SECT. i. ] THE STEAM ENGINE. 17 



of steam at 212 to that of air at 60, as 96 : 21875, or as O44 : 1. The true 

 density of steam at 212 is nearly as O48 : 1. 



The globe was filled with steam as before ; only, not knowing the effect of 

 temperature, he continued the globe longer with the steam passing through it, by 

 which it acquired a greater degree of heat ; for he found by these experiments, 

 that the least degree of cold less than the steam would condense a part of it again 

 into water, and hence the quantity could not be ascertained which would exclude 

 the air out of a given space, which was the chief end of the experiment. In this 

 experiment he succeeded in excluding the air with less steam ; for, on weighing 

 the globe, when the steam was condensed, the air let in, and all cold, it was found 

 that the weight of the water condensed from the steam was only about forty-eight 

 grains, which filled, when converted into steam, 925 cubic inches of space, so as 

 to exclude nearly all the air. From which he concluded that one cubic inch of 

 water will form 4000 inches of steam. To admit of comparison, the temperature 

 should have been observed, as I have little doubt that the steam was so rarefied by 

 heat as to cause this result. 



17. Mr. Payne also attempted to introduce a new mode of generating steam ; 

 his apparatus consisted of a cast iron vessel of the figure of a frustrum of a cone, 

 its diameter at the bottom being four feet, with a semi-globular end of copper of 

 about five feet and a half diameter. In the inside a small vessel was inserted, 

 which Payne calls a disperser, which vessel had pipes round the sides fixed to it ; 

 the bottom rested on a central pin, on which it revolved, so as to spread the water 

 it received from above, through an iron pipe. The end of this pipe passed up 

 through the head, and was enclosed very tightly, but so as to be easily moved 

 with a circular motion, so that the water might be dispersed or showered round 

 on the sides of the red hot cone, or ignited vessel, in a very exact manner. From 

 experiment he states that a pot or vessel, of the size and shape here mentioned, 

 will, being kept to a dark red heat and the water regularly dispersed, convert 6'5 

 cubic feet of water into steam in an hour. And that, by experiments made at 

 Wednesbury and Newcastle-upon-Tyne, 112 Ibs. of pit coal will by this method 

 convert twelve cubic feet of water into steam. This is near the truth of what may 

 be done ; but the method has no advantages, and the apparatus soon fails. It is 

 a duty, however, to an ingenious man to record his attempts to establish useful 

 truths, even when he fails in his object : it shows the state of knowledge at the 

 time on these subjects ; and it saves others from repeating useless experiments. The 

 mode of generating steam, just described, has been more than once revived lately. l 



18. The engine of Savery had hitherto required the attendance of a person 



1 [This is the recorded opinion of Tredgold. Since his time, however, Mr. Howard has adopted 

 a similar principle with success, an account of which is given in the Appendix. ED.] 



C 



