434 MEASURING OF AIR. 



Some control observations made occasionally by measuring- 

 the height of the four water columns separately, proved this 

 method to give correct results. 



The diameters of these orifices were measured with micro- 

 meter gauges on four diameters by two oibservers and the means 

 were taken. 



On H.P. side 10.635 inches: Area 88.831 sq. inches 

 On M.P. side 10.642 inches : Area 88.948 sq. inches. 

 Hence with the value of c. := 0.985 A =: infinity. 

 Efiuivalent area H.P. side = 87.50 sq. inches. 



M.P. side =: 87.61 sq. inches. 



As the orifices were used under conditions of atmospheric 

 temperature and calibrated under similar conditions, there are 

 no temperature corrections to be applied to the areas. 



The orifice used on the discharge side of the Compressor 

 was a plate orifice. It is a most important detail that the pres- 

 sure connections should l^e in the dead spaces, as should the 

 pressure pipes be in the stream lines, entirely erroneous readings 

 must result. This orifice was situated in a pipe 12I/8 inches 

 diameter and had an uninterrupted approach of more than 12 

 feet or 16 orifice diameters. On the downstream side there was 

 a straight run of 5 orifice diameters before reaching a right angle 

 bend in the pipe line and the conditions of use of this orifice are 

 therefore correct. As this orifice is used at a temperature of 

 80 °C to 90° C, it was calibrated with micrometer gauges both 

 at atmospheric temperature and also 85 °C. The two sets of 

 observations agreed when reduced to the same temperature using 

 the usual coefficient of expansion of brass the metal of which 

 the orifice was constructed. For this orifice we have at 85 °C. 

 D = 12.125 inches: A = ii5-4 sq. inches 

 d = 9005 (at 85°C) : a = 63.69 sq. inches 

 For the coefficient of contraction of this orifice a comparison 

 has been made of the orifice against the standard displacement 

 meter belonging to the Central Mining and Investment Corpora- 

 tion which g-ave the value as 0.675. 



Hence for the equivalent area of this orifice we have 

 a = 63.69 c = 0.675 ca = 42.99 



A = 115.4 ca/A = 03726 {ca/ AY -- 0.138S 



Vl-ica/AY = V 0.8612 = 0.9280 



and ca/ \' I — (ca/A)' = 46.33 sq. inches. 

 This calculation of the equivalent area assumes the term 



ip-Jpi )k^ to be unity. It will be shown later in the Report 



that the eft'ect of the difterence from unity is nearly negligil)le. 



A matter of considerable importance in all compressor tests 

 is the humidity of the atmosphere, for the thermal transferences 

 at the dififerent stages are dej^endent upon it. 



