1.	No.  The things that make a capacitor suitable or unsuitable are:
*	Dielectric type.  You didn't say what your type is so this is
*	Voltage rating.  25KV is very marginal and wouldn't last long unless
it was just in a very small coil.
*	Capacitance value.  1 uF is way too high for any reasonable sized
coil.  One typically needs something on the order of .005 to .02 uF for a
small-medium sized coil.  You could never build a primary that would be in
tune with so large a cap.

2.	Horizontal coils are used only in bipolar coils where both ends of
the secondary are "hot".  The choice of conical or flat vertical primaries
depends upon how much power your coil will be running at and the secondary
diameter.  Lower power and smaller (4" and below) secondaries benefit from
the higher coupling of a conical primary.  When the power level gets too
high, the higher coupling of a conical primary will cause racing sparks on
the secondary, and the reduced clearance between the top of the primary and
the top load may cause arc-overs..

3.	No.  The speed of a rotary has no bearing on the tuning of the
primary.  I suggest you start out with a static gap.

Regards, Gary Lau
Waltham, MA USA

>Original Poster: Norman Hockler <norsan-at-bright-dot-net> 
>Hi Gang...
>Would like to build a coil and I have a few questions.
>1.  I have a cap rated at 1 uf  -at- 25kv.  cap says its DC but there is no 
>polarity marking on the cap.  can I use it ???
>2. I have seen pictures of the primary coil wound  vertical, 
>horizontal  and conical...what are the differences in results.
>3. I have a small dc motor that I can control the speed ....I am thinking 
>of using it to power a Rotary spark gap.  Cant I tune the primary by 
>changing the speed of the motor??
>Appreciate your responses.