210 REPORT 1860. 



consider that the report of Professor Rankine was based upon one hour's consumption 

 of say 230 lbs. of coal, and compare that with a mass of boiler, water and firebrick, 

 weighing 20 tons, at a temperature of say 300°, it is evident that the mass of heat in 

 proportion to the coal consumed is so great, that no conclusion should be made from 

 such an experiment ; also, that when the quantity of coal said to be consumed, viz. 

 230 lbs., is compared with area of fire-grate, say 40 square feet, it is evident that 

 the result should not be depended upon, as no ordinary comparisons could be made 

 of the condition of the fires before and after the experiment. In conclusion, let me 

 ask of every party present to consider the trial trips of steam-ships and boilers in 

 their true lights, and before drawing any inferences from such short trials, make a 

 perusal of results obtained from sea voyages. The evaporative power and economy 

 of boilers is one of the most important subjects for this Society to consider. We 

 need only refer to the able Report drawn up by the Steam Shipping Committee of 

 the British Association, to show how mixed up the question of the relative efficiency 

 of the boiler and engines is generally considered. Indeed the American navy 

 returns form the only reports showing the evaporative power of the boilers in this 

 list, and the whole merit of a good evaporating boiler is often sacrificed to the cha- 

 racter of the engines. With regard to the ' Thetis,' I would recommend any mistake 

 to be remedied as soon as possible, as there are many contracts, involving much 

 responsibility, formed in consequence of this report, that will lead to serious loss and 

 disappointment to the steam-shipping interest, and the engineering profession of this 

 country. 



On the Density of Saturated Steam, and on the Law of Expansion of Super- 

 heated Steam. By William Fairbairn, LL.D., F.R.S. fyc. 



This paper contained a continuation of the experiments detailed in a paper read 

 by Mr. Fairbairn at the Aberdeen Meeting-, and which had been earned on in con- 

 junction with Mr. Tate. Experimental determinations had been obtained of the 

 density of steam fully confirming the anticipations of Mr. Thomson and Mr. Ran- 

 kine, that the vapour of water does not exactly obey the gaseous laws. They show 

 that the density of saturated steam is always greater than that given by the gaseous 

 laws, even for temperatures as low as 130° Fahr., and at pressures below that of the 

 atmosphere. The experiments at present extend over a range of temperature from 

 136° Fahr. to 292°, or from 2-6 to 00 lbs. pressure per square inch. The general 

 result obtained is expressed in the following formuke, which closely agrees with the 

 experiments, 



,=25-62+1^, (1.) 



P = -^SIr,-0-72 (2.) 



v— 25-02 ' 



where v is the specific volume or ratio of the volume of the steam to that of the 

 water which produced it, at the pressure P, expressed in inches of mercury. 



On the subject of superheating steam, the experiments throw some light, which 

 the author hopes to follow up by a special series of experiments. They show that 

 within a short distance of the maximum temperature of saturation the rate of ex- 

 pansion is variable, being higher than that of a perfect gas near the saturation point, 

 and rapidly decreasing, till at a point at no great distance above the temperature of 

 saturation it becomes sensibly identical with that of a perfect gas. 



On an Atmospheric Washing Machine. By John Fisher. 



The action of this machine was derived from streams of air forced through the 

 water from below. The author in his paper observed, that for effectual use the water 

 must never be of a higher temperature than 140° of Fahrenheit. It was stated 

 that machines on this principle, driven by steam-power, had been for some time 

 past in successful operation for cleansing the soiled laces at Messrs. Fishers' manu- 

 factory at Nottingham. 



