  Chandra Low Energy Transmission Grating Spectrograph observations of Algol
have been used to determine the abundances of C and N in the secondary star for
the first time. The analysis was performed relative to similar observations of
an adopted "standard" star HR 1099. It is demonstrated that HR 1099 and Algol
are coronal twins in many respects and that their X-ray spectra are very
similar in nearly all details, except for the observed strengths of C and N
lines. The H-like transitions of C and N in the coronae of Algol and HR 1099
demonstrate that the surface abundances of Algol B have been strongly modified
by CN-processing, as shown earlier by Schmitt & Ness (2002). It is found that N
is enhanced in Algol B by a factor of 3 compared to HR 1099. No C lines are
detected in the Algol spectrum, indicating a C depletion relative to HR 1099 by
a factor of 10 or more. These C and N abundances indicate that Algol B must
have lost at least half of its initial mass, and are consistent with
predictions of evolutionary models that include non-conservative mass transfer
and angular momentum loss through magnetic activity. Little or no dredge-up of
material subjected to CN-processing has occurred on the subgiant component of
HR 1099. It is concluded that Fe is very likely depleted in the coronae of both
Algol and HR 1099 relative to their photospheres by 0.5 dex, and C, N and O by
0.3 dex. Instead, Ne is enhanced by up to 0.5 dex.
