672 Memorandum on the Newcastle 'Engine Trials. 
XXXIV. — Memorandum on the Newcastle Engine Trials. By 
Wm. Anderson, M.Inst.C.E., Consulting Engineer to the 
Society. 
There are several matters connected with the engine-trials at 
Newcastle in July 1887, and the deductions made from them, 
which it will be beneficial to review. 
Exception has been taken to the mode adopted, in the 
engineers' report, of reducing to a standard temperature and 
pressure the quantity of water evaporated by the boilers. It 
has been pointed out that instead of assuming the water to have 
been actually evaporated at 212°, as has been done, the larger 
quantity of heat at the working pressure should have been 
allowed for. Thus, in the case cited of engine No. 3114, the 
steam in the boiler was at 120 lbs. pressure, equal to 350° tem- 
perature, and each pound contained 11 88 •75 units of heat above 
the freezing point. The water was pumped in at 83'6°, or 51-G° 
above 32° ; hence the number of units per 1 lb. of steam was 
1137"1, and not 1095 as stated in the repoi-t; and the quantity 
of water evaporated should have been estimated at nearly 4 % 
higher. The correction, if made, will not sensibly affect the 
comparative results, and it should be understood that neither 
method of reduction will give even an approximation to what 
a boiler working at some given pressure would do if worked at 
that of the atmosphere. The rate of evaporation in a boiler 
depends not only upon the quantity of heat which has to be 
imparted to the contents of the boiler, but also upon the differ- 
ence of temperature between the products of combustion in 
the furnace and flues, and the water in the boiler. The lower 
the pressure the greater this difference becomes ; but as we have 
no means of measuring the mean temperature of the furnace 
and of the products of combustion, we cannot tell what the 
difference of temperature may be, and therefore one of the 
factors in the calculation is missing. 
It is difficult also, if not impossible, to arrive at any con- 
clusion by direct experiment, because, in boilers such as those 
generally used in agricultural engines and in locomotives, the 
mass of water and the free sui'face from which the steam can 
escape are small compared with the volume of steam generated. 
At high pressures these volumes are reduced in proportion to 
the pressure : thus at 120 lbs. per square inch each bubble of 
steam would be ^ the size of the same weight of steam at atmo- 
spheric pressure. Hence ebullition in the latter case is much more 
violent, and the consequent priming of the boilers more severe. 
In some recent experiments with an eight-horse boiler I 
