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354 THE ADVANCE OF PHOTOGRAPHY
When making exposures in which a radiograph of the bones of a bandaged limb is required, it is well to bear in mind that ordinary strapping plaster and iodoform are by no means very transparent to the rays ; ordinary bandages of course offer little obstruction to the passage of the rays.
Any good brand of fast plate or film is suitable for this work, and many specially prepared plates are now on the market. In this branch of photographic work as in all others it is as well for workers to keep to brands with which they are familiar ; those who have no preference will find the Ilford X-ray plate give very satisfactory results. When a good many copies of a radiograph are required at a very short notice, a special form of X-ray paper is â– sometimes used instead of a plate.
This paper is really a very rapid bromide paper, and a large number of such papers may be placed on one another and exposed at the same time, since the rays can very readily pass through many layers of paper.
When films or papers are used in the place of plates, care must be taken to keep them quite flat, otherwise the image obtained will be distorted.
One great drawback to X-ray photography as compared with screen-work has been the length of time required for an exposure.
This has now been overcome by the employment of a coil giving a very intense discharge for a very small fraction of a second. The value of such an appliance as this cannot be over estimated in certain classes of work in which it is essential to make the exposure extremely short.
Such an X-ray set of apparatus is shown in fig. 158.
The three tubes in the top right-hand corner of the illustration are called " rectifiers." These are placed in series with the Ront gen-ray tube in the secondary circuit, so as to ensure that the current may pass through that tube in one direction only.