on, and continual vigilance for air leaks in the exhaust piping,
which will, however, be fully paid for by the great increase in economy.

It must not be inferred that a high vacuum is essential to successful
operation of this type of turbine, for excellent performance both in the
matter of steam consumption and operation is obtained with inferior
vacuum. The choice of a condenser, however, is a matter of special
engineering, and is hardly within the province of this article.

Oils

There are several oils on the market that are suitable for the purpose
of the turbine oiling system, but great care must be exercised in their
selection. In the first place, the oil must be pure mineral,
unadulterated with either animal or vegetable oils, and must have been
washed free from acid. Certain brands of oil require the use of
sulphuric acid in their manufacture and are very apt to contain varying
degrees of free acid in the finished product. A sample from one lot may
have almost no acid, while that from another lot may contain a dangerous
amount.

Mineral oils that have been adulterated, when heated up, will partially
decompose, forming acid. These oils may be very good lubricants when
first put into use, but after awhile they lose all their good qualities
and become very harmful to the machine by eating the journals in which
they are used. These oils must be very carefully avoided in the turbine,
as the cheapness of their first cost will in no way pay for the damage
they may do. A very good and simple way to test for such adulterations
is to take up a quantity of the oil in a test tube with a solution of
borax and water. If there is any animal or vegetable adulterant present
it will appear as a white milk-like emulsion which will separate out
when allowed to stand. The pure mineral oil will appear at the top as a
clear liquid and the excess of the borax solution at the bottom, the
emulsion being in between. A number of oils also contains a considerable
amount of paraffin which is deposited in the oil-cooling coil,
preventing the oil from being cooled properly, and in the pipes and
bearings, choking the oil passages and preventing the proper circulation
of the oil and cushioning effect in the bearing tubes. This is not
entirely a prohibitive drawback, the chief objection being that it
necessitates quite frequently cleaning the cooling coil, and the oil
piping and bearings.

Some high-class mineral oils of high viscosity are