104 THE SCIENTIFIC PAPERS OF 



The subject had been considered irrespective of the question of 

 heat, but that, in his opinion, was a fallacious method, for, it 

 would be seen, that without complete condensation the instrument 

 could not act ; neither could its effect, nor the limits of its action, 

 be determined, without taking into account the amount of heat 

 contained in the steam and in the water, as well as their proper 

 velocities when acted upon by pressure. 



Mr. Siemens thought the injector could only be advantageously 

 applied as a motor, in cases where the water had not only to be 

 raised but also to be heated, and its legitimate application would 

 probably remain confined to the feeding of steam boilers. Its 

 practical advantages were not overstated in the paper, where feed- 

 water of sufficiently low temperature was used. The minimum 

 temperature, to obtain an advantageous result, would be about 

 100 Fahr. In the case of a high-pressure engine, it was a 

 question whether a heater and a pump would not be more advan- 

 tageous than this instrument. The author had stated that 2'3 

 cubic feet of steam would be expended to pump one cubic foot of 

 water into the boiler. But even this calculation, unfavourable as 

 it might seem, still left a great margin in favour of the pump, 

 inasmuch as the water could be raised by waste heat to nearly 

 212. He believed that the injector would be found applicable 

 with the greatest advantage in the case of marine engines, or of 

 condensing engines in general, where there were no means of 

 heating the feed-water to above 100. Under such circumstances 

 the power expended to work the feed-pump could be entirely 

 saved, because although the injector would expend heat on the 

 water, it would return the same to the boiler ; whereas the pump 

 used the steam to work it, and gave nothing in return. 



Mr. Siemens said, the areas of the different jets of water and 

 steam, which had been stated to be adopted in practice, agreed 

 very well with his own calculations.* The areas were determined 

 by the quantity of steam necessary to condense in order to impel 

 the water. Taking the case of a pressure of 60 Ibs., or an 

 effective pressure of three atmospheres, the steam was 477 times 

 lighter than water, while its velocity was only in the ratio of 

 J i77, or nearly 22 times greater than that of the water ; the 



* Vide Minutes of Proceedings of the Institution of Mechanical Engineer*, 

 1860, pp. 48-78. 



