es a higher
percentage of moisture than is actually present in the steam. This is
due to the fact that if the perforations come close to the inner surface
of the pipe, the moisture, which in many instances clings to this
surface, will flow into the calorimeter and cause a large error. Where a
perforated nipple is used, in general it may be said that the
perforations should be at least one inch from the inner pipe surface.

A sampling nipple, open at the inner end and unperforated, undoubtedly
gives as accurate a measure as can be obtained of the moisture in the
steam passing that end. It would appear that a satisfactory method of
obtaining an average sample of the steam would result from the use of an
open end unperforated nipple passing through a stuffing box which would
allow the end to be placed at any point across the diameter of the steam
pipe.

Incidental to a test of a 15,000 K. W. steam engine turbine unit, Mr.
H. G. Stott and Mr. R. G. S. Pigott, finding no experimental data
bearing on the subject of low pressure steam quality determinations,
made a investigation of the subject and the sampling nozzle illustrated
in Fig. 18 was developed. In speaking of sampling nozzles in the
determination of the moisture content of low pressure steam, Mr. Pigott
says, "the ordinary standard perforated pipe sampler is absolutely
worthless in giving a true sample and it is vital that the sample be
abstracted from the main without changing its direction or velocity
until it is safely within the sample pipe and entirely isolated from the
rest of the steam."

[Illustration: Fig. 18. Stott and Pigott Sampling Nozzle]

It would appear that the nozzle illustrated is undoubtedly the best that
has been developed for use in the determination of the moisture content
of steam, not only in the case of low, but also in high pressure steam.

Location of Sampling Nozzle--The calorimeter should be located as near
as possible to the point from which the steam is taken and the sampling
nipple should be placed in a section of the main pipe near the boiler
and where there is no chance of moisture pocketing in the pipe. The
American Society of Mechanical Engineers recommends that a sampling
nipple, of which a description has been given, should be located in a
vertical main, rising from the boiler with its closed end extending
nearly across the pipe. Where non-return valves are used, or where there
are horizontal connections leading from the bo