(d) Electrolytic interrupters are said by some to work satisfactorily with alternating current, preferably with an aluminium cell in series. The nature and use of this type of interrupter is described later on p. 58, and we highly commend it under suitable conditions; but we do not consider an alternating main one of those con- ditions.

(e) A number of other so-called «rectifiers’ have been designed to render an alternating current unidirectional, but in our experience none of those have proved of practical value.

II. Accumulators.

Accumulators are valuable as sources of direct supply—

(1) Where portability is of prime importance;

(2) Where there is an existent source of supply, but not convenient for direct connection by wiring to the X-ray installation;

(3) In occasional cases where supply is available, but not of a nature for direct use.

1. Where an X-ray outfit is chosen mainly with a view to portability, the advantage of accumulators will depend largely upon convenient opportunity of recharging them, since they can by no means be made to produce electricity unless in the degree to which that has been previously supplied to them.

Elsewhere in this chapter (pp. 46 and 47) we suggest possible arrangements of a portable nature where the set must be self- sufficient for all purposes. With such apparatus for primary production of electrical energy, it will probably be advan- tageous in many cases to combine the use of accumulators. These may be periodically charged from the primary source, and kept in readiness for immediate use at any time; whereas it may be inconvenient to bring the generator into action when current is required.

For bedside work accumulators are ordinarily the onty source of supply worthy of consideration, though the advent of a portable form of static machine would alter the definite character of this statement. The method of charging accu- mulators for such use will depend upon local conditions of the operator.

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