Mat s, The application of a high-grade insulating varnish will renew the insplation and greatly prolong its life. The windings should be thor- oughly dried out, and the varnish applied while they are still warm. For oil or excessive dust conditions, a clear varnish should be used; but where excessive amounts of acid, alkali, or moisture is encountered, & plastic baking varnish is recommended. brushed on. The varnish may be sprayed or In the case of small rotors and stators, the most effective method is to dip the windings into the varnish. After varnishing, all metal parts adjacent to the insulation should be cleaned off with a varnish solvent. The windings should then be baked for 6 or 7 hours at a temperature not exceeding 90°C. The condition of the insulation, or the conditions under which the machine is to operate, may indicate a repetition of the foregoing varnishing and baking operations to be desir-—able. If time is at a premium and the machine cannot be spared from service long enough for adequate baking, or if facilities are not available for baking, fair results can be obtained by applying a quick airdrying varnish which will dry in a few hours at ordinary room temperature. COMMUTATION Satisfactory commutation can be maintained by periodic examinations of the commutator surface and brush rigging. Faults detected in the early stages of formation can usually be corrected at little loss of time or expense. The machine has been properly adjusted at the factory for successful operation. The position of the brush studs on the brush yoke has been determined for the correct brush angle and should never require any change, The brushholders have been properly aligned and the correct brush stagger established on the commutator. 3-55