lower chamber was 

 small or reduced in comparison with the upper chamber, or main 

 condenser, in the same ratio the vacuum would be reduced in the 

 upper chamber. It would be interesting to know, therefore, what 

 was the vacuum that could be usually obtained with this con- 

 denser, and what was the amount of steam necessary to work it. 



In the discussion of the Paper 



"ON THE COMBUSTION OF REFUSE VEGETABLE 

 SUBSTANCES, such as STRAW, EEEDS, COTTON STALKS, 

 BRUSHWOOD, MEGASS, &c., UNDER STEAM BOILERS," 

 By JOHN HEAD, Assoc. Inst. C. E., 



DR. SIEMENS * said his experience of the form of engine under 

 discussion was confined to what he had seen, as one of the jury, 

 at the Vienna Exhibition a few years ago. Messrs. Ransome, 

 Sims, and Head's apparatus was then worked very satisfactorily, 

 as was also Mr. Garrett's. The jury, he believed, decided that 

 both makers were entitled to an award, not only for their straw- 

 burning engines, but for their exhibits generally. With regard 

 to the relative merits of the two methods, he thought Mr. Head's 



* Excerpt Minutes of Proceedings of the Institution of Civil Engineers, Vol. 

 XLVIII. Session 1876-1877, pp. 99-100. 



