X-Rays, Apparatus and Methods Page 5

Another grave danger in the use of paraffine is that due to the acid which it usually contains. This attacks the wire, forming copper sulphate, which dissolves gradually into and throughout the mass of the paraffine, thus effectually destroying its insulating properties.

After cooking for some time in the insulation, to drive out the last traces of moisture, the stack of sections is subjected to a further treatment, by which it is finally cooled with all air removed. This we consider a point of the highest importance, as air present anywhere in the secondary becomes electrified and bombards to and fro, gradually softening the insulation and eventually breaking down the coil. (For confirmation of this point, see Tesla, on "High-Frequency Phenomena.") With this plan of construction we have no static leaks of energy, or small direct leaks within the coil itself, and deliver the full energy of discharge at the secondary terminals. We find ourselves able to secure in this way a full inch of spark in all sizes of coils with considerably less than 1 pound of wire, No. 34 B. & S.* We believe that, more than anything else, the large quantities of wire required to produce a given spark length with many of the coils now in use is due to the presence of air, and consequent loss of energy by static bombardment, in the secondary. As regards the insulating composition used by us, we may say that we find its power of resistance to spark discharge to be four or five times that of hard rubber. In the arrangement of our secondary, we separate it from the primary by a heavy hard-rubber tube, and, in addition, by a tube of this composition.

The Adjustable Condenser. — A coil is working to best advantage when there is a certain definite relation between its primary current, secondary spark distance, and condenser capacity. Frequency of break must also be considered. As coils have heretofore been built, however, the condenser value has been fixed once for all and admits of no change, albeit both spark gap and primary current may be so

* In our latest coils not over three-quarters of a pound to the inch of spark is used.