TRANSACTIONS OF THE SECTIONS. 233 



on a consumption of about 20 cwt. per hour. The 'Lima ' has also arrived at her 

 destination, after a most successful run; she performed the distance of 1500 miles, 

 from Valparaiso to Callao, in 141 hours, consuming 150 tons of coals, logging at an 

 average of 2G0 miles per clay during that distance, considerably faster than she had 

 ever done with her original engines, and on less than half the coals consumed. The 

 ' Bogota ' was completed and tested on the 1st of September last, and found fully 

 equal to the others. She made the run from the Cloch Light in the Clyde to the 

 Bell Buoy at Liverpool in 15 hours, against a strong head wind, and consumed 

 during that distance 15 tons of Scotch coals. 



At the Admiralty trial, which took place immediately on her arrival at Liverpool, 

 she averaged upwards of 13 knots, the engine made 25£ revolutions ; she indicated 

 1080 horse-power, and consumed about 21 cwt. per hour of Scotch coals; the 

 steam was superheated to 340 degrees on entering the cylinder, and the thermometer 

 at the water-level of the boiler showed 264 ; the pressure in the boilers was 27 lbs., 

 and the vacuum in the condensers 26 inches. She left Liverpool for Valparaiso on 

 the 11th of the present month, with sufficient coals to carry her 5000 miles, at 240 

 miles per day, and a full complement of stores for the passengers on board ; her 

 draught of water on leaving Liverpool at the load line was, aft, 14 ft. 6 in. ; forward, 

 13 ft. 9 in.; and displacement, 1700 tons. She steamed to the Holyhead Light, 

 where the pilot left her, at the rate of llf nautical miles per hour against a strong 

 head wind ; the engines were making 20 revolutions ; the steam pressure was 26 lbs. ; 

 the vacuum 26 inches ; and the consumption of coals 22 cwt. best Welsh coals per 

 hour. 



The engineers are now constructing the machinery for three other steam-ships on 

 this principle, with boilers on the cellular cylindrical spiral principle. In conclu- 

 sion, the form of engines now described gives regularity of motion while working 

 expansively to the fullest extent, the expansion principle is fully realized, and the 

 engines are of a strong architectural figure, with the various parts easily got at, and 

 reduced to simple forms, and present every facility for reversing freely by the 

 engine-driver. 



Experimental Researches to determine the Density of Steam at various Tem- 

 peratures. By William Fairbairn, LL.D., F.R.S., and Thomas 

 Tate. 

 For a perfect gas, the law which regulates the relation between temperature and 



volume is known by Gay-Lussac's or Dalton's law, and is expressed by the equation 



i)XP , 459 + ^ 



v l xP l 459-N 



Steam at the temperature of 212° has a density such that its volume is 1670 times 

 that of the water which produced it ; substituting these values of volume, temperature, 

 and pressure, we get for the volume of steam from a unit of water at any other 

 temperature, 



v= l670X15 x 4j9^ oi , v = 3;r ,459+< (2) 



These are the well-known and received formulae from which all the tables of the 

 density of steam have hitherto been deduced, and on which calculations on the duty 

 of steam-engines have been founded. They have not, however, up to the present 

 time been verified by direct experiment ; various speculations and theories have from 

 time to time been propounded, as giving more accurately the density required, which, 

 however, need the evidence and verification of direct experiment. 



Great difficulties have hitherto stood in the way of making direct experiments. 

 The temperature of saturation, or temperature at which the whole of the moisture 

 is converted into steam, whilst no part of the steam is superheated, must be deter- 

 mined with the utmost accuracy, or the results are of no value. 



The difficulties thus resolve themselves into finding some test of sufficient accuracy 

 and delicacy to determine the point of saturation. This has been overcome by what 

 may be termed the saturation gau::c ; and it is in this that the novelty of the pre- 

 sent experiments consists. 



